What is the excitatory postsynaptic potential?

An excitatory postsynaptic potential is a change in the electrical charge of a nerve cell or neuron. The neuron starts out with a negative charge, but the excitatory postsynaptic potential makes this charge more positive. If there are enough excitatory postsynaptic potentials, the neuron will send a signal to other cells.

The excitatory postsynaptic potential begins in the dendrites, which extend in all directions from the cell body like the branches of a tree. The potential continues through the cell body to the axon hillock. The axon hillock is a small hill at the beginning of an axon, extending from the cell body like a tree trunk. The axon ends at synapses, which transmit chemicals across a gap, called the synaptic cleft. These chemicals bind to receptors on the dendrites of another neuron.

When neurotransmitters bind to a neuron, they can cause either an excitatory postsynaptic potential or an inhibitory postsynaptic potential. When not receiving any signal, a neuron has a negative electrical charge. Exciting postsynaptic potentials cause this charge to be more positive or closer to zero. Inhibitory postsynaptic potentials make the cell more negatively charged.

Neurotransmitters that bind to receptors on a neuron cause ion channels to open, allowing charged particles to enter the cell. An excitatory postsynaptic potential is caused by positively charged ions flowing into the cell. A postsynaptic inhibitory potential is caused by negatively charged ions entering the cell or positively charged ions flowing out of the cell.

A single neuron can receive many signals from several different neurons. Some of these signals will be excitatory and some will be inhibitory. All postsynaptic potentials are added to calculate the net effect on the neuron.

Postsynaptic potentials add spatially and temporally. The farther away from the axon a postsynaptic potential is, the less effect it will have on the cell, since it has to travel a long way to the axon, where all the potentials add up. The longer a postsynaptic potential lasts, the greater the effect it will have on the overall charge of the cell. A postsynaptic potential lasts as long as neurotransmitters are attached to the cell.

All postsynaptic potentials add up in the axon. If the combined charge of all the signals is positive enough, the cell will fire an action potential, which travels down the axon toward the synapses. The synapses will then release neurotransmitters, which will bind to other neurons to transmit a message.

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