Chapter 3: Skeletal System Notes

Functions of the Skeleton

• Gives support and shape to the body

• Protects vital organs

• Assists in movement

• Manufactures blood cells (hematopoiesis occurs in bone marrow)

Axial and Appendicular Skeleton

• Axial Skeleton: Bones of the head, neck, thorax, and vertebral column

• Appendicular Skeleton: Bones of the extremities

Table 3-1 Bones of the Human Body (Bone Count Overview)

• Axial Skeleton (total $80$)

  • Cranium ( $8$ bones )

    • Frontal

    • Sphenoid

    • Ethmoid

    • Occipital

    • Parietal (paired)

    • Temporal (paired)

  • Face ( $14$ bones )

    • Mandible

    • Vomer

    • Maxilla

    • Zygomatic

    • Lacrimal

    • Inferior concha

    • Palatine

    • Nasal

  • Hyoid (single bone)
    → as part of axial skeleton count

  • Ear ossicles ( $3$)
    → malleus, incus, stapes

  • Vertebral column ( $26$ )

    • Cervical ( $7$ )

    • Thoracic ( $12$ )

    • Lumbar ( $5$ )

    • Sacrum ( $5$)*

    • Coccyx ( $3$)*

    • *Sacrum and Coccyx are composed of fused bones and counted as a single bone each ( asterisk notes fusion)

  • Thorax ( $25$ )

    • Sternum (1)

    • Ribs ( $12 ext{ pairs} = 24$ )

• Appendicular Skeleton (total $126$)

  • Upper extremity ( $64$ )

    • Clavicle

    • Scapula

    • Humerus

    • Ulna

    • Radius

    • Carpals ( $16$)

    • Metacarpals ( $10$)

    • Phalanges ( $28$)

  • Lower extremity ( $62$ )

    • Innominate

    • Femur

    • Tibia

    • Fibula

    • Patella

    • Tarsals ( $14$)

    • Metatarsals ( $10$)

    • Phalanges ( $28$)

• Note: Bones comprising more than one bone that are fused together and counted as one bone are indicated by asterisk: Sacrum (5), Coccyx (3)

Composition of Bone

• Two primary bone tissue types:

  • Compact bone

  • Cancellous (trabecular) bone

Wolff’s Law

• Bone density increases in response to increased mechanical forces imposed

• Bone density decreases in response to decreased forces imposed

Structure of Bone

• Epiphysis: ends of long bones

• Diaphysis: shaft (middle portion)

• Metaphysis: region between epiphysis and diaphysis (growth zone in developing bones)

Epiphyseal Plate and Related Structure

• Epiphyseal plate (growth plate) in children/adolescents: a cartilaginous layer responsible for longitudinal bone growth; it calcifies and ossifies as a person reaches skeletal maturity, leading to fusion.

• Epiphysis: end region of a long bone; primarily responsible for articulation with other bones and providing surface area for muscle attachment.

• Metaphysis: region between diaphysis and epiphysis; where the epiphyseal plate is located in growing bones, important for bone remodeling and growth.

• Epiphyseal lines: remnants after growth plate closure; indicate that bone growth in length has ceased.

• Endosteum: membrane lining the medullary cavity; involved in bone growth, repair, and remodeling.

• Medullary canal (cavity): central marrow-containing space; contains bone marrow, which is crucial for hematopoiesis (blood cell production) in red marrow and fat storage in yellow marrow.

• Periosteum: dense, fibrous outer membrane covering bone; protects the bone, serves as an attachment point for tendons and ligaments, and contains osteoblasts for bone growth and repair.

• Compact bone: dense outer layer; provides strength and protection to the bone, enabling it to withstand stress.

• Cancellous bone: spongy inner network within epiphyses; provides structural support while reducing bone weight and contains red bone marrow.

Types of Bones

• Long bones

• Short bones

• Flat bones

• Irregular bones

• Sesamoid bones

Table 3-2: Types of Bones (Examples)

• Long bones: typically longer than wide; include most of the limb bones

  • Examples: Femur, Humerus, Tibia, Radius, Ulna, Metacarpals, Metatarsals, Phalanges

• Short bones: cube-like; primarily in wrists and ankles

  • Examples: Carpals, Tarsals

• Flat bones: thin and curved; provide protection and ample surface area for muscle attachment

  • Examples: Cranial bones (frontal, parietal, occipital, temporal, sphenoid, zygomatic), Ribs, Sternum, Scapula

• Irregular bones: complex shapes that do not fit other categories

  • Examples: Vertebrae, Mandible, Facial bones

• Sesamoid bones: embedded within tendons; alter pressure, protect tendons

  • Example: Patella, hyoid bone (in neck), hallucis (under big toe)

Table 3-3 Structural Characteristics of Bones

Projections or Processes That Fit Into Joints

Projections and Processes That Attach Tendons, Ligaments, and Other Connective Tissue

Common Pathologies (Selected Conditions)

• Fractures: A break or crack in a bone, typically caused by trauma or overuse.

• Osteopenia: A condition where bone mineral density is lower than normal, but not yet severe enough to be classified as osteoporosis. It is often a precursor to osteoporosis.

• Osteoporosis: A disease where bones become weak and brittle, making them more susceptible to fractures. This occurs when the body loses too much bone, makes too little bone, or both.

• Osteomyelitis: An infection of the bone or bone marrow, usually caused by bacteria, but can also be caused by fungi or other germs.

• Legg-Calve-Perthes disease: A childhood condition that occurs when blood supply to the ball part (femoral head) of the hip joint is temporarily interrupted and the bone begins to die. This can cause the bone to flatten and eventually heal, but may lead to problems later in life.

• Slipped capital femoral epiphysis: A hip disorder in adolescents where the growth plate (epiphysis) of the thigh bone (femur) slips off the top of the bone, backward and downward. This can cause hip pain and limping.

• Osgood-Schlatter disease: An inflammation of the patellar ligament at the tibial tuberosity (the bony prominence just below the knee). It is common in adolescents, especially during growth spurts and with increased physical activity, causing pain and swelling below the knee.

Notes:

The chapter discusses skeletal structure, biology, and common pathologies relevant to clinical kinesiology and anatomy.

Key terms include the growth plate (epiphyseal plate), periosteum, endosteum, and the distinction between compact and cancellous bone.

The material links bone structure to function, mechanics (Wolff's Law), and clinical conditions affecting bone integrity and growth.