Presynaptic Cell

What is a Presynaptic Cell?

A presynaptic cell is the sending cell at a synapse. In a chemical synapse, it is usually a neuron communicating with another neuron or a target such as a muscle cell. The presynaptic cell releases neurotransmitters, which are chemical messengers that transmit signals across the synaptic cleft to the postsynaptic cell. This process is crucial for communication between neurons and is the basis for the complex signaling networks that underlie brain function and behavior.

Key Features

• Axon Terminal

  The axon terminal, also known as the presynaptic terminal, is the specialized structure at the end of the neuron's axon. It contains synaptic vesicles filled with neurotransmitters and is responsible for transmitting signals to the postsynaptic cell.

• Synaptic Vesicles

  Synaptic vesicles are small, membrane-bound compartments within the axon terminal that store neurotransmitters. Upon receiving a signal from the presynaptic cell, the vesicles fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

• Neurotransmitter Release

  At many chemical synapses, an action potential arriving at the terminal opens voltage-gated calcium channels. Calcium entry triggers neurotransmitter release from synaptic vesicles. This process, called exocytosis, involves the fusion of vesicles with the presynaptic membrane and the subsequent release of neurotransmitters into the synaptic cleft.

Presynaptic cell functions

• Signal Transmission

  The primary function of the presynaptic cell is to transmit signals to the postsynaptic cell by releasing neurotransmitters. This process enables communication between neurons and forms the basis for neural signaling networks.

• Modulation of Synaptic Strength

  Presynaptic cells can modulate the strength of the synapse by adjusting the amount of neurotransmitter released. This modulation plays a critical role in synaptic plasticity, a key mechanism underlying learning and memory processes.

• Neurotransmitter Reuptake

  Following the release of neurotransmitters, presynaptic cells may reabsorb some of the neurotransmitters from the synaptic cleft through a process called reuptake. Reuptake into glial cells, enzymatic breakdown, and diffusion can also help remove transmitter, depending on the synapse.

Presynaptic Cell and Neurological Disorders

Changes in presynaptic function are studied in neurological and psychiatric disorders. Their roles differ across conditions; a disorder cannot generally be explained by a single change in transmitter release.

Sources and further reading

Purves and colleagues: chemical synapses; review of presynaptic plasticity.