Question

What is the difference between sympathetic nerves and parasympathetic nerves on the basis of origin and function ?

Answer 1

Nerves included in the PNS are of two types- cranial nerves and spinal nerves.
Cranial nerves originate from the cranium. Man has 12 pairs of cranial nerves, which include all three types of nerves −sensory, motor, and connector. The information about the 12 pairs of cranial nerves is given in the following table:

Number	Name	Nature	Major functions
1.	Olfactory	Sensory	Smell
2.	Optic	Sensory	Sight
3.	Oculomotor	Motor	Movement of eyeball
4.	Trochlear	Motor	Rotation of eyeball
5.	Trigeminal	Mixed	Sensation of touch and taste
6.	Abducens	Motor	Rotation of eyeball
7.	Facial	Mixed	Taste, facial expression, saliva secretion, neck movement
8.	Auditory	Sensory	Hearing, equilibrium
9.	Glosso-pharyngeal	Mixed	Taste, saliva secretion
10.	Vagus	Mixed	Gastric and pancreatic secretion, GI movement, and visceral reflexes
11.	Spinal accessory	Motor	Muscle movement and visceral reflex
12.	Hypoglossal	Motor	Tongue movement

Spinal Nerves

• Spinal nerves are the nerves originating from the spinal cord by means of two roots- a dorsal root and a ventral root.

• All the spinal nerves are connector nerves.

• At the junction of the two roots, the sensory nerve and motor nerves separate. The sensory nerves continue into the dorsal root and the motor fibres continue into the ventral root.

Sympathetic nerves:
They originate from the thoraco-lumbar segment of the spinal cord. The main functions of the system are as follows:

• Dilation of iris

• Decrease in salivation (That is why our throat dries during stress)

• Increase in rate of heartbeat, dilation of bronchi

• Causes gylcogen breakdown to glucose in liver

• Inhibition of gastric and pancreatic activities

• Inhibition of peristalsis