Identifying Cranial Nerve Function - Anatomy

The six extraoccular muscles of the eye are innervated by three cranial nerves. CN III, the occulomotor nerve, innervates the superior rectus muscle, medial rectus muscle, inferior rectus muscles, and the inferior oblique muscle. CN IV, the trochlear nerve, innervates the superior oblique muscle. CN VI, the abducens nerve, innervates the lateral rectus muscle.

CN V, the trigeminal nerve, is responsible for sensory information from some regions of the face and motor function of the jaw.

Cranial nerve VIII is also called the vestibulocochlear nerve. It is a sensory nerve responsible for bringing information from the cochlea and semicircular canals to the brain. The cochlea supplies auditory information, while the semicircular canals give information about the orientation of the head.

Cranial nerve I is the olfactory nerve, which relays sensory information about smell from hair cells in the nose. Cranial nerve II is the optic nerve, which relays visual sensory information. Cranial nerve X is the vagus nerve, which is highly functional in the parasympathetic nervous system.

Cranial nerve V is also called the trigeminal nerve. It is associated with sensory receptors on the face, as well as stimulation of the chewing muscles.

Cranial nerves I, II, and VIII are associated with smell, sight, and hearing respectively. Cranial nerve I is the olfactory nerve, cranial nerve II is the optic nerve, and cranial nerve VIII is the vestibulocochlear nerve. Cranial nerves VII (facial nerve) and IX (glossopharyngeal nerve) provide the sense of taste.

Face, nose, and mouth sensations, as well as mastication (or chewing), are controlled by the trigeminal nerve.

The facial nerve is associated with taste, facial expression, and production of tears and saliva. Sensation and swallowing in the pharynx are controlled by the glossopharyngeal nerve. The vagus nerve supplies the pharynx, larynx, and the viscera of the thorax and abdomen. Eye movement is controlled by the trochlear nerve.

The vagus nerve supplies the viscera of the thorax and abdomen, including the liver, stomach, kidneys, and lungs. The accessory nerve is a motor nerve supplying the neck muscles, pharynx, and larynx. Eye movement is controlled by the abducens nerve. The trigeminal nerve is responsible for face, nose, and mouth sensations and for chewing. Eye movement is controlled by the trochlear nerve.

CN XI only has motor function (innervation of the trapezius and sternocleidomastoid muscles). The other nerves listed have the following parasympathetic functions: pupil constriction (CN III), salivation (CN VII and CN IX) and parasympathetic modulation over multiple internal organs (CN X).

Cranial nerve III is the oculomotor nerve, which controls most of the muscles needed for eye movement. Also, this nerve controls the ciliary muscle and is responsible for pupillary constriction via parasympathetic innervation. The cranial nerve that makes the eye look to the side is the abducens nerve or cranial nerve VI. The muscle that helps roate the eye down and out is the trochlear nerve or cranial nerve IV. The nerve that carries visual information from the back of the eyeballs to the brain is the optic nerve or cranial nerve II.

Cranial nerve (CN) VIII is the vestibulocochlear nerve. It is purely sensory in function, and is involved in audition, and proprioception. CN VII is the facial nerve. CN X is the vagus nerve. CN II is the optic nerve.

The vagus nerve (cranial nerve X) innervates the larynx, and is involve in speech production. The accessory nerve innervates the muscles in the neck and upper back. Cranial nerve IX is the glossopharyngeal nerve and innervates the pharynx. Cranial nerve XIII is the hypoglossal nerve that innervates the tongue.

The inferior alveolar nerve passes through the mandibular foramen. It has motor and sensory components. It serves to give the lower face and jaw sensation and is also responsible for stimulating the muscles for movement of the jaw.

The trigeminal nerve (cranial nerve V) is responsible for facial sensation and motor functions, such as biting and chewing. The trigeminal nerve has three major branches (hence: tri-): the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The opthalmic and maxillary nerves are purely sensory, and the mandibular nerve has both sensory and motor functions. VI provides sensation to the forehead, upper eyelids, and the bridge and tip of the nose. V2 provides sensation lateral to the eyelids, the cheeks, nostrils, and upper lip. V3 provides sensation to the lower lip, chin, skin over the jaw, and pre-auricular area.

Cranial nerves VII and IX supply taste sensation to the tongue. Cranal nerve VII (facial) supplies taste to the anterior two-thirds of the tongue and cranial nerve IX (glossopharyngeal) supplies somatosensation and taste to the posterior one-third of the tongue.

Cranial nerve V (trigeminal) has 3 branches: ophthalmic, maxillary, and mandibular. Each of these branches have their own branches. The maxillary branch has 3 sub-branches named zygomaticofacial, zygomaticotemporal, and infraorbital. The mandibular branch has 3 sub-branches named auriculotemporal, buccal, and mental. The ophthamic branch has 5 sub-branches named supraorbital, supratrochlear, infraorbital, lacrimal, and external nasal.

Cranial nerve XII, the hypoglossal nerve, is responsible for controlling muscles that move the tongue. The vestibulocochlear nerve is responsible for sound and balance. The abducens and trochlear are responsible for controlling extraocular muscles. The optic nerve conveys information from the photoreceptor cells of the retina of the eye.

The glossopharyngeal cranial nerve functions in supplying visceral and somatic afferent sensation from the carotid body, carotid sinus, posterior one-third of the tongue, palatine tonsils, oropharynx, mucosa of the middle ear, and pharyngotympanic tube. It also supplies taste from the posterior one-third of the tongue and visceral efferent function to parotid salivary gland.

The four cranial nerves the have sensory and motor function are cranial nerve V (trigeminal), VII (facial), IX (glossopharyngeal), and X (vagus).

Taste is unique and is controlled by the facial, glossopharyngeal, and vagus cranial nerves. This can be further explained in which facial controls the anterior two-thirds of the tongue, glossopharyngeal controls the posterior one-third, and vagus innervates taste in the pharynx.

Parasympathetic nerves are autonomic branches of the peripheral nervous system (PNS). These arise from some cranial nerves (that participate in cranial nuclei), the vagus nerve (although a cranial nerve, these fibers doe not participate in cranial ganglia and their parasympathetic action is directed to the thoracic cavity), and pelvic splanchnic efferent preganglionic nerve bodies.

The preganglionic parasympathetic nerves of CN III, CN VII, and CN IX arise from nuclei in the CNS. These fibers go on to synapse at one of four parasympathetic ganglia: ciliary, pterygopalatine, submandibular, or otic and provide parasympathetic function to the head and neck.

The autonomic nervous system can be divided into the parasympathetic system and the sympathetic system. The autonomic system is responsible for regulating the body's unconscious activity. The sympathetic system is responsible for stimulating activities associated with "fight or flight," and includes mydriasis (dilation of the pupil). The parasympathetic response is responsible for "rest and digest," and includes mucus secretion, salivation, lacrimation, urination, digestion, and defecation.