Which is correct regarding membrane receptors and signal transduction?

The statement that ANS neurotransmitters bind to membrane receptors on the effector cells, which leads to intracellular events, accurately reflects the process of signal transduction in the autonomic nervous system. Neurotransmitters, such as acetylcholine or norepinephrine, interact with their specific receptors located on the cell membrane of target cells (effector cells). This binding triggers a cascade of intracellular signaling events that can alter cellular function, such as changes in enzyme activity, ion channel permeability, or gene expression.

In contrast, the other statements misrepresent the characteristics and functions of specific receptors. Cholinergic muscarinic receptors are not ionotropic; they are actually metabotropic, meaning they mediate their effects through G-proteins and second messenger systems, not through direct ion channel opening. Similarly, cholinergic nicotinic receptors are indeed ionotropic receptors, functioning directly to open ion channels upon activation by acetylcholine. Finally, while metabotropic receptors can influence ion channels, they do so indirectly through intracellular signaling pathways rather than activating them directly. This distinction is crucial in understanding how different receptor types function within the signal transduction process.