Neural excitability

The neuronal excitability, nerve impulse or neuronal nervousness is the ability of neurons to change their electrical potential and transmit this change through their axon. Neuronal excitation is produced by a flow of charged particles across the membrane, which generates an electric current, so it depends on the existence of different concentrations of ions on both sides of the cell membrane and on the capacity of active transport to across these membranes to generate an electrochemical potential difference inside and outside the cell.

Cellular characteristics

The cell membrane is polarized, because there is an unequal distribution of electrical charges between the interior and exterior of the cell. This creates a potential difference, the exterior being positive with respect to the interior. Outside, in the interstitial fluid, the most abundant anion is chlorine. In the cytoplasm, the most abundant anions are proteins, which at cell pH are negatively ionized.

The most abundant cation in the interstitial fluid is sodium, and in the cytoplasm it is potassium, and most of the changes in potential are due to the exchange of these ions.

Arousal stimulus

The graphical representation of the variation of potential with respect to time is the action potential. The amount of stimulus necessary to provoke the activity of a neuron is called the excitability threshold. At this threshold, the response is a stimulus-independent action potential. That is, it follows the law of all or nothing. This is due to sodium voltage-gated channels.

During depolarization, the neuron is not excitable and is said to be in the absolute refractory period. During the subsequent hyperpolarization, the neuron is partially excitable, partially refractory, ie, a stronger stimulus is required to elicit a new action potential, since the excitability threshold has been increased.