Locomotion and MovementNEET Zoology · Class 11 · NCERT Chapter 17

You can expect 1 question from Locomotion and Movement in NEET 2027. The chapter has a medium weightage with around 4 questions across recent years. The most reliable scoring areas are: the sarcomere bands (A band, I band, H zone, Z line), the sliding filament theory steps, properties of the three muscle types, total bone count (206) and the axial vs appendicular split (80 + 126), and the common disorders (myasthenia gravis, tetany, gout, osteoporosis).

Movement is any change in position of a body part. It is seen in all living things, including plants (like the movement of chloroplasts towards light). Locomotion is the movement of the whole body from one place to another. Not all movements are locomotion. For example, your heart beating is movement, not locomotion. Animals use locomotion to find food, escape predators and reproduce.

Skeletal muscle is striated (has light and dark bands), voluntary (you control it), multinucleated, and gets tired with sustained effort. Examples: biceps, quadriceps. Smooth muscle is non-striated, involuntary (you cannot control it), has a single central nucleus, and does not fatigue easily. Examples: muscles of the gut wall, blood vessels, uterus. Cardiac muscle is striated but involuntary. It has a single nucleus and the fibres are branched with intercalated discs. It never fatigues during a normal lifetime. Found only in the heart.

A sarcomere runs from one Z line to the next Z line. Inside it: A band (the full length of the thick myosin filament, stays the same length during contraction), I band (only actin, between two A bands of adjacent sarcomeres, gets shorter during contraction), H zone (the middle of the A band with only myosin and no actin overlap, gets shorter or disappears), M line (midpoint of the A band, myosin filaments attach here), Z line (the anchor for actin). During contraction the I band and H zone shorten (or disappear). The A band does NOT change length.

The sliding filament theory says that during muscle contraction the thin actin filaments slide over the thick myosin filaments towards the centre of the sarcomere. The filaments themselves do not get shorter. The sarcomere shortens because the actin slides in. The shortening of millions of sarcomeres adds up to the shortening of the whole muscle. This sliding is powered by the cross bridges: the myosin heads attach to actin, bend (the power stroke), detach, and then reset. Each cycle uses one ATP molecule.

There are 206 bones in the adult human skeleton. They are divided into: Axial skeleton (80 bones): skull (22), vertebral column (26), ribs (24) and sternum (1) plus 7 hyoid and ear ossicles. Appendicular skeleton (126 bones): pectoral girdle (4), upper limbs (60), pelvic girdle (2), lower limbs (60). You should know the axial number (80), appendicular number (126) and total (206) for NEET.

Myasthenia gravis: autoimmune disease where antibodies destroy the acetylcholine receptors at the neuromuscular junction. Result: progressive muscle weakness and paralysis. Muscular dystrophy: genetic disorder causing progressive degeneration of skeletal muscle. Tetany: abnormal muscle spasms due to low calcium in the blood (hypocalcaemia). Arthritis: inflammation of joints. Osteoarthritis is age-related wear and tear; rheumatoid arthritis is autoimmune. Osteoporosis: bone density decreases, bones become fragile and break easily. Common in post-menopausal women. Gout: uric acid crystals deposit in joints (especially the big toe) causing inflammation and severe pain.