Examination of Cranial Nerves.pptx Anatomy

Neuroanatomy

1. The University of Zambia School of Medicine Department of Human Anatomy CLINICAL NEUROANATOMY Examination of Cranial Nerves Dr. Mutale 9/29/2020 1

2. The 12 Cranial Nerves (CNs) CN I = Olfactory nerve CN II = Optic nerve CN III = Oculomotor nerve CN IV = Trochlear nerve CN V = Trigeminal nerve CN V1 = Ophthalmic nerve CN V2 = Maxillary nerve CN V3 = Mandibular nerve CN VI = Abducent nerve CN VII = Facial nerve CN VIII = Vestibulocochlear nerve CN IX = Glossopharyngeal nerve CN X = Vagus nerve CN XI = Accessory nerve CN XII = Hypoglossal nerve 9/29/2020 2

3. Functional Columns of Brainstem Sensory and Motor Cranial Nerve Nuclei 9/29/2020 3

4. Nuclei of the CNs: CN I and II: Forebrain CNs III and IV: Midbrain CNs V, VI, VII and VIII: Pons CNs IX, X, XI, and XII: Medulla oblongata (last 4 cranial nerves) Of the 12 CNs, 4 are dedicated to the eye : CNs II, III, IV and VI The ophthalmic division of the Trigeminal nerve (CN V1) is sensory to the eye 9/29/2020 4

5. Mnemonic for Cranial Nerves OL d OP en OC eans TRO uble TRI besmen AB out F ish VE nom G iving VA rious Ac ute H eadaches“: OL = OLFACTORY NERVE OP = OPTIC NERVE OC = OCULOMOTOR NERVE TRO = TROCHLEAR NERVE TRI = TRIGEMINAL NERVE AB = ABDUCENT NERVE F = FACIAL NERVE VE = VESTIBULOCOCHLEAR NERVE G = GLOSOPHARYNGEAL NERVE VA = VAGUS NERVE AC =ACCESSORY NERVE H = HYPOGLOSSAL NERVE 9/29/2020 5

6. The Olfactory Nerve (CN I) Function: Sense of smell Central processes of bipolar sensory cells in olfactory epithelium Pass up through cribriform plate to 2 nd olfactory neurons in olfactory bulb In turn project to olfactory centres in the uncus and parahippocampal gyrus 9/29/2020 6

7. Testing CN I Testing Smell Use common bedside substances such as soap, fruit or scent Present these to each nostril separately and ask patient to name them Anosmia maybe present in subfrontal meningioma or following head injury or craniotomy Always exclude local disease in nose itself, such as catarrh 9/29/2020 7

8. Optic Nerve (CN II) - Visual Pathways 9/29/2020 8

9. The Visual Pathways A lesion at the following points (refer from previous slide) produces: 1: blindness in the right eye with loss of the direct light reflex 2: bitemporal hemianopia 3a and 3b: binasal hemianopia (a rare disorder) 4: produces right homonymous hemianopia with macular involvement 5: right homonymous hemianopia with sparing of the macular field 6: right homonymous central (macular) hemiscotoma 9/29/2020 9

10. Testing for Vision Visual acuity Visual fields Colour vision Fundoscopy 9/29/2020 10

11. Testing for Vision Visual acuity To be tested while correcting any refractive error by using appropriate glasses or a pinhole Involves a Snellen chart held 6 m (20 ft in the USA) from the patient, examining each eye in turn Test for each eye separately (by covering one eye at a time) Acuity better than 6/60 is dependent on central (macular) vision Lower levels of acuity may be tested by counting fingers held in front of the eye, or by perceiving a pen light switching on and off 9/29/2020 11

12. Snellen Eye Chart 20/10 What condition does this person have? What condition does this person have? 9/29/2020 12

13. Testing for Vision Visual fields Visual field is the whole extent of the field of vision in each eye It is limited by the size of the retina and by the margins of the orbit, nose and cheek There are different ways to test visual fields at the bedside, depending on what is being looked for: Moving finger test (most commonly used on the ward) Red pin confrontation test Binocular testing (for visual extinction) 9/29/2020 13

14. Visual fields Moving finger test Test visual fields for each eye by asking the patient to fixate straight ahead and to report when a finger can be seen moving in each quadrant (upper temporal, lower temporal, upper nasal and lower nasal quadrants ) Alternatively, ask the patient to report how many fingers are being shown in each quadrant 9/29/2020 14

15. Red pin confrontation test Uses a large red hatpin (head 0.5cm in diameter) held equidistant between yourself and the patient Patient covers the eye not to be tested while you face them about 1.5m away and cover your own eye Determine the field limit by checking whether you and the patient see the pin at the same time This test is accurate in detecting paracentral scotomas 9/29/2020 15

16. Visual fields Visual extinction Test for visual extinction on  double simultaneous stimulation  by asking patients how many fingers they see when fingers are presented to both sides at the same time In visual extinction, a form of hemineglect , patients do not report seeing the fingers on the affected (usually left) side of the visual field, although they can see fingers when they are presented to that side alone 9/29/2020 16

17. Colour Vision Tested using coloured plates Plates have patterns of coloured spots Some form numbers and others a random background Colour vision is mainly confined to the macular field Acquired abnormalities in colour vision are thus a sensitive test for optic neuritis and certain retinal diseases 9/29/2020 17

18. Red-Green Color Blind Test 9/29/2020 18

19. Fundoscopy Neurological examination focuses on: Papilloedema Optic atrophy Pigmentary retinal degeneration Vascular disease 9/29/2020 19

20. CN III, IV, VI (Extra-ocular Movements and Pupils) External ocular movements (EOMs) and pupils are controlled by the paired oculomotor, trochlear and abducens nerves These arise from nuclei in the brainstem and function as a physiological unit They are interconnected by the medial longitudinal fasciculus (MLF) 9/29/2020 20

21. Oculomotor Nerve (CN III) 9/29/2020 21

22. Oculomotor Nerve (CN III) 9/29/2020 22

23. Examination of EOMs Check by having the patient look in all directions without moving their head While doing this, ask them if they experience any double vision Ask the patient to follow a finger held about 1 m away Move the finger slowly in a large 'H' pattern Ask patient if double vision is noted at any point Patient keeps both eyes open 9/29/2020 23

24. Extra-ocular Muscles 9/29/2020 24

25. Actions of the Extrinsic Muscles of Eye 9/29/2020 25

26. Actions of the Extrinsic Muscles of Eye 9/29/2020 26

27. Extra-ocular Movements (CN III, IV, VI) Other things to test for EOMs: Smooth pursuit: test by having the patient follow an object moved across their full range of horizontal and vertical eye movements Convergence movements: test by having the patient fixate on an object as it is moved slowly toward a point right between the patient’s eyes Spontaneous nystagmus Dysconjugate gaze (eyes not both fixated on the same point),resulting in  diplopia  (double vision) In comatose or severely lethargic patients, eye movements can also be evaluated with oculocephalic  or  caloric testing 9/29/2020 27

28. Oculocephalic reflex Hold the eyes open and rotate the head from side to side or up and down These maneuvers obviously should not be performed in cases of head or neck injury until possible cervical spinal trauma has been ruled out by appropriate radiological studies Presence of the oculocephalic reflex is sometimes called  doll’s eyes , since the eyes move in the direction opposite to head movements 9/29/2020 28

29. Oculocephalic reflex Note that in awake patients, doll’s eyes are usually not present This is because visual fixation and voluntary eye movements mask the reflex Thus, the absence of doll’s eyes suggests brainstem dysfunction in the comatose patient but can be normal in the awake patient 9/29/2020 29

30. Caloric stimulation Another, more potent stimulus of the vestibulo -ocular reflex is  caloric stimulation Always examine the external auditory canal first with an otoscope Then, with the patient lying in the supine position and the head elevated at 30°, infuse ice water into one ear If the brainstem vestibulo -ocular reflex pathways are intact, this will produce nystagmus ,  with the fast phase directed opposite to the side of the cold water infusion 9/29/2020 30

31. Caloric stimulation A useful mnemonic for interpreting the results of this test is COWS  ( C old  O pposite,  W arm  S ame) It is important to note, however, that in comatose patients the fast phase is often absent, and all that is then observed is slow, tonic deviation of the eyes toward  the cold water After waiting 5 to 10 minutes for equilibration, try the second ear to drive the eyes in the opposite direction 9/29/2020 31

32. Pupillary Responses (CN II and CN III) First, record the pupil size and shape at rest Next, test for: Direct response , meaning constriction of the illuminated pupil Consensual response , meaning constriction of the opposite pupil Accommodation  (also called the  near response): pupils constrict while fixating on an object being moved toward the eyes. Is basically the response to looking at something moving toward the eye 9/29/2020 32

33. Pupillary Responses (CN II and CN III) In an  afferent pupillary defect  there is a decreased direct response caused by decreased visual function (CN II) in one eye However, there is spared pupillary constriction (CN III) when elicited through the consensual response Can be demonstrated with the  swinging flashlight test , in which the light is moved back and forth between the eyes every 2 to 3 seconds 9/29/2020 33

34. Pupillary Responses (CN II and CN III) The afferent pupillary defect becomes obvious when the flashlight is moved from the normal to the affected eye and the affected pupil  dilates  instead of constricting in response to light Brief oscillations of pupillary size called  hippus  occur normally in response to light and should not be confused with an afferent pupillary defect 9/29/2020 34

35. The Trigeminal Nerve (CN V) SENSORY FUNCTION Somatosensory afferents from the skin and the facial muscles enter trigeminal ( gasserian ) ganglion via three branches: Ophthalmic division Maxillary division Mandibular division 9/29/2020 35

36. Trigeminal Nerve (CN V) 9/29/2020 36

37. Trigeminal Dermatomal Distribution 9/29/2020 37

38. Examining Facial Sensation Loss of sensation in the face is best tested using a pin Test within each of the three divisions separately Check for symmetry of perceived pinprick intensity between the two sides Testing for light touch is less discriminatory If there is reduced sensation, delineate its extent by testing from a normal to an abnormal area 9/29/2020 38

39. Testing Facial sensation 9/29/2020 39

40. Corneal reflexes Should be tested by touching - not rubbing A wisp of cotton wool on the corneal surface at its margin with the conjunctiva There should be a brisk bilateral blink response The reflex should be interpreted together with facial nerve function, as the latter carries the efferent arc of the reflex 9/29/2020 40

41. The Trigeminal Nerve (CN V) MOTOR FUNCTION Motor root of the trigeminal nerve originates from a small nucleus medial to the main sensory nucleus Emerges just anterior to the sensory division, and joins the mandibular division of the sensory 5 th nerve 9/29/2020 41

42. Examining Motor Function of CN V Ask the patient to clench their teeth Palpate both masseter muscles above the angles of the jaw Palpate both temporalis muscles over the temples Test the pterygoid muscles by forceful opening of the jaw against resistance Unilateral lateral pterygoid weakness deviates the jaw to the ipsilateral side as it opens 9/29/2020 42

43. Examining Motor Function of CN V Jaw jerk reflex: Is a 5 th -nerve stretch reflex Place your finger on the chin below the lower lip Tap it lightly with a tendon hammer while the patient maintains the jaw half open and relaxed Reflex is increased in corticobulbar tract (upper motor neuron (UMN) disease 9/29/2020 43

44. Facial Nerve (CN VII) 9/29/2020 44

45. Axial Section of the Mid-to-Lower Pons, Showing the Facial Colliculus 9/29/2020 45

46. Examination of Facial Nerve Look for facial asymmetry and for abnormal involuntary facial movements Watch the patient smile, bare their teeth, and attempt to whistle Test the following: 1. Frontalis Ask the patient to raise their eyebrows while you look for asymmetry of the forehead skin creases 9/29/2020 46

47. Examination of Facial Nerve 2. Orbicularis oculi : Ask the patient to screw their eyes shut while you try to prevent this with your finger and thumb In severe weakness the eye may not close at all A preserved Bell's phenomenon causing elevation of the eye during attempted closure indicates that the patient is trying hard 3. Orbicularis oris Ask the patient to purse the lips shut and stop you from opening them 9/29/2020 47

48. Testing Facial Muscles 9/29/2020 48

49. UMN versus LMN Facial Weakness 9/29/2020 49

50. Facial muscle weakness Can be caused by lesions of: Upper motor neurons (UMNs) in the contralateral motor cortex or descending CNS pathways Lower motor neurons (LMNs) in the ipsilateral facial nerve nucleus (CN VII) or exiting nerve fibers , the neuromuscular junction, or the face muscles 9/29/2020 50

51. Facial muscle weakness Note that the UMNs for the  upper face  (the upper portions of the orbicularis oculi and the frontalis muscles of the forehead) project to the facial nuclei bilaterally Therefore, UMNs  such as in stroke cause contralateral face weakness , sparing the forehead LMNs  such as in facial nerve injury typically cause weakness involving the whole ipsilateral face 9/29/2020 51

52. Central Taste Pathways 9/29/2020 52

53. Assessment of Taste Test the sense of taste using strong solutions of sugar and common salt, and weak solutions of citric acid and quinine, as tests of ' sweet ', ' salt ', ' sour ' and ' bitter ' respectively Apply these solutions to the surface of the protruded tongue with a small swab on a spatula The patient should be asked to indicate perception of the taste before the tongue is withdrawn in order to decide whether taste is disturbed anteriorly or posteriorly 9/29/2020 53

54. Assessment of Taste Unilateral deficits in taste can occur in lesions of the lateral medulla involving the nucleus solitarius or in lesions of the facial nerve 9/29/2020 54

55. Salty- metallic ions Sweet- sugar Sour- H + Bitter- alkaloid Five Basic Tastes Umami- savory/meaty 9/29/2020 55

56. Assessment of Taste After each test the mouth must be rinsed The bitter quinine test should be applied last, as its effect is more lasting than that of the others Positive taste symptoms, e.g. taste hallucinations, may constitute the aura of temporal lobe epilepsy The chorda tympani supplies taste to the anterior two-thirds of the tongue 9/29/2020 56

57. Nerve Supply of the Tongue 9/29/2020 57

58. Vestibulocochlear Nerve (CN VIII) 9/29/2020 58

59. Vestibulocochlear Nerve (CN VIII) 9/29/2020 59

60. Orientation of Semicircular Canals 9/29/2020 60

61. Examination of CN VIII Examine one ear at a time Close one ear and whisper a word or number Ask patient to repeat what you said 9/29/2020 61

62. Other Tests for CN VIII A. Tuning folk tests used to distinguish conductive deafness and sensorineural deafness : Rinne’s test Weber’s test Schwabach’s test B. Oculocephalic test C. Positional vertigo test 9/29/2020 62

63. Common Tuning Folk Tests 9/29/2020 63

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65. Positional Vertigo Test 9/29/2020 65

66. Examination of CN IX and CN X The glossopharyngeal nerve is rarely damaged alone Examination of CN IX is usually examined together with CN X This is done by asking the patient to open the mouth and say ' aah ‘ Use a tongue depressor to obtain a good view of the soft palate and uvula Unilateral paralysis results in elevation only of the normal side and deviation of the uvula towards the normal side 9/29/2020 66

67. Gag reflex (CN IX and X) Test by touching the posterior pharynx on each side with a cotton swab In intubated patients the endotracheal tube can be shaken slightly to elicit a gag reflex It is also helpful to ask personnel who were present at the time of intubation whether a gag reflex was observed or whether a gag or cough reflex occurs during suctioning of the tracheal passages 9/29/2020 67

68. Glossopharyngeal Nerve (CN IX) 9/29/2020 68

69. Vagus (CN X) 9/29/2020 69

70. Examination of CN XI Sternomastoid : Ask the patient to turn the head while you resist with a hand on the side of the face Note contraction of the activated sternomastoid muscle on the side opposite to the direction of movement Upper trapezius muscle fibres : Ask the patient to shrug their shoulders while you press downward on them Shrug may be weak on the affected side 9/29/2020 70

71. Examination of CN XII CN XII is a purely motor nerve to tongue musculature 9/29/2020 71

72. Tongue Musculature 9/29/2020 72

73. Examination of CN XII Note any of the following when tongue is at rest on its floor in the mouth: Atrophy Fasciculations (spontaneous, quivering movements) Tremors Ask the patient to stick their tongue straight out and note: Whether it curves to one side or the other Tremors Ask the patient to move their tongue from side-to-side and to push it forcefully against the inside of each cheek 9/29/2020 73

74. Examination of CN XII What Is Being Tested?   Fasciculations and atrophy are signs of LMN lesions Tremor of the tongue, either at rest or when protruded, is common in Parkinson's disease Bilateral fasciculation of the tongue is almost pathognomonic of motor neuron disease (amyotrophic lateral sclerosis) 9/29/2020 74

75. Examination of CN XII What Is Being Tested? Unilateral tongue weakness causes the tongue to deviate toward the weak side Tongue weakness can result from lesions of the tongue muscles, the neuromuscular junction, the lower motor neurons of the hypoglossal nerve (CN XII), or the upper motor neurons originating in the motor cortex Lesions of the motor cortex cause contralateral tongue weakness 9/29/2020 75

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77. The End! 9/29/2020 77