Test: Human Neural System & Neuron as Functional Unit (September 15) - NEET MCQ

4 pairs of cranial nerves are mixed nerves. These are trigeminal, facial, glossopharyngeal and vagus nerves.

Vagus nerve is the mixed cranial nerve with maximum branches.

Abducens nerve is a motor nerve that controls the movements of the eye ball.

In a human being, the number of cranial nerves is 12 pairs. These are olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, auditory, glossopharyngeal, vagus, spinal accessory and hypglossal nerves.

Vagus nerve innervates pharynx, larynx, oesophagus, stomach, lungs, heart and intestines. Thus, injury to vagus nerve will not affect tongue movements as it does not innervate tongue.

Saltatory conduction is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.
Propagation of an action potential in a myelinated nerve involves the opening and closing of ion channels exclusively at the Nodes of Ranvier. This saltatory conduction accelerates the rate at which an action potential travels down an axon.

Neurons are the structural and functional unit of the nervous system. Each neuron consists of dendrites, axon, and soma. Dendrites are the small extension of nerve cells that receive signals from sensory receptors or other neurons. The long extension of the cell body of the nerve cell is called as axon that serves to conduct the nerve impulse away from the cell body. Cyton /soma is the metabolic center of the nerve cell where the metabolic contents are manufactured. It is not involved in nerve impulse conduction. A nephron is the anatomical and functional unit of kidney and thus is the part of the excretory system. Thus, the correct answer is option A.

Conduction of nerve impulse is faster in myelinated fibres as myelin is an insulating layer or sheath, that forms around nerves, including those in the brain and spinal cord which protect and insulates the axons thus enhance the transmission of electrical impulses.

Refractory period is the time during which another stimulus given to the neuron (no matter how strong) will not lead to a second action potential. Thus, because Na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials. The absolute refractory period takes about 1-2 ms.

The body's various functions and processes are controlled by nervous system and endocrine system. But the nervous system plays a primary role in regulating the activities of organs of bodies and to act on the stimulus from outside also. The coordination of different parts of central nervous system and peripheral nervous system together regulate all voluntary as well as involuntary functions.