Locomotion and Movement - Master Notes

I. Types of Movement

Amoeboid: Seen in pseudopodia of macrophages and leucocytes.
Ciliary: Removal of dust from trachea; passage of ova in reproductive tract.
Muscular: Limbs, jaws, tongue, and most locomotory activities.

[i] Locomotion vs Movement: All locomotions are movements, but all movements (like blinking eyes) are not locomotions.

II. Muscle Structure

Muscles are mesodermal in origin. Properties: Excitability, Contractility, Extensibility, Elasticity.

Myofibril: Contains alternate Dark (A-band) and Light (I-band).
Sarcomere: Functional unit between two Z-lines.
Actin (Thin): Regulatory proteins: Troponin and Tropomyosin.
Myosin (Thick): Has a globular head (with ATPase) and a tail.

[!] Ribcage composition: H-zone is the central part of thick filament not overlapped by thin filaments.

III. Sliding Filament Theory

Proposed by Huxley. Steps:

CNS signal reaches Neuromuscular Junction.
Acetylcholine release -> Action potential -> Ca++ release from Sarcoplasmic Reticulum.
Ca++ binds to Troponin -> Exposes active sites on Actin.
Myosin head binds to Actin forming Cross-bridge (using ATP).
Actin slides toward center. I-band shortens; A-band remains same.

IV. Human Skeletal System (206 Bones)

Axial Skeleton (80): Skull (22), Hyoid (1), Ear Ossicles (6), Vertebral Column (26), Sternum (1), Ribs (24).
--> Ribs: 1-7 (True), 8-10 (Vertebrochondral), 11-12 (Floating).
Appendicular Skeleton (126): Limbs and Girdles.
--> Forelimb: Humerus, Radius, Ulna, Carpals(8), Metacarpals(5), Phalanges(14).
--> Hindlimb: Femur, Tibia, Fibula, Tarsals(7), Metatarsals(5), Phalanges(14). Patella (knee cap).

V. Joints

Fibrous: Immovable (Skull sutures).
Cartilaginous: Limited movement (Vertebrae).
Synovial: Freely movable (Fluid-filled).
--> Ball & Socket (Shoulder); Hinge (Knee); Pivot (Atlas/Axis); Gliding (Carpals); Saddle (Thumb).

VI. Disorders

Myasthenia Gravis: Autoimmune; affects NM junction.
Muscular Dystrophy: Genetic; progressive degeneration.
Tetany: Rapid spasms due to low Ca++ in body fluid.
Arthritis: Inflammation of joints.
Osteoporosis: Age-related; low bone mass (low Estrogen).
Gout: Uric acid crystal accumulation.

[Q] During muscle contraction, which parts of the sarcomere shorten and which stay the same?

[A] Explanation:

According to the Sliding Filament Theory:
1. I-band (light band) shortens.
2. H-zone reduces or disappears.
3. Sarcomere (Z to Z distance) shortens.
4. A-band (dark band/myosin length) remains constant because filaments only slide, they don't contract themselves.

[Q] Why does Rigor Mortis occur after death?

[A] Explanation:

Detachment of the Myosin head from the Actin filament requires ATP. After death, ATP production stops. The cross-bridges remain permanently attached (locked), causing the muscles to become stiff. This state lasts until enzymes break down the muscle tissue.

[Q] Differentiate between Red and White Muscle Fibers.

[A] Explanation:

Red Fibers: High Myoglobin, many Mitochondria, rely on aerobic respiration, slow but sustain long periods (Endurance).
White Fibers: Low Myoglobin, few Mitochondria, high SR, rely on anaerobic/glycolytic pathway, fast but fatigue quickly (Sprints).

[Q] Why are some ribs called "Floating Ribs"?

[A] Explanation:

The 11th and 12th pairs of ribs are not attached ventrally to the sternum (unlike true ribs) nor to the costal cartilage of higher ribs (unlike false ribs). They remain free at their anterior ends, protecting the kidneys while allowing for torso flexibility.

[Q] Explain the "All-or-None" principle in muscle contraction.

[A] Explanation:

This principle states that a single muscle fiber will either contract completely or not at all in response to a stimulus. If the stimulus is below the "threshold," no contraction occurs. However, a whole muscle can show varying degrees of force because it contains many fibers that can be recruited independently.

[Q6] Atlas and Axis joint type.

Pivot joint; allows the "No" movement of the head.

[Q7] Role of Acetylcholine.

Neurotransmitter that triggers action potential at the motor end plate.

[Q8] Patella function.

Protects the knee joint and acts as a lever for the quadriceps.

[Q9] H-zone vs M-line.

H-zone is the gap between actin; M-line is the central membrane of the H-zone.

[Q10] Myasthenia Gravis mechanism.

Antibodies block ACh receptors at the neuromuscular junction.

[Q11] Skull articulation with vertebral column.

Dicondylic skull (two occipital condyles).

[Q12] Girdle bones count.

Pectoral: 4 (2 Scapula, 2 Clavicle). Pelvic: 2 (Coxal bones).

[Q13] Total bones in one hand.

30 (1 Humerus, 1 Radius, 1 Ulna, 8 Carpals, 5 Metacarpals, 14 Phalanges).

[Q14] Sarcolemma definition.

The plasma membrane of a muscle fiber.

[Q15] Sutures joint type.

Fibrous joint; immovable.

[Q16] Gout cause.

Uric acid buildup forming crystals in joint cavities.

[Q17] Tetany vs Tetanus.

Tetany: Low Ca++. Tetanus: Bacterial infection (lockjaw).

[Q18] Tropomyosin role.

Masks the active binding sites on actin during relaxation.

[Q19] Myofibril striation reason.

Orderly arrangement of actin (light) and myosin (dark) proteins.

[Q20] Bone with greatest longitudinal growth.

Femur (Thigh bone).

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Muscles: Mesodermal origin; make up 40-50% body weight.

Fascia: Collagenous connective tissue layer holding muscle bundles.

Sarcolemma: Plasma membrane of a muscle fiber.

Sarcoplasmic Reticulum: Storehouse of calcium ions (Ca++).

Myofilaments: Actin and Myosin proteins.

Anisotropic band: Dark band (A-band) containing myosin.

Isotropic band: Light band (I-band) containing actin.

Sarcomere: Functional unit between two successive Z-lines.

H-zone: Central part of A-band where actin doesn't overlap.

M-line: A thin fibrous membrane in the middle of H-zone.

F-actin: Polymer of 'G' (Globular) actins.

Tropomyosin: Two filaments running along F-actin grooves.

Troponin: Complex protein distributed at intervals on tropomyosin.

Meromyosin: Monomeric unit of Myosin (Heavy/Light chains).

Cross bridge: Formed when myosin head binds to actin.

ATPase: Enzyme in myosin head that hydrolyzes ATP.

Neuromuscular junction: Junction between motor neuron and sarcolemma.

Red Fibers: Aerobic; rich in myoglobin and mitochondria.

White Fibers: Anaerobic; low myoglobin, high SR content.

Axial Skeleton: Comprises 80 bones along the main axis.

Skull: 22 bones (8 Cranial + 14 Facial).

Hyoid bone: U-shaped bone at the base of buccal cavity.

Ear Ossicles: Malleus, Incus, Stapes (6 total).

Dicondylic skull: Skull with two occipital condyles (In Humans).

Vertebrae: 26 serially arranged units.

Atlas: The first cervical vertebra.

Ribs: 12 pairs; bicephalic (two articulation heads).

Sternum: Flat bone on ventral midline of thorax.

Forelimb bones: 30 per arm.

Hindlimb bones: 30 per leg.

Carpals: Wrist bones (8). Metacarpals: Palm (5).

Tarsals: Ankle bones (7). Metatarsals: Sole (5).

Femur: Thigh bone; longest bone of the body.

Patella: Knee cap; a large sesamoid bone.

Pectoral Girdle: 2 Scapulae + 2 Clavicles.

Glenoid cavity: Articulates with head of Humerus.

Coxal bones: Form the Pelvic Girdle (Ilium, Ischium, Pubis).

Acetabulum: Cavity for Femur articulation.

Joints: Points of contact between bones or cartilage.

Fibrous joints: No movement (Flat skull bones).

Synovial joints: Characterized by fluid-filled synovial cavity.

Myasthenia gravis: Fatigue and paralysis (Autoimmune).

Muscular dystrophy: Genetic degeneration of skeletal muscle.

Tetany: Wild muscle contractions due to low plasma Ca++.

Gout: Accumulation of uric acid crystals in joints.

Osteoporosis: Common in older women post-menopause.

A-band: Remains constant in width during contraction.

I-band: Shortens during contraction.

Pivot joint: Between Atlas and Axis.

Hinge joint: Knee and Elbow joints.

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