The Skeleton
The skeletal system consists of bones and tissues essential for supporting, protecting, and moving the body.
The human skeleton comprises 206 individual bones.
Axial Skeleton: Includes the bones of the skull, spine, ribs, and sternum.
Appendicular Skeleton: Consists of the bones in the arms, legs, pelvis, and shoulders.
Functions:
Supports the body and protects soft tissues.
Allows for limited movement.
The most complex part is the skull, which connects to the spine.
The rib cage consists of 12 pairs of ribs.
Responsible for movement in the limbs (shoulders, arms, hips, legs).
Comprises girdles (pectoral for shoulders, pelvic for hips) that attach limbs to the body.
Functions of Bones:
Support the body.
Protect internal organs.
Facilitate movement due to attached skeletal muscles.
Store minerals and fats.
Blood cell formation.
Types of Bones:
Long Bones (e.g., humerus): Longer than wide, with a shaft and heads at each end.
Short Bones (e.g., carpals): Generally cube-shaped with mostly spongy bone.
Flat Bones (e.g., parietal bones): Thin and flattened or curved with layers of compact and spongy bone.
Irregular Bones (e.g., vertebrae): Do not fit into other categories due to irregular shapes.
Surrounded by periosteum (a tough membrane).
Composed of compact bone (dense outer layer) and spongy bone (inner core with cavities).
Bone Marrow:
Red Bone Marrow: Produces blood cells.
Yellow Bone Marrow: Primarily fat storage.
Bones grow after birth through ossification, where cartilage is replaced by bone.
Calcification is the process of forming hard bone.
Loss of bone density leading to osteoporosis can occur in young adults.
-Cartilage: Connects skeletal bones, cushions ends, and allows smooth movement.
Types of Joints:
Immovable Joints: Limited movement (e.g., cranial bones).
Slightly Movable Joints: Limited movement (e.g., rib cage).
Freely Movable Joints: Varied movement depending on structure (e.g., knee).
Functions:
Produces body movement.
Maintains posture and stabilizes joints.
Generates heat.
Types of Muscle:
Smooth Muscle: Involuntary, non-striated, found in organs.
Cardiac Muscle: Striated, involuntary, found in the heart.
Skeletal Muscle: Voluntary, striated, and attached to the bones.
Skeletal muscles consist of bundles of long fibers with striations.
Myofibrils contain two types of filaments:
Actin (thin filaments).
Myosin (thick filaments).
The functional unit of contraction is called the sarcomere.
Muscle contraction occurs in the sarcomeres by the sliding-filament model.
Actin filaments slide along myosin filaments, causing sarcomere shortening.
Calcium ions expose myosin-binding sites on actin, initiating contraction.
Muscle contractions utilize ATP through aerobic respiration and may switch to anaerobic pathways during brief activities.
Action potentials from motor neurons release acetylcholine, leading to depolarization and muscle contraction.
Calcium ions released from the sarcoplasmic reticulum allow contraction; their absence leads to muscle relaxation.
Benefits of Exercise:
Aerobic exercise enhances heart efficiency.
Resistance training increases muscle size and strength.