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.