In the human peripheral nervous system, how many pairs of spinal nerves arise from the spinal cord to supply various regions of the body?

Introduction:
The spinal cord is a major pathway for nerve impulses between the brain and the rest of the body. From it emerge multiple pairs of spinal nerves that innervate different regions such as the neck, trunk and limbs. Knowing the exact number of these spinal nerve pairs is a standard question in human anatomy and physiology. This question asks you to recall how many such pairs exist in a normal adult human.

Given Data / Assumptions:
- The question refers specifically to pairs of spinal nerves. - Options range from 30 to 33 pairs. - We assume normal anatomy without congenital abnormalities. - The classification into cervical, thoracic, lumbar, sacral and coccygeal spinal nerves is standard.

Concept / Approach:
In humans, there are 31 pairs of spinal nerves. These are arranged segmentally along the spinal cord as follows: 8 cervical pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs and 1 coccygeal pair. Each pair emerges through intervertebral foramina and carries both sensory and motor fibres. This fixed arrangement results in a total of 31 pairs. Therefore, among the options provided, 31 pairs is the correct answer.

Step-by-Step Solution:
Step 1: Recall the breakdown of spinal nerve pairs: cervical, thoracic, lumbar, sacral and coccygeal. Step 2: Count the cervical nerves: 8 pairs (C1 to C8). Step 3: Count the thoracic nerves: 12 pairs (T1 to T12). Step 4: Count the lumbar nerves: 5 pairs (L1 to L5). Step 5: Count the sacral nerves: 5 pairs (S1 to S5). Step 6: Count the coccygeal nerves: 1 pair (Co1). Step 7: Add them all: 8 + 12 + 5 + 5 + 1 = 31 pairs of spinal nerves.

Verification / Alternative check:
Anatomy textbooks and standard nerve charts uniformly state that there are 31 pairs of spinal nerves in humans. Diagrams of the spinal cord label these segments and their corresponding nerve roots. Clinical descriptions of spinal cord injuries often refer to levels such as C5 or L4 based on this numbering. No credible source lists 30, 32 or 33 as the normal total. This consistent information verifies that the correct total is 31 pairs.

Why Other Options Are Wrong:
30 pairs: One pair less than the established anatomical count; this number does not match the standard segmental arrangement. 32 pairs: One pair more than the normal number; there is no additional standard segment to account for this extra pair. 33 pairs: Two pairs more than the correct figure; such a count is incompatible with the human vertebral and spinal segmentation.

Common Pitfalls:
Students sometimes misremember the number of cervical nerves as 7 (matching cervical vertebrae) instead of 8, which leads to an incorrect total. Others may simply confuse the total with the number of vertebrae. To avoid this, remember the specific breakdown 8, 12, 5, 5 and 1, and practice adding them until 31 becomes an automatic recall. Mnemonics such as breakfast at 8, lunch at 12 and dinner at 5 can help remember part of this sequence (for cervical, thoracic and lumbar levels).

Final Answer:
There are 31 pairs of spinal nerves in the human body.