Study Notes on Locomotion and Movement

LOCOMOTION AND MOVEMENT

1. Overview of Movement

  • Movement is a fundamental characteristic of living organisms.
    • Animals and plants display diverse movements.
    • Examples of simple movements: Streaming of protoplasm in unicellular organisms (e.g., Amoeba).
    • Examples of specialized structures: Cilia, flagella, and tentacles facilitate movement in various organisms.
    • Human beings exhibit movements in limbs, jaws, eyelids, tongue, etc.

2. Types of Movement

  • Voluntary movements leading to a change in place are termed as locomotion.
    • Different forms of locomotory movements: Walking, running, climbing, flying, and swimming.
    • Locomotory structures can serve other movement functions.
    • E.g., In Paramoecium, cilia assist in food movement and locomotion.
    • In Hydra, tentacles help in prey capture and locomotion.
    • Human limbs are vital for posture and locomotion.
    • Conclusion: Movements and locomotion are interrelated; all locomotions are movements, but not all movements are locomotions.
    • Purpose of locomotion: Searching for food, shelter, mates, breeding grounds, favorable climate, or escaping predators.

3. Types of Cellular Movements

  • Human cells exhibit three main types of movements:
    • Amoeboid Movement
    • Examples: Macrophages and leukocytes exhibit this movement.
    • Mechanism: Caused by pseudopodia from protoplasm streaming (similar to Amoeba); involves cytoskeletal elements (microfilaments).
    • Ciliary Movement
    • Occurs in internal tubular organs with ciliated epithelium (e.g., trachea).
    • Function: Removes dust particles and foreign substances; assists in ova movement through the female reproductive tract.
    • Muscular Movement
    • Involves limbs, jaws, tongue, etc.
    • Muscles's contractile property is key for locomotion and body movement coordination (muscular, skeletal, and neural systems).

4. Muscle as a Specialized Tissue

  • Muscles account for 40-50% of human body weight.
    • Properties of muscles:
    • Excitability
    • Contractility
    • Extensibility
    • Elasticity
    • Classification of muscles based on various criteria:
    • By Location:
      1. Skeletal
      2. Visceral
      3. Cardiac
    • Skeletal Muscles:
      • Voluntary, striated appearance, primarily involved in locomotion and posture.
    • Visceral Muscles:
      • Involuntary, nonstriated, found in inner walls of hollow organs (e.g., alimentary canal).
    • Cardiac Muscles:
      • Found in the heart, striated and involuntary.
      • Present in a branching pattern.

5. Structure and Function of Muscle Fibers

  • Muscle fiber anatomy includes:
    • Plasma membrane (sarcolemma) enclosing sarcoplasm (muscle cell cytoplasm).
    • Syncytium: Many nuclei within sarcoplasm.
    • Sarcoplasmic reticulum serves as a calcium ion reservoir.
    • Myofibrils: Parallel filament structures containing actin and myosin proteins.
    • Light bands (I-band) and dark bands (A-band) create striated appearance.
    • Sarcomere: Functional unit between two 'Z' lines; consists of I-band and A-band.
    • The central part of thick filaments (myosin) not overlapped by thin filaments is termed 'H' zone.

6. Contractile Proteins and Muscle Contraction

  • Structure of Contractile Proteins:
    • Actin Filaments: Formed by helically wound F-actins (made of G-actins) with tropomyosin and troponin proteins.
    • Troponin masks active binding sites on actin in resting state.
    • Myosin Filaments: Composed of polymerized proteins (meromyosins).
    • Each thick filament has a head (HMM) and tail (LMM), the head has ATPase activity and binding sites for ATP and actin.
6.1 Mechanism of Muscle Contraction
  • Sliding Filament Theory: Muscle contraction occurs through sliding of thin filaments over thick ones.
    • Initiated by signals from the central nervous system (CNS) via motor neurons.
    • A motor neuron and muscle fibers form a motor unit.
    • Neuromuscular Junction:
    • Junction between motor neuron and muscle fiber, releasing acetylcholine and generating action potential in sarcolemma.
    • Action potential triggers calcium ion release into sarcoplasm.
    • Calcium binding to troponin reveals active sites on actin for myosin attachment.
    • Cross-bridge formation leads to sliding of actin filaments and sarcomere shortening (contraction).
    • Results in reduction of I-bands; A-bands remain unchanged.
    • Muscle fibers relax by pumping Ca++ back to sarcoplasmic reticulum, breaking cross-bridges, and returning to original position.

7. Skeletal System Overview

  • The skeletal system forms a framework of bones and cartilages integral to movement.
    • Composed of 206 bones and some cartilage.
    • Two primary divisions:
    • Axial Skeleton:
      • Comprises 80 bones along the body's main axis (skull, vertebral column, ribs, sternum).
      • Skull:
      • Composed of 22 bones (8 cranial and 14 facial).
      • Vertebral Column:
      • Contains 26 vertebrae, serves to protect the spinal cord, supports the head, and provides muscular attachment points.
        • Cervical (7), Thoracic (12), Lumbar (5), Sacral (1 fused), Coccygeal (1 fused).
    • Appendicular Skeleton:
      • Comprises limb bones and girdles, each limb made up of 30 bones (e.g., humerus, radius, ulna in forelimbs).

8. Joints and Their Types

  • Joints are crucial for movement involving the bones.
    • Classified into three main types:
    1. Fibrous Joints: No movement; e.g., sutures in the skull.
    2. Cartilaginous Joints: Limited movement; e.g., between vertebrae.
    3. Synovial Joints: Allow for considerable movement, containing synovial fluid; e.g., ball-and-socket (shoulder), hinge (knee), pivot (between atlas and axis).

9. Disorders of Muscular and Skeletal System

  • Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction, leads to muscle fatigue and paralysis.
  • Muscular Dystrophy: Progressive degeneration of skeletal muscle due to genetic factors.
  • Tetany: Spasms in muscles due to low Ca++ levels.
  • Arthritis: Joint inflammation.
  • Osteoporosis: Age-related condition with decreased bone mass, increasing fracture risk, often linked to low estrogen levels.
  • Gout: Joint inflammation caused by uric acid crystal accumulation.

10. Summary

  • Movement is intrinsic to all life forms, represented in various modalities (e.g., locomotion).
  • Human cellular movements include amoeboid, ciliary, and muscular modes, critical for various functions.
  • The muscular system consists of skeletal, visceral, and cardiac muscles with unique properties, including excitability, contractility, and elasticity.
  • Muscle fibers are structured in myofibrils, each with sarcomeres functioning in contraction through the sliding filament theory.
  • The skeletal system, comprising bones and cartilage, divides into axial and appendicular skeletons.
  • Joint classifications affect movement types, impacting locomotion.

11. Exercises

  1. Diagram of a sarcomere showing regions.
  2. Define sliding filament theory of muscle contraction.
  3. Outline steps in muscle contraction.
  4. True/False statements for validation.
  5. Differences between actin/myosin, red/white muscles, pectoral/pelvic girdle.
  6. Matching items from two columns (muscle types with functions).
  7. Describe different types of movements in human cells.
  8. Distinguish skeletal from cardiac muscle.
  9. Identify joint types for specified pairs.
  10. Fill in the blanks with relevant terms related to the skeletal system.