Concept: This question tests your understanding of synaptic transmission and the types of potentials generated on the post-synaptic membrane.

Why (C) is correct: When a neurotransmitter binds to receptors on the post-synaptic membrane, it can cause either an excitatory post-synaptic potential (EPSP) or an inhibitory post-synaptic potential (IPSP). An EPSP depolarizes the membrane, making it more likely to fire an action potential, while an IPSP hyperpolarizes or stabilizes the membrane, making it less likely to fire. The effect depends on the specific neurotransmitter and the type of receptor it binds to.

Why other options are wrong:

• (A) always inhibitory: This is incorrect because many neurotransmitters cause excitation.
• (B) always excitatory: This is incorrect because many neurotransmitters cause inhibition.
• (D) neither excitatory nor inhibitory: This is incorrect as the potential developed at the synapse always has an effect, either excitatory or inhibitory.

NEET Tip: Remember that the effect of a neurotransmitter (excitatory or inhibitory) is determined by the receptor on the post-synaptic neuron, not solely by the neurotransmitter itself. For example, acetylcholine can be excitatory at the neuromuscular junction but inhibitory at the heart.

Correct Answer: (C)