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Peripheral Nerves
Communication between the brain and spinal cord (CNS) and the body is provided by the peripheral nerves.
Cranial nerves
There are twelve pairs of cranial nerves which connect directly to your brain not via the spinal cord which have mixed and singular functions
- Motor Function
- Sensory function
- Autonomic Function
- Facial Nerve (sensory + motor) relay information from the taste buds of the front two thirds of the tongue. Motor fibres control facial expression muscles and connect to the salivary and lacrimal glands.
- Glossopharyngeal and Hypoglossal Nerves (sensory + motor) relay information about taste, touch and temperature from the tongue and pharynx. Involved in controlling tongue movement and swallowing.
- Oculomotor Nerve (motor + some sensory) control voluntary movement of the eye muscles, pupil constriction, lens focusing.
- Olfactory Nerve (sensory) relay information about smell from the olfactory epithelium via the olfactory bulbs and tracts to the brains limbic system.
- Optic Nerve (sensory) relay visual information from the rod and cone cells to the visual cortex.
- Spinal Accessory Nerve (motor + some sensory) control muscle movement of the head, neck and shoulders, stimulates the muscles of the pharynx and larynx (involved in swallowing).
- Trigeminal Nerve (sensory + motor) ophthalmic and maxillary fibres relay information from face, eye and teeth. Mandibular fibres (sensory + motor) control chewing and relay sensory information from the lower jaw.
- Vagus Nerve (sensory + motor + autonomic) involved in multiple vital bodily function, passing to the lower head, throat. Neck, chest and abdomen they are involved with breathing,swallowing and heartbeat functions.
- Vestibulocochlear Nerve (sensory) relay information from the inner ear about head orientation, balance, sound and hearing.
Spinal Nerves
The 31 pairs of peripheral spinal nerves reach the cord through gaps between the vertebrae which are held apart by pads of cartilage (intervertebral discs). The nerves divide and enter the back and front of the spinal cord as spinal roots. Each nerve divides and subdivides into a number of branches;
- Dorsal branches serve the rear portion of the body
- Ventral branches serve the front and sides of the body
The branches of a spinal nerve may join with other nerves which form meshes this is where information is shared. They are known as plexuses. These plexuses send signals along secondary nerve branches to areas of complex functions or movement.
Nerves convey:
- Information to glands within the chest and abdomen.
- Motor information to muscles throughout the body.
- Sensory information to the cord about conditions within the body.
- Sense of touch from the skin.
Dermatomes
Are areas of skin that are mainly supplied by a single spinal nerve:
- Eight cervical nerves.
- Twelve thoracic nerves.
- Five lumbar nerves.
- Five sacral nerves.
Each of these nerves relay sensation (including pain) from a particular region of skin to the brain.
Along the thorax and abdomen the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different: the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints. [1]
An automatic, rapid response to a stimulus. The action is involuntary and occurs without any involvement of thought or the brain. This action occurs through a neural pathway called the reflex arc. To allow reflexes to occur very quickly, signals come directly from motor neurons in the spine, instead of being delayed by going through the brain.
Process
- A receptor at the point of stimulus relays the message that there is an adverse stimulus to a sensory neuron
- The sensory neuron carries the message from the receptor at the point of the stimulus to the spinal cord (part of the central nervous system)
- In the spinal cord, a relay neuron, or inter-
neuron, carries the message from the sensory neuron to a motor neuron - The motor neuron then carries the message to the appropriate effector, at which point, the reflex occurs.
After the spinal reflex occurs, sensory neurons send messages to the brain. The brain then relays this information and the messages are consciously interpreted. It is only at this point that you will begin to feel pain.
1 Dermatome diagram -