B. It allows sodium and potassium to move against their concentration gradient
Explanation:
The role of sodium and potassium pump in the body is to help move ions against their concentration gradient. There are two types of transport (1) active transport (2) passive transport.
Passive transport is a natural phenomenon in which ions move from high concentration to lower concentration. In such transport no ATP/energy is required. In contrast to this, active transport is a kind of transport which occurs against concentration gradient and in order to facilitate this opposite movement of ions they require ATP/energy input. Sodium and potassium pumps perform active transport in our body. In neurons they play an important role of ion exchange. They move sodium and potassium ions against their concentration gradient for which they require ATP and thus help in basic functioning of neurons.
Afferent nerve fibers carry signals from the somatic receptors to the posterior horn of the spinal cord or to the brainstem. So i beleive it is 4 but not too sure. Hope this helped a bit (:
