Human Physiology/The Nervous System
15
The Peripheral Nervous System
The Cranial Nerves
The
peripheral nervous system
includes 12 cranial
nerves 31 pairs of spinal nerves. It can be subdivided
into the
somatic
and
autonomic
systems. It is a way of
communication from the central nervous system to the
rest of the body by nerve impulses that regulate the
functions of the human body.
The twelve cranial nerves are
I
Olfactory Nerve
for smell
II
Optic Nerve
for vision
III
Oculomotor
for looking around
IV
Trochlear
for moving eye
V
Trigeminal
for feeling touch on face
VI
Abducens
to move eye muscles
VII
Facial
to smile, wink, and help us taste
VIII
Vestibulocochlear
to help with balance,
equilibrium, and hearing
IX
Glossopharengeal
for swallowing and gagging
X
Vagus
for swallowing, talking, and parasympathetic actions of digestion
XI
Spinal accessory
for shrugging shoulders
XII
Hypoglossal
for tongue more divided into different regions as muscles
The 10 out of the 12 cranial nerves originate from the brainstem, and mainly control the functions of the anatomic
structures of the head with some exceptions. CN X receives visceral sensory information from the thorax and
abdomen, and CN XI is responsible for innervating the sternocleidomastoid and trapezius muscles, neither of which
is exclusively in the head.
Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the body. In humans,
there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. The naming
convention for spinal nerves is to name it after the vertebra immediately above it. Thus the fourth thoracic nerve
originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal
nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal
nerve, C8. There are only 7 cervical vertebrae and 8 cervical spinal nerves.