Which components bind acetylcholine on the muscle cell surface?

• A. ACh receptor channels
• B. Voltage-gated Na+ channels
• C. Ca2+ channels
• D. K+ channels

Answer: (A)

Acetylcholine binds to the nicotinic acetylcholine receptor on the muscle cell’s motor end plate, which is a ligand-gated ion channel. When ACh attaches to this receptor, the channel opens and allows positively charged ions, mainly sodium, to rush into the cell (with some potassium moving out). This inward current depolarizes the membrane, creating the end-plate potential that reaches threshold to fire an action potential along the sarcolemma. This receptor is the binding site for acetylcholine on the muscle surface.

The other channels listed are voltage-gated and respond to depolarization rather than to acetylcholine binding. They participate later in signaling: voltage-gated sodium channels propagate the action potential, calcium channels help trigger calcium release from the sarcoplasmic reticulum, and potassium channels help repolarize the membrane.