The nervous system allows us to respond rapidly to environmental stimuli so that we can survive and reproduce (Campbell, 1990). Neurons are the single celled units responsible for sensing stimuli and communicating signals throughout the nervous system (Campbell, 1990). They communicate by transmitting nerve impulses, a process that involves the movement of ions into and out of the neuron (Gleitman, 1999). This essay will discuss how ion channels and ion pumps allow for the movement of ions and explain how this is incorporated into the function of a neuron. .
Neurons exhibit a resting potential which arises from the difference in ion concentrations between the inside and the outside of the neuron (Bond and McConkey, 2001). In other words, when the neuron is not firing, the inside of the cell is negative with respect to the outside and thus there exists a voltage difference (Gleitman, 1999). In order for the neuron to fire, a stimulus must act upon it that is large enough to reduce the voltage difference to the excitation threshold (Gleitman, 1999). If the stimulus is large enough, then the voltage difference collapses rapidly to zero and then begins to reverse itself, with the inside of the neuron becoming more positive (Bond and McConkey, 2001). This occurs because of the passage of charged ions into and out of the neuron (Gleitman, 1999).
Ions are molecules or single atoms which have lost or gained electrons and therefore posses a positive or negative electrical charge (Gleitman, 1999). In its resting state a neuron contains a high concentration of potassium ions dissolved in the fluid inside its membrane, and a high concentration of sodium ions dissolved in the fluid outside (Gleitman, 1999). When the excitation threshold is reached, sodium ion channels open, allowing sodium ions to rush into the neuron for about 1 millisecond before the ion channels then close again (Bond and McConkey, 2001).