Cranial Nerve

NEUROSCIENCE II

  • Course: ANA6205

  • Instructor: Maria Thomadaki, D.C.

  • Contact: mthomadaki@northeastcollege.edu

  • Location: ACA 3 104

CRANIAL NERVE I: OLFACTORY

  • Origin and Pathway:

    • Cells located in the olfactory mucosa of the upper nasal cavity.

    • Nerve fibers cross the cribriform plate to terminate in the olfactory bulb.

    • Projects to the primary olfactory cortex (piriform cortex, amygdala, and entorhinal cortex) through lateral olfactory stria.

    • Medial olfactory stria projects fibers to the contralateral olfactory bulb via the anterior commissure.

  • Key Characteristics:

    • Only sense that reaches the cortex directly, bypassing the thalamus.

  • Examination:

    • Odorants applied to each nostril with eyes closed.

  • Leisons/Issues:

    • Anosmia (loss of smell).

CRANIAL NERVE II: OPTIC

  • Origin and Pathway:

    • Originates from ganglion cells of the retina.

    • Fibers partially cross in the optic chiasma, then synapse in the lateral geniculate body.

    • Some fibers proceed in the optic tract to form the superior brachium for light reflexes to the superior colliculus.

    • From lateral geniculate nucleus, fibers travel to primary visual cortex via optic radiation.

  • Function:

    • Vision

  • Examination:

    • Visual acuity, visual field mapping, visual reflexes.

  • Lesion/Issues:

    • Anopsia (visual field loss).

  • Exit:

    • Skull via the optic canal.

CRANIAL NERVE III: OCULOMOTOR

  • Origin:

    • Oculomotor nucleus (motor)

    • Edinger-Westphal nucleus (parasympathetic)

  • Level of Nuclei:

    • Midbrain at the superior colliculus, anterior periaqueductal gray.

  • Exit:

    • Interpeduncular fossa.

  • Function:

    • Motor: Extraocular muscles (superior, medial, inferior rectus, inferior oblique, levator palpebrae superioris)

    • Parasympathetic: pupillary constriction and lens accommodation.

  • Examination:

    • Light and accommodation reflexes, vertical and medial eye movements, eyelid movement.

  • Lesion/Issues:

    • Diplopia, ptosis, lateral strabismus, mydriasis, cycloplegia.

  • Exit:

    • Skull via the superior orbital fissure.

CRANIAL NERVE IV: TROCHLEAR

  • Origin:

    • Trochlear nucleus.

  • Level:

    • Midbrain at the inferior colliculus, anterior periaqueductal gray.

  • Exit:

    • Nerves decussate in superior medullary velum, exit inferior to inferior colliculi.

  • Function:

    • Extraocular movements (superior oblique muscle).

  • Examination:

    • Downward and inward eye movements.

  • Lesion/Issues:

    • Diplopia when looking down and in, head tilt to the opposite side.

  • Exit:

    • Skull via the superior orbital fissure.

CRANIAL NERVE V: TRIGEMINAL

  • Origin/Level:

      1. Nucleus of the spinal tract (pain and temperature) / Midpons - C5

      1. Chief sensory nucleus (touch) / Midpons

      1. Mesencephalic nucleus (proprioception) / Midpons-midbrain

      1. Motor nucleus (muscles of mastication) / Midpons.

  • Exit:

    • Midpons.

  • Peripheral Branches:

    • V1 (ophthalmic - sensory, exits via SOF)

    • V2 (maxillary - sensory, exits via foramen rotundum)

    • V3 (mandibular - mixed, exits via foramen ovale).

  • Function:

    • Sensory: Face, scalp, teeth, tongue, oral/nasal mucosa, dura mater.

    • Motor: Muscles of mastication and ear muscles.

  • Examination:

    • Touch, pain, temperature, corneal reflex, jaw reflex.

  • Lesion/Issues:

    • Trigeminal neuralgia, facial anesthesia, difficulty biting down.

CNVII: FACIAL

  • Origin/Level:

    • Facial nucleus (motor) in lower pons

    • Nucleus of solitary tract (taste and parasympathetic)

    • Superior salivatory nucleus (parasympathetic).

  • Exit:

    • Cerebellopontine angle.

  • Peripheral Branches:

    • Temporal, zygomatic, buccal, marginal mandibular, cervical.

  • Function:

    • Motor: Facial expression muscles, auricular muscles, stapedius, digastric muscle.

    • Taste: Anterior 2/3 of the tongue (via chorda tympani), parasympathetic to salivary glands.

  • Examination:

    • Facial movements and taste.

  • Lesion/Issues:

    • Bell's palsy (facial paralysis), inability to wrinkle forehead/make facial expressions.

  • Exit:

    • Skull via the stylomastoid foramen.

CNVIII: VESTIBULOCOCHLEAR

  • Origin:

    • a. Vestibular nuclei

    • b. Cochlear nuclei

  • Level:

    • a. Lateral aspect of 4th ventricle

    • b. Acoustic tubercle

  • Exit:

    • Cerebellopontine angle.

  • Function:

    • Balance and equilibrium, hearing.

  • Examination:

    • Caloric test, Weber and Rinne tests, audiogram.

  • Lesion/Issues:

    • Vertigo, nystagmus, hearing loss.

CNIX: GLOSSOPHARYNGEAL

  • Origin/Level:

    • Nucleus of solitary tract, nucleus ambiguus, inferior salivatory nucleus (medulla).

  • Exit:

    • Post-olivary sulcus, medulla.

  • Function:

    • Motor to stylopharyngeus muscle.

    • Taste from posterior 1/3 of the tongue.

    • Sensory to middle ear, tonsils, nasopharynx, uvula.

    • Parasympathetic to parotid gland.

  • Examination:

    • Taste and sensation of posterior 1/3, sensory part of gag reflex.

  • Lesion/Issues:

    • Pain, loss of sensation, absent gag reflex.

CN X: VAGUS

  • Origin/Level:

    • Dorsal motor nucleus (parasympathetic), nucleus ambiguus (motor).

  • Exit:

    • Post-olivary sulcus.

  • Function:

    • Parasympathetic to thorax and abdomen.

    • Motor to pharyngeal constrictors and intrinsic laryngeal muscles.

    • Taste from larynx and epiglottis.

  • Examination:

    • Gag reflex, swallowing function.

  • Lesion/Issues:

    • Hoarseness, dysphagia, uvular deviation.

CN XI: ACCESSORY

  • Origin/Level:

    • Nucleus ambiguus, cervical segments.

  • Exit:

    • Post-olivary sulcus.

  • Branches:

    • Cranial (joins vagus) and spinal roots (motor to sternocleidomastoid and trapezius).

  • Lesion/Issues:

    • Inability to rotate head, shrug shoulders.

CN XII: HYPOGLOSSAL

  • Origin:

    • Hypoglossal nucleus.

  • Level:

    • Medulla.

  • Exit:

    • Pre-olivary sulcus.

  • Function:

    • Motor to all tongue muscles (except palatoglossus).

  • Lesion/Issues:

    • Ipsilateral tongue paralysis, atrophy.

  • Exit:

    • Skull via the hypoglossal canal.

Additional Notes

  • Supranuclear (upper motor neuron) symptoms of cranial nerves are rare (except facial nerve) due to bilateral innervation from the corticobulbar tract.