Locomotion and Movement

1. Types of Movement in Humans

  • Amoeboid: Crawling via pseudopodia. Seen in Macrophages and Leucocytes (WBCs).
  • Ciliary: Waving of tiny hair-like cilia. Seen in the Trachea (clearing dust) and Fallopian tubes (moving the egg).
  • Muscular: Contraction of muscles. Used for moving limbs, jaws, and tongue.

2. Muscle Structure & Contraction

  • The Unit: The Sarcomere is the functional unit of contraction, measured from one Z-line to the next.
  • The Proteins:
    • Actin (Thin): Includes F-actin, Tropomyosin, and Troponin (the "lock").
    • Myosin (Thick): Made of Meromyosins. The head has an ATPase enzyme and binding sites for ATP and Actin.
  • Sliding Filament Theory:
    1. Nerve signal →\rightarrow Acetylcholine release →\rightarrow Action potential.
    2. Sarcoplasmic Reticulum releases Ca++Ca^{++}.
    3. Ca++Ca^{++} binds to Troponin, unmasking the Actin binding sites.
    4. Myosin head binds to Actin (Cross-bridge) and pulls it inward (Power Stroke).

3. The Skeletal System (206 Bones)

  • Axial Skeleton (80 Bones): The body's core.
    • Skull (22): 8 Cranial + 14 Facial.
    • Vertebral Column (26): C7T12L5S(1)Co(1)C_7 T_{12} L_5 S_{(1)} Co_{(1)}.
    • Thorax: Sternum (1) + Ribs (24).
  • Appendicular Skeleton (126 Bones): The branches.
    • Limbs (120): 30 bones in each arm and leg.
    • Girdles (6): Pectoral (Shoulder: Clavicle + Scapula) and Pelvic (Hip: 2 Coxal bones).

4. Joints (Points of Articulation)

  • Fibrous: Immovable. (e.g., Skull sutures).
  • Cartilaginous: Limited movement. (e.g., Between vertebrae).
  • Synovial: Fluid-filled, freely movable.
    • Ball & Socket: Shoulder, Hip.
    • Hinge: Knee, Elbow.
    • Pivot: Atlas & Axis.
    • Gliding: Carpals (Wrist).
    • Saddle: Thumb (Carpal & Metacarpal).

5. Crucial Disorders

  • Myasthenia Gravis: Autoimmune; attacks the Neuromuscular Junction (NMJ).
  • Muscular Dystrophy: Genetic; progressive muscle degeneration.
  • Tetany: Low body fluid Calcium (Ca++Ca^{++}) causing wild spasms.
  • Osteoporosis: Age-related bone mass loss; strongly linked to low Estrogen levels.
  • Gout: Inflammation from sharp Uric acid crystals in joints.

Exam Tips

1. The "Golden Rule" of Muscle Contraction

Whenever a muscle contracts, remember exactly what happens to the bands:

  • Shortens/Disappears: The I-band shortens, the H-zone disappears, and the overall Sarcomere shortens.
  • Stays the SAME: The A-band (the thick Myosin filaments) never changes length!

2. Trap Alert: Confusing Pairs

Examiners love to test if you know the difference between these closely related terms:

  • Tetany vs. Tetanus: Tetany is a metabolic issue (low calcium = spasms). Tetanus is a bacterial infection (Lockjaw = sustained rigid contraction).
  • Myasthenia Gravis vs. Muscular Dystrophy: Myasthenia is an Autoimmune attack on receptors. Dystrophy is a Genetic defect in muscle protein structure.
  • Glenoid vs. Acetabulum:
    • Glenoid cavity is in the Pectoral girdle (Shoulder). (Think: PG).
    • Acetabulum is in the Pelvic girdle (Hip). (Think: PA).

3. The "Number" Game Check

  • 7 Cervical Vertebrae: This is a universal constant for almost all mammals (whether a mouse, a human, or a giraffe!).
  • Ribs Breakdown: 7 True, 3 False (8th, 9th, 10th attach to the 7th), 2 Floating (11th, 12th attach to nothing in front).
  • Limb Bones: Every single limb has exactly 30 bones. (Arm: 1+2+8+5+14. Leg: 1+1+2+7+5+14. Notice how the Patella in the leg replaces one Carpal from the wrist!).

4. Joint Mnemonics for Quick Recall

  • Saddle = Thumb: Think of a tiny rider sitting in a saddle on your thumb joint.
  • Pivot = "No": The joint between the Atlas (1st vertebra) and Axis (2nd vertebra) lets you pivot your head side-to-side to say "no".
  • Hinge = Door: Knees and elbows open and close in exactly one direction, just like a door hinge.