PHGY 209 Lecture Notes - Lecture 20: Chemical Synapse, Excitatory Synapse, Glutamate Receptor
21 Feb 2018
School
Department
Course
Professor
Document Summary
The pre-synaptic terminal is activated by the action potential which opens the voltage-gated calcium channels. The small increase of calcium in the pre-synaptic terminal causes the protein complexes holding the glutamate (neurotransmitter) filled vesicles to the pre-synaptic membrane to release the glutamate into the synaptic cleft. The glutamate travels across the synaptic cleft where it contacts the post-synaptic membrane of the dendritic spine. This membrane contains numerous ampa receptors (ligand-gated ion channels) which are activated by glutamate binding. This causes the post- synaptic membrane to become more permeable to sodium ions, consequently depolarizing it by ~2mv during the epsp (~20milliseconds). It is the epsp"s that provide depolarization to the initial segments and consequently induce action potentials. An initial segment will only reach the threshold if multiple excitatory synapses (on multiple dendrites) occur within a brief period of time. From 50 to 100 epsps must sum at the initial segment to initiate an action potential.
