All of our cells in our body are under constant changes. A portion of these changes is in response to a chemical change either in the extracellular fluid around the cell or inside the cell its self. Here I will examine the movement of ions across a typical cell membrane.
An undisturbed cell or inactive cell is said to be at its resting potential. A typical charge of a neuron at its resting potential is -70mv. It is the job of membrane channels to affect the transmembrane potential and ultimately alter the activity of the cell. Membrane channels are in control of ion movement across the cell membrane. In most cases of transmembrane potential it is the movement of sodium and potassium ions that create the most changes and are the most effective. Generally, there are two types of membrane channels: passive or leaky channels and active or gated channels. Passive channels are always open, therefore, allowing a constant exchange of ions between the extracellular fluid and the cytosol. Active channels open or close when stimulated by a specific stimulus. There are three stages or positions for an active channel to sustain. First would be fully closed but with the capability of opening. Secondly would be fully open. This stage is when the channel would be active. Last would be closed and without the capability of opening. This stage is when the channel would be inactive.
To further divide these channels, there are three types of gated channels. First, there are chemically regulated channels. Chemically regulated channels only open or close when they interact with a specific chemical. These channels are most abundant on the dendrites or soma of a neuron. The second type of gated channel is the voltage-regulated channel. Voltage regulated channels are found on a part of the cell membrane called the excitable membrane. This is the part of the membrane that is capable of generating an action potential.
