Question

In rabbit, the number of spinal nerves are-
A. 30 pairs
B. 37 pairs
C. 32 pairs
D. 38 pairs

Answer 1

Hint: The spinal nerves as the name indicates are the nerves arising from the spinal cord of an organism. These constitute the paired peripheral nerves. These are not single nerves but a combination of several nerves as they perform a variety of functions such as motor, sensory, and autonomous signals between the spinal nerve and the body. They differ in different organisms in numbers.

Complete answer:
Spinal nerves are termed as mixed nerves as they perform a variety of functions.
In humans, they are present in 31 pairs- 8 cervical, 12 thoracics, 5 lumbar, 5 sacral, and 1 coccygeal. The rabbit is a chordate and has a spinal cord. The spinal cord is a characteristic feature of vertebrates.

There are 37 pairs of spinal nerves present in Rabbit. Each spinal nerve arises from the spinal cord by two roots, a ventral or motor root and a dorsal or sensory root. These roots then further combine to form a nerve. Spinal nerve (each) then divides into three branches-
• Ramus dorsalis (dorsal branch)
• Ramus Ventralis (ventral branch)
• Ramus communicans (visceral branch)

The brachial plexus is formed by the ventral branches containing 4th to 9th spinal nerves. The lumbar plexus develops by the ventral branches of the $24^{th}$ to $27^{th}$ spinal nerves. Sacral plexus is developed by the ventral branches of $28^{th}$ to $31^{st}$ spinal nerves.

Hence, the correct answer is option (B).

Note: Plexus is a network (branching) of nerves. They are also termed as plexuses. These can be a network of nerves or a network of vessels. The main nerve plexus includes-
• Cervical plexus
• Brachial plexus
• Lumbar plexus
• Sacral plexus