Why might someone think that the skeleton isn’t living tissue? People might forget that bones grow because they appear dead and dried up, because of their high content of nonliving minerals (calcium and phosphorus), and because bones remain long after a dead person’s skin, muscles, and organs have decayed.
The skeleton is moved by the muscles that attach to it. Ninety percent of the body’s supply of calcium is stored in the bones and teeth. What are some important organs that are protects by bone? Possible answers include the brain protected by the cranium and the heart protected by the thoracic cage. Minerals make bones harder. What will likely happen in a person with a diet chronically low in calcium? What will happen in a child who is deprived of sunlight over a long period? The bones become soft in both cases.
The size and shape of each bone reflects its function. Some bones (e.g., in the legs and feet) are weight-bearing bones, whereas those of the skull are designed to protect the brain. Explain why the finger bones (phalanges) are classified as long bones. They are longer than they are wide, and they are neither irregular nor flat in shape.
An osteocyte is a bone cell; bone is also called osseous tissue. A haversian system is a small cylindrical unit of compact bone tissue. It is the same as an osteon. Ask students to point out the rich supply of blood within the osteon. On part B of the slide, ask students to identify spongy bone versus compact plates. Emphasize the presence of the trabecular plates in soft bone. Bone contains large number of collagen (protein) fibers.
On part A of the slide, ask students to identify each structure listed on the slide. Note the position of the epiphyseal disc. The periosteum (outer covering) carries the blood vessel to the bone. The red bone marrow sits in the Swiss cheese holes and is responsible for the formation of red blood cells. Bone marrow depression is relatively common and can be lethal.
The early fetal skeleton is made of entirely of cartilage, most of which is later replaced by bone. What parts of the adult body are still made of cartilage? Cartilage is found in the joints, the bridge of the nose, the larynx (Adam’s apple), parts of the ribs, and the ears.
Cartilage forms in the growth plate (epiphyseal disc) and pushes toward the bone shaft (diaphysis), where it ossifies. Can you predict the effects of too little or too much growth hormone? Hypersecretion of growth hormone leads to giantism, whereas hyposecretion leads to a type of dwarfism. Why are boys typically taller than girls? Estrogen fuses the growth plate earlier than testosterone.
Factors in bone growthhormones, exercise, weight-bearing activities. Ask students to visualize the leg bone of an infant and compare it with the thickness of their own leg bones. Point out that osteoblastic and osteoclastic activity has widened their bones. Exercise and weight bearing make bones grow thicker and wider. The immobility of bed rest causes the loss of calcium from the bones. A trick for keeping the termsosteoblast and osteoclast straight is to remember that the osteoblast is the “brick layer.” Consequence of immobility: Calcium moves out of the bone, causing osteomalacia (bone softening, fractures) and kidney stones.
Projections help bones form joints with each other and form points of attachment for muscles. Have students palpate (feel) examples of several bone projections on their own bodies: The tibial tuberosity is just beneath the knee. The iliac crest is the top of the pelvis. The mastoid process is behind the base of the ear. The spines on the vertebral column. The tuberosity of the calcaneus is the point of the heel bone.
The grooves and depressions form routes for blood vessels and nerves to pass over and through bones and joints.
What is the difference between simple and compound fractures? Simple fractures break the bone all the way through, but the overlying skin isn’t pierced. Compound fractures break through the skin, causing extensive tissue damage. There is a risk of infection. Why are greenstick fractures more common in children? Children’s bones are less brittle than adult bones. Because they contain more protein, they are more pliable than adult bones.
To remember these terms, think of the axial skeleton as being the axis of the body—a line up and down, around which motion occurs. The appendicular skeleton contains the appendages—the arms and legs.
Note: The axial skeleton is shown in pink.
The joints between the cranial bones are called sutures. The incomplete fusion of palatine bones in an infant results in cleft palate. Ask students to examine the slide and distinguish between the zygomatic bone and the zygomatic process. The zygomatic bone is the check bone and the zygomatic process is part of the temporal bone. What are some possible complications of having a broken mandible that has been wired shut? Possible problems include poor nutrition because of difficulty eating, aspirating (inhaling) vomit, and lingering temporomandibular joint (TMJ) stiffness after wires are removed.
The foramen magnum (view C) is the site where the brain descends as the spinal cord. Ask students to locate the occipital condyles on the slide. They sit on the first vertebra and allow a person to nod “yes.”
The paranasal sinuses reduce the weight of the skull and modulate the volume of the voice. In general, a sinus is a cavity or space. The sinuses are named after the bones in which they are found. The paranasal sinuses are lined with mucous membranes and connect with the nasal passages and throat, so infections may spread from the nose and throat into the sinuses. A sinus infection is called sinusitis. Ask students who suffer from sinusitis to tell where the pain occurs during an attack. Students will name a number of facial areas.
Although a baby’s fontanels are softer than bone and seem fragile, they are actually quite durable and can be handled normally. A bulging fontanel is one sign of increased pressure within the skull. Sunken fontanels may indicate dehydration. The sutures and fontanels facilitate the birth process.
Ask students to feel the bump at the base of the neck. This landmark is the vertebra prominens C7. Ask students to note on the slide how vertebra are named and numbered. Example: C1 to C7 are the cervical vertebra. Why are the lumbar vertebrae bigger and thicker than the other vertebrae? The lumbar vertebrae support a greater weight of the body. A lumbar puncture is done between L3 and L4. Ask students to point out this site on the slide. The vertebral curve in an infant is single C-shaped curve, but toddlers have developed all four of the curves shown on the slide because of weight bearing and the upright position.
The atlas (C1) and the axis (C2) are shown in the picture. How do these two vertebrae work together? The atlas supports the skull, and the dens of the axis forms a pivot or swivel for the atlas. The dens is also known as the odontoid process. The vertebrae are stacked, so the vertebral foramen form a bony tube through which the spinal cord descends. Fracture of the dens, usually as a result of whiplash-type injuries or shaken baby syndrome, is the most common cervical fracture, especially among the very young and the very old. Ask students to point out on the slide where the vertebral disc sits. It sits on the bodies of the vertebrae. It separates them and acts as a shock absorber.
Approximately 80% of people who have scoliosis are female. Most school screenings include a check for scoliosis. Lordosis can be caused or worsened by pregnancy or weight gain. Poor abdominal muscle tone also contributes to lordosis. Kyphosis can impair respiratory function.
The sternum looks like a dagger. The ribs are numbered. What are the differences among true, false, and floating ribs? True ribs attach to the sternum. False ribs (which include the floating ribs) attach indirectly to the sternum by cartilage. The bottom two pairs of ribs are floating; that is, they do not attach to the sternum at all.
This area of the body contains important landmarks. Have students feel their supersternal notch. Next, have them feel the sternomanubrial joint. This will be important in counting ribs. Have students refer to the slide and feel the costal angle and margin on their own bodies. Why does the costal angle increase in pregnancy? The costal angle increases to accommodate the size of the fetus. Have students locate the xiphoid process on their own bodies. Although the xiphoid process is a landmark for CPR, the chest compressions are done above the process (i.e., closer to the head) to prevent breaking the process and/or injuring underlying organs.
The bones of the appendicular skeleton are shown in tan. What similarity is there in the arrangement of the bones in the upper and lower limbs? There is one bone in the arm and thigh, two bones in the forearm and leg, and similarities in the ankles and wrists and hands and feet. Why is this portion of the skeletal system called the appendicular skeleton? It has this name because it includes the appendages.
What are the common names for the clavicle and scapula? The clavicle is called the collarbone and the scapula is called the shoulder blade or wing bone. Ask students to identify the glenoid cavity on the slide and explain what is happening there. The head of the humerus fits into the glenoid cavity to form the shoulder joint, a freely moveable joint. Ask students to identify the olecranon process and fossa on the slide and explain what is happening there. These structures form the elbow. On supination and pronation, the radius and ulna twist. (See view B.)
In general, the female pelvis is broader and shallower than the male pelvis. These differences are related primarily to childbearing. What happens to the symphysis pubis during pregnancy? Hormones prompt the disc (and other connective tissue) to expand to allow more space in the pelvic girdle to accommodate the growing fetus. The acetabulum (depression) is formed by the three parts of coxal bone. What is the difference between the pelvic girdle and the pelvis? The pelvic girdle is formed by two coxal bones. The pelvis is formed by the two coxal bones plus the sacrum and coccyx. Point out that the iliac crest is the site of bone marrow aspiration.
Which bone is usually involved in a broken “hip?” Fracture of the neck of the femur is called a broken hip. The hip joint is formed by the interaction of the femur and acetabulum. What is the interaction of the distal femur and the proximal femur called? It is called the knee. Ask student to identify on their own bodies the medial and lateral malleoli.
The ankle is formed by the tibia, fibula, and tarsal bones. The arches formed by the foot bones act as important “shock absorbers” for the body. Individuals with poor arches, or “flat feet,” sometimes experience pain in the feet or lower legs. Strong ligaments support these bones; it is a weakening of the ligaments (not the bones) that causes flat feet.
What are the two main functions of joints? They hold the bones together. They provide flexibility to the skeleton. What are examples of slightly movable joints? Examples of slightly movable joints are the symphysis pubis and the joints in the vertebral column. What are arthrology and rheumatology? Arthrology is the scientific study of joints. Rheumatology is the study of joint diseases.
The most common type of arthritis, osteoarthritis, is caused by the breakdown of articular cartilage, causing bone to rub against bone. The bursae can become inflamed from injury, overuse, or infection, causing pain in a joint (especially the shoulder). This condition is called bursitis. Synovial fluid fills the joint cavity.
The wide range of motion of the shoulder joint contributes to its being the most frequently dislocated joint. In addition, the rotator cuff muscles, which help hold the joint together, are susceptible to strain and tears from unusual or repeated motions. Hinge joints are vulnerable to injury, like twisting and hyperextension of the knee. Ask a student to explain the seriousness of the clipping penalty in football. Clipping involves tackling the knee in a way that twists it. Because it can cause such a serious injury it is heavily penalized.
Ask students to explain why the shoulder joint is named the way it is. It involves the glenoid cavity and the humerus.
Joint movements are described relative to anatomical position. A way to remember the meaning of supination is to remember that when a bowl is full of soup, it faces upward. What kind of joint movements are (1) punting a football, (2) showing off the biceps, (3) looking upward to the sky, and (4) flapping the arm as if to fly? (1) Extension of the leg, (2) flexion of the forearm, (3) hyperextension of the neck, (4) abduction and adduction of the arm.
1. The Human Body in Health and
Illness, 4th edition