Difference Between Cranial and Spinal Nerves

Main Difference – Cranial vs Spinal Nerves

Cranial and spinal nerves are the types of nerves in the peripheral nervous system. The main difference between cranial and spinal nerves is that cranial nerves arise from the brain and are distributed in the head, neck, and facial regions areas whereas spinal nerves arise from the spinal cord and are distributed in the other parts of the body such as the skin, skeletal muscles, and blood vessels. Cranial nerves are composed of 12 nerve pairs while spinal nerves are composed of 31 nerve pairs.

Key Areas Covered

1. What are Cranial Nerves
      – Definition, Types, Function
2. What are Spinal Nerves
      – Definition, Types, Function
3. What are the Similarities Between Cranial and Spinal Nerves
      – Outline Of Common Features
4. What is the Difference Between Cranial and Spinal Nerves
      – Comparison of Key Differences

Key Terms: Central Nervous System, Cranial Nerves, Peripheral Nervous System, Plexuses, Spinal Nerves, Vertebrates

What are Cranial Nerves

Cranial nerves are the 12 nerve pairs which arise from the brain. Only olfactory (CN I) and optic (CN II) nerves arise from the cerebrum whereas the rest of the nerves arise from the brain stem, from midbrain, pons or medulla. The oculomotor nerve (CN III) arise from the midbrain-pontine junction. The tracheal nerve (CN IV), which consists of the highest intracranial length of the cranial nerves, arise from the midbrain. The trigeminal nerves (CN V) arise from the pons. The abducens (CN VI), facial (CN VII), and vestibulocochlear (CN VIII) nerves arise from the pontine-medulla junction. The glossopharyngeal (CN IX), vagus (CN X), and accessory (CN XI) nerves arise from the posterior olive of the Medulla Oblongata. The hypoglossal (CN XII) arise from the hypoglossal nucleus in the brain stem. The origination of each cranial nerves from the brain is shown in figure 1.

Figure 1: Origination of Cranial Nerves

Function of Cranial Nerves

What are Spinal Nerves

Spinal nerves are paired nerves that originate from the nerve roots of the spinal cord. 31 pairs of spinal nerves can be found in vertebrates. All 31 nerve pairs are classified into five groups as 8 cervical nerve pairs, 12 thoracic nerve pairs, 5 lumber nerve pairs, 5 sacral nerve pair, and one pair of coccygeal nerve pair. The spinal nerves are attached to the spinal cord by two roots. They are the dorsal sensory root and the ventral motor root. The sensory impulses such as temperature, touch, pain, pressure, and position sense are carried to the brain by the sensory root. The impulses from the central nervous system are carried to the effector organs by the motor root.

Figure 2: Spinal Nerve Plexus

Once the spinal nerves exit from the spinal cord, they pass the intervertebral foramen. Ultimately, these spinal nerves form networks called plexuses, consisting of four branches. The four branches are cervical plexus, brachial plexus, lumbar plexus, and sacral plexus. The cervical plexus carries nerves to neck and shoulders. The brachial plexus carries nerves to arm and upper back. The lumbar plexus carries nerves to abdomen and leg muscles. The sacral plexus carries nerves to the back of the thigh, lower leg, and the entire foot. 

Similarities Between Cranial and Spinal Nerves

• Cranial and spinal nerves are components of the peripheral nervous system.
• Both cranial and spinal nerves are involved in connecting organs and muscles of the body to the central nervous system for the coordination of body functions.

Difference Between Cranial and Spinal Nerves

Definition

Cranial Nerves: Cranial nerves are the nerves that arise directly from the brain and pass through separate apertures in the skull.

Spinal Nerves: Spinal nerves are a series of paired nerves that originate from the nerve roots of the spinal cord on both sides.

Number of Pairs

Cranial Nerves: Cranial nerves comprise 12 nerve pairs.

Spinal Nerves:  Spinal nerves comprise 31 nerve pairs.

Numbering

Cranial Nerves: Cranial nerves are numbered I to XII.

Spinal Nerves: Spinal nerves are classified into five groups as 8 cervical nerve pairs, 12 thoracic nerve pairs, 5 lumber nerve pairs, 5 sacral nerve pair, and one pair of coccygeal nerve pair.

Distribution

Cranial Nerves: Cranial nerves are distributed in head, neck and facial regions.

Spinal Nerves: Spinal nerves are distributed in the skin, sweat glands, mucosa, blood vessels, joints, and skeletal muscles.

Structure

Cranial Nerves: Cranial nerves may contain sensory/motor/mixed neurons.

Spinal Nerves: All spinal nerves are composed of both sensory and motor neurons.

Function

Cranial Nerves: Cranial nerves are involved in vision, sense of the smell, hearing, sense of taste, and eye movements.

Spinal Nerves: Spinal nerves are involved in movement, sensation, and sweat secretion.

Dorsal and Ventral Roots

Cranial Nerves: Cranial nerves form dorsal and ventral roots.

Spinal Nerves: Spinal nerves do not form dorsal and ventral roots.

Conclusion

Cranial and spinal nerves are the two components of the peripheral nervous system. Both types of nerves are involved in connecting the internal organs and muscles to the central nervous system to coordinate the functions of the body. Cranial nerves arise from the brain and are distributed in the brain, neck, and facial areas. In contrast, spinal nerves arise from the spinal cord and are distributed in the rest of the body. Therefore, the main difference between cranial and spinal nerves is in their paths.

Reference:

1. “Summary of the Cranial Nerves.” TeachMeAnatomy. N.p., 18 July 2017. Web. Available here. 25 July 2017.
2. “Spinal Nerves.” HealthPagesorg Anatomy Surgery Pregnancy Nutrition Fitness. N.p., n.d. Web. Available here. 25 July 2017.

Image Courtesy:

1. “1321 Spinal Nerve Plexuses” By OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Brain human normal inferior view with labels en-2 By Brain_human_normal_inferior_view_with_labels_en.svg: *Brain_human_normal_inferior_view.svg: Patrick J. Lynch, medical illustratorderivative work: Beaoderivative work: Dwstultz (talk) – Brain_human_normal_inferior_view_with_labels_en.svg (CC BY 2.5) via Commons Wikimedia

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