ingerületösszehúzódás

ingerületösszehúzódás is a Hungarian term that translates to excitation-contraction coupling. It describes the physiological process by which an electrical stimulus (excitation) leads to a mechanical response (contraction) in muscle cells. This coupling is crucial for all forms of muscle movement, from voluntary actions like walking to involuntary processes like the beating of the heart.

The process begins with an electrical signal, typically an action potential, arriving at the muscle fiber. This electrical signal travels along the sarcolemma, the cell membrane of the muscle fiber, and down specialized invaginations called T-tubules. These T-tubules conduct the electrical impulse deep into the muscle cell.

The arrival of the action potential at the T-tubules triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum, a network of internal membranes within the muscle cell. These calcium ions then bind to regulatory proteins, such as troponin, which are associated with the thin filaments (actin) of the muscle fiber. This binding causes a conformational change in the actin-myosin complex.

The conformational change exposes the binding sites on the actin filaments, allowing the myosin heads to bind to actin. This binding initiates a power stroke, where the myosin heads pull the actin filaments towards the center of the sarcomere, the basic contractile unit of the muscle. This sliding of filaments results in muscle shortening, or contraction.

The process is reversible. When the electrical stimulus ceases, calcium ions are actively pumped back into the sarcoplasmic reticulum, causing the regulatory proteins to return to their original positions. This prevents further interaction between actin and myosin, and the muscle fiber relaxes.