Detailed Notes Chapter-17-Locomotion And Movement

Introduction

1. Movement in Living Beings:

   • Movement is a significant feature of both animals and plants.
   • Various forms of movement are observed, ranging from simple protoplasmic streaming in unicellular organisms like Amoeba to complex movements in multicellular organisms.

2. Types of Movements:

   • Movement can manifest in different forms, including:
     • Streaming of protoplasm in unicellular organisms.
     • Movement of cilia, flagella, and tentacles in various organisms.
     • Voluntary movements in humans, involving limbs, jaws, eyelids, tongue, etc.

3. Locomotion:

   • Some movements result in a change of place or location, termed locomotion.
   • Locomotory movements include walking, running, climbing, flying, and swimming.
   • Locomotory structures may overlap with those involved in other types of movements. For example, in Paramecium, cilia serve both in movement of food and locomotion.

4. Interconnectedness of Movements and Locomotion:

   • Movements and locomotion are closely linked and cannot be studied separately.
   • While all locomotions are movements, not all movements are locomotions.
   • Examples illustrate how structures used for one purpose, such as tentacles in Hydra, can serve both in capturing prey and in locomotion.

5. Purpose of Locomotion:

   • Animals perform various methods of locomotion depending on their habitats and situational demands.
   • Locomotion is generally driven by the need to:
     • Search for food, shelter, mates, suitable breeding grounds, or favorable climatic conditions.
     • Escape from enemies or predators.

17.1 TYPES OF MOVEMENT

1. Amoeboid Movement:

   • Description: Cells in the human body, such as macrophages and leukocytes, exhibit amoeboid movement.
   • Mechanism: Amoeboid movement is achieved through the formation of pseudopodia, which are extensions formed by the streaming of protoplasm.
   • Cellular Components: Cytoskeletal elements like microfilaments play a role in facilitating this movement.

2. Ciliary Movement:

   • Description: Ciliary movement occurs in internal tubular organs lined by ciliated epithelium.
   • Function: Coordinated movements of cilia, such as those in the trachea, help in removing dust particles and foreign substances from the respiratory tract. Additionally, ciliary movement aids in the passage of ova through the female reproductive tract.

3. Muscular Movement:

   • Description: Movement of limbs, jaws, tongue, etc., in humans involves muscular movement.
   • Mechanism: Muscular movement relies on the contractile property of muscles.
   • Function: Muscular movement is essential for locomotion and various other bodily movements in humans and many multicellular organisms.
   • Coordination: Locomotion requires coordinated activity among the muscular, skeletal, and neural systems.

17.2 MUSCLE

1. General Overview:

   • Muscles are specialized tissues of mesodermal origin.
   • They constitute about 40-50% of the body weight in human adults.
   • Muscles possess unique properties like excitability, contractility, extensibility, and elasticity.

2. Classification of Muscles:

   • Muscles can be classified based on location, appearance, and regulation of their activities.
   • Three main types based on location are:
     • Skeletal muscles: Associated with skeletal components, striped appearance under the microscope (striated), and voluntary control.
     • Visceral muscles: Found in inner walls of hollow visceral organs, smooth in appearance (non-striated), and involuntary control.
     • Cardiac muscles: Found in the heart, striated in appearance, and involuntarily controlled.

3. Structure of Skeletal Muscle:

   • Skeletal muscles are organized into muscle bundles or fascicles held together by connective tissue called fascia.
   • Each muscle bundle contains multiple muscle fibers.
   • Muscle fibers are multinucleated and surrounded by a plasma membrane called sarcolemma.
   • Sarcoplasmic reticulum stores calcium ions necessary for muscle contraction.
   • Myofibrils, composed of myofilaments, are responsible for muscle contraction.
   • Myofibrils have alternating dark (A-band, containing myosin) and light (I-band, containing actin) bands.
   • Actin and myosin filaments are arranged parallel to each other and to the longitudinal axis of the myofibrils.
   • Sarcomere, the functional unit of contraction, is the portion of the myofibril between two Z-lines.
   • During muscle contraction, thin filaments (actin) slide over thick filaments (myosin), reducing the H-zone and overlapping the A-bands and I-bands.

17.2.1 Structure of Contractile Proteins

1. Structure of Actin (Thin) Filament:

   • Each actin filament consists of two filamentous (F) actins helically wound to each other.
   • Filamentous actin (F-actin) is a polymer of monomeric (G) actins.
   • Tropomyosin proteins run close to the actin filaments, with two filaments of tropomyosin running along the length of each actin filament.
   • Troponin, a complex protein, is distributed at regular intervals on the tropomyosin.
   • In the resting state, a subunit of troponin covers the active binding sites for myosin on the actin filaments, preventing muscle contraction.

2. Structure of Myosin (Thick) Filament:

   • Each myosin filament is also a polymerized protein, consisting of multiple monomeric proteins called meromyosins.
   • Meromyosin consists of two main parts: a globular head with a short arm (heavy meromyosin, HMM) and a tail (light meromyosin, LMM).
   • The globular head of meromyosin projects outward at regular intervals and angles from the surface of the polymerized myosin filament, forming cross arms.
   • The globular head of myosin is an active ATPase enzyme, capable of binding ATP and actin.

17.2.2 Mechanism of Muscle Contraction

1. Sliding Filament Theory:

   • Muscle contraction occurs through the sliding of thin filaments (actin) over thick filaments (myosin).
   • Initiated by a neural signal from the central nervous system (CNS) via a motor neuron to the neuromuscular junction.
   • Release of neurotransmitter (acetylcholine) at the neuromuscular junction generates an action potential in the sarcolemma.
   • Action potential spreads through the muscle fiber, causing the release of calcium ions (Ca++) into the sarcoplasm.

2. Calcium Ion Binding and Cross-Bridge Formation:

   • Calcium ions bind to troponin on actin filaments, exposing active sites for myosin.
   • Myosin heads bind to the exposed active sites on actin, forming cross-bridges.
   • Utilizing energy from ATP hydrolysis, myosin pulls attached actin filaments toward the center of the A-band, shortening the sarcomere and causing contraction.

3. Cross-Bridge Cycling and Relaxation:

   • Myosin releases ADP and Pi, returning to its relaxed state.
   • ATP binds to myosin, breaking the cross-bridge.
   • ATP is hydrolyzed by myosin, repeating the cycle of cross-bridge formation and breakage, further sliding of filaments.
   • Muscle relaxation occurs when calcium ions are pumped back into the sarcoplasmic reticulum, masking actin filaments.

4. Muscle Fibers and Types:

   • Muscle fibers vary in reaction time and fatigue resistance.
   • Repeated muscle activation leads to the accumulation of lactic acid, causing fatigue.
   • Muscle fibers contain myoglobin, a red-colored oxygen-storing pigment.
   • Red fibers have high myoglobin content, appear reddish, and are aerobic due to abundant mitochondria for ATP production.
   • White fibers have low myoglobin content, appear pale, and rely on anaerobic processes for energy.