1. Movement vs. Locomotion
Every locomotion is a movement, but every movement is not locomotion.
- Movement: Any change in position of a body part (e.g., blinking, breathing).
- Locomotion: Voluntary movements that result in a change of location (e.g., walking, running, swimming).
Types of Movement in Humans
- Amoeboid: Exhibited by macrophages and leucocytes in blood.
- Ciliary: Occurs in our internal tubular organs (e.g., removal of dust in trachea, passage of ova through fallopian tubes).
- Muscular: Movement of our limbs, jaws, and tongue.
2. Structure of Skeletal Muscle
A muscle is made of bundles called Fascicles, held together by a connective tissue layer called Fascia. Each fascicle contains many muscle fibers.
The Sarcomere (The Functional Unit)
The muscle fiber contains myofibrils, which have alternate dark and light bands.
- A-Band (Anisotropic): Contains Myosin (Thick filament).
- I-Band (Isotropic): Contains Actin (Thin filament).
- Sarcomere: The portion of a myofibril between two successive Z-lines.
3. Mechanism of Muscle Contraction
We follow the Sliding Filament Theory, which states that contraction occurs by the sliding of thin filaments over thick filaments.
- The Trigger: A neural signal reaches the neuromuscular junction, releasing Acetylcholine.
- Ion Release: This causes the release of Calcium ions ($Ca^{2+}$) into the sarcoplasm.
- Binding: $Ca^{2+}$ binds to Troponin, uncovering the active sites on Actin.
- Cross-Bridge: Myosin heads bind to Actin using energy from ATP hydrolysis.
- The Slide: The Actin filaments are pulled toward the center of the A-band, shortening the sarcomere.
4. The Human Skeletal System (206 Bones)
For a “Rich” study experience, we divide the skeleton into two main parts:
A. Axial Skeleton (80 Bones)
- Skull: 22 bones (Cranial + Facial).
- Vertebral Column: 26 units (Cervical, Thoracic, Lumbar, Sacral, Coccygeal).
- Sternum: 1 bone (Breastbone).
- Ribs: 12 pairs (7 True, 3 False, 2 Floating).
B. Appendicular Skeleton (126 Bones)
- Limbs: 30 bones in each limb ($30 \times 4 = 120$).
- Girdles: Pectoral (Shoulder) and Pelvic (Hip) girdles (6 bones).
5. Types of Joints
Joints are points of contact between bones or between bones and cartilages.
| Joint Type | Movement Level | Example |
| Fibrous | No Movement | Sutures in the Skull |
| Cartilaginous | Limited Movement | Between adjacent vertebrae |
| Synovial | Free Movement | Ball and Socket (Shoulder), Hinge (Knee) |
6. Disorders of Muscular & Skeletal System
This table is high-yield for NEET and Board Exams.
| Disorder | Key Feature |
| Myasthenia gravis | Auto-immune; leads to fatigue and paralysis of muscles. |
| Muscular dystrophy | Genetic; progressive degeneration of skeletal muscle. |
| Tetany | Rapid spasms due to low $Ca^{2+}$ in body fluid. |
| Arthritis | Inflammation of joints. |
| Osteoporosis | Age-related; decreased bone mass (common in post-menopausal women). |
| Gout | Inflammation due to accumulation of Uric Acid crystals. |
📽️ Recommended Video Masterclass
Visualize the sliding filament theory in action with this high-quality animation:
💡 NEET & Board Focus (High Yield)
- White Fibers vs. Red Fibers: Red fibers have high Myoglobin and many mitochondria (aerobic), while White fibers have less myoglobin (anaerobic).
- The H-Zone: The central part of the thick filament (Myosin) not overlapped by thin filaments.
- Acetabulum: The cavity in the pelvic girdle where the thigh bone (Femur) fits.