presünapse

The presynaptic terminal is the part of a neuron that is responsible for transmitting signals to other neurons, muscles, or glands. It is located at the end of an axon and contains synaptic vesicles filled with neurotransmitters. When an action potential reaches the presynaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft, a small gap between the presynaptic terminal and the postsynaptic neuron. The neurotransmitters then bind to receptors on the postsynaptic neuron, initiating a response that can either excite or inhibit the postsynaptic neuron.

The release of neurotransmitters is a calcium-dependent process. When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open, allowing calcium ions to enter the terminal. This increase in calcium concentration triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft. The neurotransmitters then diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron.

The presynaptic terminal also contains enzymes that break down neurotransmitters after they have been released. This ensures that the neurotransmitters are quickly removed from the synaptic cleft, allowing the presynaptic terminal to be ready for the next action potential. The presynaptic terminal is a crucial component of the nervous system, as it is responsible for transmitting signals between neurons and coordinating the activity of the nervous system.