NERVES

Nerves are not to be confused with neurons. A “nerve” is actually a bundle of many, many neuronal processes. It is not a cell like a neuron, rather it is a collection of cellular parts. This means that a nerve is a large collection of myelinated axons (but can be myelinated “dendritic axons” in the case of sensory neurons).

A Spinal Nerve

1.Motor Nerves – These are nerves that contain only motor nerve fibers (motor neuron axons). These transmit messages from the CNS to the periphery.2. Sensory Nerves – These are nerves that contain only sensory nerve fibers (sensory neuron axons and/or dendrites). These transmit messages from the peripheral receptors to the CNS.3. Mixed Nerves – These are nerves that contain both motor and sensory nerve fibers (motor and sensory neuron axons). These can conduct messages along sensory axons from the periphery to the CNS or from the CNS to the periphery.

Spinal NervesAll along the length of the spinal cord 31 pairs of spinal nerves emerge. These consist of mixed nerves as follows:a. 8 pairs of cervical

nerves.b. 12 pairs of thoracic

nerves.c. 5 pairs of lumbar

nerves.d. 5 pairs of sacral

nerves.e. 1 pair of coccygeal

nerves.

Cranial nervesThe brain communicates with the body through the spinal cord and twelve pairs of cranial nerves. Ten of the twelve pairs of cranial nerves that control hearing, eye movement, facial sensations, taste, swallowing and movement of the face, neck, shoulder and tongue muscles originate in the brainstem. The cranial nerves for smell and vision originate in the cerebrum.

Cranial nervesNumber Name Function

I olfactory smellII optic SightIII oculomotor moves eye, pupil IV trochlear moves eye V trigeminal face sensation VI abducens moves eye VII facial moves face, salivate VIII vestibulocochlear hearing, balance IX glossopharyngeal taste, swallow X vagus heart rate, digestion XI accessory moves head XII hypoglossal moves tongue