Lihasärsykkeet

Lihasärsykkeet refer to the electrical signals that travel along muscle fibers, initiating muscle contraction. These impulses are generated by motor neurons and transmitted across the neuromuscular junction. When a motor neuron is activated, it releases a neurotransmitter, typically acetylcholine, which binds to receptors on the muscle fiber membrane. This binding triggers a change in the electrical potential of the muscle fiber, creating an action potential. This action potential then propagates along the sarcolemma, the outer membrane of the muscle cell, and into the T-tubules.

Inside the muscle fiber, the action potential causes the release of calcium ions from the sarcoplasmic reticulum. These calcium ions bind to troponin, a protein complex associated with actin filaments. This binding causes a conformational change in tropomyosin, another protein, exposing the myosin-binding sites on actin. Myosin heads then bind to actin, forming cross-bridges. Through a process involving the hydrolysis of ATP, the myosin heads pivot, pulling the actin filaments towards the center of the sarcomere. This sliding of filaments results in the shortening of the muscle fiber, which is observed as muscle contraction. The frequency and strength of lihasärsykkeet determine the force and duration of the muscle contraction. Relaxation occurs when the nerve impulse stops, calcium ions are pumped back into the sarcoplasmic reticulum, and the actin-myosin interaction ceases.