NEET Biology — Locomotion and Movement Complete Chapter Guide

Chapter Overview & Weightage

Locomotion and Movement covers types of movement, skeletal muscle structure, the sliding filament mechanism of contraction, the skeletal system, types of joints, and muscular disorders. The muscle contraction mechanism is the core of this chapter for NEET.

This chapter carries 3-4% weightage in NEET with 2-3 questions. Muscle contraction mechanism (sliding filament theory), types of joints, and skeletal system facts dominate.

Key Concepts You Must Know

Tier 1 (Core)

Skeletal muscle structure: muscle → fascicles → muscle fibres → myofibrils → sarcomere
Sarcomere: A band (dark, myosin), I band (light, actin), H zone (myosin only), Z line (boundaries)
Sliding filament theory: actin slides over myosin, sarcomere shortens, I band and H zone shrink, A band stays same
Role of calcium: released from sarcoplasmic reticulum → binds troponin → tropomyosin shifts → myosin binding sites exposed
Neuromuscular junction: nerve impulse → ACh release → muscle depolarisation

Tier 2 (Frequently tested)

Types of joints: fibrous (skull sutures), cartilaginous (vertebrae), synovial (knee, shoulder)
Synovial joint subtypes: ball-and-socket, hinge, pivot, gliding, saddle
Skeletal system: 206 bones in adult, axial (80) + appendicular (126)
Types of muscles: skeletal (voluntary, striated), smooth (involuntary, non-striated), cardiac (involuntary, striated)

Tier 3 (Occasionally tested)

Disorders: myasthenia gravis, muscular dystrophy, tetany, osteoporosis, arthritis, gout
ATP role: myosin ATPase breaks ATP for cross-bridge cycling
Rigor mortis: no ATP → permanent cross-bridges → stiffness after death

Important Formulas

Component	At Rest	During Contraction
Sarcomere length	~2.5 μm	Decreases
A band	Full length	Stays same
I band	Full length	Decreases
H zone	Visible	Decreases or disappears
Z lines	Far apart	Move closer

Key rule: A band length does NOT change during contraction — only I band and H zone shrink.

Nerve impulse arrives at neuromuscular junction
ACh released → muscle fibre depolarisation
Ca $^{2+}$ released from sarcoplasmic reticulum into sarcoplasm
Ca $^{2+}$ binds to troponin on thin filaments
Tropomyosin shifts, exposing myosin-binding sites on actin
Myosin heads (cross-bridges) attach to actin → power stroke
ATP binds to myosin → cross-bridge detaches → cycle repeats
Ca $^{2+}$ pumped back into SR → relaxation

The fact that the A band stays constant during contraction is tested almost every year. It’s the single most important fact about the sliding filament mechanism for NEET. Also remember: it’s the actin (thin filaments) that slide — myosin stays stationary.

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: During muscle contraction, which of the following does NOT change in length?

(A) I band (B) A band (C) H zone (D) Sarcomere

Solution:

The A band (anisotropic band, dark band) contains the full length of myosin filaments. Since myosin doesn’t move or shorten during contraction (actin slides over it), the A band length remains constant.

I band, H zone, and overall sarcomere length all decrease during contraction.

Answer: (B) A band

PYQ 2 — NEET 2023

Problem: Ball and socket joint is present in:

(A) Knee (B) Shoulder (C) Elbow (D) Between atlas and axis

Solution:

Knee: hinge joint (flexion and extension only)
Shoulder: ball-and-socket joint (head of humerus fits into glenoid cavity of scapula — allows movement in all directions)
Elbow: hinge joint
Atlas-axis: pivot joint (allows rotational movement of head)

Hip joint is also ball-and-socket. These two (shoulder and hip) are the main examples.

Answer: (B) Shoulder

PYQ 3 — NEET 2022

Problem: The

mineral component of bone matrix is:

(A) Calcium phosphate (B) Calcium carbonate (C) Calcium chloride (D) Sodium phosphate

Solution:

Bone matrix has two components: organic (collagen fibres, about 1/3) and inorganic (mineral salts, about 2/3). The primary mineral is calcium phosphate in the form of hydroxyapatite [ $Ca_{10}(PO_4)_6(OH)_2$ ]. This gives bone its hardness and rigidity.

Answer: (A) Calcium phosphate

Difficulty Distribution

Difficulty	% of Questions	What to Expect
Easy	45%	Joint type identification, bone count facts, muscle types
Medium	40%	Sliding filament mechanism steps, sarcomere changes
Hard	15%	Cross-bridge cycling details, disorder mechanisms

Expert Strategy

Day 1: Sarcomere and sliding filament mechanism. Draw the sarcomere, label all bands and zones. Then draw it in the contracted state. This visual comparison teaches you what changes and what doesn’t.

Day 2: Skeletal system — focus on classification of joints with examples. Know the axial vs appendicular skeleton division. Bone count (206) is a direct fact question.

Day 3: Event sequence of muscle contraction and the role of Ca $^{2+}$ . Understand neuromuscular junction and the role of ACh. Revise with NCERT diagrams.

Make a comparison table: skeletal vs smooth vs cardiac muscle. Compare: striation, voluntary/involuntary, nuclei per cell (multi/single/1-2), intercalated discs (only cardiac), location. This table covers 2-3 potential NEET questions.

Common Traps

Trap 1 — A band stays constant, not I band. The most tested trap. A band = myosin region = constant. I band = actin-only region = shrinks as actin slides inward.

Trap 2 — Calcium comes from the sarcoplasmic reticulum, not outside the cell. The Ca $^{2+}$ that triggers contraction is released from the SR (an internal store), not from the extracellular fluid. However, in cardiac muscle, some Ca $^{2+}$ does enter from outside.

Trap 3 — ATP is needed for both contraction AND relaxation. ATP breaks the cross-bridge (releases myosin from actin) and powers the Ca $^{2+}$ pump that returns Ca $^{2+}$ to SR. Without ATP, muscles stay contracted — this explains rigor mortis.

Trap 4 — Intercalated discs are exclusive to cardiac muscle. These gap junctions allow electrical coupling between cardiac muscle cells for synchronised contraction. Skeletal muscle has neuromuscular junctions instead — each fibre is independently innervated.