Definitions [1]
Definition: Locomotion
Locomotion is the voluntary movement of an individual from one place to another.
Key Points
Key Points: Introduction of Locomotion and Movement
- Locomotion is the movement of a living being from one place to another (e.g., walking, running, swimming).
- All locomotion is movement, but not all movements are locomotion (e.g., blinking or moving limbs without changing place).
- Movement is a basic feature of living organisms, seen in both plants and animals (e.g., Amoeba shows protoplasmic streaming).
- Different organisms use different structures for movement, like cilia, flagella, tentacles, and limbs.
- The purpose of locomotion includes finding food, shelter, mates, suitable conditions, and escaping predators.
Key Points: Types of Movement
- Human body cells show three types of movements: Amoeboid, Ciliary, and Muscular.
- Amoeboid movement - caused by pseudopodia; involves microfilaments; seen in leucocytes and macrophages.
- Ciliary movement - occurs in organs lined by ciliated epithelium; removes dust in the trachea; moves ova in the fallopian tube.
- Muscular movement - due to the contractile property of muscles; seen in jaws, limbs, eyelids, alimentary canal, and ureters.
- Muscular movement is used for locomotion and other movements in humans and most multicellular organisms.
- Locomotion requires coordinated activity of muscular, skeletal, and neural systems.
Key Points: Muscles
- Muscles are specialised tissues of mesodermal origin and contribute to 40–50% of an adult human's body weight.
- Muscles have four properties - Excitability, Contractility, Extensibility, and Elasticity.
- Skeletal muscles — associated with the skeletal system; striated (light & dark bands); voluntary; responsible for locomotion and body posture changes.
- Visceral muscles — form the inner walls of internal organs; non-striated; involuntary; assist in the movement of food through the digestive tract and gametes.
- Cardiac muscles - found only in the heart; striated with a branching pattern; involuntary in action.
Key Points: Structure of Contractile Proteins
- Each thin filament (actin) is made of two 'F' (Filamentous) actins helically wound together. Each 'F' actin is a polymer of monomeric 'G' (Globular) actins.
- Two tropomyosin filaments run alongside 'F' actins. Troponin proteins are distributed at regular intervals on tropomyosin.
- In the resting state, a troponin subunit masks the active binding sites for myosin on actin filaments.
- Each thick filament (myosin) is made of many monomeric proteins called meromyosins. Each meromyosin has a globular head, short arm, and tail.
- Meromyosin is of two types - HMM (Heavy Meromyosin) - the globular head + short arm, and LMM (Light Meromyosin) - the tail.
- The globular head (HMM) projects outward, forming a cross arm. It acts as an active ATPase enzyme and has binding sites for both ATP and actin.
Key Points: Mechanism of Muscle Contraction
- Muscle contraction follows the sliding filament theory, where thin (actin) filaments slide over thick (myosin) filaments.
- Contraction begins with a signal from the CNS through a motor neuron; the neuron and muscle fibres together form a motor unit.
- The neuromuscular junction (motor-end plate) is the point where the motor neuron connects to the muscle fibre.
- Acetylcholine is released, which generates an action potential and causes the release of Ca²⁺ from the sarcoplasmic reticulum.
- Calcium ions activate actin, allowing myosin heads to bind and form cross-bridges.
- Cross bridges pull actin filaments, causing sliding, shortening of the sarcomere, and muscle contraction (I-band shortens, A-band remains the same).
- ATP helps in breaking and reforming cross-bridges; when Ca²⁺ is pumped back, the muscle relaxes.
Key Points: Skeletal System
- The skeletal system consists of bones and cartilage and provides shape and support to the body.
- It plays an important role in movement, along with the muscular system (e.g., jaw for chewing, limbs for walking).
- Bones are hard due to calcium salts, while cartilage is flexible due to chondroitin salts.
- Humans have 206 bones in adulthood, while a newborn has about 300 bones that fuse during growth.
- The skeletal system is divided into two parts: the axial skeleton and the appendicular skeleton.
Key Points: Joints and Its Classification
- Joints connect bones and help in body movement.
- They act as points of contact between bones or between bone and cartilage.
- Muscles act on joints like a fulcrum to produce movement.
- Joints are of three types: fibrous, cartilaginous and synovial.
- Fibrous joints → no movement (e.g., skull sutures).
- Cartilaginous joints → limited movement (e.g., between vertebrae).
- Synovial joints → free movement (e.g., ball & socket, hinge, pivot).
Key Points: Disorders of Muscular and Skeletal System
- Myasthenia gravis - an autoimmune disorder affecting the neuromuscular junction; causes fatigue, weakness, and paralysis of skeletal muscles.
- Muscular dystrophy - progressive degeneration of skeletal muscles; mainly caused by a genetic disorder.
- Tetany - rapid spasms/wild contractions in muscles due to low Ca²⁺ (calcium) levels in body fluids.
- Arthritis - inflammation of joints causing pain and stiffness.
- Osteoporosis - an age-related disorder; decreased bone mass and increased risk of fractures; caused by a decrease in oestrogen levels.
- Gout - inflammation of joints due to the accumulation of uric acid crystals; causes intense pain and swelling.
