Question

The number of spinal nerves in man is
A) 27 pairs
B) 31 pairs
C) 37 pairs
D) 47 pairs

Answer 1

Hint: Each pair binds a particular area of the body with the spinal cord. Every spinal nerve divides into two roots near the spinal cord. One, made up of sensory fibres, passes from the dorsal root into the spinal cord; the cell bodies reside beyond the spinal cord in a spinal ganglion.

Complete Answer:
A mixed nerve is a spinal nerve that holds motor, autonomic impulses and sensory, between the body and the spinal cord. A component of the peripheral nervous system is the spinal nerves.

Now, let us find the solution from the options-
- There are 31 spinal nerve pairs in the human body, one on each part of the vertebral spine. Thus, option A is not the correct option.
- Spinal nerves emerge from the spinal cord of vertebrates. There are 31 pairs in humans: 12 thoracic, 8 cervical, 5 sacral, 5 lumbar and 1 coccygeal, respectively. Each pair binds a particular area of the body with the spinal cord.
- Each spinal nerve is often a mixed nerve developed from its ventral and dorsal roots by a mixture of nerve fibres. The afferent sensory root is the dorsal root that brings sensory data to the brain. Thus option C is not the correct option.
- The efferent motor root is really the ventral root which holds motor data from the cortex. Thus, option D is not the correct option.

Thus, the correct answer is option (B) 31 pairs.

Note: The sensory fibres are broken into classes of viscera and somatic. Somatic afferents execute impulses obtained outside of the body or generated by muscle and joint movements, which are also recognized as proprioceptive fibres from the muscles and joints.