CN IX, X, and XI Nerves: Glossopharyngeal Nerve

CN IX, X, and XI Nerves Overview

• These cranial nerves exit the skull through the jugular foramen.
• Glossopharyngeal nerve (IX), vagus nerve (X), and spinal accessory nerve (XI) pass through this opening.

CN IX: Glossopharyngeal Nerve

• This nerve provides sensory and motor innervation to the tongue and pharynx.
• The glossopharyngeal nerve (IX) originates from the brainstem.
  • It provides motor innervation to the stylopharyngeus muscle via the nucleus ambiguus.
  • This nerve also has a dual role that includes motor and sensory functions related to swallowing, taste, and respiratory reflexes.
• After exiting the jugular foramen the Glossopharyngeal never branches:
  • It gives off a motor branch that only innervates the anterolateral stylopharyngeus muscle.
  • Nasopharynx, oropharynx, and laryngopharynx are also innervated by the Glossopharyngeal never.
  • Pharynx branch terminates in the pharynx.
    • The lingual branch provides sensation from the posterior 1/3 of the tongue.
    • The tonsillar branch innervates the tonsil.
    • The pharyngeal branch connects to the pharyngeal plexus and provides sensory information.
• The nerve's pathway includes a sensory component, relaying information from the external ear, tympanic membrane, posterior 1/3 of the tongue, eustachian tube, middle ear cavity, tonsil, and carotid body to the sensory cortex via the spinal trigeminal nucleus and the solitary nucleus.
• The glossopharyngeal nerve has the following modalities:
  • Motor - SVE (Special Visceral Efferent): Nucleus ambiguus controls motor function to the stylopharyngeus muscle.
  • Parasympathetic - GVE (General Visceral Efferent): Inferior salivatory nucleus stimulates the parotid gland.
  • Taste - SVA (Special Visceral Afferent): Solitary nucleus & tract manage taste from posterior 1/3 of the tongue.
  • Somatic Sensory - GSA (General Somatic Afferent): Spinal trigeminal nucleus & tract controls general sensation from posterior 1/3 of tongue, pharynx, external ear, and tympanic membrane.
  • Visceral Sensory - GVA (General Visceral Afferent): Solitary nucleus & tract detects carotid body and gag sensation from the oropharynx.
• Damage from CN IX is rare, but isolated lesions of CN IX can be diagnosed based on the following symptoms:
  • Taste loss at the posterior 1/3 of the tongue.
  • Lack of gag reflex.

CN X: Vagus Nerve

• The vagus nerve (X) is the longest cranial nerve.
  • It starts in the head and extends to the abdomen.
  • The nerve originates from the medulla and exits through the jugular foramen with the glossopharyngeal and accessory nerves to innervate the soft palate, pharynx, and intrinsic muscles of the larynx.
• The fibers from dorsal vagal comprise the PNS pathway that stimulates visceral organs.
  • This pathway innervates the glands of the pharynx and larynx and exhibits craniosacral flow to the thorax and abdomen to facilitate general sensory pathways.
• The vagus nerve (X) has the following modalities:
  • Motor - SVE (Special Visceral Efferent): Nucleus ambiguus controls motor function to pharyngeal muscles and intrinsic muscles of the larynx.
  • Parasympathetic - GVE (General Visceral Efferent): Dorsal motor nucleus of vagus manages and innervates thoracic & abdominal viscera, smooth muscle/glands of the pharynx & larynx.
  • Somatic Sensory - GSA (General Somatic Afferent): Spinal trigeminal nucleus & tract controls posterior meninges, skin on the back of the ear, external acoustic meatus, pharynx, and larynx.
  • Visceral Sensory - GVA (General Visceral Afferent): Solitary nucleus & tract detects larynx, thoracic & abdominal viscera,ortic arch stretch receptors and chemoreceptors in aortic bodies.
• To clinically test for the Vagus nerve, one needs to observe the speech for hoarseness and test the gag reflex.
  • During testing, the uvula will deviate to the normal side due to the damaged side that displays weakness due to a lesion, trauma, or neurological conditions.

Gag Reflex Mechanism

• The gag reflex tests the integrity of the glossopharyngeal (CN IX) and vagus (CN X) nerves.
• Touch stimulation of the oropharynx initiates the sensory component.
  • The sensory information then relays to the solitary nucleus in the medulla via the glossopharyngeal nerve (CN IX).
  • Then the motor signal goes to the muscles of the pharynx and soft palate via the ambiguus motor nucleus.
• A foreign body pushes into the nasopharynx to protect the gag reflex.
  • Contraction of the constrictors causes the pharynx to elevate the soft palate to close the nasopharyngeal region to indicate a properly functioning gag reflex.

CN XI: Accessory Nerve

• CN XI innervates the sternocleidomastoid and trapezius muscles for motor function.
• The nerve enters the cranial cavity through the posterior cranial fossa and then passes to the jugular foramen.
• The accessory nerve has somatic motor functions.
• The course and distribution of the accessory nerve include both spinal and cranial parts.
  • The nerve exits from the medulla oblongata and has a spinal part that contacts the internal jugular foramen.
  • A retrograde course is then enacted through the foramen magnum, to the jugular foramen, to trapezius and sternocleidomastoid.
    • Both trapezius and sternocleidomastoid can be used to test the nerves function, or a lesion impacting it's function.
• Upper motor neuron (UMN) and lower motor neuron (LMN) fibers dictate their function.
  • The corticobulbar tract for the trapezius is controlled by the opposite cortex and the corticobulbar tract for the sternocleidomastoid relay occurs on the same side of the spinal accessory nucleaus.
• A lesion of the accessory nerve will present differently, depending on if it an UMN or LMN.
  • UMN lesion on the right side presents with weakness on the left side for trapezius and weakness on the right side for for sternocleidomastoid.
  • LMN lesion on the right side will have weakness on the same side of the trapezius and sternocleidomastoid.
• Clinically, the accessory nerve can be tested by asking the patient to turn their head to the left and applying resistance from the left side.
  • Additionally, the trapezius will is checked by checking the patients upward pressure and shrug of the shoulders, while applying resistance by pushing downward.

Cranial Accessory Nerve

• Contacts the spinal accessory nerve very briefly, then joins the vagus nerve at the inferior ganglion of vagus.

CN XII: Hypoglossal Nerve

• CN XII manages function for extrinsic and intrinsic muscles of the tongue.
  • The Nerve has somatic motor functions.
• The nerve rootlets pass between the pyramids and olives, forming a nerve that crosses the posterior cranial fossa.
  • The nerve passes laterally between subarachnoid spaces.
  • The nerve exists via the hypoglossal canal in the occipital bone.
• All the intrinsic/extrinsic motor control of the tongue, except for palatoglossus (CN X), are controlled by CN XII.
• All tongue muscles receive dual cortical innervation, with the genioglossus being exceptions, so a damage to CN XII would lead to deviation of the tongue from the side.
• Both upper and lower motor neuron problems of the hypoglossal nerve will alter a patients ability to speak.