Assertion (A): Acetylcholine transmits the nerve impulse across a synapse.
Reason (R) : Acetylcholine is secreted by adrenergic neurons.

Question

Assertion (A): Acetylcholine transmits the nerve impulse across a synapse. 
Reason (R) : Acetylcholine is secreted by adrenergic neurons.

Accepted Answer

The correct option is (3): A is true and R is false.

This option is correct because the Assertion (A) is a factual and accurate statement in neurobiology, while the Reason (R) contains a fundamental factual error regarding the classification of neurons. The Assertion states that Acetylcholine transmits the nerve impulse across a synapse, which is unequivocally true. Acetylcholine (ACh) is a classic chemical neurotransmitter released from the presynaptic terminal, diffuses across the synaptic cleft, and binds to receptors on the postsynaptic membrane to either excite or inhibit the target cell, thereby transmitting the impulse. However, the Reason states that Acetylcholine is secreted by adrenergic neurons. Neurons are named for the chemical messenger they release: those releasing Acetylcholine are termed **cholinergic neurons** (e.g., motor neurons and parasympathetic postganglionic neurons). In contrast, **adrenergic neurons** are those that release catecholamines, such as Norepinephrine (noradrenaline) or Epinephrine (adrenaline). Since the Reason incorrectly links Acetylcholine to adrenergic neurons, the statement is false.

The incorrect option is (1): Both A and R are true and R is correct explanation of A.
This option is incorrect because the Reason (R) is factually false. The core premise of a cholinergic system is that its neurons synthesize and release Acetylcholine; adrenergic neurons are entirely separate and release norepinephrine or epinephrine. Therefore, since R is false, this option, which claims R is true, must be rejected. Furthermore, even if R were true, it would describe the *origin* of the neurotransmitter, not the *mechanism* by which it transmits the impulse, meaning R could not be the "correct explanation" for A.

The incorrect option is (2): Both A and R are true but R is not correct explanation of A.
This option is incorrect because, similar to option 1, it incorrectly assumes that both the Assertion (A) and the Reason (R) are true statements. While A is true, R is false, as Acetylcholine is secreted by cholinergic neurons, not adrenergic neurons. For this option to be valid, the only point of contention should be the explanatory relationship between two factually correct statements. Since the foundational premise that R is true fails, the entire option is invalidated on grounds of factual error.

The incorrect option is (4): A and R are false.
This option is incorrect because it falsely claims that the Assertion (A) is a false statement. The assertion that Acetylcholine transmits nerve impulses across a synapse is a core principle in the physiology of the nervous system, making it true. The chemical transmission of a signal from a nerve cell to a muscle cell or another nerve cell is fundamentally dependent on the release of neurotransmitters like Acetylcholine. Since A is true, and this option claims A is false, it is the wrong choice.