7. When a postsynaptic potential reaches threshold, an action potential is triggered
8.
Excess neurotransmitter is removed from the synaptic cleft by:
a.
diffusion away from synaptic cleft
b.
degradation by enzymes in the synaptic cleft
c.
uptake by neuroglia or reuptake into presynaptic neuron by active
transport
Excitatory and Inhibitory Postsynaptic Potentials
A neurotransmitter (NT) causes either an excitatory or an inhibitory graded potential. If a NT depolarizes the postsynaptic membrane (brings the membrane closer to threshold) it is excitatory, and the depolarizing postsynaptic potential is called an Excitatory Postsynaptic Potential (EPSP). A NT that causes hyperpolarization of the postsynaptic membrane is inhibitory. Therefore, a hyperpolarizing postsynaptic potential is called an Inhibitory Postsynaptic Potential (IPSP).
Spatial and Temporal Summation at Postsynaptic Potentials
Summation is the process by which graded potentials are added together. The greater the summation of EPSPs, the greater the chance that threshold will be reached. There are 2 types of summation:
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