Functional neuroanatomy of the neurological examination: Cranial nerves

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Functional neuroanatomy of the neurological examination: Cranial nerves Chris Thomson BVSc(Hons), Dip ACVIM (Neurol), Dip ECVN, PhD Associate Professor

1 Functional neuroanatomy of the neurological examination: Cranial nerves Chris Thomson BVSc(Hons), Dip ACVIM (Neurol), Dip ECVN, PhD Associate Professor Neurobiology, Dept. of Vet. Med., University of Alaska, Fairbanks, Alaska. Ref: Parry and Volk: Imaging the cranial nerves. Vet Radiol & US, 2011, 52, 1, Suppl 1, pp S32-S41 1

General principles Sensory, motor, or mixed Parasympathetic CNN III, VII, IX, X Sensory (afferent) connections Reflex function Sensory nucleus trigeminal sensory complex Sensory perception

2 General principles Sensory, motor, or mixed Parasympathetic CNN III, VII, IX, X Sensory (afferent) connections Reflex function Sensory nucleus trigeminal sensory complex Sensory perception somatosensory cortex, cerebellum Motor LMN somatic or visceral (autonomic) Nuclear arrangement in brainstem Ξ to fragmented spinal cord columns Only one CN that is pure CNS Attachment mainly ventral/ventrolateral except??? Which cranial nerve is affected? 2

3 Fig 1.7 Thomson and Hahn Fig 10.2 Thomson and Hahn, Functional CNN nuclear columns in the brainstem 3

4 Fig 10.1 Thomson and Hahn 4 Dog brain, ventral aspect, cranial nerves

5 Cranial nerves, attachment and main functions Cranial nerve Brain attachment Function I Olfactory Telencephalon Olfaction II Optic Diencephalon Vision sensory, parasympathetic, motor III Oculomotor Mesencephalon Pupil constriction, extraocular muscles (which ones?) IV Trochlear Mesencephalon Extraocular muscles (which ones?) V Trigeminal Pons/myelencephalon Facial sensation, masticatory muscles (which ones?) VI Abducens Myelencephalon Extraocular muscles VII Facial Pons/myelencephalon Taste, GVA head, salivary, lacrimal glands, Muscles of facial expression Masticatory muscle (which one?) VIII Vestibulocochlear Pons/myelencephalon Hearing, balance IX Glossopharyngeal Myelencephalon Taste, salivary glands, Swallowing, X Vagus Myelencephalon Taste, parasympathetic to body viscera swallowing, laryngeal, XI Accessory Myelencephalon Laryngeal function, neck muscles XII Hypoglossal Myelencephalon Tongue muscles 5

6 To move both eyes to the right requires stimulation of 6

7 Vision CN II Optic nerve Visible CNS Optic chiasm Fig 10.5 Thomson and Hahn, Variable degree of cross over Herbivores 80-90% Cats 65% Inversely related to stereoscopic vision The more overlap of the visual fields, the less decussation at the optic chiasm Optic pathway and binocular vision 7

8 Vision Pathway (cat) 80% fibres -> Lateral geniculate nucleus -> Optic radiation -> Visual cortex 20% fibres to the midbrain Visual reflexes e.g. PLR and head / eye turning Cerebral cortex midbrain connections Required for Perception of movement Spatial orientation 8

9 Visual Reflexes Rostral colliculus Tectonuclear (bulbar) extraocular muscles Tectospinal cervical muscles Function??? Fig 10.9 Thomson and Hahn, Optic pathway and its connections 9

10 Pupillary light reflex Consensual reflex strength inversely proportional to degree of decussation at the optic chiasm - More decussation, the stronger direct PLR e.g. cat versus horse Swinging light test Fig 10.8 Thomson and Hahn, Pupillary light reflex pathway 10

11 Menace Response CN II, CN VII Menace deficit in cerebellar disease Mechanism? Pathway? visual cortex, cerebellum, facial nucleus Cerebellar influence on cortex permitting the response? Ipsilateral cerebellar and menace deficit Fig 13.8 Thomson and Hahn 11

12 The menace response appears in kittens / puppies by weeks of age 12

To the trigeminal sensory complex Mesencephalon Pons Myelencephalon Projects

13 Somatosensory input from head Fig 10.6 Thomson and Hahn, trigeminal sensory complex Afferents: CNN V, VII, IX, X To the trigeminal sensory complex Mesencephalon Pons Myelencephalon Projects to contralateral somatosensory cortex Fig 10.6 Thomson and Hahn, spinal cord, XS; What level? Substantia gelatinosa. 13

14 What cranial nerve is being assessed in these images?

microvilli Location Membranous labyrinth inner ear/petrous temporal bone

15 Fig 8.8 Thomson and Hahn Vestibular System Proprioceptors Hair cells with microvilli Location Membranous labyrinth inner ear/petrous temporal bone Function to maintain posture Head, neck, trunk, limbs, eyes During rest and motion Anti-gravity function Facilitate extensor muscle activity 15

16 Fig 8.1 Thomson and Hahn X 3 Dynamic equilibrium Static equilibrium 16

Hair cell function in head equilibrium (balance) Deflection of microvilli towards/away from kinocilium Stimulates sensory nerve endings of vestibular portion CN VIII Static head equilibrium Detection

17 Hair cell function in head equilibrium (balance) Deflection of microvilli towards/away from kinocilium Stimulates sensory nerve endings of vestibular portion CN VIII Static head equilibrium Detection by hair cells in sac structures Saccule sagittal/vertical plane Utriculus dorsal/horizontal planes Detect effect of gravity; constant tonic discharge Dynamic head equilibrium Angular acceleration/deceleration Detection by hair cells in semi-circular ducts Ducts in three planes: x, y, z Detect effect of acceleration in 3 planes 17

18 Fig 18.7 Uemura

19 Fig 8.2 Thomson and Hahn Effect of gravity or linear acceleration on macula of sacculus or utriculus Deflection of microvilli towards kinocilium depolarisation (stimulation) away from kinocilium hyperpolarisation (inhibition) Saccule sagittal/vertical plane Utriculus dorsal/horizontal plane 19

20 Fig 8.3 Thomson and Hahn, effect of acceleration on SCD Head rotation Causes endolymph flow in 1+ pairs of ducts Deflects cupula -> bending microvilli Stimulating or inhibiting sensory nerve ending Microvilli deflected Towards kinocilium stimulates nerve endings Away from kinocilium, inhibits neural discharge 20

21 What are the effects of vestibular nuclei stimulation? 21

22 Fig 8.5 Thomson and Hahn Vestibular nuclei connections To temporal lobe Fig 8.6 Thomson and Hahn 22

Consequences of peripheral vestibular apparatus input Vestibular portion of CNVIII Input to vestibular nuclei 4 pairs in myelencephalon Output to Spinal cord

23 Consequences of peripheral vestibular apparatus input Vestibular portion of CNVIII Input to vestibular nuclei 4 pairs in myelencephalon Output to Spinal cord postural adjustment Extraocular muscles eye movement and position Cerebellum head proprioception Forebrain conscious perception Reticular formation Including vomiting centre

24 Fig 8.9 Thomson and Hahn Effect of vestibular lesions; uneven stimulation of VN at rest, 24

25 What signs occur with abnormal vestibular function?

26 Distance penlight test: for subtle anisocoria and strabismus 26

27 Differentiating VD Depends on what other structures are compromised (collateral damage) not compromised Other structures Inner/middle ear peripheral VD Brainstem central VD Cerebellum paradoxical VD Fig 13.1 Thomson and Hahn 27

28 Paradoxical Vestibular Disease Fig 8.10 Thomson and Hahn Lesion in caudal cerebellar peduncle or flocculonodular lobe Loss of inhibitory output to vestibular nuclei; XS stimulation on side of the lesion 28

Paradoxical Vestibular Disease Signs Head tilt to opposite side from lesion Nystagmus to side of lesion Ipsilateral ataxia and proprioceptive deficits

29 Paradoxical Vestibular Disease Signs Head tilt to opposite side from lesion Nystagmus to side of lesion Ipsilateral ataxia and proprioceptive deficits Lesion location Vestibulocerebellum or caudal cerebellar peduncle (see de Lahunta and Glass for more detail) Mechanism Loss of inhibition of vestibular nuclei

30 Hearing CN VIII Fig Thomson and Hahn 30

31 SV CD Stria vascularis ST BM Mouse cochlea, Spiral ganglion 31

32 Tortora, Fig 17-22

CN V to tensor tympanii and CN VII to stapedius mm.

33 Hearing CN VIII Conscious hearing auditory cortex, temporal lobe Reflex function Muscles of the middle ear CN V to tensor tympanii and CN VII to stapedius mm. (t for trigeminal, s for seven) Muscle contraction affects compliance of tympanum (tympanometry) Caudal colliculus Head/eye turning in response to auditory stimuli Tectonuclear (bulbar) extraocular muscles Tectospinal cervical muscles What animal type? 33

dogs» melanocytes stria vascularis and hair cell degeneration Albinos OK Acquired damage to hair

34 Onset of hearing, deafness Onset of hearing Kittens 5 days Puppies 14 days Deafness normal by 4-5 weeks Conduction Otitis externa/media Sensorineural Congenital White coat blue eyes, some merle dogs» melanocytes stria vascularis and hair cell degeneration Albinos OK Acquired damage to hair cells» inflammation, neoplasia, ototoxicity

Fig 10.18 Thomson and Hahn Brainstem auditory evoked reflex Fig 10.

VIII II cochlear nuclei III dorsal nucleus of trapezoid body IV?

35 Fig Thomson and Hahn Brainstem auditory evoked reflex Fig Thomson and Hahn Auditory pathway in the brain I spiral ganglia, CN VIII II cochlear nuclei III dorsal nucleus of trapezoid body IV? (lateral lemniscus and nucleus) V caudal colliculus VI? (medial geniculate nucleus) 35 VII?

36 What else can BAER be used for? 36

37 A curious fact about CN VIII It s only an afferent nerve right? Olivocochlear reflex (superior olivary nucleus = nucleus of the trapezoid body) Protective hyperpolarisation of hair cells Discriminative neutralises background noise 37

38 Other CNN nuclei (VII, IX, X, XI) Fig 10.2 Thomson and Hahn Solitary tract and nucleus sensory input: taste, carotid sinus, thoracic and abdominal viscera Parasympathetic nucleus of VII and IX (Salivatory n.) efferent to salivary glands Parasympathetic nucleus of X Visceral efferent to thoracic and abdominal viscera 38 Nucleus ambiguus somatic efferent to larynx and pharynx

Fig 10-20 Thomson & Hahn Recurrent laryngeal nerve damage

39 Fig Thomson & Hahn Recurrent laryngeal nerve damage can cause paralysis of the muscle and failure of glottal opening

40 Fig Thomson and Hahn, Innervation of the pharynx and larynx Dyce, Figs 4-12 (2) and 4-14 (5) 40

41 Which cranial nerves innervate the following function of the tongue? Motor Sensory (touch) Taste Fig Thomson and Hahn, 41

42 Autonomic innervation of the head Parasympathetic (craniosacral origin) CNN III, VII, IX, X Functions? Sympathetic = (thoracolumbar origin) T1-3 (C8-T5) Not via CNN via sympathetic fibres from the cranial thorax Functions? 42

43 43

Cranial Nerves. Steven McLoon Department of Neuroscience University of Minnesota

Cranial Nerves. Steven McLoon Department of Neuroscience University of Minnesota Cranial Nerves Steven McLoon Department of Neuroscience University of Minnesota 1 Course News Change in Lab Sequence Week of Oct 2 Lab 5 Week of Oct 9 Lab 4 2 Sensory and Motor Systems Sensory Systems: