A&P notes

Synaptic Transmission Overview

• Synaptic transmission is the process by which neurotransmitters are released by a neuron and bind to receptors on a target cell, leading to a physiological response.

Steps of Synaptic Transmission at a Nicotinic Synapse

1. Action Potential Arrival

• The process begins when an action potential travels down the axon of a presynaptic neuron, reaching the axon terminal.

2. Calcium Ion Influx

• The action potential trigger opens voltage-gated calcium channels, allowing Ca²⁺ ions to flow into the neuron.

3. Neurotransmitter Release

• The influx of calcium ions causes synaptic vesicles filled with neurotransmitters (in this case, acetylcholine) to fuse with the presynaptic membrane.

• This fusion releases neurotransmitters into the synaptic cleft via exocytosis.

4. Binding to Receptors

• Acetylcholine diffuses across the synaptic cleft and binds to nicotinic receptors on the postsynaptic membrane.

5. Postsynaptic Potential Generation

• The binding of acetylcholine to nicotinic receptors opens ion channels, allowing Na⁺ ions to enter the postsynaptic cell.

• This influx of sodium ions causes depolarization of the postsynaptic neuron, leading to an excitatory postsynaptic potential (EPSP).

6. Termination of Signal

• The action of acetylcholine is terminated by the enzyme acetylcholinesterase, which breaks down acetylcholine into acetate and choline, stopping the signal transmission.

• Choline is taken back up into the presynaptic neuron to be reused for acetylcholine synthesis.