Cranial Nerves

Pundit Asavaritikrai, PhD, MD.Department of Anatomy, Faculty of Science

Mahidol Universityneuronum@yahoo.com

Overview

• Brain Stem– Ascend./Descend. P’w– Vital centres

• Consciousness• Respiration• CVS

– Cranial nerves

Cranial Nerves & Cranial Nerve Reflexes

• CN I• CN II• CN III, IV, & VI• CN V• CN VII,• CN VIII • CN IX & X• CN XI• CN XII

Memorize 2-3 sections/division

Midbrain

Pons

Open Medulla

Closed Medulla

CN I & II

• CN I & II– brain extension– not real nerves– Special sensory afferents

CN I Olfactory Nerve

• Olfaction• Memory and Behavior• Pheromones

• Anterior olfactory nucleus• Amydala• Piriform cortex• Enthorhinal cortex

CN II Optic Nerve

• Vision• Intraocular movement

(+ III)• Blinking (+ V & VII)• Circadian rhythm

The III, IV & VI

CN III Oculomotor Nerve

• Intraocular movement– Autonomic

• Lens shape• Pupil size

• Extrinsic Eye movement– Coordinate with CN IV & VI

Control of Pupil Size• Parasympathetic

• #1 = Edinger-Westphal nuc.

• #2 = ciliary ganglion

– pupillary constrictor– fibers travel in outer margi

n of CN III

Pupillary Light Reflex

• In: CN II– Pretectal area– Posterior Com.

• Out: CN III-EW nuc.

Relative Afferent Pupillary Defect (RAPD) (CN II CN III)

Adie’s Pupil

• Abnormally dilated pupil• Can be tonic, sectional,

vermiform iris• Abnormal postganglionic

parasympathetic fibers

Argyll-Robertson’s Pupil

• Associated with Syphillis– Normal pupil

accommodation– Does not constrict to light– Pretectal area damage

• Prostitute’s pupil = Accommodate but does not react

• Sympathetic• #1 = T1 lateral neurons• #2 = SCG

– Pup. dilator, tarsus m, sweat gl.

• Defects: Horner’s syndrome

(เล็�ก แห้�ง ตก ไม่ งอก)• Causes:

– pulmonary apex– lateral medulla (+vestibular defects; vertigo) =

Wallenberg syndrome

Sympathetic Control of Pupil

Ptosis

• Abnormal CN III– LPS– NMJ (Myasthenia)

• Sympathetic– Superior tarsal m.

• Does not involve CN VII (ปิ�ดไม่ สนิ�ท)

CN III, IV, & VI

CN III, IV, VI

• Function

• Coordination

• Control of coordination (conjugation)

MLF (medial longitudinal fasciculus)

• Internuclear connection• Nonvestibular pathways

(among CN nuclei)– VI-contralateral III– III-VII, VII-V, V-XII, XII-VII

• Vestibular pathways:– Eye– Ear– Neck– Limb extensors

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Disorders of the MLF

• Internuclear Ophthalmoplegia

CN III, IV, & VI:Coordination of Eye Movements

Coordination of Eye Movements

• Conjugate eye movement

• Dysconjugate eye movement (vergence)

Dysconjugate Eye Movement

• Vergence– ‘dysconjugate but still coordinate’– involving vergence center in the midbrain, no MLF

• Near triad (Accommodation)– Stimulus: Near object– Executor: cerebral cortex

SC

pretectal area• Ocular vergence (midbrain RF, both sides)• Lens rounding up (EW, both sides)• Pupil constriction (EW, both sides)

CN III, IV, & VI:Supranuclear Control of

Eye Movements

Supranuclear Control

Idea there must be some control above III, IV, VI (= supranuclear control)

• 1. Gaze– Saccades (quick)– Smooth persuit (slow)– Foveation

• 3. Vestibulo-ocular reflex• 4. Nystagmus

Dysconjugated Eye Movement

• No MLF

• Near vision– Accommodation– Pupil constriction– Vergence

Conjugate Eye Movements

• Yoking mechanism• Via MLF

E.g. CN VI contralat. CN III

• Clinical use:

e.g. Internuclear ophthalmoplegia

1. Smooth Persuit

• Conjugate movement that maintains foveation of a moving object

• Can be Voluntary or Involuntary

• Mechanisms– Stimuli = retinal slip– Processor = Area 19 & 39 (Angular gyrus)

– Executor = Area 8 ipsilateral CN VI

contralateral CN III

2. Reactive gaze(Saccadic eye movement)

• Rapid jerky involuntary conjugate movement

• (Faster than smooth persuit)• Stimuli = changing point of fixation, ligh

t, noise, noxious stimuli– Processor = Area 7 (parietal)– Executor = Area 8 & SC

contralat. PPRFparamedian pontine reticular

formation (pontine gaze centers)

PPRF excites CN VI LRe.g. Lt. Frontal eye field excites

contralateral CN VI

• Clinical use– eye movements towards the side of

lesion (ตาม่องฟ้�องล็�ชั่��นิ) p394

3. Vestibulo-Ocular Reflex (VOR)

• Conjugate movement that maintains eye position while head moves

• ~ involuntary/reflexive smooth persuit– Stimuli = warm water, head turning to that side– Processor & Executor = vestibular nuc.

inhibit ipsilateral CN VIinhibit MLF contralateral CN III

3. Vestibulo-Ocular Reflex (VOR)• Ex. Stimulation of Rt. Vest. Nuc.

inhibit Rt. CN VI & LR eyes deviate to left

• Ex. Inhibition of Rt. Vest. Nuc by:– cold water in the Rt.– turning head to the Lt.– lesion of Rt. vestibular input

Rt LR turns the eye to the Rt

• Clinical use:– Doll’s eye reflex

Vestibulo-ocular Reflex

• Contralateral CN VI n.

• From CN VI n ipsi. CN III n

Nystagmus

• Vestibular

• Optokinetic

Vestibular Nystagmus• Relationship between

– smooth persuit (slow phase), and– saccadic eye movement (fast phase)

‘E.g. Right nystagmus refers to the fast phase ofsaccadic eye movement to the right’

• Types:– Physiologic nystagmus:

• Optokinetic nystagmus• Vestibular nystagmus• Cold caloric testing*

slow eye (VOR) will move the eyes to the side of cold waterSaccades will move the eyes to opposite side of cold water(COWS)

– Pathologic nystagmus:• Nystagmus at rest• Positional nystagmus• Vertical nystagmus• Pendular nystagmus

Nystagmus

• VOR occurs– in slow phase

• Fast phase– is mediated by– Superior collic.

p398

Doll’s eye phenomenon & Caloric test

The CN V

• Facial sensation• Mastication• Jaw jerk reflex

CN V: Sensory Distribution

Jaw Jerk Reflex• In: CN V3 (s)

• Mesencephalic Nc

• Out: CN V3 (m)• Bilat.

• Motor nuc. Of V

CN VII Facial Nerve

•GSA•SSA•SSE*•GVE

Cranial Nerve Motor Nuclei = A group of Lower Motor Neurons (LMN)

Taste: Gustation

UMN lesion of Facial Nerve

• Upper Face: – Dual innervation

• Lower Face:– Contralateral Innervation

• *UMN lesion of CN VII– Contralateral paralysis of

(only) the lower face

Corneal Blink Reflex

CN VIII Vestibulo-Cochlear Nerve

CN VII, IX, X

Mixed

Efferents:

• SVE:– CN VII motor nuclei: Face

• Bilat. & Contralat. Ctc. Innerv.• Defects: facial palsy

– Ambiguus nuclei (IX & X): Pharynx & Larynx

• Bilateral cortical innervation• Defects: dysphagia

• GVE:– Sup. & Inf. Salivatory nucleus– Dorsal motor nucleus of X

CN VII, IX, X

Afferents:• GSA: pharynx/ear• SVA: taste

– Solitary nucleus & tract (VII, IX, X)

• GVA: pressure receptor, thoracic, abdomen

– Medullar reticular formation• IX baroreceptors (carotid a.)• X baroreceptors (LV, aortic arch)

CN IX Glossopharyngeal Nerve

CN X Vagal Nerve & XI Spinal Accessory Nerve

Gag Reflex

CN XI, XII

CN XII Hypoglossal Nerve

References

• Nadeau SE, et al, Medical Neuroscience 1st Ed., 2004: pp 358-418 (Cycle 8), Saunders.

• Haines DE, et al, Fundamental Neuroscience for Basic and Clinical Application, 3rd Ed., 2006: pp 209-228 Elsevier.

Fathers of Neuroscience

Camillo Golgi

(1843-1926)Santiago Ramon y Cajal

(1852-1934)

Father of Neurosurgery & Father of Neurology

Harvey Williams Cushing (1869-1939)

Jean-Martin Charcot

(1825-1893)

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Pierre Janet, William James, Pierre Marie, Albert Londe, Sigmund Freud,

Charles-Joseph Bouchard, Axel Munthe, and Alfred Binet