Skeletal and muscular system

Skeletal and Muscular System

Skeletal System

  • 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.

Axial Skeleton

  • 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.

Appendicular Skeleton

  • Responsible for movement in the limbs (shoulders, arms, hips, legs).

  • Comprises girdles (pectoral for shoulders, pelvic for hips) that attach limbs to the body.

Classification of Bones Based on Shape

  • 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:

    1. Long Bones (e.g., humerus): Longer than wide, with a shaft and heads at each end.

    2. Short Bones (e.g., carpals): Generally cube-shaped with mostly spongy bone.

    3. Flat Bones (e.g., parietal bones): Thin and flattened or curved with layers of compact and spongy bone.

    4. Irregular Bones (e.g., vertebrae): Do not fit into other categories due to irregular shapes.

Structure of Bone

  • 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.

Growth of Bones

  • 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.

Joints

-Cartilage: Connects skeletal bones, cushions ends, and allows smooth movement.

  • Types of Joints:

    1. Immovable Joints: Limited movement (e.g., cranial bones).

    2. Slightly Movable Joints: Limited movement (e.g., rib cage).

    3. Freely Movable Joints: Varied movement depending on structure (e.g., knee).

Muscular System

  • Functions:

    • Produces body movement.

    • Maintains posture and stabilizes joints.

    • Generates heat.

  • Types of Muscle:

    1. Smooth Muscle: Involuntary, non-striated, found in organs.

    2. Cardiac Muscle: Striated, involuntary, found in the heart.

    3. Skeletal Muscle: Voluntary, striated, and attached to the bones.

Muscle Structure

  • 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

  • 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.

Regulation of Muscle Contraction

  • 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.

Exercise and Fitness

  • Benefits of Exercise:

    • Aerobic exercise enhances heart efficiency.

    • Resistance training increases muscle size and strength.

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