NERVE IMPULSE
Nerve impulse is a wave of bioelectric/electrochemical
disturbance that passes along a neuron during conduction of an excitation. The nerve impulse travels along a neuron
or across synapse between one neuron and another, or between neuron and an effector Nature of nerve impulse or conduction of nerve impulse is an electrochemical process. It has been found that impulse conduction depends upon permeability of axon membrane
(axolemma) and osmotic equilibrium and electrical equivalence between the axoplasm and extracellular fluid (ECF) present outside the axon Generation and Conduction of Nerve Impulse
o When a neuron is not conducting any impulse, i.e, resting,
the axonal membrane is comparatively more permeable to potassium ions (K) and nearly impermeable to sodium ions
(Na). Similarly, the membrane is impermeable to negatively
charged proteins present in the axoplasm. Consequently the axopläsm inside the axon contains high concentration of
K+ and negatively charged proteins and low concentration of Na. In conträst, the fluid outside the axon contains a
low concentration of K* a high concentration of Na and thus forming a concentration gradient.
The ionic gradients are maintained by sodium- potassiunm pump which transports 3 Nat outwards for 2 Kt into the
cell.
l. As a result the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes
negatively charged and therefore, is polarised. The electrical potential difference across the resting plasma membrane is called as the resting potential. The state of the resting
membrane is called polarised state.
When a stimulus is applied, the permeability of the membrane
to Na ions is greatly increased at the point of stimulation. It is due to the fact that the Nat channels open and the K channel
remain closed. Thus, sodium channels permit the influx of Naions by diffusion. This results in the positive charge inside
and negative charge outside. The change in polarity across the plasma membrane is known as action potential (nerve impulse) and the membrane is said to be depolarised.
