Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): In a chemical synapse, transmission of nerve impulse is unidirectional.
Reason (R): Only the presynaptic membrane releases neurotransmitters.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Neurotransmitter vesicles are present only on the presynaptic side.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
At a chemical synapse, a neurotransmitter carries the signal across the synaptic cleft.

Step 2: Check the Assertion
The impulse passes only from presynaptic to postsynaptic neuron, so transmission is unidirectional. (A) is true.

Step 3: Check the Reason
Only the presynaptic membrane has vesicles that release the transmitter, and receptors are on the postsynaptic membrane. (R) is true.

Step 4: Explanation
Because the chemical can be released from one side only, transmission is one-way. So R explains A.

Final Answer:
Both are true and the Reason explains the Assertion. \[ \boxed{\text{(A) }\text{Both (A) and (R) are true and (R) is the correct explanation of (A).}} \]