Anatomy L54: The Last Four Cranial Nerves

Dorsal Motor Nucleus of the Vagus

First neuronal cell bodies responsible for parasympathetic innervation of smooth muscle of digestive system (to splenic flexure), respiratory system and heart.

Nucleus solitarius

Taste fibers from posterior third of tongue, carotid body and carotid sinus

Hypoglossal Nerve (XII)

- Exits cranial cavity through hypoglossal canal of occipital bone - In neck it loops around occipital artery to enter lateral side of the tongue - innervates: Intrinsic and extrinsic muscles (hyoglossus, styloglossus & genioglossus) of tongue

Effects of Lesions of vagus nerve

- Hyperactivity of vagus-stomach ulcers; disruption of swallowing, vomiting, and cough reflex - Disruption or loss of carotid sinus reflex - Disruption of normal respiratory functions; loss of taste sensation from posterior third of tongue - Probable loss of somatosensory sensation from the skin of external ear, tympanic membrane, and posterior third of tongue

Spinal accessory nerve lesion

- Shoulder pain in neck and upper back due to straining of supporting muscles (rhomboids and levator scapulae) with subsequent traction on the brachial plexus. - Limited or loss of sustained abduction of the shoulder.

Vagus nerve (CN X)

- Somatomotor innervates skeletal muscles of larynx, pharynx and soft palate - Visceromotor component innervates smooth muscle of the trachea, bronchi gastrointestinal tract to splenic flexure, regulate heart rhythm. - Sensory component innervates laryngeal mucosa, meninges of posterior cranial fossa, external ear, heart and abdominal organs.

Inferior Ganglion of the Glossopharyngeal nerve

1) special sense (taste) & somatosensory information from the posterior 1/3 of tongue 2) Somatosensory information from the oropharynx 3) Somatosensory information from the middle ear, auditory tube & mastoid air cells 4) General viscerosensory information from the carotid body (chemoreception) & carotid sinus (baroreception)

Inferior Salivary Nucleus

Cell bodies of origin for visceromotor fibers that are involved in innervation of the parotid gland

Glossopharyngeal nerve

Cranial nerve IX. Sensory and motor nerve. Sense of taste for the back of the tongue. Receives information about blood pressure and oxygen/carbon dioxide levels. Movement of the muscles for swallowing and the parotid salivary glands.

Spinal trigeminal nucleus

General sensory from posterior third of tongue, pharynx, middle ear, auditory tube & mastoid air cells

Superior Ganglion of vagus nerve

Innervate external auditory meatus, meninges of the posterior cranial fossa and external surface of tympanic membrane. Its central fibers terminate in spinal trigeminal nucleus of brainstem.

Inferior Ganglion of the vagus nerve (nodose ganglion)

Innervate mucosa of larynx, respiratory system, heart and digestive system. Its central processes (axons) terminate in the nucleus solitarius of brainstem.

Spinal accessory nerve CN XI

Location: C1-C5 of spinal cord is in the posterior portion of the anterior (ventral) horn. - fibers leave spinal cord between the posterior (dorsal) and anterior (ventral) roots to enter cranial cavity through foramen magnum. - fibers then exit cranial cavity through the jugular foramen. - innervates the sternocleidomastoid and trapezius

Nucleus Ambiguus

Motor innervation of pharynx, larynx, upper esophagus (swallowing, palate elevation). Cell bodies of origin for somatomotor fibers that innervate stylopharyngeus

Hypoglossal nucleus

Neuronal cell bodies for the hypoglossal nerve.

Hypoglossal nerve lesion

• In unilateral hypoglossal nerve damage at the level of brain stem, an attempt to protrude the tongue, it will deviate to the side of the lesion. • If supranuclear lesion tongue deviates to opposite site of the lesion

Effects of Lesions of glossopharyngeal nerve

• When a foreign object touches the back of the mouth (oropharynx), it will stimulate the sensory fibers carried by pharyngeal branch of CNIX. The efferent part is carried by vagus nerve → gag reflex. So absent gag reflex is a result of damaged CNIX. • Loss of secretion of parotid gland causing reduction in salivation