How can acetylcholine act both in milliseconds and over seconds? · Lobeworks/17

It has two receptor families.

How can acetylcholine act both in milliseconds and over seconds?

It has two receptor families. Nicotinic receptors are ion channels, so acetylcholine opens them within a millisecond; at the neuromuscular junction this fires every muscle fibre the motor neuron reaches. Muscarinic receptors are coupled to G proteins, so their effects start more slowly and last seconds; in the cortex they mostly close potassium channels and make neurons more excitable. Acetylcholinesterase in the cleft ends the fast signal within about a millisecond, which keeps neuromuscular transmission sharp, while in the brain the slower muscarinic actions shape attention and arousal.