Role of Synapses in the Nervous System

Synaptic Transmission – Basic Neurochemistry

Write a short note on a synapse.
Answer.

• The neurons form long chains along which impulses travel from one neuron to the other and so on for long distances in different directions.
• The site of contact between two neurons where nerve impulses pass from one neuron to another is called a synapse. It is important to know that at the synapse, the contact between the neurons is by contiguity and not by continuity.

Synapse Structure Each synapse consists of

1. The presynaptic membrane of one neuron,
2. Synaptic cleft and
3. The postsynaptic membrane of another neuron.

The pre-and postsynaptic membranes are separated by a small gap (20 nm wide) called synaptic clef.

Thus, the following are the three essential components of a synapse:

• Presynaptic knob/membrane
• Synaptic cleft
• Postsynaptic membrane

Mechanism of transmission of the impulse

• The arrival of nerve impulses at a presynaptic knob (terminal) causes the release of a neurotransmitter from presynaptic vesicles into the synaptic cleft, which binds with the receptors on the postsynaptic membrane. This binding produces a response in the postsynaptic membrane in the form of depolarization or hyperpolarization.
• The excitatory nerve impulse causes depolarization of the postsynaptic membrane, while an inhibitory impulse causes its hyperpolarization. When the depolarization reaches a threshold, an action potential is produced in the postsynaptic neuron. In this way, action potentials are transferred from one neuron to another neuron.