The main difference between Cranial Nerves and Spinal Nerves is that Cranial Nerves originate from the brain, whereas Spinal Nerves originate from the spinal cord.
Cranial Nerves vs. Spinal Nerves
Neuron or nerve cell is the functional and structural unit of the nervous system, and there are about 10 billion neurons in our nervous system, which communicate with each other in a definite manner. Nerves are connected to our spinal cord and brain. The spinal and cranial nerves are the kinds of nerves which are present in the peripheral nervous system. The cranial nerves constitute 12 nerve pairs which originate from the brain. Only optic (CN II) and olfactory (CN I) nerves originate from the cerebrum while the rest of the nerves originate from the brain stem, from pons, midbrain or medulla. Spinal nerves, on the other hand, are the paired nerves that arise from nerve roots of the spinal cord. The cranial nerves are made up of 12 nerve pairs, whereas spinal nerves are made up of 31 nerve pairs. All the 31 nerve pairs of spinal nerves are categorized into five groups as 12 thoracic nerve pairs, 5 lumber nerve pairs, 8 cervical nerve pairs, one pair of coccygeal nerve pair and 5 sacral nerve pairs. Cranial nerves can be classified as motor nerves, sensory nerves, or a combination of both the nerves. It means that the axons which are present in these nerves arise from the sensory ganglia outward to the cranium or motor nuclei inside the brain stem. Conversely, all the spinal nerves are mixed and contain the fibers of both the motor and sensory neurons.
What are Cranial Nerves?
Cranial nerves originate from the brain and have 12 nerve pairs in the human body. Some of these nerves are motor nerves, some are sensory nerves, and very few are the mixed nerves. The branches of all of these nerves connect to the nose, tongue, retina, ear, eye, neck, face, muscles, and the pharynx. Vagus (the 10th Cranial Nerve) is more significant than the total 12 pairs of cranial nerves which are present in the human body. Vagus is responsible for controlling the secretions of the pancreas and the rate of heartbeat. It is a mixed nerve.
What are Spinal Nerves?
All the spinal nerves of the human beings originate from the spinal cord. The spinal nerves play the most important role in the reflex actions, and because of the reflex actions of the spinal cord, it protects us from the dangerous stimuli. In a human body, there are 31 pairs of the spinal nerves. All of them are mixed nerves because they contain both the sensory and motor fibers. The sensory nerves which originate from the Dorsal Horn of the spinal cord, carry information from organs of the body to the spinal cord. Conversely, the motor fibers which originate from the Ventral Horns of the spinal cord, supply information which is vital for the movement of the muscles.
- Cranial nerves are the nerves that originate through the brain and are scattered in the neck, head, and facial regions, whereas, spinal nerves originate from the spinal cord and these are scattered in the other portions of the body like skeletal muscles, skin and the blood vessels.
- Cranial nerves have 12 nerve pairs; on the other hand, spinal nerves have 31 nerve pairs.
- We number the cranial nerves from I to XII. Conversely, spinal nerves are categorized into five groups as 12 thoracic nerve pairs, 5 lumber nerve pairs, 8 cervical nerve pairs, one pair of coccygeal nerve pair, and 5 sacral nerve pairs.
- Cranial nerves are dispersed in the neck, head, and the facial regions, on the flip side, spinal nerves are dispersed in the sweat glands, mucosa, blood vessels, skin, joints, and the skeletal muscles.
- Cranial nerves may consist of motor/sensory/mixed neurons; on the other side, all the spinal nerves are made up of both the motor and sensory neurons.
- Cranial nerves form ventral and dorsal roots; on the other hand, spinal nerves do not form ventral and dorsal roots.
- Cranial nerves have a lot of functions like hearing, sense of taste, vision, sense of the smell and eye movements, while, spinal nerves are responsible for performing functions like sensation, movement, and sweat secretion.
The above discussion summarizes that cranial and spinal nerves are the fragments of the peripheral nervous system. They consist of the nerves that arise from the brain and the spinal cord, respectively.