Question

How do presynaptic and postsynaptic neurons work?

Answer 1

The presynaptic and postsynaptic neurons differ in the direction of their signal transmission or impulse. The former carries the impulse towards the synapse, while the latter carries an impulse away from the synapse.

Complete answer:
The presynaptic neurons are found near the axon. They release neurotransmitters after the axon potential enters the axon terminal. The postsynaptic neurons are located near the dendrites. They accept neurotransmitters that have crossed the synapse. They might develop an axon potential if the neurotransmitters are strong enough to carry one. The neurotransmitters are the chemical messengers that carry electrical signals in the form of chemical information and are present in the synaptic vessels of the neuron. The neuronal junction that allows the transmission of signals from one neuron to another is called a synapse. They form a connection between the axon terminals and dendrites or cell bodies of the two neurons. The gap between these two structures is called the synaptic cleft. When an action potential is generated in a neuron, it reaches the axon terminal and activates the voltage-gated calcium channels. Calcium ions move inside the neuron, along the concentration gradient, and fuse with the synaptic vessels to release the neurotransmitters.

Neurotransmitters released in the synaptic cleft binds with the specific receptor molecules on the membrane of the postsynaptic neurons. This binding creates the opening or closing of ion channels on the membrane. An electrical signal is generated in the postsynaptic neuron, which would lead to the depolarization or hyperpolarization of the neuron. Through this process, the electrical signals that were converted into chemical signals in the neurotransmitters are again converted back into electrical form in the postsynaptic neuron.

The axon terminal has many branches, and thus it is connected with several postsynaptic neurons. Therefore, a single neuron may receive several synaptic inputs. The working of postsynaptic neurons occurs through spatial or temporal summation. Spatial summation occurs when the threshold is crossed, after the release of multiple neurotransmitters from various presynaptic neurons. Temporal summation occurs when the threshold is crossed, after the repeated release of a particular neurotransmitter.

Note: In the postsynaptic neurons, the firing of an action potential depends upon the type of neurotransmitters binding the receptor molecules. If the neurotransmitter opens the ligand-gated channel, it is most likely to produce an excitatory potential that would develop an action potential. If the ligand-gated channels are closed, it is less likely to produce an action potential of its own and thus will develop an inhibitory potential.