Figure 3. Excitatory and inhibitory synapses in the cortex
Cortical pyramidal neurons receive excitatory and inhibitory innervation
from projection and local neurons. In most cases, long-distance
projections are excitatory, and local innervation si inhibitory.
Cortical neurons also form excitatory connections within the same
regions. Glutamate is the principle excitatory transmitter for
excitation, and GABA is the key inhibitory transmitter. At postsynaptic
sites, both AMPA and KA receptors may contribute to excitatory
transmission, although these excitatory synapses are not homogenous.
Some synapses only express functional AMPA receptors, and some synapses
contain both of them. At presynaptic sites, there are KA receptors as
well. For inhibitory transmission, GABAA receptor
mediate most of inhibitory transmission. GABAB subtype
receptor may distribute presynaptically to modulate the transmission.