5.7.2 Cranial and Spinal Nerves in Man

The peripheral nervous system consists of the nerves that branch out from the central nervous system and connect it to other body parts. It includes cranial nerves, which arise from the brain, and spinal nerves, which arise from the spinal cord. There are twelve pairs of cranial nerves and thirty-one pairs of spinal nerves.

Definition

Cranial Nerves: Cranial nerves are the nerves that arise from the brain. There are twelve pairs of cranial nerves. Each nerve pair splits to serve the two sides of the brain and body.

Spinal Nerves: Spinal nerves are the nerves that arise from the spinal cord. There are thirty-one pairs of spinal nerves, one on each side of the vertebral column.

Main Idea

• The peripheral nervous system includes cranial nerves and spinal nerves.
• Cranial nerves arise from the brain.
• There are twelve pairs of cranial nerves.
• Spinal nerves arise from the spinal cord.
• There are thirty-one pairs of spinal nerves.
• Cranial nerves send electrical signals between the brain and different parts of the neck, head and torso.
• Spinal nerves carry motor, sensory and autonomic signals between the spinal cord and the body.

Core Concept

• Cranial nerves = 12 pairs; arise from the brain
• Spinal nerves = 31 pairs; arise from the spinal cord
• Cranial nerves = numbered I to XII using Roman numerals
• Spinal nerves = named by region: cervical, thoracic, lumbar, sacral, coccygeal
• Cranial nerves = categorized based on number and function
• Spinal nerves = mixed nerves; formed from dorsal and ventral roots

Detailed Explanation

Cranial Nerves

• The peripheral nervous system consists of the nerves that branch out from the central nervous system and connect it to other body parts.
• The peripheral nervous system includes cranial nerves which arise from the brain and the spinal nerves, which arise from the spinal cord.
• A number of cranial nerves send electrical signals between the brain and different parts of the neck, head and torso.
• These signals help us to smell, taste, hear and move our facial muscles.
• The cranial nerves begin toward the back of brain.
• There are twelve cranial nerve pairs.
• Each nerve pair splits to serve the two sides of the brain and body.
• For example, we have one pair of olfactory nerves. One olfactory nerve is on the left side of the brain and one is on the right side of the brain.
• The twelve nerves are numbered from I to XII using Roman numerals according to the order in which they emerge from the front of the brain to the back of the brain.
• The twelve cranial nerves each have a specific function.
• The cranial nerves have been categorized based on number and function.

Summary Table of Cranial Nerves

Spinal Nerves

• A spinal nerve carries motor, sensory and autonomic signals between spinal cord and the body.
• Each spinal nerve is a mixed nerve.
• It is formed from the combination of nerve root fibers from its dorsal and ventral roots.
• There are 31 pairs of spinal nerves, one on each side of the vertebral column.
• These include:
• Eight cervical nerve pairs — nerves starting in the neck and running mostly to face and head.
• Twelve thoracic nerve pairs — nerves in the upper body that extend to chest, upper back and abdomen.
• Five lumbar nerve pairs — nerves in the low back that run to legs and feet.
• Five sacral nerve pairs — nerves in the low back extending into the pelvis.
• One pair of coccygeal nerves.
• The spinal nerves are part of the peripheral nervous system.
• Outside the vertebral column, the nerve divides into branches.
• The dorsal ramus contains nerves that serve the posterior portions of the trunk.
• The ventral ramus contains nerves that serve the remaining anterior parts of the trunk and the upper and lower limbs.

Summary Table of Spinal Nerves

Intermediate Level

Cranial Nerves

Spinal Nerves

Types of Nerve Fibres

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Peripheral nervous system includes cranial and spinal nerves.
• 2. Cranial nerves arise from the brain.
• 3. There are twelve pairs of cranial nerves.
• 4. Cranial nerves are numbered I to XII.
• 5. Cranial nerves help us smell, taste, hear, and move facial muscles.
• 6. Cranial nerves are categorized based on number and function.
• 7. Spinal nerves arise from the spinal cord.
• 8. There are thirty-one pairs of spinal nerves.
• 9. Spinal nerves are named by region.
• 10. Eight cervical nerve pairs.
• 11. Twelve thoracic nerve pairs.
• 12. Five lumbar nerve pairs.
• 13. Five sacral nerve pairs.
• 14. One pair of coccygeal nerves.
• 15. Spinal nerves are mixed nerves.
• 16. Spinal nerves are formed from dorsal and ventral roots.
• 17. Dorsal ramus serves posterior trunk.
• 18. Ventral ramus serves anterior trunk and limbs.
• 19. Cranial nerves include olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, auditory, glossopharyngeal, vagus, accessory, hypoglossal.
• 20. Spinal nerves carry sensory, motor, and autonomic signals.

Remember

• - Cranial nerves = 12 pairs; arise from brain
• - Spinal nerves = 31 pairs; arise from spinal cord
• - Cranial nerves = numbered I to XII
• - Spinal nerves = named by region
• - **Cervical** = 8 pairs
• - **Thoracic** = 12 pairs
• - **Lumbar** = 5 pairs
• - **Sacral** = 5 pairs
• - **Coccygeal** = 1 pair
• - Spinal nerves = mixed nerves
• - Dorsal root = sensory fibers
• - Ventral root = motor fibers

Common Mistakes

• 1. Confusing cranial and spinal nerves — Cranial from brain; spinal from spinal cord.
• 2. Mixing up the numbers — 12 pairs of cranial nerves; 31 pairs of spinal nerves.
• 3. Forgetting the types of cranial nerves — Sensory, motor, mixed.
• 4. Mixing up the functions — Olfactory = smell; optic = sight; vagus = digestion/heart rate.
• 5. Confusing the regions of spinal nerves — Cervical, thoracic, lumbar, sacral, coccygeal.
• 6. Forgetting the number of pairs in each region — Cervical 8, thoracic 12, lumbar 5, sacral 5, coccygeal 1.
• 7. Thinking spinal nerves are sensory only — They are mixed nerves.
• 8. Mixing up dorsal and ventral roots — Dorsal = sensory; ventral = motor.
• 9. Forgetting the rami — Dorsal ramus = posterior; ventral ramus = anterior.
• 10. Believing cranial nerves only serve the head — Vagus nerve serves the body's organs.

Quick Revision

The peripheral nervous system consists of the nerves that branch out from the central nervous system and connect it to other body parts. The peripheral nervous system includes cranial nerves which arise from the brain and the spinal nerves, which arise from the spinal cord. A number of cranial nerves send electrical signals between the brain and different parts of the neck, head and torso. There are twelve cranial nerve pairs. Each nerve pair splits to serve the two sides of the brain and body. The twelve nerves are numbered from I to XII using Roman numerals. The twelve cranial nerves each have a specific function. A spinal nerve carries motor, sensory and autonomic signals between spinal cord and the body. Each spinal nerve is a mixed nerve. It is formed from the combination of nerve root fibers from its dorsal and ventral roots. There are 31 pairs of spinal nerves one on each side of the vertebral column. These include: eight cervical nerve pairs, twelve thoracic nerve pairs, five lumbar nerve pairs, five sacral nerve pairs, and one pair of coccygeal nerves. Outside the vertebral column, the nerve divides into branches. The dorsal ramus contains nerves that serve the posterior portions of the trunk. The ventral ramus contains nerves that serve the remaining anterior parts of the trunk and the upper and lower limbs.

60-Second Revision

• Cranial nerves = 12 pairs; arise from brain
• Spinal nerves = 31 pairs; arise from spinal cord
• Cranial nerves = numbered I to XII
• Spinal nerves = named by region
• Cervical = 8 pairs
• Thoracic = 12 pairs
• Lumbar = 5 pairs
• Sacral = 5 pairs
• Coccygeal = 1 pair
• Spinal nerves = mixed nerves
• Dorsal root = sensory fibers
• Ventral root = motor fibers
• Warning: Cranial nerves arise from the brain; spinal nerves arise from the spinal cord

NEXT TOPIC

• Chapter:
• 5. Nervous System of Man

• Topic:
• 5.7.3 PERIPHERAL NERVOUS SYSTEM

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