Primary Somatosensory Cortex
Postsynaptic membrane repolarization
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Following a brief period of 
depolarization, the postsynaptic membrane repolarizes to its resting potential within a few milliseconds (ms).
- The process begins when the neurotransmitter, acetylcholine (ACh), is
broken down (catalyzed) by the enzyme, acetylcholinesterase (AChE), which is present in the postsynaptic membrane and synaptic cleft. Choline, one product of the reaction, is taken back up by the presynaptic neuron and used to make new ACh.
- As the ACh is removed, the gated receptors (= ion channels) in the postsynaptic membrane close. This blocks the diffusion pathways for Na+ and K+ and stops further depolar-ization.
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- After the channels close, Na+ and K+ that passed through the membrane during depolarization are redistributed by Na+/K+ pump proteins.
- The pumps actively move Na+ ions out of the cell and K+ ions in.
- Leak channels then allow K+ ions to diffuse back out of the cell.
- The K+ efflux continues until the resting membrane potential (or equilibrium, -70mV) is re-established.
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