21.How muscles perform movement?
Muscles play a vital role in generating movement in the body through a process called muscle contraction. Muscle contraction occurs when muscle fibers generate tension and shorten, resulting in the movement of bones or other body parts. This process involves several key components:
Muscle Fibers:
Muscles are made up of individual muscle fibers, also known as muscle cells. These muscle fibers contain contractile proteins called actin and myosin, which are responsible for muscle contraction.
Sliding Filament Theory:
The sliding filament theory explains how muscle contraction occurs. According to this theory, during muscle contraction, myosin heads on the myosin filaments bind to actin filaments, forming cross-bridges. The myosin heads then pull the actin filaments, causing them to slide along the myosin filaments. This sliding action results in the shortening of the sarcomeres, which are the functional units of muscle fibers.
Role of Calcium and ATP:
Muscle contraction is initiated by an electrical signal called an action potential, which travels along motor neurons to reach the muscle fibers. The action potential triggers the release of calcium ions from the sarcoplasmic reticulum within the muscle fibers. Calcium ions then bind to troponin, a protein on the actin filaments, exposing the myosin-binding sites on actin.
Motor Unit Activation:
Motor neurons transmit the action potential from the central nervous system to the muscle fibers. Each motor neuron branches out to innervate multiple muscle fibers, forming a motor unit. When a motor neuron is activated, all the muscle fibers within its motor unit contract simultaneously.
Energy Production:
Muscle contraction requires energy in the form of adenosine triphosphate (ATP). ATP is needed for the cross-bridge cycling between actin and myosin, allowing for repeated muscle contractions. ATP is generated through various metabolic pathways, including aerobic metabolism (in the presence of oxygen) and anaerobic metabolism (in the absence of oxygen).
Muscle Synergists and Antagonists:
Muscles rarely work in isolation and often work together in synergy or opposition. Synergistic muscles work together to produce a desired movement, coordinating their contractions. Antagonistic muscles have opposing actions and work in pairs. When one muscle contracts, its antagonist relaxes, allowing for smooth and controlled movement.
