Locomotion and Movement

Key Concepts

Types of Movement

Living organisms exhibit various types of movements. In the human body, cells show three main types:

1. Amoeboid Movement: Exhibited by specialized cells like macrophages and leucocytes in blood. Effected by pseudopodia and microfilaments.
2. Ciliary Movement: Occurs in internal tubular organs lined by ciliated epithelium, such as the trachea and female reproductive tract (passage of ova).
3. Muscular Movement: Required for movement of limbs, jaws, tongue, etc. It involves the contractile property of muscles.

Muscle Types

Muscles are specialized tissues of mesodermal origin, classified into three types based on location and appearance:

• Skeletal Muscles: Striated, voluntary, and closely associated with the skeleton. Primarily involved in locomotion.
• Visceral Muscles: Smooth (non-striated), involuntary, located in the inner walls of hollow organs like the alimentary canal.
• Cardiac Muscles: Striated, involuntary, and branched; found only in the heart.

Structure of a Skeletal Muscle

A skeletal muscle consists of muscle bundles or fascicles held together by a collagenous layer called fascia. Each fascicle contains many muscle fibres.

• Sarcolemma: The plasma membrane of the muscle fibre.
• Sarcoplasmic Reticulum: Storehouse of calcium ions (Ca++).
• Myofibrils: Contain alternate dark (A-band, myosin) and light (I-band, actin) bands.
• Sarcomere: The functional unit of contraction between two 'Z' lines.

Structure of Contractile Proteins

• Actin (Thin Filament): Composed of two 'F' actins, tropomyosin, and troponin. Troponin masks the active binding sites for myosin in a resting state.
• Myosin (Thick Filament): Polymerized protein composed of meromyosins. Each meromyosin has a globular head (ATPase enzyme) and a tail.

Mechanism of Muscle Contraction (Sliding Filament Theory)

Contraction is triggered by a neural signal from the CNS.

1. Ca++ Release: Signal triggers release of Ca++ from sarcoplasmic reticulum.
2. Unmasking: Ca++ binds to troponin, exposing active sites on actin.
3. Cross-bridge Formation: Myosin heads bind to actin using ATP.
4. Power Stroke: Myosin pulls actin filaments towards the centre of the 'A' band.
5. ATP Binding: New ATP binds to myosin, breaking the cross-bridge.
6. Recycling: The process repeats until Ca++ is pumped back.

Human Skeletal System

Consists of 206 bones, divided into:

1. Axial Skeleton (80 bones): Skull (22), vertebral column (26), sternum, and ribs (12 pairs).
2. Appendicular Skeleton (126 bones): Bones of limbs (forelimbs and hind limbs) and their girdles (pectoral and pelvic).

Joints

Points of contact between bones or between bones and cartilages:

• Fibrous: No movement (e.g., skull sutures).
• Cartilaginous: Limited movement (e.g., between vertebrae).
• Synovial: Considerable movement (e.g., ball and socket, hinge, pivot, glide, and saddle joints).

Disorders of Muscular and Skeletal System

• Myasthenia gravis: Autoimmune disorder affecting the neuromuscular junction.
• Muscular dystrophy: Genetic degeneration of skeletal muscle.
• Tetany: Rapid spasms due to low Ca++ in body fluid.
• Arthritis: Inflammation of joints.
• Osteoporosis: Decreased bone mass due to aging (often linked to low estrogen).
• Gout: Accumulation of uric acid crystals in joints.

Activities (for understanding, not part of notes)

• Compare the range of motion allowed by different types of synovial joints.
• Identify the bones of the axial and appendicular skeletons on a human skeleton model.
• Demonstrate the antagonistic action of muscles (e.g., biceps and triceps).