Impulse conduction

A neuron not conducting a nerve impulse is said to be “resting”. Although it is resting, it remains changed and potentially ready to fire. The potential to fire is produced by an interstitial fluid within. The inside of nerve cell is electrically negative, and the interstitial fluid electrically, positive. A resulting membrane potential, is measured in electrical potential between the two compartments. The resulting membrane potentials, measured in millivolts (mV) results from this difference in electrical potential between the two compartments.

The resting membrane potential (RMP) of neurons is between -45and-75mV.

The cell is depolarized when an influx of sodium makes the membrane potential more sensitive (i.e.; rising to zero).In most cells this is due to an electrical stimulus transmitted by an adjacent cells. Depolarization is the restoration of the membrane polarity and sodium and potassium are retuned to their usual places via the sodium – potassium pump.

After an action potential is generated no segment of the nerve fiber can conduct another action potential for a brief period of time (<1ms).>absolute refractory period. Sodium and potassium are returning to their original locations during the period and sodium cannot enter the nerve cell. During his period, called the relative refractory period, only a stimulus stronger than the ordinary one can produce an action potential. On an average a return to a resting potential takes approximately 10-30ms.Myelin sheath surrounds most of the large nerve fibers and is separated by the nodes of Ranvier. Action potentials are generated only at the nodes, and thus they skip between them rather than depolarize the entire membrane. This jumping characteristic is known as saltatory conduction. Conduction using this process is rapid. The nerve impulse conduction is also related to the diameter of the fiber, the greater the diameter, the faster the impulse.

Category: Physiology Notes