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How Neurons Work: Communication Through Electrical Impulses

An explanation of how neurons communicate, within the cell and among cells.

Electrical charges within one neuron

Electrical impulses move from the cell body of the neuron to the axon. The neuron axon has a slight negative charge of around -70 millivolts because it normally contains more negative ions. This negative charge is the neuron's resting potential. When the neurons are excited to a certain level, the ion channels open in the cell membrane of the axon at the part that is closest to the cell body. This lets positive ions flow into the axon. This changes the potential to a positive potential, which is called the action potential. Once it reaches a value of around +50 millivolts, those ion channels close, and other ion channels open to move positive ions out of the axon. This brings the axon back to it's negative resting potential. In this way, the positive ions move along the axon, from node to node. Axons have a fatty coating that acts as insulation, called the myelin sheath. This has gaps which are the nodes. Ion channels are located at each node, so the electrical impulse is retriggered at each one. See the photo below for clarification.

Differences in stimuli

The difference between a strong and weak stimulus is the number of neurons that are excited at the same time, and their rate of firing. The rate of firing can be influenced by damage to the myelin sheath, which would slow down the movement of ions. Axons without myelin sheaths have slower impulses than axons with myelin sheaths.

Communication between neurons

Neurons send and receive signals but they do not attach to one another. Between neurons are synaptic clefts, fluid filled gaps where an electrical impulse is transmitted from one neuron to another. This is possible because the cell membrane becomes permeable, allowing ions to move through the ion channels in the membrane out of the cell. Groups of chemicals known as neurotrasmitters send messages from one neuron to the other. These neurotransmitters are located in synaptic vesicles, which are small spheres with thin membranes. These are inside the axon terminal. When the axon terminal receives the action potential from the axon, giving it a positive charge, the synaptic vesicles move to the cell membrane and release the neurotransmitters into the synaptic cleft.

Here, neurotransmitters bind with receptors from the dendrites or cell bodies of other neurons. This is a selective process, because neurotransmitters and receptors have different shapes. Like a lock and key, they have to fit in order to bind. Still, receptors can slightly change form to allow for more binding, and neurotransmitters have similar shapes although they are different.

The binding action is either excitatory or inhibitory. The neuron receiving this message is actually receiving messages from thousands of other neurons at the same time. If there are more excitatory messages, the neuron will fire, but if there are more inhibitory messages, the neuron will not fire.

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