Locomotion and Movement
NCERT Line-by-Line Breakdown for NEET 2026
Unit 5: Human PhysiologyMovement is a significant feature of living beings. Streaming of protoplasm in amoeba is a simple form of movement. Locomotion refers to voluntary movements resulting in a change of place or location. In this chapter, we explore Types of Movement, the Mechanism of Muscle Contraction, and the Human Skeletal System.
1. Types of Movement
Cells of the human body exhibit three main types of movements:
| Type | Mediated By | Location/Example |
|---|---|---|
| Amoeboid | Pseudopodia (via Microfilaments). | Macrophages and Leucocytes (WBCs). |
| Ciliary | Cilia. | Trachea (removes dust), Fallopian tubes (moves ova). |
| Muscular | Contractile property of muscles. | Limbs, Jaws, Tongue. |
2. Muscle (The Contractile Tissue)
Mesodermal in origin. Constitutes 40-50% of body weight.
Structure of Skeletal Muscle
Muscle → Muscle Bundles (Fascicles) → Muscle Fibers (Cells) → Myofibrils.
[Image of structure of sarcomere]- A-Band (Anisotropic): Dark band. Contains Myosin (Thick) + overlapping Actin.
- I-Band (Isotropic): Light band. Contains only Actin (Thin).
- Z-Line: Elastic fiber holding Actin filaments.
- M-Line: Membrane holding Myosin filaments.
- H-Zone: Central part of A-Band where Actin does NOT overlap.
Contractile Proteins
- Actin (Thin): Polymer of G-Actin. Contains regulatory proteins Tropomyosin and Troponin (Masks active binding sites).
- Myosin (Thick): Polymer of Meromyosins. Head has ATPase enzyme and Actin binding sites.
3. Sliding Filament Theory
Contraction is initiated by a neural signal releasing Acetylcholine at the neuromuscular junction.
- Action potential spreads → Releases Calcium (Ca++) from Sarcoplasmic Reticulum.
- Ca++ binds to Troponin → Unmasks active sites on Actin.
- Myosin head binds to Actin → Forms Cross Bridge.
- Power Stroke: Myosin pulls Actin towards M-line → Sarcomere shortens (Contraction).
- ATP binds to Myosin → Cross bridge breaks.
Red Muscles (Aerobic, High Myoglobin) vs White Muscles (Anaerobic, Low Myoglobin).
4. Skeletal System
Consists of 206 bones and cartilages. Divided into Axial and Appendicular skeleton.
- Skull (22): Cranial (8) + Facial (14). Hyoid (1). Ear Ossicles (6).
- Vertebral Column (26): C7, T12, L5, S1(fused), C1(fused).
- Sternum (1): Flat bone.
- Ribs (24): True (1-7), False (8-10), Floating (11-12).
- Limbs (120): 30 bones per limb. (Humerus, Radius, Ulna, Carpals, etc. / Femur, Tibia, Fibula, Tarsals, etc.)
- Girdles (6): Pectoral (Clavicle + Scapula) & Pelvic (Coxal bone: Ilium, Ischium, Pubis).
5. Joints & Disorders
A. Joints
- Fibrous (Immovable): Sutures in skull.
- Cartilaginous (Slightly Movable): Between vertebrae.
- Synovial (Freely Movable): Fluid filled cavity.
- Ball & Socket: Shoulder, Hip.
- Hinge: Elbow, Knee.
- Pivot: Atlas & Axis.
- Gliding: Carpals.
- Saddle: Thumb (Carpal & Metacarpal).
B. Disorders
- Myasthenia Gravis: Auto-immune. Affects neuromuscular junction. Weakness/Paralysis.
- Muscular Dystrophy: Genetic. Progressive degeneration of skeletal muscle.
- Tetany: Rapid spasms (low Ca++).
- Arthritis: Inflammation of joints. (Rheumatoid = Auto-immune; Osteoarthritis = Age-related; Gout = Uric acid crystals).
- Osteoporosis: Decreased bone mass. Age-related (Estrogen deficiency common cause).
📝 Rapid Fire MCQs
Q1. Which ion is essential for unmasking of active sites for myosin?
- A) Na+
- B) K+
- C) Ca++
- D) Mg++
Click to check Answer
Answer: C) Ca++ (Binds to Troponin).
Q2. Glenoid cavity articulates:
- A) Clavicle with Acromion
- B) Scapula with Acromion
- C) Clavicle with Scapula
- D) Humerus with Scapula
Click to check Answer
Answer: D) Humerus with Scapula (Shoulder joint).