Glossopharyngeal Nerve

INTRODUCTION:
  • The glossopharyngeal nerve, known as the ninth cranial nerve (CN IX), is a mixed nerve that carries afferent sensory and efferent motor information.
  • It exits the brainstem out from the sides of the upper medulla, just rostral (closer to the nose) to the vagus nerve. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, while the sensory division originates from the cranial neural crest.
STRUCTURE:
Medulla oblongata
           ↓
Glossopharyngeal nerve ( laterally across or below the flocculus) (b/w internal jugular vein & internal artery)
           ↓
Jugular foramen
           ↓Descends
Beneath the styloid process
↓Curves forward
Stylopharyngeus and middle pharyngeal constrictor muscle
↓passes under
Hyoglossus muscle
↓supplies
Palatine tonsil, the mucous membrane of the fauces and base of the tongue, and the serous glands of the mouth.


BRANCHES Tympanic
  1. Stylopharyngeal
  2. Tonsillar
  3. Nerve to carotid sinus
  4. Branches to the posterior third of tongue
  5. Lingual branches
  6. A communicating branch to the Vagus nerve
  7. Note: The glossopharyngeal nerve contributes in the formation of the pharyngeal plexus along with the vagus nerve.
FUNCTIONAL COMPONENTS:
  • The glossopharyngeal nerve has five distinct general functions:
  1. Branchial motor (special visceral efferent) – supplies the stylopharyngeus muscle.
  2. Visceral motor (general visceral efferent) – provides parasympathetic innervation of the parotid gland via the otic ganglion
  3. Visceral sensory (general visceral afferent) – carries visceral sensory information from the carotid sinus and carotid body.
  4. General sensory (general somatic afferent) – provides general sensory information from inner surface of the tympanic membrane, upper pharynx (GVA), and the posterior one-third of the tongue.
  5. Visceral afferent (special visceral afferent) – provides taste sensation from the posterior one-third of the tongue, including circumvallate papillae.
  • The glossopharyngeal nerve as noted above is a mixed nerve consisting of both sensory and motor nerve fibers. The sensory fibers' origin include the pharynx, middle ear, posterior one-third of the tongue (including taste buds); and the carotid body and sinus. These fibers terminate at the medulla oblongata. The motor fibers' origin is the medulla oblongata, and they terminate at the parotid salivary gland, the glands of the posterior tongue, and the stylopharyngeus muscle (which dilates the pharynx during swallowing).
BRAINSTEM CONNECTIONS:
  • The glossopharyngeal nerve is mostly sensory. 
  • The glossopharyngeal nerve also aids in tasting, swallowing and salivary secretions. 
  • Its superior and inferior (petrous) ganglia contain the cell bodies of pain fibers. It also projects into many different structures in the brainstem:
  1. Solitary nucleus: Taste from the posterior one-third of the tongue and information from carotid baroreceptors and carotid body chemoreceptors
  2. Spinal nucleus of the trigeminal nerve: Somatic sensory fibers from the middle ear
  3. Lateral Nucleus of Ala Cinerea: Visceral pain
  4. Nucleus ambiguus: The lower motor neurons for the stylopharyngeus muscle
  5. Inferior salivatory nucleus: Parasympathetic input to the parotid and mucous glands.
FUNCTIONS: 
There are a number of functions of the glossopharyngeal nerve:
  • It receives general somatic sensory fibers (ventral trigeminothalamic tract) from the tonsils, the pharynx, the middle ear and the posterior 1/3 of the tongue.
  • It receives special visceral sensory fibers (taste) from the posterior one-third of the tongue.
  • It receives visceral sensory fibers from the carotid bodies, carotid sinus.
  • Nerve supply of circumvallate papillae is glossopharyngeal nerve
  • It supplies parasympathetic fibers to the parotid gland via the otic ganglion.
  • It supplies motor fibers to stylopharyngeus muscle, the only motor component of this cranial nerve.
  • It contributes to the pharyngeal plexus.

Exam Question
  • Pain sensation from ear in tonsillitis is due to glossopharyngeal nerve.
  • Nerve supply of circumvallate papillae is glossopharyngeal nerve
  • Taste sensations from the posterior 1/3rd of tongue are carried by glossopharyngeal nerve.
  • Glossopharyngeal nerve innervates the oral pharynx
  • Sensory supply to tongue is by glossopharyngeal nerve
  • Glossopharyngeal nerve travels through the jugular foramen in the base of the skull
  • Glossopharyngeal nerve supplies the posterior part of the tongue because it develops from Hypobranchial eminence 
  • Stylopharyngeus Muscle supplied by glossopharyngeal nerve
  • Sensory nerve supply of the palatine tonsils is by glossopharyngeal nerve
  • General sensation from the posterior 1/3rd of tongue are carried by glossopharyngeal nerve.

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