Question

Structure of synapse is given. Analyse it and answer the following questions.
(a) Identify the chemical labelled as `X'.
(b) Mention their role in the transmission of impulse to only one direction.

Hint:

Remember: In a synapse, neurotransmitters are released only by the presynaptic end, while receptors are present only on the postsynaptic membrane. That is why nerve impulse travels in one direction only.

Answer 1

Step 1: Identify the labelled part `X'.
In the given synapse diagram, the label `X' indicates the chemical substances present in the synaptic cleft. These chemicals are called neurotransmitters.
Step 2: Explain what neurotransmitters do.
Neurotransmitters are released from the synaptic vesicles of the presynaptic membrane when a nerve impulse reaches the end of the axon. These chemicals diffuse across the synaptic cleft and carry the signal to the postsynaptic membrane.
Step 3: State the answer for part (a).
Therefore, the chemical labelled as `X' is neurotransmitter (for example, acetylcholine in many synapses).
Step 4: Explain transmission in one direction.
Transmission of nerve impulse across a synapse takes place only in one direction because neurotransmitters are released only from the presynaptic terminal. The receptors for these neurotransmitters are present only on the postsynaptic membrane.
Step 5: Conclude the role in one-way conduction.
As a result, the impulse passes from the presynaptic neuron to the postsynaptic neuron only, and not in the reverse direction. This ensures unidirectional transmission of nerve impulses.