What causes the release of Acetylcholine (ACh)?

The release of Acetylcholine (ACh) is primarily triggered by the influx of calcium ions into the presynaptic terminal of neurons. When a nerve impulse reaches the terminal, it causes depolarization of the membrane, leading to the opening of voltage-gated calcium channels. The subsequent increase in intracellular calcium concentration prompts the synaptic vesicles containing ACh to fuse with the presynaptic membrane and release ACh into the synaptic cleft through a process known as exocytosis.

This process is crucial for the transmission of nerve impulses across synapses, enabling communication between neurons as well as between neurons and effector cells, such as muscle cells. The presence of calcium is essential; without it, ACh would not be released, and neurotransmission would be severely impaired. Thus, the influx of calcium is the pivotal mechanism that facilitates the release of ACh in the nervous system.