In the following question, a statement of Assertion (A) is given followed by corresponding statement of Reason . Of the statements, mark the correct answer:
Assertion (A) The pre-synaptic neuron transmits an impulse (action potential) across the synaptic cleft to the post-synaptic neuron.
Reason (R) For the transmission of impulses at synapses, chemicals called neurotransmitters are responsible.
both and are true, but is not the correct explanation of
— Concept: This question tests your understanding of synaptic transmission, specifically the roles of pre-synaptic and…Concept: This question tests your understanding of synaptic transmission, specifically the roles of pre-synaptic and post-synaptic neurons and neurotransmitters.
Why (B) is correct:
1. Assertion (A) is true: The pre-synaptic neuron does transmit an impulse (action potential) to the post-synaptic neuron across the synaptic cleft. However, this transmission is not direct electrical transmission across the cleft; it's mediated by chemicals.
2. Reason (R) is true: For the transmission of impulses at chemical synapses, chemicals called neurotransmitters are indeed responsible. These neurotransmitters are released from the pre-synaptic neuron and bind to receptors on the post-synaptic neuron.
3. R is not the correct explanation of A: While both statements are true, the reason (R) explains how the transmission occurs (via neurotransmitters), but the assertion (A) describes what happens (transmission across the cleft). The assertion implies a direct transmission across the cleft, which is not entirely accurate without mentioning the chemical mediation. The assertion itself is a general statement about impulse transmission, and the reason provides the mechanism. The assertion doesn't state that the impulse directly crosses the cleft, but rather that it is transmitted across it, which is true via chemical means. However, R doesn't fully explain A because A is a statement of fact, and R is the mechanism. If A had stated 'The pre-synaptic neuron directly transmits an electrical impulse across the synaptic cleft', then R would clearly contradict it. As it stands, A is a general statement, and R provides the specific mechanism, but R doesn't fully explain the 'transmission across the synaptic cleft' in a way that makes it a direct cause-effect explanation for the assertion.
Why other options are wrong:
A) R is not the correct explanation of A, as A describes the event and R describes the mechanism.
C) Both A and R are true statements.
D) Both A and R are true statements.
Common Mistake: Students often confuse the 'transmission across the synaptic cleft' as a direct electrical jump, forgetting the crucial role of chemical neurotransmitters in most synapses.
NEET Tip / Mnemonic: Remember that 'Chemical Synapses' use 'Chemicals' (neurotransmitters) to transmit signals, while 'Electrical Synapses' have direct 'Electrical' connections (gap junctions).
Correct Answer: (B)
both and are true, but is not the correct explanation of