NCERT Solutions for Class 11 Biology Chapter 17 Locomotion and Movement
NCERT Solutions for Class 11 Biology Chapter 17 Locomotion and Movement provides comprehensive revision notes and textbook solutions covering types of movement, structure of contractile proteins, mechanism of muscle contraction, human skeletal system, joints, and disorders of the muscular and skeletal systems.
Overview of Topics & Subtopics (Click to Jump)
1. Types of Movement & Structure of Skeletal Muscle
Short Note:
• Types of Movements in Human Body Cells:
- Amoeboid: Exhibited by macrophages and leucocytes using pseudopodia formed by microfilaments.
- Ciliary: Occurs in internal tubular organs lined by ciliated epithelium (e.g., clearing dust in trachea, passage of ova through fallopian tubes).
- Muscular: Movement of limbs, jaws, tongue, etc., requiring contractile property of muscles.
• Types of Muscles: Skeletal (striated, voluntary), Visceral (non-striated, involuntary), and Cardiac (striated, branched, involuntary).
• Skeletal Muscle Structure: Made up of muscle bundles (fascicles) held together by connective tissue fascia. Each muscle fiber contains parallel myofibrils showing alternate dark (A-band or Anisotropic band) and light (I-band or Isotropic band) striations.
• Sarcomere: Functional unit of contraction present between two consecutive Z-lines. Contains central H-zone (myosin only) bisected by M-line.
2. Structure of Contractile Proteins & Mechanism of Muscle Contraction
Short Note:
• Contractile Proteins:
- Thin Filament (Actin): Composed of double-helical F-actin polymers, wrapped by filamentous Tropomyosin and complex Troponin (masks active myosin-binding sites in resting state).
- Thick Filament (Myosin): Polymer of Meromyosins. Each meromyosin has a globular head (with active ATPase site & actin-binding site) and a tail.
• Sliding Filament Theory:
1. Action potential arrives at Neuromuscular Junction → releases Acetylcholine (ACh) → triggers Ca²⁺ release from Sarcoplasmic Reticulum into sarcoplasm.
2. Ca²⁺ binds to Troponin → unmasks myosin-binding sites on actin.
3. ATP hydrolysis on myosin head provides energy → forms Cross Bridge with actin.
4. Myosin head pulls actin filaments toward M-line → Z-lines come closer → Sarcomere shortens (I-band reduces, H-zone disappears, A-band length remains unchanged).
3. Human Skeletal System (Axial & Appendicular)
Short Note:
• The human skeleton consists of 206 bones divided into two main divisions:
- Axial Skeleton (80 bones):
* Skull: 22 bones (8 Cranial + 14 Facial) + 1 Hyoid + 6 Ear ossicles (Malleus, Incus, Stapes).
* Vertebral Column: 26 serially arranged vertebrae (7 Cervical, 12 Thoracic, 5 Lumbar, 1 Sacral fused, 1 Coccygeal fused).
* Sternum & Ribs: 1 Sternum + 12 pairs of Ribs (7 True ribs, 8th–10th False/Vertebrochondral ribs, 11th–12th Floating ribs).
- Appendicular Skeleton (126 bones):
* Limbs: 30 bones in each limb (Forelimbs: Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges; Hindlimbs: Femur, Tibia, Fibula, Patella, Tarsals, Metatarsals, Phalanges).
* Girdles: Pectoral girdle (Clavicle + Scapula) and Pelvic girdle (2 Coxal bones formed by fusion of Ilium, Ischium, and Pubis).
4. Joints & Disorders of Muscular and Skeletal Systems
Short Note:
• Types of Joints:
- Fibrous Joints: Immovable (e.g., sutures of skull bones).
- Cartilaginous Joints: Permit limited movement (e.g., joints between adjacent vertebrae).
- Synovial Joints: Characterized by fluid-filled synovial cavity; freely movable (e.g., Ball & Socket joint, Hinge joint, Pivot joint, Gliding joint, Saddle joint).
• Disorders:
- Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction causing fatigue, weakening, and paralysis of skeletal muscle.
- Muscular Dystrophy: Progressive degeneration of skeletal muscle (mostly genetic).
- Tetany: Rapid spasms/cramps in muscle due to low Ca²⁺ in body fluid.
- Arthritis: Inflammation of joints (Gout: inflammation due to accumulation of uric acid crystals).
- Osteoporosis: Age-related disorder characterized by decreased bone mass and increased fracture risk (often due to decreased estrogen level).
Intext & Conceptual Questions
The Sliding Filament Theory states that contraction of a muscle fiber occurs by the sliding of thin (actin) filaments over thick (myosin) filaments:
1. Initiation: Neural signal triggers release of Calcium ions (Ca²⁺) from sarcoplasmic reticulum into sarcoplasm.
2. Cross-Bridge Formation: Ca²⁺ binds to Troponin, removing the mask on active sites of Actin. The myosin head hydrolyzes ATP, binds to actin, and forms a cross-bridge.
3. Power Stroke: Myosin pulls actin towards the center of the A-band (M-line), causing shortening of the sarcomere (contraction).
4. Relaxation: A new ATP binds to myosin head, releasing the cross-bridge. Ca²⁺ is pumped back into sarcoplasmic reticulum, masking actin sites again.
• Ball and Socket Joint: Between Humerus and Pectoral Girdle (Shoulder joint).
• Hinge Joint: Knee joint / Elbow joint.
• Pivot Joint: Between Atlas and Axis vertebrae.
• Gliding Joint: Between Carpals in the wrist.
• Saddle Joint: Between Carpal and Metacarpal of thumb.
Textbook Chapter End Exercise Questions
| Feature | Red Muscle Fibers | White Muscle Fibers |
|---|---|---|
| Myoglobin Content | High content of red oxygen-storing pigment (Myoglobin). | Low content of Myoglobin, giving a pale/white appearance. |
| Mitochondria | Contain abundant mitochondria. | Contain fewer mitochondria. |
| Sarcoplasmic Reticulum | Less developed sarcoplasmic reticulum. | Extensive and well-developed sarcoplasmic reticulum. |
| Respiration & Fatigue | Depend on aerobic respiration; slow rate of fatigue. | Depend on anaerobic respiration; fatigue quickly. |
| Feature | Pectoral Girdle | Pelvic Girdle |
|---|---|---|
| Location & Connection | Located in shoulder region; articulates forelimbs with axial skeleton. | Located in hip region; articulates hindlimbs with axial skeleton. |
| Consisting Bones | Consists of two halves, each with a Clavicle and Scapula. | Consists of two Coxal bones (each formed by fusion of Ilium, Ischium, and Pubis). |
| Articular Cavity | Contains Glenoid cavity for articulation with head of humerus. | Contains Acetabulum cavity for articulation with head of femur. |
Read More & Chapter Resources
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