by Paul Brodie

Created on: November 01, 2010

Every action or non-action in the body is controlled by the brain. Neurons are the cells that communicate between the brain and the other parts of the body. Neurons, like other cells, have a cell body, which is called the soma. Inside of the soma there is a center of the cell called a nucleus. The body of the neuron is made by a plasma membrane, which is made of a lipid bi-layer, meaning a double layer of lipid, or fat, cells. The neuron has branches that extend from the sides in all directions. Each of these branches is called a dendrite. The dendrites reach out to other neurons and receive signals from them. The signals from the other neurons come through a part of the neuron called the axon. The axon extends from the neuron at a point called the axon hillock, where the soma and axon connect. The axon also has a lipid bi-layer covering called the myelin sheath. In addition to the dendrites, the soma can receive signals from other neurons as well. The axon acts as the transmitter for the neuron, sending signals away. The end of the axon is called the terminal button. The terminal button converts an electric signal into a chemical signal, releasing neurotransmitters (chemicals) across a gap called the synapse and into the receiving cell.

The process through which a neuron receives and sends signals is electro-chemical. When a signal comes in it is received as an electrical charge, this is known as the action potential. Each neuron has a resting potential, that is, a charge that is present when there aren’t any signals coming in or going out. The resting potential is -70mV. When an action potential comes into the cell it causes a chain reaction by changing the resting potential of the cell. There are different types of potentials that could come in, one is excitatory and another is inhibitory. These are known as post-synaptic potentials (PSP). The plasma membrane across the dendrites, soma and axon has sodium (Na) and potassium (K) ions surrounding them, both inside and outside the cell structure.  These two ions are what make the resting potential negative. Both ions are positively charged, at the resting potential of the cell there are more positively charged ions outside the cell than inside, which makes the outside more positive. The action potential changes the electrostatic pressure by opening a channel for the ions to move from inside to out and outside in.

Along the membrane there are channels for sodium and potassium. These channels open

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