Where are nicotinic receptors found?

• A. In skeletal muscle alone
• B. In brain alone
• C. In heart muscle only
• D. In all autonomic ganglia and at the neuromuscular endplate of skeletal muscles and also adrenal medulla

Answer: (D)

Nicotinic acetylcholine receptors are ligand-gated ion channels that mediate fast synaptic transmission where acetylcholine is released. They are found at the neuromuscular junctions of skeletal muscle (Nm type), in all autonomic ganglia (Nn type), and on adrenal medulla chromaffin cells (also Nn type). This distribution supports their roles in activating skeletal muscle contraction, transmitting signals through the autonomic ganglia, and triggering epinephrine release from the adrenal medulla. In contrast, skeletal muscle is not driven by receptors in heart muscle itself—cardiac tissue mainly uses muscarinic receptors for ACh effects—so statements limiting nicotinic receptors to heart or brain alone don’t fit the full picture. Therefore, the correct description is that nicotinic receptors are present in all autonomic ganglia and at the neuromuscular endplate of skeletal muscles and also in the adrenal medulla.