Cranial nerve Part 2

Facial nerve: This has both sensory and motor components. The motor fibers arise from the nucleus in pons. It passes through the internal auditory meatus in the petrous part of the temporal bone.

The nerve leaves the skull through the stylomastoid foramen and divides into branches behind the ramus of the mandible to supply the muscles of facial expression. These muscles are essential for the display of emotions on the face. It also supplies the stapedius muscle.

The special sensory part contains fibers which carry sensation of taste from the anterior two thirds of the tongue. The general sensory component carries skin sensations from external auditory meatus, small area behind the ear and the external surface of the tympanic membrane.

Vestibulo-cochlear nerve: As the name indicates the vestibulo-cochlear nerve has two parts. The cochlear part is responsible for carrying sound impulses from the inner ear (cochlea) and is essential for hearing.

The vestibular part carries impulses from the semicircular canals and is necessary for maintaining balance.

The nerve passes through the internal auditory meatus of the petrous part of the temporal bone and enters the brainstem at the junction of pons and medulla. The cochlear part ends in the cochlear nucleus in the pons. The vestibular part ends in the vestibular nucleus also situated in pons.

Glosso-pharyngeal nerve: This nerve supplies the tongue (glossus) and the pharynx. It contains both motor and sensory parts. It carries taste sensation from the posterior one third of the tongue.

It also carries general sensation from the inner lining of the pharynx. The motor part supplies a muscle called stylopharyngeus muscle which elevates the larynx and pharynx.

Vagus nerve: This is the longest cranial nerve and supplies organs from the neck to the abdomen. The word vagus is derived from Latin meaning wandering. It has both sensory and motor fibers.

. The motor fibers arise in a nucleus called the nucleus ambiguous in the medulla. The nerve leaves the skull through an opening called the jugular foramen in the occipital bone.

In the neck it gives of pharyngeal, superior laryngeal, recurrent and superior cardiac nerves. The pharyngeal nerve supplies the mucus membrane and the muscles of the pharynx.

The superior laryngeal nerve divides into two branches. The external branch supplies the Cricothyroid muscle of larynx. The internal branch supplies the mucus membrane of larynx.

The recurrent nerve supplies all the muscles of the larynx except the Cricothyroid muscle.

The superior cardiac nerve joint a network of nerves called the cardiac plexus. It is part of the Parasympathetic limb of the Autonomic nervous system. The cardiac plexus also receives Sympathetic nerves.

. The parasympathetic fibers supplied through the vagus nerve to the heart decrease the heart rate while the sympathetic nerves increase the heart rate.

In the thorax the vagus nerve gives off inferior cardiac, anterior bronchial, posterior bronchial and esophageal nerves.

The inferior cardiac branch joins the cardiac plexus. The anterior bronchial branch joins the anterior pulmonary plexus while the posterior bronchial branch joins the posterior pulmonary plexus. The pulmonary plexuses also receive branches from the Sympathetic limb of the Autonomic nervous system.

The parasympathetic fibers to the lungs cause constriction of the bronchi while the sympathetic nerve fibers cause dilation of the bronchi.

The esophageal nerve supplies the esophagus and causes rhythmic contraction of the smooth muscles of the esophagus needed for propelling food forward.

The branches in the abdomen supply the stomach, intestines, liver, pancreas, spleen, kidneys and adrenal glands. The nerve is responsible for causing rhythmic movement of intestine called peristalysis which is essential for propelling food forward. It is also necessary for the secretory functions of liver and pancreas.

Accessory nerve: The nerve has cranial and spinal roots. The cranial part arises from the nucleus in medulla. It joins the spinal root which travels up from the upper spinal cord and leaves the skull through an opening called the jugular foramen in the occipital bone.

It then separates from the spinal root and joins the branches of the vagus nerve which supply the pharynx and larynx.

The spinal root arises from the upper spinal cord goes up through the foramen magnum in the occipital bone to join the cranial part. After coming out of the skull it separates from the cranial part and supplies the sterno-mastoid and trapezius muscles.

The sterno-mastoid muscle is situated in the side of the neck. You can feel the contraction of this muscle if you keep your palm on one side of the neck and turn the neck towards the opposite side. The trapezius muscles are flat triangular muscles covering the back of neck and shoulder.

Hypoglossal nerve: It is a motor nerve. It arises from its nucleus in the medulla. It comes out of the skull through an opening in the occipital bone. It supplies all the intrinsic muscles of the tongue and thus controls the movements of the tongue. It also supplies three of the four extrinsic muscles of the tongue.

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Cranial nerves

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