Excitatory postsynaptic potentials make neurons more positive, leading to signals being sent to other cells. They begin in dendrites, continue through the cell body to the axon hillock, and terminate in synapses. Neurotransmitters can cause either excitatory or inhibitory postsynaptic potentials, and all potentials are added together to calculate the net effect on the neuron. If the combined charge is positive enough, the cell will fire an action 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. An axon hillock is a small hill at the beginning of an axon, extending out from the cell body like the trunk of a tree. The axon terminates in 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 it receives no signal, a neuron has a negative electrical charge. Excitatory postsynaptic potentials make this charge more positive or closer to zero. Inhibitory postsynaptic potentials make the cell charge more negative.
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. An inhibitory postsynaptic potential is caused by negatively charged ions entering the cell or positively charged ions leaving the cell.
A single neuron can receive many signals from different neurons. Some of these signals will be excitatory and some inhibitory. All postsynaptic potentials are added together to calculate the net effect on the neuron.
The postsynaptic potentials are summed spatially and temporally. The further away from the axon hillock a postsynaptic potential is, the less effect it will have on the cell, because it has to travel a long way to the axon hillock where all the potentials are added together. 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 bound to the cell.
All postsynaptic potentials are added together with the axon hillock. If the combined charge of all the signals is positive enough, the cell will fire an action potential, which travels up the axon to the synapses. The synapses will then release neurotransmitters, which will bind to other neurons to transmit a message.
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