glutamatergic synaptic transmission

where is glutamate stored in glutamatergic nerve terminals

glutamate is stored within small synaptic vesicles inside nerve terminal

what triggers release of glutamate from presynaptic vesicles

arrival of action potential at nerve terminal causes depolarisation of terminal membrane which opens voltage gated Ca2+ channels and allows Ca2+ influx

what role does Ca2+ play in glutamate release

Ca2+ binds to specific vesicular proteins that mediate fusion of synaptic vesicle membrane with plasma membrane - results in glutamate release into synaptic cleft

what happens to glutamate after it is released into synaptic cleft

glutamate binds to glutamate receptors on postsynaptic membrane 

what type of receptors are glutamate receptors and what ions are they permeable to

ligand-gated ion channels permeable to Na+, K+, Ca2+

what ions move through glutamate receptor channels upon activation

Na⁺ enters the postsynaptic neuron, a small amount of K⁺ exits, and in some receptor types, Ca²⁺ may also enter

what occurs when Na+ influx through glutamate receptors

entry of Na+ causes depolarisation

• shift in membrane potential toward more positive values from resting potential of -70mV

what is excitatory postsynaptic potential (EPSP)

it is the transient (short-lived, temporary) depolarisation of postsynaptic membrane caused by Na+ influx following glutamate receptor activation

what happens when multiple EPSPs occur close together in time or space

EPSPs can summate (add together) which leads to greater overall depolarisation of postsynaptic membrane

at what membrane potential can summated EPSPs trigger action potential

if depolarisation reaches approx -55mV, it activates voltage gated Na+ channels initiating actiion potential

summary of synaptic excitation in the brain

summation of EPSPs leading to depolarisation that triggers action potential where this process is mediated by glutamate

how is glutamate replenished in neurones after release

glutamine released by glial cells → taken up by neurones → converted to glutamate by mitochondrial enzyme glutaminase