Glossopharyngeal Nerve Anatomy Quiz

Glossopharyngeal Nerve

• Contains motor, parasympathetic and sensory nuclei
• Motor nucleus is the nucleus ambiguus, common to CN 9, 10 and 11
• Parasympathetic nucleus is the inferior salivatory nucleus
• Sensory nucleus is the nucleus of the solitary tract, common to CN 7, 9 and 10
• Supplies the stylopharyngeus muscle
• Contributes to the pharyngeal plexus
• Inferior salivatory nucleus supplies parasympathetic innervation to the parotid gland
• Sensory ganglia lie at the level of the jugular foramen
  • Superior ganglion contains cell bodies for GSA fibers
  • Inferior ganglion contains cell bodies for SVA and GVA fibers
• GSA fibers, from the auricle, pass to the spinal nucleus of the trigeminal nerve
• SVA fibers, from the posterior 1/3 of the tongue, and GVA fibers, from the pharynx, terminate in the nucleus of the solitary tract
• GVA fibers from the carotid sinus and carotid body terminate in the nucleus of the solitary tract and are relayed to the parasympathetic nucleus of the vagus nerve

Vagus Nerve

• Contains motor, parasympathetic and sensory nuclei
• Motor nucleus is the nucleus ambiguus, common to CN 9, 10 and 11
• Parasympathetic nucleus is the dorsal nucleus of vagus
• Sensory nucleus is the nucleus of the solitary tract, common to CN 7, 9 and 10
• Supplies the constrictor muscles of the pharynx through the pharyngeal plexus
• Supplies the intrinsic muscles of the larynx through the superior and inferior laryngeal nerves
• Parasympathetic nucleus supplies innervation to organs in the thorax, abdominal organs, and the alimentary tract as far as the distal 1/3 of the transverse colon
• Sensory ganglia lie at the level of the jugular foramen
  • Superior ganglion contains cell bodies for GSA fibers
  • Inferior ganglion contains cell bodies for SVA and GVA fibers
• GSA fibers, from the auricula, pass to the spinal nucleus of the trigeminal nerve
• SVA fibers, from the posterior part of the tongue, and GVA fibers relay sensory information from the larynx and soft palate, and terminate in the nucleus of the solitary tract

Accessory Nerve

• Motor nucleus formed of cranial and spinal roots
  • Cranial root originates from the nucleus ambiguus
  • Spinal root originates from the spinal nucleus of the nerve, located lateral to the anterior gray horn within the first five segments of the spinal cord
• Cranial root joins the vagus nerve and contributes to the pharyngeal plexus
• Spinal root innervates the SCM and trapezius muscles

Hypoglossal Nerve

• Motor nucleus innervates
  • Intrinsic tongue muscles
  • Styloglossus, hyoglossus, and genioglossus muscles
• Part of the hypoglossal nucleus responsible for innervation of the genioglossus muscle receives only unilateral corticonuclear fibers from the contralateral side

Clinical Note: Hypoglossal Nerve Damage

• Tongue deviates towards the side of the lesion when protruded
• Interruption of corticonuclear fibers to the hypoglossal nucleus only affects the genioglossus muscle
• Tongue deviates to the contralateral side of the lesion when protruded

Cranial Nerve Summary

• GSE (motor) receive fibers from the motor cortex through corticonuclear fibers
• GSA (sensory) relay to the spinal nucleus of the trigeminal nerve
• GVA (visceral sensations) relay to the nucleus of the solitary tract
• GVE (parasympathetic) relay to private parasympathetic nuclei
• SVE (motor to branchiomeric muscles) relay to private nuclei for CN V and VII, and the nucleus ambiguus for IX, X, and XI
• SSA (visual, auditory, equilibrium)
• SVA (taste, smell)
  • Taste information travels to the upper part of the nucleus of the solitary tract (gustatory nucleus)
• Cranial nerves that convey sensory fibers have sensory ganglia outside of the central nervous system where the cell bodies of the first order neurons lie
  • Examples include the trigeminal ganglion, geniculate ganglion, spiral ganglion, and vestibular ganglion
• Motor nuclei of the cranial nerves receive corticonuclear fibers from both hemispheres except
  • Part of the facial nucleus responsible for the innervation of the lower part of the face
  • Part of the hypoglossal nucleus responsible for the innervation of the genioglossus muscle
• Parasympathetic nuclei of the cranial nerves receive afferent impulses from the hypothalamus through descending autonomic pathways

Olfactory Nerve

• Olfactory receptor cells are responsible for detecting odorants
• Olfactory nerves relay signals from the olfactory receptor cells
• The olfactory bulb processes olfactory signals and contains mitral and tufted cells
• The olfactory tract relays signals from the olfactory bulb
  • The medial olfactory stria carries fibers that cross at the anterior commissure to terminate in the contralateral olfactory bulb
  • The lateral olfactory stria carries fibers that reach the olfactory areas of the cortex
• Olfactory areas include:
  • Primary olfactory cortex: periamygdaloid and prepyriform areas
  • Secondary olfactory cortex: entorhinal area (Bodmann 28)
• Olfaction is important for lower mammals for:
  • Mating
  • Reproduction
  • Finding food
  • Sensing danger

Clinical Note: Olfactory Nerve

• Anosmia is loss of smell and can be caused by:
  • Infections of the olfactory mucosa
  • Damage to olfactory nerves, bulb, and tract
  • Fractures of the cribriform plate of the ethmoid bone

Optic Nerve

• Optic receptor cells detect light
  • Cones are responsible for vision in high light levels and provide clear and color vision
  • Rods are responsible for vision in low light levels
• Bipolar cells relay signals from the optic receptor cells
• Ganglion cells relay signals from the bipolar cells
• The macula lutea is responsible for central vision and primarily contains cones.
• The fovea centralis is responsible for the sharpest vision and only contains cones.

Visual Field

• Visual input travels from the optic nerve to the:
  • Optic chiasm, where fibers from the nasal hemiretinas cross
  • Optic tract
  • Lateral geniculate body, which relays information to the visual cortex via the optic radiation
• The optic radiation passes through the retrolentiform part of the internal capsule
• Meyer’s loop conveys fibers from the contralateral lower quadrant of the retina (contralateral upper quadrant of the visual field)

Visual Reflexes

• Direct and consensual light reflexes test the pupillary response to light
• Accommodation reflex tests the ability to focus on near objects
• Visual body reflexes: include scanning objects and protective closing of the eyes
• Corneal reflex tests the blink reflex and is not vision related
• Pupillary skin reflex tests the pupillary response to painful stimulation of the skin and is not vision related

Pathway for the Pupillary Light Reflex

• Lesions along the pathway can lead to anisocoria (unequal pupil sizes)

Accommodation Convergence Reflex

• The medial rectus muscles contract, pupils constrict, and the lens changes shape to focus on near objects

Oculomotor Nerve

• Contains both motor and parasympathetic nuclei
  • Motor nucleus innervates 5 of the 7 extrinsic eye muscles
  • Parasympathetic nucleus (Edinger Westphal nucleus) innervates the ciliary ganglion which then innervates the constrictor pupillae and ciliary muscles

Medial Longitudinal Fasciculus (MLF)

• The MLF connects the 3rd, 4th, 6th, and 8th cranial nerves

Clinical Note: Oculomotor Nerve Palsy

• Oculomotor nerve palsy can cause:
  • Paralysis of the related eye muscles
  • Eye deviation to the lateral side
  • Diplopia (double vision)
  • Ptosis (drooping eyelid)
  • Mydriasis (dilated pupil)
  • Impairment of the pupillary light reflex
  • Impairment of the accommodation convergence reflex

Pupillary Light Reflex

• The pupillary light reflex is both direct and indirect (consensual)

Accommodation Convergence Reflex

• Involved in focusing on near objects
• Controlled by the oculomotor nerve

Trochlear Nerve

• Motor nucleus innervates the superior oblique muscle
• The only cranial nerve to leave the brainstem through its posterior aspect
• Crosses to the other side as it emerges from the brainstem

Test your knowledge on the anatomy and functions of the glossopharyngeal nerve. This quiz covers its motor, sensory, and parasympathetic nuclei, as well as its role in pharyngeal plexus and innervation of glands. Ideal for students studying neuroanatomy.