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George E. Carvell, PhD, PT   University of Pittsburgh
 
LOCAL POTENTIALS III: SYNAPTIC POTENTIALS Excitatory Post Synaptic Potentials
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BC&P Fig 5.13  p. 115
Presynaptic Axon Terminal
Most Excitatory Synapses occur on Postsynaptic Dendritic Spines (fig 2.18)
LEGEND: Figure 5.13 “The generation of an EPSP. (a) An impulse arriving in the presynaptic terminal causes the release of neurotransmitter. (b) The molecules bind to transmitter-gated ion channels in the postsynaptic membrane. If Na+ enters the postsynaptic cell through the open channels, the membrane will become depolarized. (c) The resulting change in membrane potential (Vm), as recorded by a microelectrode in the cell, is the EPSP.”
BC&P p 115
The Action Potential invading the axon terminal depolarizes the membrane. This opens voltage-gated Ca2+ channels (not shown) and Ca2+ rushes in. Intracellular Ca2+ triggers a cascade of events to: 1. move the NT filled vesicles to the active zone, 2. fuse the vesicle and
presynaptic axon terminal membranes, 3. open the fused
membranes and 4. release the NT into the synaptic cleft.
Neurotransmitter (NT) filled synaptic vesicles
Binding of NT to Postsynaptic Receptor Complex opens Ion Pore and Na+ rushes in to depolarize membrane = Excitatory Post Synaptic Potential (EPSP)
EPSP is a local, graded, non-propogated depolarizing potential
Fast, Increased-Conductance Ionotropic Synapse
BC&P
fig 2.18
p 40