FoundationalConceptsNeuroscience

axon Presynaptic terminal with

neurotransmitter storage vesicles

axon Presynaptic terminal with

neurotransmitter storage vesicles

Synaptic clett

Postsynaptic dendrites

Figure 6.3. Electron micrograph of chemical synapses.

The molecules of neurotransmitter rapidly bounce and bang around
in the synaptic cleft, moved by the forces of thermal agitation and
diffusion. Very quickly they bump into all sorts of things, including
neurotransmitter receptor proteins located in the cell membranes of
postsynaptic neurons. If the appropriate neurotransmitter molecule
makes contact with the appropriate receptor protein, it sticks, or
binds, like a key in a lock. The interaction of the neurotransmitter
with its corresponding receptor protein changes the shape of the re-
ceptor protein, which passes a signal to the postsynaptic neuron. Neu-
rotransmitter receptor proteins may also be located in the presynaptic
membrane of the axon terminal, and thus a signal may be passed
from the axon back onto itself, allowing for various kinds of feedback
regulation.
No sooner is neurotransmitter released from the axon terminal
into the synaptic cleft than processes take place to remove it from
the synaptic cleft, to inactivate the signaling. This occurs in one of