Class 11 Notes

Class 11 Biology Notes Chapter 20 (Chapter 20) – Examplar Problems (English) Book

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Philoid

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Examplar Problems (English)
Detailed Notes with MCQs of Chapter 20: Locomotion and Movement. This is a crucial chapter, not just for understanding how we move, but also because questions frequently appear from this section in various government exams. Pay close attention to the details, especially the structural aspects and the mechanism of muscle contraction.

Chapter 20: Locomotion and Movement - Detailed Notes

1. Introduction

  • Movement: A significant feature of living beings. It's a change in position of a body part relative to the whole body (e.g., blinking, jaw movement).
  • Locomotion: Voluntary movement resulting in a change of place or location (e.g., walking, running, swimming). Key Distinction: All locomotion involves movement, but not all movement results in locomotion.
  • Purpose of Locomotion: Search for food, shelter, mate, suitable breeding grounds, favourable climatic conditions, escape from predators.

2. Types of Movement in Human Cells/Body

  • Amoeboid Movement:
    • Performed by pseudopodia (false feet) formed by protoplasmic streaming.
    • Involves cytoskeletal elements like microfilaments (actin).
    • Examples: Macrophages, Leucocytes (WBCs) in blood.
  • Ciliary Movement:
    • Performed by cilia, which are hair-like outgrowths of the cell membrane.
    • Requires coordinated movement of cilia rows.
    • Examples: Trachea (removing dust/foreign particles), Fallopian tubes (propelling the ovum).
  • Muscular Movement:
    • Involves the contractile property of muscles.
    • Responsible for most locomotion and other movements (limbs, jaws, tongue, etc.).
    • Requires coordination of muscular, skeletal, and neural systems.

3. Muscle

  • A specialized tissue of mesodermal origin.
  • Properties: Excitability, Contractility, Extensibility, Elasticity.
  • Types of Muscles:
    • Skeletal Muscle:
      • Associated with skeletal components; responsible for body posture and locomotion.
      • Voluntary control (under conscious control via the somatic nervous system).
      • Striated appearance (due to arrangement of actin and myosin).
      • Multinucleated (syncytium), unbranched fibers.
      • Example: Biceps, Triceps, muscles of limbs.
    • Visceral Muscle (Smooth Muscle):
      • Located in the inner walls of hollow visceral organs (alimentary canal, reproductive tract, blood vessels).
      • Involuntary control (autonomic nervous system).
      • Non-striated, smooth appearance.
      • Uninucleated, spindle-shaped (fusiform) cells.
      • Slow, sustained contractions.
    • Cardiac Muscle:
      • Muscle of the heart wall (myocardium).
      • Involuntary control.
      • Striated appearance.
      • Uninucleated, branched fibers.
      • Cells joined by intercalated discs (contain gap junctions and desmosomes) allowing rapid spread of impulse and functioning as a unit (syncytium).
      • Non-fatiguing.

4. Structure of Skeletal Muscle

  • Organization: Muscle → Fascicles (bundles of muscle fibers) → Muscle Fiber (muscle cell) → Myofibrils → Myofilaments (Actin & Myosin).
  • Connective Tissue: Epimysium (covers entire muscle), Perimysium (covers fascicles), Endomysium (covers individual muscle fibers).
  • Muscle Fiber (Cell):
    • Sarcolemma: Plasma membrane.
    • Sarcoplasm: Cytoplasm, contains numerous mitochondria (sarcosomes), glycogen granules, myoglobin.
    • Sarcoplasmic Reticulum (SR): Endoplasmic reticulum, stores Calcium ions (Ca++).
    • Myofibrils: Parallel contractile threads running lengthwise. Contain repeating functional units called sarcomeres.
  • Sarcomere (Functional Unit of Contraction):
    • Region between two successive Z-lines.
    • Z-line: Anchors thin filaments (Actin).
    • I-Band (Isotropic): Light band, contains only thin filaments (Actin). Bisected by the Z-line. Shortens during contraction.
    • A-Band (Anisotropic): Dark band, contains thick filaments (Myosin) and overlapping thin filaments. Length remains constant during contraction.
    • H-Zone: Lighter region in the middle of the A-band, contains only thick filaments (Myosin). Disappears/narrows during contraction.
    • M-Line: Fine line in the centre of the H-zone, holds thick filaments together.
  • Contractile Proteins:
    • Actin (Thin Filament): Composed of two intertwined F-actins (polymers of G-actin). Associated with regulatory proteins.
    • Myosin (Thick Filament): Polymerized protein. Each monomer (Meromyosin) has a globular head (Heavy Meromyosin - HMM) with an actin-binding site and ATP-binding site, a short arm, and a tail (Light Meromyosin - LMM). The heads project outwards at angles.
  • Regulatory Proteins (on Actin):
    • Tropomyosin: Filamentous protein running along F-actin, covers myosin-binding sites on actin in the resting state.
    • Troponin: Complex of three proteins (TnI, TnT, TnC) distributed at intervals on tropomyosin. TnC binds Ca++.

5. Mechanism of Muscle Contraction (Sliding Filament Theory)

  • Proposed by Andrew Huxley and Rolf Niedergerke, and Hugh Huxley and Jean Hanson.
  • States that contraction occurs by the sliding of thin filaments (actin) over thick filaments (myosin).
  • Steps:
    1. Signal: CNS sends a signal via a motor neuron.
    2. Neuromuscular Junction (NMJ) / Motor End Plate: Synapse between motor neuron and sarcolemma.
    3. Neurotransmitter Release: Arrival of nerve impulse releases Acetylcholine (ACh).
    4. Action Potential Generation: ACh binds to receptors on sarcolemma, causing depolarization and generating an action potential.
    5. Spread of Action Potential: Travels along the sarcolemma and down T-tubules.
    6. Calcium Release: Action potential triggers the Sarcoplasmic Reticulum to release stored Ca++ into the sarcoplasm.
    7. Activation of Actin: Ca++ binds to Troponin C (TnC). This causes a conformational change in Troponin, pulling Tropomyosin away from the active (myosin-binding) sites on Actin.
    8. Cross-Bridge Formation: Energized myosin heads (ATP hydrolyzed to ADP + Pi) bind to the exposed active sites on actin, forming a cross-bridge.
    9. Power Stroke: Binding triggers the myosin head to pivot/bend, pulling the actin filament towards the M-line (centre of the sarcomere). ADP and Pi are released.
    10. Cross-Bridge Detachment: A new ATP molecule binds to the myosin head, causing it to detach from actin.
    11. Reactivation of Myosin Head: ATP is hydrolyzed to ADP + Pi, re-energizing and resetting the myosin head for the next cycle.
    12. Sliding: Steps 8-11 repeat as long as Ca++ and ATP are present, causing the sarcomere to shorten (Z-lines move closer, I-band shortens, H-zone disappears).
  • Relaxation:
    1. Motor neuron signal stops.
    2. ACh is broken down by acetylcholinesterase.
    3. Sarcolemma repolarizes.
    4. Ca++ is actively pumped back into the Sarcoplasmic Reticulum (requires ATP).
    5. Troponin-Tropomyosin complex covers actin active sites again.
    6. Cross-bridges detach, muscle relaxes and returns to original length (due to elasticity).
  • Energy: ATP is the immediate source. Regenerated from Creatine Phosphate and cellular respiration (aerobic and anaerobic).
  • Muscle Fatigue: Accumulation of lactic acid (due to anaerobic respiration during strenuous exercise) leads to fatigue.
  • Oxygen Debt: Amount of oxygen required to oxidize accumulated lactic acid and replenish ATP/Creatine Phosphate stores after exercise.
  • Muscle Fibers:
    • Red Fibers (Slow-twitch): High myoglobin content, many mitochondria, aerobic respiration, slow contraction rate, fatigue-resistant. (e.g., postural muscles).
    • White Fibers (Fast-twitch): Low myoglobin, fewer mitochondria, rely on anaerobic respiration, fast contraction rate, fatigue quickly. (e.g., eye muscles).

6. Skeletal System

  • Framework of bones and cartilages.
  • Functions: Support, Protection, Movement (leverage), Blood cell formation (hematopoiesis in bone marrow), Storage of minerals (Calcium, Phosphate).
  • Human Skeleton: 206 bones in adults. Divided into Axial and Appendicular skeletons.
  • Axial Skeleton (80 bones): Forms the main axis of the body.
    • Skull (22 bones + 6 ear ossicles + 1 Hyoid = 29 bones):
      • Cranial bones (8): Frontal (1), Parietal (2), Temporal (2), Occipital (1), Sphenoid (1), Ethmoid (1). Protect the brain.
      • Facial bones (14): Form the front part of the skull. Include Mandible (lower jaw), Maxilla (upper jaw), Nasal, Zygomatic, Lacrimal etc.
      • Hyoid bone (1): U-shaped bone at the base of the buccal cavity, not articulated with any other bone.
      • Ear Ossicles (Malleus, Incus, Stapes) x 2 = 6 bones.
    • Vertebral Column (26 vertebrae): Protects spinal cord, supports head, attachment point for ribs/muscles.
      • Cervical (7) - Neck region (C1-Atlas, C2-Axis).
      • Thoracic (12) - Chest region, articulate with ribs.
      • Lumbar (5) - Abdominal region, largest vertebrae.
      • Sacral (1 - fused from 5) - Pelvic region.
      • Coccygeal (1 - fused from 4) - Tail bone.
      • Vertebral Formula: C7 T12 L5 S(5) C(4) -> C7 T12 L5 S1 C1 (in adults)
      • Intervertebral discs (cartilaginous) between vertebrae act as shock absorbers.
    • Sternum (1 bone): Flat bone on the ventral midline of the thorax (breastbone).
    • Ribs (12 pairs = 24 bones):
      • True Ribs (Pairs 1-7): Attach directly to sternum via hyaline cartilage.
      • False Ribs (Pairs 8-10): Attach indirectly to sternum (cartilage joins cartilage of 7th rib).
      • Floating Ribs (Pairs 11-12): Do not attach to sternum ventrally.
      • Rib cage = Thoracic vertebrae + Ribs + Sternum. Protects heart and lungs.
  • Appendicular Skeleton (126 bones): Bones of the limbs and their girdles.
    • Pectoral Girdle (Shoulder Girdle) (4 bones):
      • Clavicle (Collar bone) - 2
      • Scapula (Shoulder blade) - 2 (Large triangular flat bone with acromion process and glenoid cavity for articulation with humerus).
    • Upper Limb (Forelimb) (30 bones x 2 = 60 bones):
      • Humerus (1) - Upper arm.
      • Radius & Ulna (1 each) - Forearm.
      • Carpals (8) - Wrist bones.
      • Metacarpals (5) - Palm bones.
      • Phalanges (14) - Finger bones (2 in thumb, 3 in each other finger).
    • Pelvic Girdle (Hip Girdle) (2 Coxal bones):
      • Each Coxal bone is formed by the fusion of Ilium, Ischium, and Pubis.
      • Acetabulum: Cavity where the femur head articulates.
      • The two halves meet ventrally to form the Pubic symphysis (cartilaginous joint).
    • Lower Limb (Hindlimb) (30 bones x 2 = 60 bones):
      • Femur (1) - Thigh bone (longest, strongest bone).
      • Patella (1) - Knee cap (sesamoid bone).
      • Tibia & Fibula (1 each) - Lower leg (Tibia is larger, weight-bearing).
      • Tarsals (7) - Ankle bones.
      • Metatarsals (5) - Sole bones.
      • Phalanges (14) - Toe bones (2 in big toe, 3 in each other toe).

7. Joints (Articulations)

  • Points of contact between bones, or between bones and cartilage. Essential for movement.
  • Classification based on Structure/Movability:
    • Fibrous Joints (Immovable / Synarthroses):
      • Bones held together by dense fibrous connective tissue.
      • No joint cavity.
      • Example: Sutures in the skull, Gomphosis (tooth in socket).
    • Cartilaginous Joints (Slightly Movable / Amphiarthroses):
      • Bones joined by cartilage (hyaline or fibrocartilage).
      • No joint cavity.
      • Example: Joints between vertebral bodies (intervertebral discs - fibrocartilage), Pubic symphysis (fibrocartilage), joint between first rib and sternum (hyaline).
    • Synovial Joints (Freely Movable / Diarthroses):
      • Characterized by a fluid-filled synovial cavity between articulating bones.
      • Articular cartilage (hyaline) covers bone ends.
      • Joint capsule (outer fibrous layer, inner synovial membrane which secretes synovial fluid for lubrication and nourishment).
      • Often reinforced by ligaments.
      • Types of Synovial Joints:
        • Ball and Socket: Shoulder, Hip joints (multiaxial movement).
        • Hinge: Elbow, Knee, Interphalangeal joints (uniaxial movement - flexion/extension).
        • Pivot: Atlanto-axial joint (between Atlas C1 and Axis C2 - rotation), Radioulnar joint (pronation/supination).
        • Gliding (Plane): Intercarpal, Intertarsal joints (sliding/gliding movement).
        • Saddle: Carpometacarpal joint of the thumb (biaxial movement).
        • Condyloid (Ellipsoidal): Metacarpophalangeal joints (knuckles), Radiocarpal joint (wrist).

8. Disorders of Muscular and Skeletal System

  • Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction. Antibodies block/destroy acetylcholine receptors. Leads to weakening and rapid fatigue of skeletal muscles.
  • Muscular Dystrophy: Progressive degeneration of skeletal muscle, mostly due to genetic defects (e.g., Duchenne Muscular Dystrophy - absence of dystrophin protein).
  • Tetany: Rapid spasms (wild contractions) in muscle due to low Ca++ in body fluid (e.g., due to parathyroid hormone deficiency).
  • Arthritis: Inflammation of joints.
    • Osteoarthritis: Degenerative joint disease, wear and tear of articular cartilage. Common in older age.
    • Rheumatoid Arthritis: Autoimmune disease where the body's immune system attacks the synovial membrane, causing inflammation, pain, swelling, and joint deformity.
    • Gout: Inflammation of joints due to accumulation of uric acid crystals (often affects the big toe).
  • Osteoporosis: Age-related disorder characterized by decreased bone mass and increased chances of fractures. Decreased estrogen levels (post-menopause) are a common cause. Can also be caused by calcium/vitamin D deficiency.
  • Sprain: Injury to a ligament (stretching or tearing).
  • Strain: Injury to a muscle or tendon (stretching or tearing).

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on the chapter 'Locomotion and Movement' for your practice:

  1. Which of the following structures shortens during skeletal muscle contraction according to the sliding filament theory?
    a) A-Band
    b) I-Band
    c) Myosin filament length
    d) Z-line thickness

  2. The functional unit of contractile system in striated muscle is:
    a) Sarcolemma
    b) Myofibril
    c) Sarcomere
    d) Z-line

  3. Calcium ions (Ca++) required for muscle contraction are stored in:
    a) Sarcoplasm
    b) Sarcolemma
    c) Sarcoplasmic Reticulum
    d) T-tubules

  4. Which protein masks the active sites for myosin on the actin filament in a resting muscle?
    a) Troponin
    b) Tropomyosin
    c) Myosin
    d) Actin

  5. The joint between the Atlas (C1) and Axis (C2) vertebrae is an example of which type of synovial joint?
    a) Hinge joint
    b) Ball and socket joint
    c) Pivot joint
    d) Saddle joint

  6. Which of the following is NOT part of the axial skeleton?
    a) Sternum
    b) Vertebral column
    c) Ribs
    d) Clavicle

  7. Myasthenia gravis is an autoimmune disorder that affects:
    a) Synovial membranes
    b) Neuromuscular junctions
    c) Bone matrix deposition
    d) Sarcoplasmic reticulum function

  8. Which of the following represents the correct count of bones in the human vertebral column formula for an adult?
    a) C7 T10 L5 S1 C1
    b) C7 T12 L5 S1 C1
    c) C7 T12 L5 S(5) C(4)
    d) C8 T12 L5 S1 C1

  9. Gout, a type of arthritis, is caused by the accumulation of:
    a) Lactic acid crystals
    b) Calcium phosphate crystals
    c) Uric acid crystals
    d) Cholesterol crystals

  10. The type of muscle tissue found in the wall of the stomach is:
    a) Skeletal muscle
    b) Cardiac muscle
    c) Visceral (Smooth) muscle
    d) Striated voluntary muscle

Answer Key:

  1. b) I-Band
  2. c) Sarcomere
  3. c) Sarcoplasmic Reticulum
  4. b) Tropomyosin
  5. c) Pivot joint
  6. d) Clavicle (It's part of the pectoral girdle - appendicular skeleton)
  7. b) Neuromuscular junctions
  8. b) C7 T12 L5 S1 C1 (Note: S(5) and C(4) represent fused vertebrae count before fusion)
  9. c) Uric acid crystals
  10. c) Visceral (Smooth) muscle

Revise these notes thoroughly. Focus on the names of bones, parts of the sarcomere, the sequence of events in muscle contraction, types of joints, and the causes of common disorders. Good luck with your preparation!

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