Cranial Nerves: Nuclei, Innervation, Dysfunction

• This study material covers cranial nerves, their nuclei, exit points, innervations, and examples of dysfunction.

Cranial Nerves Overview

• The study material encompasses cranial nerves and their related nuclei
• Discusses exit points and innervations
• Gives instances of cranial nerve dysfunction

Key Terms

• GSE: General Somatic Efferent
• SVE: Special Visceral Efferent
• GVE: General Visceral Efferent
• GSA: General Somatic Afferent
• GVA: General Visceral Afferent
• SVA: Special Visceral Afferent
• SSA: Special Somatic Afferent

Brainstem Nuclei - Efferent

• Midbrain: Includes the Edinger-Westphal nucleus, oculomotor nucleus, and trochlear nucleus (red nucleus).
• Pons: Contains the trigeminal motor nucleus, facial motor nucleus, abducens nucleus, and superior salivatory nucleus.
• Medulla: Includes the inferior salivatory nucleus, nucleus ambiguus, hypoglossal nucleus, and dorsal vagal (and glossopharyngeal) nucleus.
• Rostral Spinal Cord: Contains the accessory nucleus with medial, lateral, and intermediate motor columns.

Brainstem Nuclei - Afferent

• Midbrain: Includes the mesencephalic nucleus.
• Pons: Contains the vestibular nucleus, spinal trigeminal nucleus, and principal trigeminal nucleus.
• Medulla: Includes the solitary nucleus, vestibular nucleus, cochlear nucleus, and spinal trigeminal nucleus.
• Rostral Spinal Cord: Contains the solitary nucleus and spinal trigeminal nucleus.

Cranial Nerve Listing and Exit Points

• I: Olfactory
• II: Optic
• III: Oculomotor
• IV: Trochlear
• V: Trigeminal
• VI: Abducens
• VII: Facial
• VIII: Vestibulocochlear
• IX: Glossopharyngeal
• X: Vagus
• XI: Spinal Accessory
• XII: Hypoglossal
• Cribriform Plate: CN I
• Optic Canal: CN II
• Superior Orbital Fissure: CN III, IV, V1, VI
• Forament Rotundum: CN V2
• Forament Ovale: CN V3
• Internal Auditory Meatus: CN VII, VIII
• Jugular Foramen: CN IX, X
• Foramen Magnum/Jugular: CN XI
• Hypoglossal Foramen: CN XII

Jugular Foramen Compression - Vernet Syndrome

• Loss of taste in the posterior 1/3 of the tongue (IX)
• Dysarthria and dysphagia (X)
• Ipsilateral flaccid paralysis of neck muscles, with the patient "looking toward the lesion" (XI)

CN III - Innervation

• Oculomotor Nucleus: Medial, inferior, and superior rectus muscles, inferior oblique, superior levator palpebrae
• Edinger-Westphal Nucleus: Ciliary muscles, pupillary sphincter (iris)
• Trochlear: Superior oblique
• Abducens: Lateral rectus
• Lateral rectus and contralateral medial rectus work in concert
• Damage results in internuclear opthalmoplegia

CN V - Trigeminal Nerve

• Somatosensory: Has three divisions from the trigeminal ganglion includes ophthalmic branch V1, maxillary branch V2, and mandibular branch V3.
• Motor Fibers: Masseter, temporalis, and tensor tympani (regulation of auditory input)
• “Trigeminal for Tensor Tympani” and “Seventh for Stapedius”
• Sensory fibers operate similar to DCML and ALS pathways for most of the head, C2 covers the occiput.
• V2,3 damage = trigeminal neuralgia.
  • Can cause episodic pain
  • ipsilateral loss of sensation
  • loss of afferent corneal reflex (V1).

CN VII - Facial Nerve

• Motor: Five branches supplying facial expression muscles.
• Corneal Reflex: Also controls corneal reflex and stapedius muscle (regulation of auditory input)
• Parasympathetic: Control of lacrimal, sublingual, and submandibular glands
• Visceral: Regulates taste in the anterior 2/3 of tongue
• Governs minor somatosensory aspects

CN VIII - Vestibulocochlear Nerve

• Vestibular: Semicircular canals (balance)
• Auditory: Cochlea (hearing)

CN IX - Glossopharyngeal Nerve

• Taste: posterior 1/3 of tongue
• Regulates carotid chemo and baro-receptors
• Motor: Stylopharyngeus muscle
• Parasympathetic: Manages control of parotid gland

CN X - Vagus Nerve

• Visceral: epiglottis and pharynx are taste related as well as aortic arch chemo and baro-receptors.
• Motor: Pharyngeal muscles when swallowing, laryngeal muscles for speech.
• Regulates parasympathetic operation of heart, lungs, and the GI tract

CN XI - Spinal Accessory Nerve

• Controls the trapezius, and sternocleidomastoid muscles
• Injury means paralysis towards the lesion

CN XII - Hypoglossal Nerve

• Controls Intrinsic and extrinsic tongue muscles

Cranial Nerve Nuclei Locations

• Caudal Pons: Spinal trigeminal, abducens, facial, and vestibular nuclei
• Rostral Medulla: Spinal trigeminal, vestibular, cochlear and solitary nuclei. Can operate salivatory nucleus (superior VII, inferior IX)
• Middle Medulla: Spinal trigeminal, vestibular, vagal motor, solitary, ambiguous and hypoglossal nuclei
• Caudal Medulla: Spinal trigeminal, solitary, ambiguous, vagal motor, and hypoglossal nuclei

Cerebellopontine Angle - Vestibular Schwannoma

• Known as "acoustic neuroma" and is a tumor of the myelin sheath of CN VIII, compressing several cranial nerves
• Develops where CN VIII enters the auditory meatus
• Symptom:
  • Tinnitus (ringing in ears)
  • Balance problems
  • Facial pain and sensory loss
  • Ipsilateral ataxia
  • Contralateral hemiparesis
  • Dysphagia, impaired gag reflex
• Lesion:
  • CN VIII
  • CN V, VII
  • Cerebellar tracts
  • Corticospinal tract
  • CN IX, X (Vernet’s syndrome)