Cranial Nerves

1. Cranial Nerves Pundit Asavaritikrai, PhD, MD. Department of Anatomy, Faculty of Science Mahidol University neuronum@yahoo.com

2. Overview • Brain Stem • Ascend./Descend. P’w • Vital centres • Consciousness • Respiration • CVS • Cranial nerves

3. 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

5. Memorize 2-3 sections/division

6. Midbrain

8. Pons

9. Open Medulla

10. Closed Medulla

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

13. CN I Olfactory Nerve • Olfaction • Memory and Behavior • Pheromones • Anterior olfactory nucleus • Amydala • Piriform cortex • Enthorhinal cortex

14. CN II Optic Nerve • Vision • Intraocular movement (+ III) • Blinking (+ V & VII) • Circadian rhythm

15. The III, IV & VI

16. CN III Oculomotor Nerve • Intraocular movement • Autonomic • Lens shape • Pupil size • Extrinsic Eye movement • Coordinate with CN IV & VI

17. Control of Pupil Size • Parasympathetic • #1 = Edinger-Westphal nuc. • #2 = ciliary ganglion • pupillary constrictor • fibers travel in outer margin of CN III

18. Pupillary Light Reflex • In: CN II • Pretectal area • Posterior Com. • Out: CN III-EW nuc.

19. Relative Afferent Pupillary Defect (RAPD) (CN II  CN III)

20. Adie’s Pupil • Abnormally dilated pupil • Can be tonic, sectional, vermiform iris • Abnormal postganglionic parasympathetic fibers

21. 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

22. Sympathetic Control of Pupil • Sympathetic • #1 = T1 lateral neurons • #2 = SCG • Pup. dilator, tarsus m, sweat gl. • Defects: Horner’s syndrome (เล็ก แห้ง ตก ไม่งอก) • Causes: • pulmonary apex • lateral medulla (+vestibular defects; vertigo) = Wallenberg syndrome

23. Ptosis • Abnormal CN III • LPS • NMJ (Myasthenia) • Sympathetic • Superior tarsal m. • Does not involve CN VII (ปิดไม่สนิท)

24. CN III, IV, & VI

25. CN III, IV, VI • Function • Coordination • Control of coordination (conjugation)

26. 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 p389

27. Disorders of the MLF • Internuclear Ophthalmoplegia

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

29. Coordination of Eye Movements • Conjugate eye movement • Dysconjugate eye movement (vergence)

30. 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)

31. CN III, IV, & VI:Supranuclear Control of Eye Movements

32. 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

33. Dysconjugated Eye Movement • No MLF • Near vision • Accommodation • Pupil constriction • Vergence

34. Conjugate Eye Movements • Yoking mechanism • Via MLF E.g. CN VI  contralat. CN III • Clinical use: e.g. Internuclear ophthalmoplegia

35. 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

36. 2. Reactive gaze(Saccadic eye movement) • Rapid jerky involuntary conjugate movement • (Faster than smooth persuit) • Stimuli = changing point of fixation, light, noise, noxious stimuli • Processor = Area 7 (parietal) • Executor = Area 8 & SC  contralat.PPRF paramedian pontine reticular formation (pontine gaze centers)  PPRF excites CN VI  LR e.g. Lt. Frontal eye field excites contralateral CN VI • Clinical use • eye movements towards the side of lesion (ตามองฟ้องลีชั่น) p394

37. 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 VI • inhibit MLF contralateral CN III

38. 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

39. Vestibulo-ocular Reflex • Contralateral CN VI n. • From CN VI n •  ipsi. CN III n

40. Nystagmus • Vestibular • Optokinetic

41. Vestibular Nystagmus • Relationship between • smooth persuit (slow phase),and • saccadic eye movement (fast phase) ‘E.g. Right nystagmus refers to the fast phase of saccadic eye movement to the right’ • Types: • Physiologicnystagmus: • Optokinetic nystagmus • Vestibular nystagmus • Cold caloric testing*  slow eye (VOR) will move the eyes to the side of cold water • Saccades will move the eyes to opposite side of cold water (COWS) • Pathologic nystagmus: • Nystagmus at rest • Positional nystagmus • Vertical nystagmus • Pendular nystagmus

42. Nystagmus • VOR occurs • in slow phase • Fast phase • is mediated by • Superior collic.

43. p398

44. Doll’s eye phenomenon & Caloric test

45. The CN V • Facial sensation • Mastication • Jaw jerk reflex

46. CN V: Sensory Distribution

47. Jaw Jerk Reflex In: CN V3 (s) Mesencephalic Nc Out: CN V3 (m) Bilat. Motor nuc. Of V

48. CN VII Facial Nerve • GSA • SSA • SSE* • GVE

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

50. Taste: Gustation