LOCOMOTION AND MOVEMENT

Types of Movement in Human Cells

  1. Amoeboid Movement:
    • Definition: Movement exhibited by specialized cells like macrophages and leucocytes, resembling Amoeba’s motion.
    • Mechanism:
      • Pseudopodia formation through streaming of protoplasm.
      • Involvement of cytoskeletal elements, particularly microfilaments.
  2. Ciliary Movement:
    • Occurrence: In internal tubular organs with ciliated epithelium.
    • Examples:
      • Coordinated cilia movements in the trachea aid in removing inhaled dust particles.
      • Facilitates the passage of ova through the female reproductive tract.
  3. Muscular Movement:
    • Role: Essential for various body movements, including limb, jaw, and tongue actions.
    • Contractile Property: Muscles contract to generate force, enabling locomotion and other bodily movements.
    • Coordination: Requires synchronized activity of muscular, skeletal, and neural systems.

Muscle: Structure and Classification

  1. Overview:
    • Muscle is a specialized tissue of mesodermal origin.
    • Constitutes 40-50% of the body weight in humans.
    • Possesses unique properties: excitability, contractility, extensibility, and elasticity.
  2. Muscle Classification:
    • Based on Location:
      • Skeletal Muscles:
        • Associated with skeletal components.
        • Striped appearance (striated muscles).
        • Voluntary control by the nervous system.
        • Involved in locomotion and posture changes.
      • Visceral Muscles:
        • Found in the inner walls of visceral organs.
        • Smooth appearance (smooth muscles or nonstriated).
        • Involuntary control.
        • Functions in the transport of food and gametes.
      • Cardiac Muscles:
        • Found in the heart.
        • Striated appearance.
        • Involuntary nature; The nervous system indirectly regulates.
  3. Structure of Skeletal Muscle:
    • Organized into muscle bundles or fascicles held by fascia.
    • The muscle bundle contains muscle fibers.
    • Muscle fiber: sarcolemma, sarcoplasm, and multiple nuclei.
    • The sarcoplasmic reticulum stores calcium ions.
    • Myofibrils or myofilaments (actin and myosin) give the striated appearance.
    • Sarcomere: Functional unit of contraction between two ‘Z’ lines.
  4. Myofibril Structure:
    • Actin and Myosin:
      • Light bands (I-band) contain actin.
      • Dark bands (A-band) contain myosin.
      • Actin and myosin are arranged parallel to each other.
      • ‘Z’ line bisects the ‘I’ band; thin filaments attached to ‘Z’ line.
      • ‘M’ line in the ‘A’ band holds thick filaments together.
      • Sarcomere: Functional unit between two ‘Z’ lines.
    • Resting State:
      • Thin filaments partially overlap the free ends of thick filaments.
      • A central part of the thick filament not overlapped is the ‘H’ zone.

Structure of Contractile Proteins

  1. Actin Filament (Thin Filament):
    • Composed of two helically wound ‘F’ (Filamentous) actins.
    • Each ‘F’ actin is a polymer of monomeric ‘G’ (Globular) actins.
    • Tropomyosin, another protein, runs close to ‘F’ actins.
    • Troponin, a complex protein, is distributed at regular intervals on tropomyosin.
    • In the resting state, the troponin subunit masks active binding sites for myosin on actin filaments.
  2. Myosin Filament (Thick Filament):
    • A polymerized protein consisting of monomeric proteins called Meromyosins.
    • Each Meromyosin has a globular head with a short arm (Heavy Meromyosin – HMM) and a tail (Light Meromyosin – LMM).
    • The globular head, known as the cross arm, projects outwards at regular intervals.
    • The globular head is an active ATPase enzyme with binding sites for ATP and active sites for actin.

Mechanism of Muscle Contraction

  1. Sliding Filament Theory:
    • Muscle contraction involves the sliding of thin filaments over thick filaments.
    • Initiated by a neural signal from the central nervous system (CNS) via a motor neuron.
  2. Motor Unit:
    • Motor neurons and connected muscle fibers form a motor unit.
    • The neuromuscular junction or motor-end plate is the junction between a motor neuron and the muscle fiber’s sarcolemma.
  3. Neuromuscular Junction Activation:
    • Neural signal releases acetylcholine, generating an action potential in the sarcolemma.
    • Action potential spreads through the muscle fiber, releasing calcium ions into the sarcoplasm.
  4. Calcium Ion Binding:
    • Calcium binds with troponin on actin filaments, exposing active sites for myosin.
    • Myosin head binds to exposed active sites, forming a cross-bridge.
  5. Cross-Bridge Formation:
    • Myosin pulls attached actin filaments towards the center of ‘A’ band, shortening the sarcomere (contraction).
    • ‘Z’ line attached to actins is also pulled inwards during contraction.
  6. Cross-Bridge Breakage:
    • Myosin releases ADP and P1, returning to its relaxed state.
    • ATP binds, breaking the cross-bridge.
    • ATP hydrolysis by myosin head repeats the cycle, causing further sliding.
  7. Relaxation:
    • Ca++ ions are pumped back to sarcoplasmic cisternae, masking actin filaments.
    • ‘Z’ lines return to their original position, causing relaxation.

SKELETAL SYSTEM

  1. Framework of Bones and Cartilages:
    • Essential for body movement.
    • Bone and cartilage are specialized connective tissues.
    • The bone matrix contains hard calcium salts, and cartilage has pliable chondroitin salts.
  2. Composition:
    • 206 bones and a few cartilages in humans.
    • Divided into axial and appendicular skeleton.
  3. Axial Skeleton (80 Bones):
    • Skull: Cranial (8 bones) and facial (14 bones) elements.
    • Hyoid: U-shaped bone at the base of the buccal cavity.
    • Ear Ossicles: Malleus, Incus, Stapes in each middle ear.
    • Vertebral Column (26): Cervical (7), thoracic (12), lumbar (5), sacral (1 fused), coccygeal (1 fused).
    • Sternum: Flat bone on the ventral midline of the thorax.
    • Ribs (12 pairs): True ribs (1-7), false ribs (8-10), floating ribs (11-12).
  4. Appendicular Skeleton:
    • Limb Bones (30 in each limb): Humerus, radius, ulna, carpals (8), metacarpals (5), phalanges (14).
    • Thigh Bone: Femur.
    • Leg Bones: Tibia, fibula, tarsals (7), metatarsals (5), phalanges (14).
    • Knee Cap: Patella.
  5. Girdles:
    • Pectoral Girdle: Clavicle and scapula on each side. Articulates with the humerus and forms shoulder joint.
    • Pelvic Girdle: Coxal bones (fusion of ilium, ischium, and pubis). Articulates with the thigh bone.
  6. Articulation:
    • Pectoral and pelvic girdles allow articulation of upper and lower limbs with the axial skeleton.

JOINTS

  1. Functionality:
    • Essential for all types of body movements, including locomotion.
    • Joints serve as points of contact between bones or between bones and cartilage.
    • Muscular force is applied at joints, acting as fulcrums for movement.
  2. Classification:
    • Fibrous Joints:
      • No movement allowed.
      • Example: Flat skull bones fuse end-to-end with dense fibrous connective tissues (sutures) forming the cranium.
    • Cartilaginous Joints:
      • Bones joined by cartilages.
      • Example: Joint between adjacent vertebrae in the vertebral column, allowing limited movements.
    • Synovial Joints:
      • Characterized by a fluid-filled synovial cavity between articulating surfaces.
      • Allows considerable movement.
      • Examples: Ball and socket joint (humerus and pectoral girdle), hinge joint (knee), pivot joint (atlas and axis), gliding joint (between carpals), saddle joint (between carpal and metacarpal of the thumb).
  3. Joint Movements:
    • Ball and Socket Joint:
      • Example: Between humerus and pectoral girdle.
    • Hinge Joint:
      • Example: Knee joint.
    • Pivot Joint:
      • Example: Between atlas and axis.
    • Gliding Joint:
      • Example: Between carpals.
    • Saddle Joint:
      • Example: Between carpal and metacarpal of the thumb.

DISORDERS OF THE MUSCULAR AND SKELETAL SYSTEM

  1. Myasthenia Gravis:
    • Definition: Autoimmune disorder affecting the neuromuscular junction.
    • Effects: Leads to fatigue, weakening, and paralysis of skeletal muscles.
  2. Muscular Dystrophy:
    • Definition: Progressive degeneration of skeletal muscles, often of genetic origin.
  3. Tetany:
    • Description: Rapid spasms (wild contractions) in muscles.
    • Cause: Low calcium levels in body fluids.
  4. Arthritis:
    • Description: Inflammation of joints.
    • Characteristics: Pain, swelling, and reduced joint mobility.
  5. Osteoporosis:
    • Definition: Age-related disorder characterized by decreased bone mass.
    • Consequences: Increased susceptibility to fractures.
    • Common Cause: Decreased levels of estrogen.
  6. Gout:
    • Description: Inflammation of joints.
    • Cause: Accumulation of uric acid crystals.
    • Symptoms: Joint pain and swelling.

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