Cranial Nerves: Nuclei, Innervation, Dysfunction

• This lecture discusses cranial nerves and their nuclei, exit points, innervations, and examples of cranial nerve dysfunction.

Cranial Nerve Components:

• GSE (General Somatic Efferent) - Supplies motor innervation to skeletal muscles.
• SVE (Special Visceral Efferent) - Innervates muscles derived from branchial arches.
• GVE (General Visceral Efferent) - Provides autonomic motor innervation to smooth muscles and glands.
• GSA (General Somatic Afferent) - Carries sensory information from the skin, muscles, and joints.
• GVA (General Visceral Afferent) - Transmits sensory information from visceral organs.
• SVA (Special Visceral Afferent) - Conveys taste and smell sensations.
• SSA (Special Somatic Afferent) - Involved in vision, hearing, and balance.

Brainstem Nuclei

• Efferent nuclei are organized with GSE medially, then SVE and GVE laterally.
• Specific locations of efferent nuclei
  • Midbrain: Edinger-Westphal nucleus, oculomotor nucleus, trochlear nucleus.
  • Pons: Trigeminal motor nucleus, facial motor nucleus, abducens nucleus, superior salivatory nucleus.
  • Medulla: Inferior salivatory nucleus, nucleus ambiguus, hypoglossal nucleus, dorsal vagal nucleus.
  • Rostral spinal cord: Accessory nucleus.
• Locations of afferent nuclei
  • Pons: Vestibular, spinal trigeminal, and principal trigeminal nuclei.
  • Medulla: Solitary, vestibular, cochlear, and spinal trigeminal nuclei.
  • Rostral Spinal Cord: Solitary and spinal trigeminal nuclei.
  • Midbrain: Mesencephalic nucleus.

Cranial Nerve List (I-XII)

• 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

Cranial Nerve Exit Points

• Cranial nerves exit the skull through specific foramina:
  • Cribriform plate: CN I
  • Optic canal: CN II
  • Superior orbital fissure: CN III, IV, V1, VI
  • Foramen rotundum: CN V2
  • Foramen ovale: CN V3
  • Internal auditory meatus: CN VII, VIII
  • Jugular foramen: CN IX, X
  • Foramen magnum: CN XI
  • Hypoglossal foramen: CN XII

Jugular Foramen Compression

• Vernet syndrome: Jugular foramen compression can result in:
  • Loss of taste in the posterior 1/3 of the tongue (CN IX).
  • Dysarthria and dysphagia (CN X).
  • Ipsilateral flaccid paralysis of neck muscles (CN XI), causing the head to turn towards the lesion.

Cranial Nerves Innervating the Eye

• CN III (Oculomotor):
  • Innervates medial, inferior, and superior rectus muscles, and the inferior oblique.
  • Controls the superior levator palpebrae.
  • Edinger-Westphal nucleus controls ciliary muscles and pupillary sphincter.
• CN IV (Trochlear): Controls superior oblique muscle.
• CN VI (Abducens): Controls lateral rectus muscle.
• Lateral rectus and contralateral medial rectus muscles work together.

Trigeminal Nerve (CN V)

• Somatosensory: Three divisions from the trigeminal ganglion
  • Ophthalmic (V1) branch
  • Maxillary (V2) branch
  • Mandibular (V3) branch
• Sensory fibers are analogous to the DCML and ALS for most of the head region.
• Motor:
  • Masseter and temporalis muscles
  • Tensor tympani (regulation of auditory input).
• Clinical relevance:
  • V2 and V3 branches can trigger trigeminal neuralgia.
  • The trigeminal also conveys episodic pain ('tic douloureaux').
  • Can lead to ipsilateral loss of sensation and loss of the afferent corneal reflex (V1).

Facial Nerve (CN VII)

• Motor: Supplies the muscles of facial expression via five branches.
• Special Sensory: Taste from the anterior 2/3 of the tongue
• Also controls the stapedius muscle (regulation of auditory input).
• Parasympathetic: Lacrimal glands, sublingual glands, and submandibular glands control.

Vestibulocochlear Nerve (CN VIII)

• SSA, containing:
  • Vestibular portion: Semicircular canals for balance.
  • Auditory portion: Cochlea for hearing.

Glossopharyngeal Nerve (CN IX)

• Controls the stylopharyngeus muscle
• Involved in parasympathetic control of the parotid gland.
• Special Sensory for taste in the posterior 1/3 of the tongue
• Has visceral sensory components: Carotid chemo- and baroreceptors.

Vagus Nerve (CN X)

• Has multiple functions
  • Pharyngeal muscles for swallowing
  • Laryngeal muscles for voice
• Primarily involved with parasympathetic control of the heart, lungs, and GI tract.

Spinal Accessory Nerve (CN XI)

• Controls the trapezius and sternocleidomastoid muscles.
• Damage leads to ipsilateral paralysis, causing the patient to "look towards the lesion."

Hypoglossal Nerve (CN XII)

• Controls both intrinsic and extrinsic tongue muscles.

Cerebellopontine Angle Vestibular Schwannoma

• Also known as Acoustic Neuroma.
• This tumor of the myelin sheath of CN VIII compresses several cranial nerves.
• It develops where CN VIII enters the auditory meatus.
  • Tinnitus (ringing in the ears).
  • Balance problems.
  • Facial pain and sensory loss.
  • Ipsilateral ataxia.
  • Contralateral hemiparesis.
  • Dysphagia (impaired gag reflex).
• Lesions:
  • Damage to CN VIII: Can cause hearing loss, tinnitus, and balance issues.
  • Damage to CN V and VII: Facial pain and sensory loss can occur.
  • Damage to CN IX and X: Impaired gag reflex and dysphagia.
  • Corticospinal tract: Can cause contralateral hemiparesis
  • Cerebellar tracts: Contribute to ipsilateral ataxia.
  • (Damage mimicking) Vernet's syndrome.

Explore cranial nerves, their nuclei in the brainstem, and innervation patterns. Understand the different components like GSE, SVE, GVE, GSA, GVA, SVA, and SSA. Learn about examples of cranial nerve dysfunction and their associated symptoms.