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Skeletal System

Reviewed by: BD Editors

The skeletal system provides support and protection for the body’s internal organs and gives the muscles a point of attachment. Humans have an endoskeleton , where our bones lie underneath our skin and muscles. In other animals, such as insects, there is an exoskeleton on the outside of the body.

In humans, the skeletal system consists of bones, joints and associated cartilages. An adult human has 206 bones in their body and variety of different joints.

Image shows a human skeleton with the major bones labeled.

The human skeleton can be divided into two components: the axial skeleton and the appendicular skeleton. The axial skeleton is formed around the central axis of the body and thus includes the skull, spine , and ribcage. It protects the brain, spinal cord, heart, lungs, esophagus and major sense organs like the eyes, ears, nose, and tongue. The appendicular skeleton is related to the limbs and consists of the bones of the arms and legs, as well as the shoulder and hip girdles.

Skeletal System Function

The first and most apparent function of the skeletal system is to provide a framework for the body. The presence of a firm bony skeleton allows the organism to have a distinctive shape adapted towards a particular lifestyle. For instance, in a fast-moving animal like the cheetah, the skeleton contains long, thin limb bones and an extremely flexible spine. The structure of the skeleton also allows it to absorb the impact of running at high speeds.

The bones of birds are hollow, light and create a streamlined body adapted for flight. Many animals even have sexual dimorphism in their skeletons. In humans, while this dimorphism is fairly limited, there are differences in the angle of the pelvic bones, to accommodate pregnancy.

Integration with the Muscular System

The skeletal system also provides an important form of attachments to the muscular system. Bones and exoskeletons are hard and do not bend or move when muscles are flexed. This means that the contraction of muscle cells will lead to the shortening of muscles, while the bone retains its shape. This basic structure allows muscles to move different parts of the body, using forces generated while pulling on the skeletal system.

The next obvious function of the skeletal system is the role it plays protecting the fragile internal organs. In humans, this is seen in the skull, which surrounds the brain completely. It is also exhibited by the ribcage, which surrounds the lungs and heart but still allows for expansion. Even invertebrates like snails and prawns often have hard exoskeletons to protect themselves from predators.

The rigid endoskeleton allows the body to rise up above the ground or stand upright, and bears the weight of the organism, and provides the scaffolding for movement. Muscles generate the force required to move bones at joints. Muscle fibers contain actin and myosin, two protein filaments that can slide past each other to change the length of the muscle. When a nerve impulse arrives at the neuromuscular junction, it signals the muscle to contract. The force generated by the contracting muscle either pulls two bones together or apart, based on the nature of the interaction between the muscle and joint.

Blood Cell Production

The central part of a bone contains the bone marrow , the primary site for blood cell production in adult humans. There are two types of bone marrow in adults. Around 50% is red bone marrow containing hematopoietic stem cells and supportive tissue. The rest is yellow bone marrow made of fat and its proportion increases with age.

Bone marrow will revert to a higher proportion of red marrow if the body suffers an injury and needs to create more red blood cells. The bone marrow composition also changes during pregnancy and lactation in mammals. Over the course of gestation, blood volume increases by about 1.5 liters, and even the concentration of red blood cells and white blood cells increase.

Production of other Cell Types

In addition to producing red blood cells, bone marrow within the skeletal system is the production site of a number of other cells. These include lymphocytes , which are immune cells that travel the lymphatic system. In addition to providing immune functions, the skeletal system is also responsible for hosting stem cells which can differentiate into muscle cells, cartilage-producing cells, and cells that create bone (osteoblasts).

Osteoblasts in bone also have an endocrine function, secreting a hormone called osteocalcin. It requires vitamin K to be synthesized and is an anabolic hormone. It mediates an increase in insulin levels and increases the sensitivity of the body to insulin. Osteocalcin contributes to an increase in bone mass and bone mineralization.

Storing Minerals

The bones of the skeletal system act as a storehouse for calcium ions , changing the quantum of mineralized deposits within bones to maintain plasma calcium ion concentration within a narrow range. Calcium ions can affect crucial sodium ion channels in the plasma membrane of every cell, thereby affecting overall homeostasis.

For this reason, changes to the concentration of calcium ions have particularly adverse effects on excitable cells in the nervous system, and in cardiac, skeletal and smooth muscle. Different interacting hormones maintain the balance of calcium ions in the plasma and bones, especially the parathyroid hormone secreted from the parathyroid glands in the neck.

Skeletal System Parts

The anatomy of the skeletal system is complex, and it includes hundreds of bones in the human body . The anatomy of the system varies widely between organisms, as evolution has selected for various adaptations in certain species which change the structure and function of their bones.

Bones serve a variety of functions, but the most important is supporting movement of the limbs and body. Two bones or cartilages are held together at a joint through tough connective tissues called ligaments. Muscles are securely attached to bones through flexible but inelastic connective tissue called tendons. Muscles, joints, tendons, and ligaments are part of the intricate machinery that allows the movement of different bones.

Functionally, joints can be divided into three classes based on the range of movement they allow in the associated bones. Immovable joints are formed when two bones are held together by fibrous connective tissue with no synovial fluid. These kinds of joints hold the bones of the cranium together.

Partially movable joints are also called cartilaginous joints and are present in the spine and ribs. The third type of joints are called synovial joints and have a fluid-filled synovial cavity that allows the interfacing bones the largest range of movement. Based on the structure of the synovial joints, they can be classified into 6 types, including the hinge joints of the fingers and the ball and socket joints of the hips and shoulders.

Cellular Composition

Each bone is made of complex sets of cells, tissues and a specialized extracellular matrix . The two main cell types are called osteoblasts and osteoclasts with mostly opposing functions. While osteoblasts are involved in the formation of bone, osteoclasts are associated with a reduction in bone mass. The extracellular matrix of the bone consists of collagen and other organic fibers as well as the inorganic component containing calcium salts such as hydroxyapatite. In the interior of bones, a soft tissue called the bone marrow plays an important role in immunity and hematopoiesis. The bone is also richly supplied with nerves and blood vessels.

Skeletal System Structure

In general, the skeletal system is structured to provide support against gravity and protect an animal’s internal organs. While this article mainly discusses the human skeletal system, most animals have some sort of skeleton. Some animals, like sponges, can have an extremely simplified skeleton made of calcium deposits within the animal. Others, like the turtle, have drastically modified their skeletal system to provide extra protection.

While this article mostly discusses an endoskeleton, many animals use an exoskeleton for the same purposes. Instead of bones being on the inside, the bones, protective plates, or chitinous skeleton actually surrounds the muscles. While this may seem completely different, the structure of the system is still very similar. The only difference is that muscles and tendons connect to the inside of the system, rather than to the surface of bones.

The structure of the skeletal system reflects an animal’s evolution, as well as the needs it has to survive. For example, humans have a tailbone. This is an evolutionary relic, from the time when our ancestors had tails and were swinging from the trees. As we became bipedal, we lost the need for a tail, and it was reduced to a single, nonfunctional bone. Likewise, all animals are constantly adapting and changing their skeletal system through evolutionary time.

Skeletal System Diseases

Diseases of the skeletal system could be confined to one section of the skeleton such as changes to the curvature of the spine, or they could be a genetic disorder affecting all bones and joints such as arthritis or osteoporosis.

The spine in healthy individuals is S-shaped, with a convex curvature for the thoracic region and the concave tilt in the cervical and lumbar regions. This shape for the spine is ideally suited for an upright walking posture. If either the thoracic or lumbar regions have a change in curvature or there is sideways bend to the spine, it can lead to back pain, difficulty with breathing, digestion, mobility, and reproduction.

Curvature of the Spine

The bulk of the weight of the upper body is transmitted along the central axis towards the legs. When the bones or muscles of the back or not functioning optimally, it can lead initially to accommodative changes in posture and thereafter to pain, injury or permanent deformity. Since the spine surrounds the spinal cord, abnormalities in the skeletal structure of the spine can affect the nervous system, either manifesting as pain, tingling or numbing in the extremities. Additionally, the spine supports the ribcage, enclosing the heart, lungs, and diaphragm. Thus, spinal deformities can also lead to shortness of breath, palpitations or even cardiac arrhythmias.

Kyphosis is the term for the convex curve of the thoracic region and excessive curvature in this region is called hyperkyphosis. Extreme hyperkyphosis presents as a hunchback. This could arise from genetic factors or poor posture due to obesity or osteoporosis or arthritis.

The normal concave structure of the lumbar region is called lordosis , and when the region is overly arched, it is called lumbar hyperlordosis. In hyperlordosis, shoulders appear to be pushed back, while the abdominal region seems to be jutting forward.

Image shows a person with hyperlordosis. In a healthy spine, the midpoint of the spine (A) would be directly above the knee (B).

Hyperlordosis can arise from genetic factors, poor posture, or even deficient muscle strength. When the spine has a sideways tilt, or a lateral bend, it is called scoliosis and could be associated with both hyperkyphosis and hyperlordosis.

Osteoporosis

Osteoporosis is a condition marked by bone resorption. This reduces bone mass and density, thereby enhancing the probability of fractures from even minor stressors such as sneezing. Although osteoporosis is commonly associated with aging, smoking, obesity, diet, some medications and alcohol consumption can contribute to the progression of the ailment.

Weight training, exercise, and a diet containing adequate calcium, iron, phosphorous as well as Vitamin D, help in enhancing bone density and bone mass. There is some evidence that the pH of blood plays a role in the release of calcium stores from bones and the extent of bone mineralization since calcium salts are often used as buffers in acidic environments in the body. A whole-foods, plant-based diet has been shown greatly reduce blood acidification. As a result, it also lowers cases of osteoporosis.

Arthritis includes a number of joint disorders that are characterized by stiffness, inflammation, and pain. While there is a range of potential causes, arthritis usually worsens with age, affecting the joints that are used most frequently – especially the joints in fingers, hips, and knees. Arthritis, therefore, causes disability, restricts movement and impairs fine motor skills.

Interesting Facts

Three bones in the inner ear, called malleus, incus and stapes, are the smallest bones in the human body. The thigh bone, or femur, is the largest bone.
The hyoid bone situated behind the lower jaw is also called a ‘floating’ bone because it is not part of any joint, and is not directly attached to any other bone.
The position of the hyoid bone makes it extremely resistant to fractures. However, autopsies that reveal a broken hyoid bone indicate death from strangulation.
Newborn babies have about 300 bones. Many of these bones fuse together to form the 206 bones of the adult.
Teeth are part of the skeletal system. However, they are not bones.

1. Which of these is an inflammatory condition?

2. Meat, carbonated beverages, cheese, eggs and even milk have been linked to a decrease in blood pH. How might these things affect bone health?

3. Why is the hyoid bone called a floating bone?

4. Why do babies have more bones than adults?

5. Which of the following are functions of the skeletal system?

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Skeletal System Anatomy and Physiology

Dive into the intricate framework of the human body with our skeletal system study guide —perfect for nursing students eager to understand the anatomy and physiology behind every bone and joint.

Functions of the skeletal system, classification of bones, gross anatomy, microscopic anatomy, axial skeleton, facial bones, the hyoid bone, fetal skull, cervical vertebrae, thoracic vertebrae, lumbar vertebrae, appendicular skeleton, bones of the shoulder girdle, bones of the pelvic girdle, fibrous joints, cartilaginous joints, types of synovial joints based on shape.

Besides contributing to body shape and form, our bones perform several important body functions.

Support. Bones, the “steel girders” and “reinforced concrete” of the body, form the internal framework that supports the body and cradle its soft organs; the bones of the legs act as pillars to support the body trunk when we stand, and the rib cage supports the thoracic wall.
Protection. Bones protect soft body organs; for example, the fused bones of the skull provide a snug enclosure for the brain , the vertebrae surround the spinal cord , and the rib cage helps protect the vital organs of the thorax.
Movement. Skeletal muscles, attached to bones by tendons, use the bones as levers to move the body and its parts.
Storage. Fat is stored in the internal cavities of bones; bone itself serves as a storehouse for minerals, the most important of which are calcium and phosphorus; because most of the body’s calcium is deposited in the bones as calcium salts , the bones are a convenient place to get more calcium ions for the blood as they are used up.
Blood cell formation. Blood cell formation, or hematopoiesis , occurs within the marrow cavities of certain bones.

Anatomy of the Skeletal System

The skeleton is subdivided into two divisions: the axial skeleton, the bones that form the longitudinal axis of the body, and the appendicular skeleton, the bones of the limbs and girdles.

Axial & Appendicular Skeleton-Skeletal System Anatomy and Physiology for Nurses

The adult skeleton is composed of 206 bones and there are two basic types of osseous, or bone, tissue: compact bone and spongy bone, and are classified into four groups according to shape: long, short, flat, and irregular.

Compact bone. Compact bone is dense and looks smooth and homogeneous.
Spongy bone. Spongy bone is composed of long, needle-like pieces of bone and lots of open space.
Long bones. Long bones are typically longer than they are wide; as a rule, they have a shaft with heads at both ends, and are mostly compact bone.
Short bones. Short bones are generally cube-shaped and mostly contains spongy bone; sesamoid bones , which form within tendons, are a special type of short bone.
Flat bones. Flat bones are thin, flattened, and usually curved; they have two thin layers of compact bone sandwiching a layer of spongy bone between them.
Irregular bones. Bones that do not fit one of the preceding categories are called irregular bones.

Classification of Bones-Skeletal System Anatomy and Physiology for Nurses

The structure of a long bone is shown both through gross anatomy and microscopic anatomy.

The gross structure of a long bone consists of the following:

Diaphysis. The diaphysis, or shaft, makes up most of the bone’s length and is composed of compact bone; it is covered and protected by a fibrous connective tissue membrane, the periosteum .
Sharpey’s fibers. Hundreds of connective tissue fibers called perforating or Sharpey’s , fibers secure the periosteum to the underlying bone.
Epiphyses. The epiphyses are the ends of the long bone; each epiphysis consists of a thin layer of compact bone enclosing an area filled with spongy bone.
Articular cartilage. Articular cartilage, instead of a periosteum, covers its external surface; because the articular cartilage is glassy hyaline cartilage, it provides a smooth, slippery surface that decreases friction at joint surfaces.
Epiphyseal line. In adult bones, there is a thin line of bony tissue spanning the epiphysis that looks a bit different from the rest of the bone in the area; this is the epiphyseal line.
Epiphyseal plate. The epiphyseal line is a remnant of the epiphyseal plate (a flat plate of hyaline cartilage) seen in young, growing bone; epiphyseal plates can cause the lengthwise growth of a long bone; by the end of puberty, when hormones inhibit long bone growth, epiphyseal plates have been completely replaced by bones, leaving only the epiphyseal lines to mark their previous location.
Yellow marrow. In adults, the cavity of the shaft is primarily a storage area for adipose (fat) tissue called the yellow marrow, or medullary , cavity.
Red marrow. However, in infants, this area forms blood cells and red marrow is found there; in adult bones, red marrow is confined to cavities in the spongy bone of flat bones and epiphyses of some long bones.
Bone markings. Even when looking casually at bones, one can see that their surfaces are not smooth but scarred with bumps, holes, and ridges; these bone markings reveal where muscles, tendons, and ligaments were attached and where blood vessels and nerves passed.
Categories of bone markings. There are two categories of bone markings: (a) projections , or processes , which grow out from the bone surface, and (b) depressions , or cavities which are indentations in the bone; a little trick for remembering some of the bone markings are all the terms beginning with T are projections, while those beginning with F (except facet) are depressions.

To the naked eye , spongy bone has a spiky, open appearance, whereas compact bone appears to be very dense.

Osteocytes. The mature bone cells, osteocytes, are found within the matrix in tiny cavities called lacunae .
Lamellae. The lacunae are arranged in concentric circles called lamellae around central ( Haversian ) canals.
Osteon. Each complex consisting of central canals and matrix rings is called an osteon, or Haversian system .
Canaliculi. Tiny canals, canaliculi, radiate outward from the central canals to all lacunae; the canaliculi form a transportation system that connects all the bone cells to the nutrient supply through the hard bone matrix.
Perforating canals. The communication pathway from the outside of the bone to its interior (and the central canals) is completed by perforating ( Volkmann’s ) canals, which run into the compact bone at right angles to the shaft.

The axial skeleton, which forms the longitudinal axis of the body, is divided into three parts: the skull, the vertebral column, and the bony thorax.

The skull is formed by two sets of bones: the cranium and the facial bones.

The cranium encloses and protects the fragile brain tissue and is composed of eight large flat bones.

Skull and Facial Bones-Skeletal System Anatomy and Physiology for Nurses

Frontal bone. The frontal bone forms the forehead, the bony projections under the eyebrows, and the superior part of each eye’s orbits.
Parietal bones. The paired parietal bones form most of the superior and lateral walls of the cranium; they meet in the midline of the skull at the sagittal suture and form the coronal suture , where they meet the frontal bone.
Temporal bones. The temporal bones lie inferior to the parietal bones; they join them at the squamous sutures.

There are several bone markings that appear at the temporal bone :

External acoustic meatus . The external acoustic meatus is a canal that leads to the eardrum and middle ear; it is the route by which sound enters the ear.
Styloid process. The styloid process, a sharp, needlelike projection , is just inferior to the external auditory meatus.
Zygomatic process. The zygomatic process is a thin bridge of bone that joins with the cheekbone ( zygomatic bone ) anteriorly.
Mastoid process. The mastoid process, which full of air cavities ( mastoid sinuses ), is a rough projection posterior and inferior to the external acoustic meatus ; it provides an attachment site for some muscles of the neck.
Jugular foramen. The jugular foramen, at the junction of the occipital and temporal bones, allows passage of the jugular vein , the largest vein of the head, which drains the brain; just anterior to it in the cranial cavity is the internal acoustic meatus , which transmits cranial nerves VII and VIII.
Occipital bone . The occipital bone joins the parietal bones anteriorly at the lambdoid suture ; in the base of the occipital bone is a large opening, the foramen magnum , which surrounds the lower part of the brain allows the spinal cord to connect with the brain.
Sphenoid bone. The butterfly-shaped sphenoid bone spans the width of the skull and forms part of the floor of the cranial cavity; in the midline of the sphenoid is a small depression , the sella turcica or Turk’s saddle , which forms a snug enclosure for the pituitary gland.
Foramen ovale. The foramen ovale, a large oval opening in line with the posterior end of the sella turcica, allows fibers of cranial nerve V to pass to the chewing muscles of the lower jaw.
Optic canal. The optic canal allows the optic nerve to pass to the eye.
Superior orbital fissure. The slitlike superior orbital fissure is where the cranial nerves controlling eye movements pass.
Sphenoid sinuses. The central part of the sphenoid bone is riddled with air cavities, the sphenoid sinuses.
Ethmoid bone. The ethmoid bone is very irregularly shaped and lies anterior to the sphenoid; it forms the roof of the nasal cavity and part of the medial walls of the orbits.
Crista galli. Projecting from its superior surface is the crista galli; the outermost covering of the brain attaches to this projection.
Cribriform plates . These holey areas, the cribriform plates, allow nerve fibers carrying impulses from the olfactory receptors of the nose to reach the brain.
Superior and middle nasal conchae . Extensions of the ethmoid bone, the superior and middle nasal conchae, form part of the lateral walls of the nasal cavity and increase the turbulence of air flowing through the nasal passages.

Fourteen bones compose the face; twelve are paired, only the mandible and vomer are single.

Maxillae. The two maxillae, or maxillary bones , fuse to form the upper jaw; all facial bones except the mandible join the maxillae; thus, they are the main or “keystone”, bones of the face; the maxillae carry the upper teeth in the alveolar margin .
Palatine bones. The paired palatine bones lie posterior to the palatine processes of the maxillae; they form the posterior part of the hard palate.
Zygomatic bones. The zygomatic bones are commonly referred to as the cheek bones; they also form a good-sized portion of the lateral walls of the orbits, or eye sockets.
Lacrimal bones. The lacrimal bones are finger-sized bones forming part of the medial walls of each orbit; each lacrimal bones has a groove that serves as a passageway for tears.
Nasal bones. The small rectangular bones forming the bridge of the nose are the nasal bones.
Vomer bone. The single bone in the medial line of the nasal cavity is the vomer; the vomer forms most of the bony nasal septum .
Inferior nasal conchae. The interior nasal conchae are thin, curved bones projecting medially from the lateral walls of the nasal cavity.
Mandible. The mandible, or lower jaw, is the largest and strongest bone of the face; it joins the temporal bones on each side of the face, forming the only freely movable joints in the skull; the horizontal part of the mandible ( the body ) forms the chin; two upright bars of bone ( the rami ) extend from the body to connect the mandible to the temporal bone.

Though not really part of the skull, the hyoid bone is closely related to the mandible and temporal bones.

Location. It is suspended in the midneck region about 2 cm (1 inch) above the larynx , where it is anchored by ligaments to the styloid processes of the temporal bones.
Parts. Horseshoe-shaped, with a body and two pairs of horns, or cornua, the hyoid bone serves as a movable base for the tongue and as an attachment point for neck muscles that raise and lower the larynx when we swallow and speak.

The skull of a fetus or newborn infant is different in many ways from an adult skull.

Fetal Skull-Skeletal System Anatomy and Physiology for Nurses

Size. The adult skull represents only one-eighth of the total body length, whereas that of a newborn infant is one-fourth as long as its entire body.
Fontanels. In the newborn, the skull also has a fibrous regions that have yet to be converted to bone; these fibrous membranes connecting the cranial bones are called fontanels.
Anterior fontanel. The largest fontanel is the diamond-shaped anterior fontanel; the fontanel allows the fetal skull to be compressed slightly during birth.

Vertebral Column (Spine)

Serving as the axial support of the body, the vertebral column, or spine, extends from the skull, which it supports, to the pelvis, where it transmits the weight of the body to the lower limbs.

Vertebral Column-Skeletal System Anatomy and Physiology for Nurses

Composition. The spine is formed from 26 irregular bones connected and reinforced by ligaments in such a way that a flexible, curved structure results.
Spinal cord. Running through the central cavity of the vertebral column is the delicate spinal cord, which the vertebral column surrounds and protects.
Vertebrae. Before birth, the spine consists of 33 separate bones called vertebrae , but 9 of these eventually fuse to form the two composite bones, the sacrum and the coccyx , that construct the inferior portion of the vertebral column.
Cervical vertebrae. Of the 24 single bones, the 7 vertebrae of the neck are cervical vertebrae.
Thoracic vertebrae. The next 12 are the thoracic vertebrae.
Lumbar vertebrae. The remaining 5 supporting the lower back are lumbar vertebrae.
Intervertebral discs. The individual vertebrae are separated by pads of flexible fibrocartilage-intervertebral discs- that cushion the vertebrae and absorb shock while allowing the spine flexibility.
Primary curvatures. The spinal curves in the thoracic and sacral regions are referred to as primary curvatures because they are present when we are born.
Secondary curvatures. The curvatures in the cervical and lumbar regions are referred to as secondary curvatures because they develop some time after birth.
Body or centrum. Disc-like, weight-bearing part of the vertebra facing anteriorly in the vertebral column.
Vertebral arch. Arch formed from the joining of all posterior extensions, the laminae and pedicles , from the vertebral body.
Vertebral foramen. Canal through which the spinal cord passes.
Transverse processes. Two lateral projections from the vertebral arch.
Spinous process. Single projection arising from the posterior aspect of the vertebral arch (actually the fused laminate).
Superior and inferior articular processes. Paired projections lateral to the vertebral foramen, allowing a vertebra to form joints with adjacent vertebrae.

The seven cervical vertebrae (C1 to C7) form the neck region of the spine.

Atlas. The atlas ( C1 ) has no body; the superior surfaces of its transverse processes contain large depressions that receive the occipital condyles of the skull.
Axis. The axis ( C2 ) acts as a pivot for the rotation of the atlas (and skull) above; it has a large upright process, the dens , which acts as the pivot point.
Foramina. The transverse processes of the cervical vertebrae contain foramina ( openings ) through which the vertebral arteries pass on their way to the brain above.

The twelve thoracic vertebrae (T1 to T12) are all typical.

Size. They are larger than the cervical vertebrae and are distinguished by the fact that they are the only vertebrae to articulate with the ribs.
Shape . The body is somewhat heart-shaped and has two costal facets on each side, which receive the heads of the ribs.
Transverse processes. The two transverse processes of each thoracic vertebrae articulate with the nearby knoblike tubercles of the ribs.
Spinous process. The spinous process is long and hooks sharply downward, causing the vertebra to look like a giraffe’s head viewed from the side.

The five lumbar vertebrae (L1 to L5) have massive, blocklike bodies.

Spinous processes. Their short, hatchet-shaped spinous processes make them look like a moose head from the lateral aspect.
Strength. Because most of the stress on the vertebral column occurs in the lumbar region, these are the sturdiest of the vertebrae.

The sacrum is formed by the fusion of five vertebrae.

Sacrum-Skeletal System Anatomy and Physiology for Nurses

Alae. The winglike alae articulate laterally with the hip bones, forming the sacroiliac joints.
Median sacral crest. Its posterior midline surface is roughened by the median sacral crest, the fused spinous processes of the sacral vertebrae.
Posterior sacral foramina. This is flanked laterally by the posterior sacral foramina.
Sacral canal. The vertebral canal continues inside the sacrum as the sacral canal and terminates in a large inferior opening called the sacral hiatus .

The coccyx is formed from the fusion of three to five tiny, irregular shaped vertebrae.

Tailbone. It is the human “tailbone”, a remnant of the tail that other vertebrate animals have.

Thoracic Cage

The sternum, ribs, and thoracic vertebrae make up the bony thorax; The bony thorax is routinely called the thoracic cage because it forms a protective, cone-shaped cage of slender bones around the organs of the thoracic cavity.

The sternum (breastbone) is a typical flat bone and the result of the fusion of three bones- the manubrium , body , and xiphoid process .

Landmarks. The sternum has three important bony landmarks- the jugular notch , the sternal angle , and the xiphisternal joint .
Jugular notch. The jugular notch (concave upper border of the manubrium) can be palpated easily, generally it is at the level of the third thoracic vertebra.
Sternal angle. The sternal angle results where the manubrium and the body meet at a slight angle to each other, so that a transverse ridge is formed at the level of the second ribs.
Xiphisternal joint. The xiphisternal joint, the point where the sternal body and xiphoid process fuse, lies at the level of the ninth thoracic vertebra.

Twelve pairs of ribs form the walls of the bony thorax.

True ribs. The true ribs, the first seven pairs, attach directly to the sternum by costal cartilages.
False ribs. False ribs, the next five pairs, either attach indirectly to the sternum or are not attached to the sternum at all.
Floating ribs. The last two pairs of false ribs lack the sternal attachments, so they are called the floating ribs.

The appendicular skeleton is composed of 126 bones of the limbs and the pectoral and pelvic girdles, which attach the limbs to the axial skeleton.

Each shoulder girdle, or pectoral girdle , consists of two bones – a clavicle and a scapula.

Humerus and Scapula-Skeletal System Anatomy and Physiology for Nurses

Clavicle. The clavicle, or collarbone , is a slender, doubly curved bone; it attaches to the manubrium of the sternum medially and to the scapula laterally, where it helps to form the shoulder joint; it acts as a brace to hold the arm away from the top of the thorax and helps prevent shoulder dislocation.
Scapulae. The scapulae, or shoulder blades , are triangular and commonly called “wings” because they flare when we move our arms posteriorly.
Parts of the scapula. Each scapula has a flattened body and two important processes- the acromion and the coracoid .
Acromion. The acromion is the enlarged end of the spine of the scapula and connects with the clavicle laterally at the acromioclavicular joint .
Coracoid. The beaklike coracoid process points over the top of the shoulder and anchors some of the muscles of the arm; just medial to the coracoid process is the large suprascapular notch, which serves as a nerve passageway.
Borders of the scapula. The scapula has three borders- superior, medial (vertebral), and lateral (axillary).
Angles of the scapula. It also has three angles- superior, inferior, and lateral; the glenoid cavity , a shallow socket that receives the head of the arm bone, is in the lateral angle.
Factors to free movement of the shoulder girdle. Each shoulder girdle attaches to the axial skeleton at only one point- the sternoclavicular joint ; the loose attachment of the scapula allows it to slide back and forth against the thorax as muscles act; and, the glenoid cavity is shallow, and the shoulder joint is poorly reinforced by ligaments.

Bones of the Upper Limb

Thirty separate bones form the skeletal framework of each upper limb; they form the foundations of the arm, forearm, and hand.

Forearm Anatomy-Skeletal System Anatomy and Physiology for Nurses

The arm is formed by a single bone, the humerus, which is a typical long bone.

Anatomical neck. Immediately inferior to the head is a slight constriction called anatomical neck.
Tubercles. Anterolateral to the head are two bony projections separated by the intertubercular sulcus – the greater and lesser tubercles , which are sites of muscle attachment.
Surgical neck. Just distal to the tubercles is the surgical neck, so named because it is the most frequently fractured part of the humerus.
Deltoid tuberosity. In the midpoint of the shaft is a roughened area called the deltoid tuberosity, where the large, fleshy deltoid muscle of the shoulder attaches.
Radial groove. Nearby, the radial groove runs obliquely down the posterior aspect of the shaft; this groove marks the course of the radial nerve, an important nerve of the upper limb.
Trochlea and capitulum. At the distal end of the humerus is the medial trochlea, which looks somewhat like a spool, and the lateral ball-like capitulum; both of these processes articulate with the bones of the forearm.
Fossa. Above the trochlea anteriorly is a depression, the coronoid fossa ; on the posterior surface is the olecranon fossa ; these two depressions, which are flanked by medial and lateral epicondyles , allow the corresponding processes of the ulna to move freely when the elbow is bent and extended.

Two bones, the radius, and the ulna, form the skeleton of the forearm.

Radius. When the body is in the anatomical position, the radius is the lateral bone; that is, it is on the thumb side of the forearm; when the hand is rotated so that the palm faces backward, the distal end of the radius crosses over and ends up medial to the ulna.
Radioulnar Joints. Both proximally and distally the radius and ulna articulate at small radioulnar joints and the two bones are connected along their entire length by the flexible interosseous membrane .
Styloid process. Both the ulna and the radius have as styloid process at their distal end.
Radial tuberosity. The disc-shaped head of the radius also forms a joint with the capitulum of the humerus; just below the head is the radial tuberosity, where the tendon of the biceps muscle attaches.
Ulna. When the upper limb is in the anatomical position, the ulna is the medial bone (on the little-finger side) of the forearm.
Trochlear notch. On its proximal end are the coronoid process and the posterior olecranon process, which are separated by the trochlear notch; together, these two processes grip the trochlea of the humerus in a pliers-like joint.

The skeleton of the hand consists of carpals, the metacarpals, and the phalanges.

Carpal bones. The eight carpal bones, arranged in two irregular rows of four bones each, form the part of the hand called carpus , or, more commonly, the wrist ; the carpals are bound together by ligaments that restrict movements between them.
Metacarpals. The metacarpals are numbered 1 to 5 from the thumb side of the hand to the little finger; when the fist is clenched, the heads of the metacarpals become obvious as the “ knuckles “.
Phalanges. The phalanges are the bones of the fingers; each hand contains 14 phalanges; there are three in each finger (proximal, middle, and distal), except in the thumb, which has only two )proximal and distal.

The pelvic girdle is formed by two coxal bones, or ossa coxae, commonly called hip bones.

Pelvic girdle. The bones of the pelvic girdle are large and heavy, and they are attached securely to the axial skeleton; bearing weight is the most important function of this girdle because the total weight of the upper body rests on the bony pelvis.
Sockets. The sockets, which receives the thigh bones, are deep and heavily reinforced by ligaments that attach the limbs firmly to the girdle.
Bony pelvis. The reproductive organs, urinary bladder , and part of the large intestine lie within and are protected by the bony pelvis.
Ilium. The ilium, which connects posteriorly with the sacrum at the sacroiliac joint , is a large, flaring bone that forms most of the hip bone; when you put your hands on your hips, they are resting over the alae , or winglike portions, of the ilia.
Iliac crest. The upper edge of an ala, the iliac crest, is an important anatomical landmark that is always kept in mind by those who give intramuscular injections; the iliac crest ends anteriorly in the anterior superior iliac spine and posteriorly in the posterior superior iliac spine .
Ischium. The ischium is the “sit-down” bone, so called because it forms the most inferior part of the coxal bone.
Ischial tuberosity. The ischial tuberosity is a roughened area that receives weight when you are sitting.
Ischial spine. The ischial spine, superior to the tuberosity, is another important anatomical landmark, particularly in pregnant women, because it narrows the outlet of the pelvis through which the baby must pass during the birth process.
Greater sciatic notch. Another important structural feature of the ischium is the greater sciatic notch, which allows blood vessels and the large sciatic nerve to pass from the pelvis posteriorly into the thigh.
Pubis. The pubis, or pubic bone , is the most anterior part of the coxal bone.
Obturator foramen. An opening that allows blood vessels and nerves to pass into the anterior part of the thigh.
Pubic symphysis. The pubic bones of each hip bones fuse anteriorly to form a cartilaginous joint, the pubic symphysis.
Acetabulum. The ilium, ischium, and pubis fuse at a deep socket called the acetabulum, which means “vinegar cup”; the acetabulum receives the head of the thigh bone.
False pelvis. The false pelvis is superior to the true pelvis; it is the area medial to the flaring portions of the ilia.
True pelvis. The true pelvis is surrounded by bone and lies inferior to the flaring parts of the ilia and the pelvic brim; the dimensions of the true pelvis of the woman are very important because they must be large enough to allow the infant’s head to pass during childbirth.
Outlet and inlet. The dimensions of the cavity, particularly the outlet (the inferior opening of the pelvis measured between the ischial spines, and the inlet (superior opening between the right and left sides of the pelvic brim) are critical, and thus they are carefully measured by the obstetrician.

Bones of the Lower Limbs

The lower limbs carry the total body weight when we are erect; hence, it is not surprising that the bones forming the three segments of the lower limbs (thigh, leg, and foot) are much thicker and stronger than the comparable bones of the upper limb

The femur , or thigh bone, is the only bone in the thigh; it is the heaviest, strongest bone in the body.

Parts. Its proximal end has a ball-like head, a neck, and greater and lesser trochanters (separated anteriorly by the intertrochanteric line and posteriorly by the intertrochanteric crest ).
Gluteal tuberosity. These markings and the gluteal tuberosity, located on the shaft, all serve as sites for muscle attachment.
Head. The head of the femur articulates with the acetabulum of the hip bone in a deep, secure socket.
Neck. However, the neck of the femur is a common fracture site, especially in old age.
Lateral and medial condyles. Distally on the femur are the lateral and medial condyles, which articulate with the tibia below; posteriorly these condyles are separated by the deep intercondylar fossa .
Patellar surface. Anteriorly on the distal femur is the smooth patellar surface, which forms a joint with the patella, or kneecap.

Connected along their length by an interosseous membrane , two bones, the tibia and fibula, form the skeleton of the leg.

Tibia. The tibia, or shinbone , is larger and more medial; at the proximal end, the medial and lateral condyles articulate with the distal end of the femur to form the knee joint.
Tibial tuberosity. The patellar (kneecap) ligament attaches to the tibial tuberosity, a roughened area on the anterior tibial surface.
Medial malleolus. Distally, a process called medial malleolus forms the inner bulge of the ankle.
Anterior border. The anterior surface of the tibia is a sharp ridge, the anterior border, that is unprotected by the muscles; thus, it is easily felt beneath the skin.
Fibula. The fibula, which lies along the tibia and forms joints with it both proximally and distally, is thin and sticklike; the fibula has no part in forming the knee joint.
Lateral malleolus. Its distal end, the lateral malleolus, forms the outer part of the ankle.

The foot, composed of the tarsals, metatarsals, and phalanges, has two important functions.; it supports our body weight and serves as a lever that allows us to propel our bodies forward when we walk and run.

Tarsus. the tarsus, forming the posterior half of the foot, is composed of seven tarsal bones .
Calcaneus and Talus. Body weight is carried mostly by the two largest tarsals, the calcaneus, or heel bone , and the talus (ankle), which lies between the tibia and the calcaneus.
Metatarsals. Five metatarsals form the sole.
Phalanges. 14 phalanges form the toes; each toe has three phalanges, except the great toe, which has two.
Arches. The bones in the foot are arranged to form three strong arches: two longitudinal (medial and lateral) and one transverse.

Joints, also called articulations , have two functions: they hold the bones together securely, but also give the rigid skeleton mobility .

Classification. Joints are classified in two ways- functionally and structurally.
Functional classification. The functional classification focuses on the amount of movement the joint allows.
Types of functional joints. There are synarthroses or immovable joints; amphiarthroses , or slightly movable joints, and diarthrosis , or freely movable joints.
Diarthroses. Freely movable joints predominate in the limbs, where mobility is important.
Synarthroses and amphiarthroses. Immovable and slightly movable joints are restricted mainly to the axial skeleton, where firm attachments and protection of internal organs are priorities.
Structural classification. Structurally, there are fibrous , cartilaginous , and synovial joints; these classifications are based on whether fibrous tissue, cartilage, or a joint cavity separates the bony regions at the joint.

In fibrous joints, the bones are united by fibrous tissue.

Examples. The best examples of this type of joint are the sutures of the skull; in sutures, the irregular edges of the bones interlock and are bound tightly together by connective tissue fibers, allowing essentially no movement.
Syndesmoses. In syndesmoses, the connecting fibers are longer than those of sutures; thus the joint has more “give”; the joint connecting the distal ends of the tibia and fibula is a syndesmosis.

In cartilaginous joints, the bone ends are connected by cartilage.

Examples. Examples of this joint type that are slightly movable are the pubic symphysis of the pelvis and the intervertebral joints of the spinal column, where the articulating bone surfaces are connected by pads (discs) of fibrocartilage.
Synarthrotic cartilaginous joints. The hyaline cartilage epiphyseal plates of growing long bones and the cartilaginous joints between the first ribs and the sternum are immovable cartilaginous joints.

Synovial Joints

Synovial joints are joints in which the articulating bone ends are separated by a joint cavity containing a synovial fluid ; they account for all joints of the limbs.

Articular cartilage. Articular cartilage covers the ends of the bones forming the joints.
Fibrous articular capsule . The joint surfaces are enclosed by a sleeve or a capsule of fibrous connective tissue, and their capsule is lined with a smooth synovial membrane (the reason these joints are called synovial joints).
Joint cavity. The articular capsule encloses a cavity, called the joint cavity, which contains lubricating synovial fluid.
Reinforcing ligaments. The fibrous capsule is usually reinforced with ligaments.
Bursae. Bursae are flattened fibrous sacs lined with synovial membrane and containing a thin film of synovial fluid; they are common where ligaments, muscles, skin, tendons, or bones rub together.
Tendon sheath. A tendon sheath is essentially an elongated bursa that wraps completely around a tendon subjected to friction , like a bun around a hotdog.

The shapes of the articulating bone surfaces determine what movements are allowed at a joint; based on such shapes, our synovial joints can be classified as plane, hinge, pivot, condyloid, saddle, and ball-and-socket joints.

Plane joint. In a plane joint, the articular surfaces are essentially flat, and only short slipping or gliding movements are allowed; the movements of plane joints are nonaxial , that is, gliding does not involve rotation around any axis; the intercarpal joints of the wrist are best examples of plane joints.
Hinge joint. In a hinge joint, the cylindrical end of one bone fits into a trough-shaped surface on another bone; angular movement is allowed in just one plane, like a mechanical hinge; hinge joints are classified as uniaxial ; they allow movement in only one axis, and examples are the elbow joint, ankle joint, and the joints between the phalanges of the fingers.
Pivot joint. In a pivot joint, the rounded end of one bone fits into a sleeve or ring of bone; because the rotating bone can turn only around its long axis, pivot joints are also uniaxial joints ; the proximal radioulnar joint and the joint between the atlas and the dens of the axis are examples.
Condyloid joint. In a condyloid joint, the egg-shaped articular surface fits into an oval concavity in another; condyloid joints allow the moving bone to travel (1) from side to side and (2) back and forth but the bone cannot rotate around its long axis; movement occurs around two axes, hence these are biaxial joints .
Saddle joints. In saddle joints, each articular surface has both convex and concave areas, like a saddle; these biaxial joints allow essentially the same movements as condyloid joints; the best examples of saddle joints are the carpometacarpal joints in the thumb.
Ball-and-socket joint. In a ball-and-socket joint, the spherical head of one bone fits into a round socket in another; these multiaxial joints allow movement in all axes, including rotation, and are the most freely moving synovial joints; the shoulder and hip are examples.

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Anatomy and Physiology Nursing Test Banks . This nursing test bank includes questions about Anatomy and Physiology and its related concepts such as: structure and functions of the human body, nursing care management of patients with conditions related to the different body systems.

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6.1 The Functions of the Skeletal System

Learning objectives.

By the end of this section, you will be able to:

Define bone, cartilage, and the skeletal system
List and describe the functions of the skeletal system

Bone , or osseous tissue , is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body. In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage , a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement. The skeletal system is the body system composed of bones and cartilage and performs the following critical functions for the human body:

supports the body
facilitates movement
protects internal organs
produces blood cells
stores and releases minerals and fat

Support, Movement, and Protection

The most apparent functions of the skeletal system are the gross functions—those visible by observation. Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body.

Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin.

Bones also facilitate movement by serving as points of attachment for your muscles. While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract. From a mechanical point of view, bones act as levers and joints serve as fulcrums ( Figure 6.2 ). Unless a muscle spans a joint and contracts, a bone is not going to move. For information on the interaction of the skeletal and muscular systems, that is, the musculoskeletal system, seek additional content.

Bones also protect internal organs from injury by covering or surrounding them. For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain ( Figure 6.3 ).

Career Connection

Orthopedist.

An orthopedist is a doctor who specializes in diagnosing and treating disorders and injuries related to the musculoskeletal system. Some orthopedic problems can be treated with medications, exercises, braces, and other devices, but others may be best treated with surgery ( Figure 6.4 ).

While the origin of the word “orthopedics” (ortho- = “straight”; paed- = “child”), literally means “straightening of the child,” orthopedists can have patients who range from pediatric to geriatric. In recent years, orthopedists have even performed prenatal surgery to correct spina bifida, a congenital defect in which the neural canal in the spine of the fetus fails to close completely during embryologic development.

Orthopedists commonly treat bone and joint injuries but they also treat other bone conditions including curvature of the spine. Lateral curvatures (scoliosis) can be severe enough to slip under the shoulder blade (scapula) forcing it up as a hump. Spinal curvatures can also be excessive dorsoventrally (kyphosis) causing a hunch back and thoracic compression. These curvatures often appear in preteens as the result of poor posture, abnormal growth, or indeterminate causes. Mostly, they are readily treated by orthopedists. As people age, accumulated spinal column injuries and diseases like osteoporosis can also lead to curvatures of the spine, hence the stooping you sometimes see in the elderly.

Some orthopedists sub-specialize in sports medicine, which addresses both simple injuries, such as a sprained ankle, and complex injuries, such as a torn rotator cuff in the shoulder. Treatment can range from exercise to surgery.

Mineral Storage, Energy Storage, and Hematopoiesis

On a metabolic level, bone tissue performs several critical functions. For one, the bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and phosphorus. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.

Bone also serves as a site for fat storage and blood cell production. The softer connective tissue that fills the interior of most bone is referred to as bone marrow ( Figure 6.5 ). There are two types of bone marrow: yellow marrow and red marrow. Yellow marrow contains adipose tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy. Red marrow is where hematopoiesis —the production of blood cells—takes place. Red blood cells, white blood cells, and platelets are all produced in the red marrow.

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6.1 The Functions of the Skeletal System

Learning objectives.

By the end of this section, you will be able to:

List and describe the functions of the skeletal system

Attribute specific functions of the skeletal system to specific components or structures

The skeletal system is the body system composed of bones, cartilages, ligaments and other tissues that perform essential functions for the human body. Bone tissue, or osseous tissue , is a hard, dense connective tissue that forms most of the adult skeleton, the internal support structure of the body. In the areas of the skeleton where whole bones move against each other (for example, joints like the shoulder or between the bones of the spine), cartilages, a semi-rigid form of connective tissue, provide flexibility and smooth surfaces for movement. Additionally, ligaments composed of dense connective tissue surround these joints, tying skeletal elements together (a ligament is the dense connective tissue that connect bones to other bones). Together, they perform the following functions:

Support, Movement, and Protection

Some functions of the skeletal system are more readily observable than others. When you move you can feel how your bones support you, facilitate your movement, and protect the soft organs of your body. Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilages of your skeletal system compose the scaffold that supports the rest of your body. Without the skeletal system, you would be a limp mass of organs, muscle, and skin. Bones facilitate movement by serving as points of attachment for your muscles. Bones also protect internal organs from injury by covering or surrounding them. For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain (see Figure 6.1.1 ).

Mineral and Fat Storage, Blood Cell Formation

On a metabolic level, bone tissue performs several critical functions. For one, the bone tissue acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and phosphorus. These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes. Calcium ions, for example, are essential for muscle contractions and are involved in the transmission of nerve impulses.

Bones also serve as a site for fat storage and blood cell production. The unique connective tissue that fills the interior of most bones is referred to as bone marrow . There are two types of bone marrow: yellow bone marrow and red bone marrow. Yellow bone marrow contains adipose tissue, and the triglycerides stored in the adipocytes of this tissue can be released to serve as a source of energy for other tissues of the body. Red bone marrow is where the production of blood cells (named hematopoiesis, hemato- = “blood”, -poiesis = “to make”) takes place. Red blood cells, white blood cells, and platelets are all produced in the red bone marrow. As we age, the distribution of red and yellow bone marrow changes as seen in the figure ( Figure 6.1.2 ).

Career Connection – Orthopedist

This photo shows a man wearing a black arm brace on his upper arm and forearm. The brace is composed of an L shaped metal piece attached to an adjustable joint and four adjustable straps. The joint occurs at the elbow. One of the metal bars projects proximally from the joint up the forearm towards the shoulder. This bar is secured with two black straps to a foam cuff that wraps around the entire upper arm. The other metal bar projects distally from the joint, down the forearm, to the wrist. This bar is secured by two smaller foam wraps, one wrapping around the middle of the forearm and the other wrapping around the wrist.

Section Review

The major functions of the skeletal system are body support, facilitation of movement, protection of internal organs, storage of minerals and fat, and blood cell formation.

Review Questions

Critical thinking questions.

Suppose your red bone marrow could not be formed. What functions would your body not be able to perform?
Suppose your osseous tissue could not store calcium. What functions would your body not be able to perform?

Answers for Critical Thinking Questions

Without red bone marrow, you would not be able to produce blood cells. The red bone marrow is responsible for forming red and white blood cells as well as platelets. Red blood cells transport oxygen to tissues, and remove carbon dioxide. Without red blood cells, your tissues would not be able to produce ATP using oxygen. White blood cells play a role in the immune system fighting off foreign invaders in our body – without white blood cells you would not be able to recover from infection. Platelets are responsible for clotting your blood when a vessel ruptures. Without platelets you would bleed to death and die.
The calcium in osseous tissue provides mineral support to bones. Without this calcium, the bones are not rigid and cannot be supportive. The calcium in osseous tissue is also an important storage site, that can release calcium when needed. Other organ systems rely on this calcium for action (specifically, muscle contraction and neural signaling). Without calcium storage, blood calcium levels change dramatically and affect muscle contraction and neural signaling.

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Anatomy & Physiology

One organ at a time..., chapter 7: skeletal system.

Notes: Skeletal System | Lecture Slides

Coloring: Matrix Coloring | Bone Anatomy | Aging of the Hand | Bones of the Foot | Bones of the Hand

Label the Skeleton | Label the Skull | Label the Carpals and Tarsals

Investigation: Can you Estimate a Person's Height from Their Bones?

Investigation: The Mystery of the Bones (2 day Project) (optional)

Study Guide - Skeletal System

Practice Quizzes:

Bone Structure Terms Long Bone Anatomy Bone Matrix

Skull (picture) Skull on Quizlet (matching)

Skeletal System Carpals | Tarsals

Skeleton Lab with Lab Practical

*Examine a disarticulated skeleton (male and female), identify each bone and specific structures on each bone and conclude the unit with a Lab Practical Test

Lab Guide - lists all the bone structures for students to identify on bones

Bones Printables - make your own flashcards for studying

Lab Practical (Practice) | Printout Blank Sheets

Bones Album - labeled bones from the lab

Skull | Skull_2 | Skull 3 |

Femur | Femur 2 | Lower Leg | Pelvis | Pelvis 2

Lower Arm | Radius/Ulna | Humerus

Vertebrae | Foot |

Biology Article

Skeletal System

Human skeletal system.

The skeletal system functions as the basic framework of a body and the entire body are built around the hard framework of Skeleton. It is the combination of all the bones and tissues associated with cartilages and joints. Almost all the rigid or solid parts of the body are the main components of the skeletal system. Joints play an important role in the skeletal system as it helps in permitting the different types of movements at different locations. If the skeleton were without joints, then there would be no sign of the movements in the human body.

Skeletal System Anatomy

This skeletal system can be divided into the axial and appendicular systems. In an adult body, it is mainly composed of 206 individual bones which are organized into two main divisions:

Axial skeleton

Appendicular skeleton.

The axial skeleton runs along the body’s central axis, therefore it is called the central core of the human body. The axial skeleton is composed of 80 bones and it consists of:

Skull Bone – It includes 8 cranial bones, 14 facial bones, 6 auditory ossicles, and the Hyoid Bone
The bone of the Thoracic Cage – It includes 25 bones of the thorax- a breastbone and 24 ribs.
The bone of the Vertebral column- It includes 24 vertebrae bones, the sacrum bone, and the coccyx bone.

Also check: Function of Parietal Bones

Appendicular skeleton

The appendicular skeleton is composed of 126 bones and it comprises of the-

Pelvic girdle
Upper Limbs
Lower Limbs
Shoulder Girdle or the Pectoral

Read more: Parts and Names of Human Skeleton

Skeletal System Physiology

The primary functions of the skeletal system include movement, support, protection production of blood cells , storage of minerals and endocrine regulation.

The primary function of the skeletal system is to provide a solid framework to support and safeguard the human body and its organs. This helps in maintaining the overall shape of the human body.

Also check: Function of Short Bones

The skeletal system also helps to protect our internal organs and other delicate body organs, including the brain, heart, lungs and spinal cord by acting as a buffer. Our cranium (skull) protects our brain and eyes, the ribs protect our heart and lungs and our vertebrae (spine, backbones) protect our spinal cord.

Bones provide the basic structure for muscles to attach themselves onto so that our bodies are able to move. Tendons are tough inelastic bands that attach our muscle to that particular bone.

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The Human Body (Anatomy)
Anatomy (All Human Body Systems)
Skeletal System

An Introduction to the Skeletal System

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The skeleton forms the frame for the body and makes up about 1/5th of the body's weight. It is made up of 206 bones. It also includes cartilage , joints , and ligaments . Besides for forming our body frame the skeleton has several other jobs.

• It is the anchor and support for all our muscles and even our organs.

• It protects our vital organs like our brain, spinal cord, heart and lungs.

• It allows us to move with muscles attached by tendons using the bones as levers.

• It is a place for our body to store fat and minerals , like calcium.

• It is where the body makes most of its new blood cells .

Bones come in many shapes and sizes.

The long bones have a long shaft and two bigger ends. These include the bones of the arms and legs. The largest bone in the body, the femur , is a long bone. It is 2 feet long and hollow to make it lighter. It is very strong to support the body's weight.

The short bones are cube-shaped and include the bones of the wrist (carpals) and ankle (tarsals).

The flat bones are thin, curved and flattened like the sternum and skull.

Lastly, there are irregular bones like the vertebra and pelvis.

Each section of the skeleton has a job. Below see all the parts of the skeleton and how they work together to make the body a strong, moving machine.

To Learn about the Anatomy of Bone : Click Here

To Learn about Joints : Click Here

To Learn about the most common joints in the body - Synovial Joints : Click Here

For a Skeleton Labeling Page , hit the pdf below.

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Next generation science standards (ngss), grade 6-8 - ms-ls1 from molecules to organisms: structures and processes.

LS1.A: Structure and Function • All living things are made up of cells, which is the smallest unit that can be said to be alive. An organism may consist of one single cell (unicellular) or many different numbers and types of cells (multicellular). (MS-LS1-1) • Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2) • In multicellular organisms, the body is a system of multiple interacting subsystems. These subsystems are groups of cells that work together to form tissues and organs that are specialized for particular body functions. (MS-LS1-3)

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Spine and back
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Musculoskeletal system

Author: Gordana Sendić, MD • Reviewer: Jana Vasković, MD Last reviewed: November 03, 2023 Reading time: 28 minutes

The musculoskeletal system (locomotor system) is a human body system that provides our body with movement , stability, shape, and support. It is subdivided into two broad systems:

Muscular system , which includes all types of muscles in the body. Skeletal muscles, in particular, are the ones that act on the body joints to produce movements. Besides muscles, the muscular system contains the tendons which attach the muscles to the bones.
Skeletal system , whose main component is the bone . Bones articulate with each other and form the joints , providing our bodies with a hard-core, yet mobile, skeleton. The integrity and function of the bones and joints is supported by the accessory structures of the skeletal system; articular cartilage , ligaments , and bursae .

Besides its main function to provide the body with stability and mobility, the musculoskeletal system has many other functions; the skeletal part plays an important role in other homeostatic functions such as storage of minerals (e.g., calcium) and hematopoiesis, while the muscular system stores the majority of the body's carbohydrates in the form of glycogen.

This article will introduce you to the anatomy and function of the musculoskeletal system.

Key facts about the musculoskeletal system
Definition	A human body system that provides the body with movement, stability, shape, and support
Components	Muscular system: skeletal muscles and tendons Skeletal system: bones, joints; associated tissues (cartilage, ligaments, joint capsule, bursae)
Function	Muscles: Movement production, joint stabilization, maintaining posture, body heat production Bones: Mechanical basis for movements, providing framework for the body, vital organs protection, blood cells production, storage of minerals

Muscular system

Muscle contraction, functions of the muscular system, functions of the skeletal system, osteoporosis, muscular dystrophy, related articles.

The muscular system is an organ system composed of specialized contractile tissue called the muscle tissue . There are three types of muscle tissue, based on which all the muscles are classified into three groups:

Cardiac muscle , which forms the muscular layer of the heart ( myocardium )
Smooth muscle , which comprises the walls of blood vessels and hollow organs
Skeletal muscle , which attaches to the bones and provides voluntary movement.

Based on their histological appearance, these types are classified into striated and non-striated muscles; with the skeletal and cardiac muscles being grouped as striated , while the smooth muscle is non-striated . The skeletal muscles are the only ones that we can control by the power of our will, as they are innervated by the somatic part of the nervous system . In contrast to this, the cardiac and smooth muscles are innervated by the autonomic nervous system , thus being controlled involuntarily by the autonomic centers in our brain .

Skeletal muscles

The skeletal muscles are the main functional units of the muscular system. There are more than 600 muscles in the human body. They vary greatly in shape in size, with the smallest one being the stapedius muscle in the inner ear, and the largest one being the quadriceps femoris muscle in the thigh.

The skeletal muscles of the human body are organized into four groups for every region of the body:

Muscles of the head and neck , which include the muscles of the facial expression , muscles of mastication , muscles of the orbit , muscles of the tongue , muscles of the pharynx , muscles of the larynx , and muscles of the neck
Muscles of the trunk , which include the muscles of the back , anterior and lateral abdominal muscles , and muscles of the pelvic floor
Muscles of the upper limbs , which include muscles of the shoulder , muscles of the arm , muscles of the forearm and muscles of the hand
Muscles of the lower limbs , which include hip and thigh muscles , leg muscles and foot muscles

The fact that there are more than 600 muscles in the body can be quite intimidating. If you’re tired of all the big, comprehensive anatomy books, take a look at our condensed muscle anatomy reference charts , which contain all the muscle facts in one place organized into neat tables!

Structurally, the skeletal muscles are composed of the skeletal muscle cells which are called the myocytes (muscle fibres, or myofibrils ). Muscle fibers are specialized cells whose main feature is the ability to contract. They are elongated, cylindrical, multinucleated cells bounded by a cell membrane called sarcolemma . The cytoplasm of skeletal muscle fibers ( sarcoplasm ), contains contractile proteins called actin and myosin. These proteins are arranged into patterns, forming the units of contractile micro-apparatus called sarcomeres .

Each muscle fiber is enclosed with a loose connective tissue sheath called endomysium . Multiple muscle fibers are grouped into muscle fascicles or muscle bundles, which are encompassed by their own connective tissue sheath called the perimysium . Ultimately, a group of muscle fascicles comprises a whole muscle belly which is externally enclosed by another connective tissue layer called the epimysium . This layer is continuous with yet another layer of connective tissue called the deep fascia of skeletal muscle, that separates the muscles from other tissues and organs.

This structure gives the skeletal muscle tissue four main physiological properties:

Excitability - the ability to detect the neural stimuli ( action potential );
Contractibility - the ability to contract in response to a neural stimulus;
Extensibility - the ability of a muscle to be stretched without tearing;
Elasticity - the ability to return to its normal shape after being extended.

Learn everything about the skeletal muscle structure with our articles, video tutorials, quizzes and labelled diagrams.

The most important property of skeletal muscles is its ability to contract . Muscle contraction occurs as a result of the interaction of myofibrils inside the muscle cells. This process either shortens the muscle or increases its tension, generating a force that either facilitates or slows down a movement.

There are two types of muscle contraction; isometric and isotonic. A muscle contraction is deemed as isometric if the length of the muscle does not change during the contraction, and isotonic if the tension remains unchanged while the length of the muscle changes. There are two types of isotonic contractions:

Concentric contraction , in which the muscle shortens due to generating enough force to overcome the imposed resistance. This type of contraction serves to facilitate any noticeable movement (e.g. lifting a barbell or walking on an incline).
Eccentric contraction , in which the muscle stretches due to the resistance being greater than the force the muscle generates. During an eccentric contraction, the muscle maintains high tension. This type of contraction usually serves to slow down a movement (e.g. lowering a barbell or walking downhill).

The sequence of events that results in the contraction of a muscle cell begins as the nervous system generates a signal called the action potential . This signal travels through motor neurons to reach the neuromuscular junction , the site of contact between the motor nerve and the muscle. A group of muscle cells innervated by the branches of a single motor nerve is called the motor unit .

The incoming action potential from the motor nerve initiates the release of acetylcholine (ACh) from the nerve into the synaptic cleft , which is the space between the nerve ending and the sarcolemma. The ACh binds to the receptors on the sarcolemma and triggers a chemical reaction in the muscle cell. This involves the release of calcium ions from the sarcoplasmic reticulum , which in turn causes a rearrangement of contractile proteins within the muscle cell. The main proteins involved are actin and myosin, which in the presence of ATP, slide over each other and pull on the ends of each muscle cell together, causing a contraction. As the nerve signal diminishes, the chemical process reverses and the muscle relaxes.

A tendon is a tough, flexible band of dense connective tissue that serves to attach skeletal muscles to bones. Tendons are found at the distal and proximal ends of muscles, binding them to the periosteum of bones at their proximal ( origin ) and distal attachment ( insertion ) on the bone. As muscles contract, the tendons transmit the mechanical force to the bones, pulling them and causing movement.

Being made of dense regular connective tissue, the tendons have an abundance of parallel collagen fibers, which provide them with high tensile strength (resistance to longitudinal force). The collagen fibers within a tendon are organized into fascicles, and individual fascicles are ensheathed by a thin layer of dense connective tissue called endotenon . In turn, groups of fascicles are ensheathed by a layer of dense irregular connective tissue called epitenon . Finally, the epitenon is encircled with a synovial sheath and attached to it by a delicate connective tissue band called mesotenon .

Learn more about the microstructure of tendon in this study unit:

The main function of the muscular system is to produce movement of the body. Depending on the axis and plane, there are several different types of movements that can be performed by the musculoskeletal system. Some of the most important ones include:

Flexion and extension : movement of decreasing or increasing the angle between the bones involved in the movement, respectively. This motion takes place in the sagittal plane around a frontal axis. An example of flexion is bending the leg at the knee joint , whereas extension would be straightening knee from a flexed position.
Adduction and abduction : movements of bringing the parts of the body towards or away from the midline, respectively. These movements are carried out in the frontal plane around a sagittal axis. For example, abduction of the arm at the shoulder joint involves moving the arm away from the side of the body, while adduction involves bringing it back towards the body.
Rotation is the movement in which a part of the body rotates around its vertical (longitudinal) axis in the transverse plane. This movement is defined relative to the midline, where internal rotation involves rotating the segment towards to the midline, while external rotation involves moving it away from the midline. Examples include lateral or medial rotation of the thigh .
Supination and pronation are special types of rotatory movements usually used to describe the movements of the forearm . Supination is essentially a lateral rotation of the forearm which turns the palms anteriorly (if the arm is anatomical position) or superiorly, when the elbow is flexed. These movements are also sometimes used to describe movements in the ankle and foot , in which supination means rolling the foot outwards, while pronation means rolling the foot inwards.

Both during movement and stationary positions, muscles contribute to the overall support and stability of joints . Many muscles and their tendons pass over joints and thereby stabilize the articulating bones and hold them in position. In addition, the muscles also play an important role in maintaining posture . While the movements occur mainly due to muscles intermittently contracting and relaxing, the posture is maintained by a sustained tonic contraction of postural muscles. These muscles act against gravity and stabilize the body during standing or walking. The postural muscles include the muscles of the back and abdominal muscles.

Another important function of muscles is heat production . Muscle tissue is one of the most metabolically active tissues in the body, in which approximately 85 percent of the heat produced in the body is the result of muscle contraction. This makes the muscles essential for maintaining normal body temperature.

Wondering what’s the best way to learn and understand the functional anatomy of the muscles? Check out our 3D muscle anatomy videos !

To improve your understanding of muscular system terminology, take a closer look at some commonly used roots, prefixes and suffixes related to the muscular system in the video below.

How well do you know the main muscles of the body? Test your knowledge with our quiz in different difficulty levels!

Skeletal system

The adult human skeleton is composed of 206 bones and their associated cartilages. The bones are supported by ligaments, tendons, bursae, and muscles. The bones of the body are grouped within the two distinct divisions:

Axial skeleton , that includes the bones along the long axis of the body. The axial skeleton consists of the vertebral column , bones of the head and bones of the thoracic cage .
Appendicular skeleton , that involves the bones of the shoulder and pelvic girdle , as well as the bones of the upper and lower extremities .

Bones are rigid structures made of calcified dense connective tissue. Bone tissue is composed of a mineralized bone matrix that consists of type 1 collagen fibers dispersed throughout the ground substance . The cellular component of the bones is represented by three types of specialized bone cells called osteocytes, osteoblasts and osteoclasts .

The bones consist of two distinct layers that differ in histological appearance and characteristics;

Compact (cortical) bone is the outer much denser layer of the bone which gives it its smooth, white, and solid appearance. The outer surface of the compact bone is covered with a layer of dense connective tissue called the periosteum. On its inner surface, the compact bone is covered with endosteum , which is the boundary between the compact and spongy bones .
Spongy (cancellous) bone is the deep airy layer of the bone. Unlike the compact bone, spongy bone is highly vascularized and more metabolically active. It is typically found within the ends of long bones and in the vertebrae. In certain bones, like the hip bone , sternum or femur, the central part of spongy bone houses the bone marrow, which is the site of hematopoiesis in the adult.

Types of bones

Bones can be classified according to their shapes as follows:

Long bones have a tubular shape, with a longer longitudinal and a shorter transverse diameter. They are composed mostly of compact bone, while the spongy bone and bony marrow fill the ends of the bones. Examples of long bones include the humerus , ulna , tibia and clavicle .
Short bones have a roughly cuboid or round shape, and only contain a thin layer of compact bone surrounding the spongy bone. Examples include the tarsal and carpal bones .
Flat bones are mostly thin, flattened and usually curved. They contain two parallel layers of compact bones surrounding a layer of spongy bone. Examples include most of the skull bones , scapula , sternum and sacrum .
Sesamoid bones are small, rounded unique types of bones that are embedded in muscle tendons where the tendon passes over a joint. The largest sesamoid bone in the body is the patella , but several other smaller sesamoid bones can be found in the hand and foot, usually in close proximity to the joints.
Irregular bones do not fit into any of the other categories. Generally, irregular bones contain foramina through which soft tissue and neurovascular structures pass. Examples include the vertebrae , hip bone and some bones of the skull.

Wondering how to cut time in learning the bones of the body? Try our skeletal system quizzes !

A typical long bone consists of a long shaft ( diaphysis ) that extends into a neck ( metaphysis ) and head ( epiphysis ) on its proximal and distal ends. It also features various markings and formations that give passage to neurovascular structures, as well as the attachment sites to the ligaments and tendons. Some of those features include:

Sulcus – a shallow groove on the bone surface (e.g. radial sulcus of humerus)
Condyle – rounded articular area (e.g. lateral condyle of tibia)
Epicondyle – eminence superior to a condyle (medial epicondyle of femur)
Crest – ridge of bone (e.g. iliac crest)
Facet – smooth, flat area, usually covered with cartilage (e.g. articular facet on vertebrae)
Foramen – passage through a bone (e.g. foramen magnum on the occipital bone)

Cartilage is a flexible connective tissue found in multiple organ systems of the body. Cartilage is composed of specialized cells called chondrocytes , collagen fibers and abundant ground substance rich in proteoglycan and elastin fibers.

Cartilage is classified into the following types based on its composition:

Hyaline cartilage is composed of type II collagen and an abundance of ground substance, which gives it a glossy appearance. It is the most abundant type of cartilage found in joints (articular cartilage), as well as the nose, larynx , trachea and ribs .
Elastic cartilage is similar to hyaline cartilage but contains more elastic fibers. It is found in structures such as the pinna of the ear , auditory tube and epiglottis .
Fibrocartilage is composed of plenty of collagen fibers type I and a smaller amount of ground substance. Examples of fibrocartilage include intervertebral discs , pubic and other symphyses.

The musculoskeletal system specifically contains articular cartilage, a type of cartilage that lines the articulating surfaces of bones. The articular cartilage provides congruence to the articulating bones and allows them to bear weight and glide over each other with very little friction.

Each bone of the musculoskeletal system is connected to one or more bones via a joint . Joints provide a fulcrum to the bones, on which they pivot and thereby allow movements of body parts. However, movement is not a necessary attribute of a joint as some joints do not move, such as joints between the bones of the skull. The integrity or stability of a joint is provided by several factors including the bony congruence and structures that cross the joint, such as tendons and ligaments.

Based on the type of tissue that holds the neighboring bones together and the range of motion they exhibit, joints can be classified into the following:

Synovial joints are freely mobile joints in which the bones are not in direct contact, but are separated by a potential space called the synovial cavity . The synovial cavity is lined by a synovial membrane that secretes the synovial fluid which nourishes and lubricates the articulating surfaces in order to reduce friction. The articulating bones in most synovial joints are lined with hyaline cartilage. These joints usually have a wide range of motion, which is defined by the joint capsule, the supporting ligaments and muscles that cross the joint. Examples of synovial joints include the knee, shoulder, sternoclavicular and elbow joints .
Fibrous joints are the articulations in which the bones are connected by dense fibrous connective tissue. The bones in fibrous joints are firmly held together so that the joint allows negligible movement. Fibrous joints are found between the cranial sutures , the distal tibiofibular and cuboideonavicular joints.
Cartilaginous joints are articulations in which the bones are connected by cartilage. The bones have a range of motion between synovial and fibrous joints. Cartilaginous joints are subdivided into synchondrosis (e.g. costochondral joints ) and symphysis joints (e.g. pubic symphysis).

According to the movements they allow and/or the shape of their articulating surface, the synovial joints can be further subdivided into 6 major types:

Ball and socket joints (e.g. hip joint )
Condyloid joints (e.g. metacarpophalangeal joint)
Hinge joints (e.g. elbow joint)
Pivot joints (e.g. atlanto-axial joint)
Saddle joints (e.g. carpometacarpal joint)
Plane joints (e.g. acromioclavicular joint )

Ligaments are fibrous bands made of dense regular connective tissue which are similar in structure to tendons. Unlike the tendons that connect muscles to bone, the ligaments connect bone to bone . Besides the musculoskeletal system, the ligaments are also found in many other parts of the body, where they usually stabilize and hold internal organs in place and transmit neurovascular structures.

In the musculoskeletal system, ligaments stabilize the articulating bones and reinforce the joints. Depending on their anatomic position relative to the joint capsule, ligaments are classified into:

Capsular ligaments are essentially thickenings of the joint capsule that form either elongated bands or triangular structures. These ligaments serve to reinforce the integrity of the joint capsule. An example of the capsular ligament is the iliofemoral ligament of the hip joint.
Intracapsular ligaments are the ligaments that lie internal to the joint capsule. These ligaments reinforce the connection of the articulating surfaces of the joint, but allow a far wider range of motion than other ligaments. Examples include anterior and posterior cruciate ligament of the knee joint.
Extracapsular ligaments are ligaments that lie outside the joint capsule. These ligaments provide the most stability to the articulating bones, and are important for preventing dislocations. Extracapsular ligaments can lie in close proximity (e.g. medial collateral ligament of the ankle joint ) or a bit further from the joint capsule ( vertebral ligaments ).

Bursae are small sac-like outpouchings of the joint cavity lined by synovial membrane. They are found around the joints, providing cushioning of the associated bones, tendons and muscles and reducing friction between adjacent structures.

The majority of synovial bursae are located near the large joints of the arms and legs. For example, one of the bursae of the knee joint is the suprapatellar bursa , found superior to the patella, between the femur and the tendon of the quadriceps femoris muscle . The suprapatellar bursa allows for these structures to slide over each other without friction during flexion and extension of the knee joint.

To improve your understanding of skeletal system terminology, take a closer look at some commonly used roots, prefixes and suffixes related to the skeletal system in the video below.

Time for a skeletal system workout with our integrated quiz!

The skeletal system serves a variety of functions. The bones give the shape to the body and provide the site of attachment to muscles, tendons, ligaments and cartilage. These tissues function together as a whole to generate a force that provides the biomechanical basis of movement .

Due to its structural integrity, the skeletal system protects the internal organs, most importantly the brain, which is surrounded by the skull, as well as the heart and lungs , which are protected by the rib cage.

Moreover, the skeletal system serves several metabolic functions . The bones are the storage site of important minerals, most notably calcium and phosphorus. This makes the bones essential for balancing calcium levels in the blood, which is regulated by adjusting the rate of bone resorption.

Lastly, the bone marrow found in spongy bone is the site of hematopoiesis , which is a process of production of new blood cells. Cells that are produced in the bone marrow are red blood cells, platelets and white blood cells, such as monocytes, granulocytes and lymphocytes .

We created a custom summary quiz about the anatomy and histology of the main features of the musculoskeletal system. You can adjust and filter individual structures to make this quiz your own!

Clinical correlation

There is a variety of conditions that affect the muscles, bones, and joints. Disorders of the musculoskeletal system may range from diseases to minor physical disabilities. The following are some clinical conditions of the musculoskeletal system:

Osteoporosis is a condition that affects bone strength (the word osteoporosis literally means "porous bones"). It is a condition in which the bones become fragile and brittle, leading to a higher risk of fractures than in normal bone. As a result, even a minor bump or accident can cause serious fractures.

Osteoporosis is the “bone of the old”, especially, in women. The hard, rock-like quality of bone is dependent upon calcium. When too much calcium is dissolved from bones or not enough is replaced, bones lose density and are easily fractured. Estrogen, the female sex hormone, helps maintain proper calcium levels in bones. Once the ovaries stop producing the hormone, women are at higher risk of developing osteoporosis. A collapse of bony vertebrae of the spinal column results in loss of height and stooped posture. Hip fractures are a common occurrence.

Sarcopenia is a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes such as physical disability, poor quality of life and death.

Arthritis is a group of conditions affecting the joints . These conditions cause damage to the joints, usually resulting in pain and stiffness due to aging. Arthritis can affect many different parts of the joint and nearly every joint in the body.

As an individual ages, the joint tissues become less resilient to wear and tear and start to degenerate. This degeneration manifest as swelling, pain, and often-times, loss of mobility of joints. Changes occur in both joint soft tissues and the articulating bones, a condition called osteoarthritis . A more serious form of disease is called rheumatoid arthritis . The latter is an autoimmune disease wherein the body produces antibodies against joint tissues causing chronic inflammation resulting in severe joint damage, pain and immobility.

Muscular dystrophy is a group of muscle diseases that weaken the musculoskeletal system and hamper locomotion. Muscular dystrophies are characterized by progressive skeletal muscle weakness , defects in muscle proteins, and the death of muscle fibres (muscle cells) and tissue.

It is a group of inherited diseases in which the muscles that control movement progressively weaken. The prefix, dys-, means abnormal, while the root, -trophy, refers to maintaining normal nourishment, structure and function. The most common form in children is called Duchenne muscular dystrophy and affects only males. It usually appears between the ages of 2 to 6 and the afflicted live typically into late teens to early 20s.

Other conditions involving the musculoskeletal system include:

Lupus erythematosus
Myasthenia gravis
Rotator cuff tear
Carpal tunnel syndrome
Osteomalacia

References:

Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
Netter, F. (2019). Atlas of Human Anatomy (7th ed.). Philadelphia, PA: Saunders.
Standring, S. (2016). Gray's Anatomy (41st ed.). Edinburgh: Elsevier Churchill Livingstone.
Ross, Lawrence M; Lamperti, Edward D, eds. (2006). Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System.
R.M.H McMinn: Last's anatomy (Regional and Applied), 9th edition, Ana-Maria Dulea (2014

Illustrations:

Musculoskeletal system - Irina Münstermann
Eccentric and concentric muscle contractions (diagram) - Yousun Koh

Articles within this topic:

Ball and socket joint
Complete list of bone markings
Ellipsoid joint
Head and neck anatomy
Hinge-joint
How to learn all muscles with quizzes and labeled diagrams
Intercostal muscles
Lateral abdominal muscles
Learn skull anatomy with skull bones quizzes and diagrams
Lower limb anatomy
Muscle anatomy reference charts
Muscles of the neck: An overview
Muscles of the trunk
Musculoskeletal system development
Parietal bone
Pectoralis minor muscle
Pivot joint
Rectus abdominis muscle
Synovial membrane
Upper limb muscles and movements

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Did you know that human babies are born with more bones than an adult? Human babies have more than 270 bones. Human adults have 206 bones. What's the reason for the difference? Many baby bones fuse together as they develop and grow to become one single bone. Here's another fun fact: your skeleton comprises 30-40% of your body weight.

Learning about the skeleton can be tons of fun. Children are often amazed to learn about their bodies and how the skeleton functions. You can amaze your young students with fun facts and guessing games. For example, ask your class how many bones they have in their feet? The answer is 26 bones.

Classroom Resources of Teaching about the Human Skeletal System

While a classroom skeleton model would be fantastic, it's not always in the school budget. Clip art can be a fantastic resource and substitute for a full scale model. Worksheets and activities also help children embrace learning and remembering. Teacher Planet has all the resources, lesson plans and even worksheets you need to bring the skeletal system to your classroom.

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