Answer
An excitatory neurotransmitter is able to depolarize the membrane of a postsynaptic neuron(cell) and bring its membrane potential closer to thresh hold, or closer to threshold . An inhibitory neurotransmitter has the opposite effect on the membrane potential of the postsynaptic neuron; it hyperpolarizes the postsynaptic neuron so that its membrane potential is driven farther from threshold. It is harder for a hyperpolarized cell to reach threshold and generate an action potential.
Work Step by Step
Some neurotransmitters are excitatory, some are inhibitory, and some can be both excitatory and inhibitory, dependent on the nature of the post synaptic membrane receptors:
Some excitatory neurotransmitters include glutamate, the catecholamine neurotransmitters ,and serotonin. Dopamine can be both inhibitory and excitatory. The inhibitory neurotransmitters are g-amino-butyric acid (GABA), and glycine. Acetylcholine is mainly excitatory, but it can also be inhibitory.
Resting membrane potential is about -60-70 mV; threshold is about -55 mV. Usually when a cell generates an action potential the membrane potential shoots up to about +30-+40 mV. This is iusully the the result of the inflow of K+ ions. When the cell hyperpolarizes the membrane potential goes below polarization levels. At a membrane potential of below -70 mV , that is 75-85 mV the cell is hyperpolarized. Usually hype polarization is caused by the continued egress of K+ ions after the Na+ channels have closed. After the K+ channels close the membrane potential is restored to normal depolarization level by the Na+/K+ATPase pump.
