| used in more ways than one.
EPSPs
bs IPSP
Lo. \( (W\ 7 bo y= Zp
_\ =< aX }) j/^4 t= __ Action potential propagation ( y= =<
bo SSS = {f »WA \ Axon hillock\Figure 6.4. Excitatory and inhibitory postsynaptic potentials are generated
throughout the dendritic field of a neuron by excitatory and inhibitory sig-
nals received from other neurons. The effects of these EPSPs and IPSPs are
summed at the axon hillock, where an action potential, when triggered, be-
gins its propagation along the length of the axon.
Neurons are thus continuously doing computation, summing up
all the incoming EPSPs and IPSPs. If the voltage at the axon hillock
reaches the threshold for opening voltage-gated sodium channels,
then a nerve impulse will begin there and propagate along the length
of the axon, triggering the release of neurotransmitter when the sig-
nal reaches the axon terminal.
To first approximation, we can consider neurons to store and
release a single specific type of neurotransmitter. Thus, there are
glutamatergic neurons, GABAergic neurons, and so forth. It turns out