Compare the following:
Central neural system (CNS) and Peripheral neural system (PNS)
(a) Central Neural System (CNS) and Peripheral Neural System (PNS):
The Central Neural System (CNS) includes the brain and the spinal cord and is the site of information processing and control.
The Peripheral Neural System (PNS) comprises all the nerves of the body associated with the CNS (brain and spinal cord). The nerve fibres of the PNS are of two types: afferent fibres and efferent fibres.
Resting potential and action potential
(b) Resting Potential and Action Potential:
Resting potential is the electrical potential difference across the nerve membrane when the fibre is at rest. It is restored when K⁺ diffuses outside the membrane at the site of excitation, making the fibre once more responsive to further stimulation.
Action potential is generated when the polarity at the site is reversed due to a rise in stimulus-induced permeability to Na⁺. This is extremely short-lived and quickly followed by a rise in permeability to K⁺. The impulse (action potential) is conducted along the length of the axon as this sequence is repeated.
Explanation
The textbook context clearly distinguishes CNS as comprising the brain and spinal cord (site of information processing), while PNS includes all nerves associated with the CNS. For the second comparison, the context describes how action potential involves polarity reversal and Na⁺ permeability, while resting potential is restored by K⁺ diffusion. These distinctions are fundamental concepts from Chapter 18: Neural Control and Coordination.