Synaptic transmission – Level 3 Applied Human Biology BTEC Revision

Synaptic transmission is the way in which information is communicated between neurons through the synapse.
It is a complex process that is central to the functions of the nervous system.
Synaptic transmission can be either chemical or electrical, but in the human body it is mostly a chemical process.

The synapse is the small physical gap between the axon terminal of one neuron and the dendrites, or cell body, of the next neuron.
Neurotransmitters are chemicals that carry the signals across the synapse.
When an action potential reaches the pre-synaptic neuron (the neuron transmitting the message), it causes the release of neurotransmitters stored in vesicles.
These neurotransmitters cross the synapse and bind to complementary receptors on the post-synaptic neuron (the neuron receiving the message).
This triggers an action potential in the post-synaptic neuron, allowing the signal to continue its path.

The transmission starts with an action potential reaching the axon terminal of the pre-synaptic neuron.
This triggers the opening of calcium ion channels causing an influx of calcium ions.
The change in ion concentration leads to the release of neurotransmitters into the synapse.
The neurotransmitters diffuse across the synaptic gap and bind to the receptors on the post-synaptic neuron.
This binding causes ion channels to open on the post-synaptic neuron, triggering an action potential and continuing the neuronal signal.

After the neurotransmitters have transmitted the impulse, they need to be removed from the synapse to prevent continual activation of the post-synaptic neuron. This is called reuptake.
Enzymatic breakdown is another way neurotransmitter levels in the synapse are controlled. Enzymes break down certain neurotransmitters which are then reabsorb by the pre-synaptic neuron.
The balance in release and removal of neurotransmitters is critical for proper synaptic function and neural communication.