Key Points

Movement is a change in posture or position of any body part, while locomotion is a voluntary movement that results in a change of place or location. All locomotions are movements, but all movements are not locomotions.

Cells in the human body exhibit three main types of movements: amoeboid (e.g., macrophages), ciliary (e.g., in the trachea), and muscular (e.g., limbs and jaw).

Muscles are classified into three types: Skeletal (striated, voluntary), Visceral or Smooth (non-striated, involuntary), and Cardiac (striated, branched, involuntary).

A sarcomere is the functional unit of muscle contraction, extending between two Z-lines. It contains a central dark 'A' band (myosin) and two lighter half 'I' bands (actin) on either side.

Actin forms the thin filaments, which also include troponin and tropomyosin. Myosin forms the thick filaments, with globular heads that act as ATPase enzymes and bind to actin.

This theory states that muscle contraction occurs when thin actin filaments slide over thick myosin filaments, causing the sarcomere to shorten. The lengths of the actin and myosin filaments themselves do not change.

A nerve impulse releases acetylcholine, causing an action potential in the sarcolemma. This triggers the release of calcium ions ((Ca^{++})) from the sarcoplasmic reticulum.

(Ca^{++}) ions bind to troponin, exposing active sites on actin. Myosin heads then bind to actin, forming cross-bridges and pulling the actin filaments inward using energy from ATP hydrolysis.

Red fibers have high myoglobin content and many mitochondria for sustained aerobic activity. White fibers have low myoglobin, rely on anaerobic glycolysis, and are suited for rapid, intense contractions.

The human skeleton has 206 bones and is divided into the Axial skeleton (80 bones: skull, vertebral column, sternum, ribs) and the Appendicular skeleton (126 bones: limbs and girdles).

The vertebral column consists of 26 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 1 fused sacral, and 1 fused coccygeal. The first vertebra is the atlas.

The rib cage includes 12 pairs of ribs, the thoracic vertebrae, and the sternum. Ribs 1-7 are true ribs, 8-10 are vertebrochondral (false) ribs, and 11-12 are floating ribs.

The pectoral (shoulder) girdle consists of the clavicle and scapula. The pelvic (hip) girdle is formed by two coxal bones, each a fusion of the ilium, ischium, and pubis.

Joints are classified as Fibrous (immovable, e.g., skull sutures), Cartilaginous (limited movement, e.g., vertebrae), and Synovial (considerable movement, fluid-filled cavity).

Key examples are the ball and socket joint (shoulder), hinge joint (knee), pivot joint (atlas and axis), gliding joint (carpals), and saddle joint (thumb).

Myasthenia gravis is an autoimmune disorder affecting the neuromuscular junction. Muscular dystrophy is a genetic disorder causing progressive muscle degeneration. Tetany involves rapid muscle spasms due to low body fluid (Ca^{++}).

Arthritis is the inflammation of joints. Osteoporosis is an age-related disorder with decreased bone mass. Gout is joint inflammation caused by the accumulation of uric acid crystals.