This section describes the cranial nerves, their function, and origin/pathways when
applicable.
There are 12 pairs of cranial
nerves. These nerves arise
from the brain and brain
stem, carrying motor and or
sensory information.
Cranial nerve I: Olfactory nerve
The olfactory nerve is composed of axons from the olfactory
receptors in the nasal sensory epithelium. It carries olfactory
information (sense of smell) to the olfactory bulb of the brain. This
is a pure sensory nerve fiber.
Cranial nerve II: Optic nerve
The optic nerve is composed of axons of the ganglion cells in the eye. It carries visual
information to the brain. This is a pure sensory nerve fiber. This nerve travels posteromedially
from the eye, exiting the orbit at the optic canal in the lesser wing of the sphenoid bone. The
optic nerves join each other in the middle cranial fossa to form the optic chiasm.
Cranial nerve III: Oculomotor nerve
The oculomotor nerve is composed of motor axons coming from the
oculomotor nucleus and the edinger-westphal nucleus in the rostral
midbrain located at the superior colliculus level. This is a pure
motor nerve. It provides somatic motor innervation to four of the
extrinsic eye muscles: the superior rectus, inferior rectus, medial
rectus, and the inferior oblique muscles. It also innervates the
muscles of the upper eyelid and the intrinsic eye muscles (the
pupillary eye muscle.) Together, CN III, CN IV and CN VI control the six muscles of the eye.
Cranial nerve IV: Trochlear nerve
The trochlear nerve provides somatic motor innervation to the superior oblique eye muscle. This
cranial nerve originates at the trochlear nucleus located in the tegmentum of the midbrain at the
inferior colliculus level and exits the posterior side of the brainstem. It is also a pure motor nerve
fiber.
Cranial nerve V: Trigeminal nerve
The trigeminal is the largest cranial nerve . It provides sensory
information from the face, forehead, nasal cavity, tongue, gums and
teeth (touch, and temperature) and provides somatic motor
innervation to the muscles of mastication or “chewing”.
This cranial nerve has 3 branches: the ophthalmic, maxillary and
mandibular branches.
It is composed of both sensory and motor axons. The sensory fibers are located in the trigeminal
ganglion and the motor fibers project from nuclei in the pons.
Cranial nerve VI: Abducens nerve
The abducens nerve carries somatic motor innervation to one of the extrinsic eye muscles, the
lateral rectus muscle. It is another pure motor nerve fiber and originates from the abducens
nucleus located in the caudal pons at the facial colliculus level.
Cranial nerve VII: Facial nerve
The facial nerve carries somatic motor innervation to the many
muscles for facial expression. It carries sensory information form the
face (deep pressure sensation) and taste information from the
anterior two thirds of the tongue. It arises at the pons in the
brainstem and it emerges through openings in the temporal bone and
stylomastoid foramen and has many branches. It is composed of both
sensory and motor axons.
Cranial nerve VIII: Vestibulocochlear
nerve
The vestibulocochlear nerve innervates the hair cell receptors of the
inner ear. It carries vestibular information to the brain from the
semicircular canals, utricle, and saccule providing the sense of
balance. It also carries information from the cochlea providing the
sense of hearing. This cranial nerve branches into the Vestibular
branch (balance) and the cochlear branch (hearing). The cochlear
fibers originate from the spiral ganglion. It is pure sensory nerve fiber.
Cranial nerve IX: Glossopharyngeal nerve
The glossopharyngeal nerve innervates the pharynx (upper part of
the throat), the soft palate and the posterior one-third of the tongue.
It carries sensory information (touch, temperature, and pressure)
from the pharynx and soft palate. It carries taste sensation from the
taste buds on the posterior one third of the tongue. It provides
somatic motor innervation to the throat muscles involved in
swallowing. It provides visceral motor innervation to the salivary
glands. This cranial nerve also supplies the carotid sinus and reflex
control to the heart . It is composed of both sensory and motor axons
and originates from the nucleus ambiguous in the reticular formation of the medulla.
Cranial nerve X: Vagus nerve
The vagus nerve consists of many rootlets that come off of the
brainstem just behind the glossopharyngeal nerve. The branchial
motor component originates from the nucleus ambiguous in the
reticular formation of the medulla. The visceral component
originates from the dorsal motor nucleus of the vagus located in the
floor of the fourth ventricle in the rostral medulla and in the central
grey matt er of the caudal medulla. It is the longest cranial nerve
innervating many structures in the throat, including the muscles of
the vocal cords, thorax and abdominal cavity. It provides sensory information (touch,
temperature and pressure) from the external auditory meatus (ear canal) and a portion of the
external ear. It carries taste sensation from taste buds in the pharynx. It also provides sensory
information from the esophagus, respiratory tract, and abdominal viscera (stomach, intestines,
liver, etc.). It provides visceral motor innervation to the heart, stomach, intestines, and
gallbladder. It is part of the ANS, the parasympathetic branch. It is composed of both sensory
and motor axons. Other parasympathetic ganglia include CN III , CN VII and CN IX .
Cranial nerve XI: Spinal Accessory nerve
The spinal accessory nerve has two branches. The cranial branch
provides somatic motor innervation to some of the muscles in the
throat involved in swallowing. This cranial branch is accessory to
CN X, originating in the caudal nucleus ambiguous, with the fibers
of the cranial root traveling the same extracranial path as the
branchial motor component of the vagus nerve. The spinal branch
provides somatic motor innervation to the trapezius muscles,
providing muscle movement for the upper shoulders head and neck.
It is pure motor nerve fiber.
Cranial nerve XII: Hypoglossal nerve
The hypoglossal nerve provides somatic motor innervation to the muscles of the tongue. This
pure motor nerve originates from the hypoglossal nucleus located in the tegmentum of the
medulla.