21.3.1 Generation and Conduction of Nerve Impulse

• Neurons are excitable cells because their membranes are in a polarised state
• Different types of ion channels are present on the neural membrane. These ion channels are selectively permeable to different ions.
• When a neuron is not conducting any impulse, the axonal membrane is comparatively more permeable to potassium ions (K+) and nearly impermeable to sodium ions (Na+).
• the axoplasm inside the axon contains high concentration of K+ and negatively charged proteins and low concentration of Na+
• the fluid outside the axon contains a low concentration of K+ , a high concentration of Na+ and thus form a concentration gradient
• ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na + outwards for 2 K + into the cell
• the outer surface of the axonal membrane possesses a positive charge while its inner surface is negatively charged and therefore is polarised.
• The electrical potential difference across the resting plasma membrane is called as the resting potential.
• The electrical potential difference across the plasma membrane at the site A is called the action potential or depolarisation
• Action potential is infact termed as nerve impluse
• The rise in the stimulus-induced permeability to Na+ is extremely short lived. It is quickly followed by a rise in permeability to K.