Three types of movement exist in living organisms: ciliary (respiratory tract, fallopian tubes), flagellar (spermatozoa), and muscular (locomotion and organ function).

Skeletal muscle is striated, voluntary, and multinucleated; smooth muscle is non-striated, involuntary, and uninucleate; cardiac muscle is uniquely striated and involuntary, with intercalated discs.

The sarcomere (Z-line to Z-line) is the functional contractile unit; the A band (dark) is always constant in width; the I band (light, actin-only) and H zone (myosin-only) both decrease during contraction.

In the sliding filament theory, actin slides over stationary myosin without either filament changing its own length, causing sarcomere shortening.

The contraction sequence is: nerve impulse → ACh → action potential → T-tubules → Ca2+ from SR → troponin-C activated → tropomyosin shifts → cross-bridge → power stroke → ATP binds (detach) → ATP hydrolyzed (re-energize).

ATP has two roles: hydrolysis re-energizes the myosin head; binding causes detachment from actin; without ATP, rigor mortis occurs.

The adult human skeleton has 206 bones: 80 axial (skull 22, vertebrae 26, ribs 24, sternum 1, hyoid 1) and 126 appendicular; the hyoid bone uniquely does not articulate with any other bone.

Joints are classified as fibrous (immovable, skull sutures), cartilaginous (slightly movable, pubic symphysis), and synovial (freely movable, 6 subtypes: hinge, pivot, ball-and-socket, gliding, saddle, ellipsoid).

Six musculoskeletal disorders are NEET-relevant: myasthenia gravis (autoimmune ACh receptor destruction), muscular dystrophy (genetic dystrophin deficiency), tetany (hypocalcemia), osteoarthritis (degenerative), rheumatoid arthritis (autoimmune synovitis), osteoporosis (post-menopausal bone loss), and gout (uric acid crystals).

The three most tested NEET facts are: the A band is always constant; cardiac muscle is striated and involuntary; and the total adult bone count is 206 (80 axial + 126 appendicular).