Why do some receptors act in milliseconds and others over seconds or minutes? · Grey Matter

An ionotropic receptor is itself a channel, so binding opens the pore directly and current flows within a fraction of a millisecond; AMPA, NMDA, GABA-A, glycine and nicotinic receptors work this way.

Why do some receptors act in milliseconds and others over seconds or minutes?

An ionotropic receptor is itself a channel, so binding opens the pore directly and current flows within a fraction of a millisecond; AMPA, NMDA, GABA-A, glycine and nicotinic receptors work this way. A metabotropic receptor has no pore: it activates a G protein, which then opens or closes separate channels or switches on enzymes that make second messengers, and each step adds time. Its effects start after tens to hundreds of milliseconds and can last seconds to minutes, because the messengers and the phosphorylations they cause outlive the transmitter. The two designs split the work: ionotropic receptors carry the content of signals, metabotropic ones adjust how cells respond to them.