hermolihasliitoksessa

Hermolihasliitos is the junction where a nerve cell axon terminal communicates with a muscle fiber. This specialized synapse is responsible for transmitting nerve impulses from the nervous system to the muscle, triggering muscle contraction. The process begins when an action potential arrives at the axon terminal of a motor neuron. This arrival causes voltage-gated calcium channels to open, allowing calcium ions to enter the terminal.

The influx of calcium ions triggers the fusion of synaptic vesicles, which contain the neurotransmitter acetylcholine, with the presynaptic membrane. Acetylcholine is then released into the synaptic cleft, the space between the nerve terminal and the muscle fiber. Acetylcholine diffuses across the cleft and binds to acetylcholine receptors located on the postsynaptic membrane of the muscle fiber.

This binding opens ligand-gated ion channels, allowing sodium ions to flow into the muscle fiber and potassium ions to flow out. The influx of sodium ions causes depolarization of the muscle fiber membrane, creating an end-plate potential. If this potential reaches a threshold, it triggers an action potential in the muscle fiber, which propagates along the muscle fiber membrane and into the T-tubules.

This action potential ultimately leads to the release of calcium ions from the sarcoplasmic reticulum within the muscle fiber. The increased concentration of calcium ions in the sarcoplasm then initiates the sliding filament mechanism, causing the muscle fiber to contract. After the signal has been transmitted, acetylcholine is rapidly broken down by the enzyme acetylcholinesterase in the synaptic cleft to prevent continuous stimulation of the muscle fiber.