Board exam focus — Locomotion and Movement (CBSE & HBSE)

This chapter examines how animals move and change position. It covers the types of movement (amoeboid, ciliary, muscular), the detailed structure of skeletal muscle and its contractile proteins, the sliding filament theory of muscle contraction, the human skeletal system and its divisions, types of joints, and important disorders of the muscular and skeletal systems such as myasthenia gravis, tetany, arthritis, osteoporosis and gout.

Types of Movement & Muscle Structure

Movement vs Locomotion

• Movement is a characteristic feature of all living organisms (e.g., streaming of cytoplasm, beating of cilia).
• Locomotion is the movement that results in change of place or position of the whole organism (e.g., walking, swimming, flying).
• All locomotion is movement, but not all movements are locomotion.

Types of Movement in Humans

Properties of Muscle

Muscles show excitability, contractility, extensibility and elasticity. Three types based on structure and function:

Structure of Skeletal Muscle

• A muscle is made of bundles called fascicles held by collagenous connective tissue.
• Each fascicle contains muscle fibres (myocytes).
• The fibre membrane = sarcolemma; cytoplasm = sarcoplasm; ER = sarcoplasmic reticulum (stores Ca2+).
• Each fibre contains many parallel myofibrils, which show the characteristic banding.

Sarcomere — Functional Unit

The sarcomere is the region between two Z-lines (Z-discs) and is the functional unit of contraction.

• I-band (Isotropic): light band, contains only thin (actin) filaments; bisected by the Z-line.
• A-band (Anisotropic): dark band, contains thick (myosin) filaments (may overlap with actin).
• H-zone: central part of A-band with only myosin.
• M-line: centre of the H-zone.

Contractile Proteins & Sliding Filament Theory

Contractile Proteins

Thick filament — Myosin

• Made of many meromyosin molecules.
• Each meromyosin has a globular head (HMM, with ATPase and actin-binding sites) and a tail (LMM).
• The head forms cross-bridges with actin.

Thin filament — Actin + regulatory proteins

• F-actin (two helical strands of G-actin monomers).
• Tropomyosin runs along the groove of actin.
• Troponin sits at intervals on tropomyosin and masks the active sites of actin in a resting muscle.

Sliding Filament Theory (Huxley)

Muscle contraction occurs by the sliding of thin (actin) filaments over thick (myosin) filaments, shortening the sarcomere without the filaments themselves shortening.

Sequence of Events:

1. A motor neuron signal reaches the neuromuscular junction, releasing acetylcholine, generating an action potential in the sarcolemma.
2. The impulse spreads along T-tubules and triggers release of Ca2+ from the sarcoplasmic reticulum.
3. Ca2+ binds to troponin, removing the masking by tropomyosin and exposing the active sites on actin.
4. The energized myosin head binds actin forming a cross-bridge.
5. The cross-bridge pulls (power stroke) the actin toward the centre of the sarcomere; ADP + Pi are released.
6. A fresh ATP binds the myosin head, detaching it; ATP hydrolysis re-energizes the head for the next cycle.
7. The cycle repeats as long as Ca2+ and ATP are available.
8. On relaxation, Ca2+ is pumped back, active sites are masked again, and the muscle relaxes.

Key Point: Both contraction AND relaxation require ATP. After death, ATP depletion prevents detachment of cross-bridges, causing rigor mortis.

Red vs White Muscle Fibres

Skeletal System, Joints & Disorders

The Human Skeletal System

The skeleton consists of 206 bones in an adult, divided into:

Axial Skeleton (80 bones)

• Skull (29): 8 cranial + 14 facial + ear ossicles (6) + 1 hyoid.
• Vertebral column (26): cervical (7), thoracic (12), lumbar (5), sacrum (1, fused), coccyx (1, fused).
• Ribs (24, i.e., 12 pairs): true (7), false (3), floating (2).
• Sternum (1).

Appendicular Skeleton (126 bones)

• Forelimbs / hindlimbs (each limb: 30 bones).
• Pectoral girdle (clavicle + scapula).
• Pelvic girdle (ilium + ischium + pubis fused as coxal/hip bones).

Joints

A joint is the point of contact between bones (or bone and cartilage). Movement is impossible without joints.

Types of Synovial Joints:

• Ball and socket: shoulder, hip (all-direction movement).
• Hinge: knee, elbow (one-plane movement).
• Pivot: between atlas and axis (rotation).
• Gliding: between carpals.
• Saddle: between carpal and metacarpal of the thumb.

Disorders of the Muscular and Skeletal System

• Myasthenia gravis: an autoimmune disorder affecting the neuromuscular junction, causing fatigue, weakness and paralysis of skeletal muscles.
• Muscular dystrophy: progressive degeneration of skeletal muscle (genetic).
• Tetany: rapid spasms (wild contractions) of muscles due to low Ca2+ in body fluid.
• Arthritis: inflammation of joints.
• Osteoporosis: age-related disorder with decreased bone mass and increased fracture risk; linked to lowered estrogen levels.
• Gout: inflammation of joints due to accumulation of uric acid crystals.

Board Tip: Tetany is caused by a fall in blood calcium, while gout is caused by uric acid deposition — do not confuse the two.

Frequently asked questions

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Do these notes follow CBSE and HBSE?

Yes. The Locomotion and Movement notes are NCERT-aligned and include guidance for both CBSE and Haryana Board (HBSE), with important questions and MCQs for revision.

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Concept explanations, key formulas and definitions, fully solved examples and board-pattern practice questions for Locomotion and Movement.