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 – 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 Which cranial nerve is affected? • except ???

2 Fig 1.7 Thomson and Hahn

Fig 10.2 Thomson and Hahn, Functional CNN nuclear columns in the brainstem 3 Fig 10.1 Thomson and Hahn 4 Dog brain, ventral aspect, cranial nerves Cranial nerves, attachment and main functions

Cranial nerve Brain attachment Function sensory, parasympathetic, motor I Olfactory Telencephalon Olfaction II Optic Diencephalon Vision 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 5 XII Hypoglossal Myelencephalon Tongue muscles To move both eyes to the right requires stimulation of …

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6 Vision – CN II

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

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

9 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, 10 Pupillary light reflex pathway 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 The menace response appears in kittens / puppies by ______weeks of age

12 Somatosensory input from head

Fig 10.6 Thomson and Hahn, trigeminal sensory complex Substantia Afferents: CNN V, VII, IX, X gelatinosa. To the trigeminal sensory complex • Mesencephalon • Pons • Myelencephalon 13 Projects to contralateral somatosensory cortex Fig 10.6 Thomson and Hahn, spinal cord, XS; What level? http://www.winslowvetmobile.com/

What cranial nerve is being assessed in these images? http://www.saltoftheearth. 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 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 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 Fig 18.7 Uemura 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)

19 Saccule – sagittal/vertical plane Utriculus – dorsal/horizontal plane 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 20 – Away from kinocilium, inhibits neural discharge What are the effects of vestibular nuclei stimulation?

21 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 – postural adjustment • Extraocular muscles – eye movement and position • Cerebellum – head proprioception • Forebrain – conscious perception • Reticular formation – Including vomiting centre Fig 8.9 Thomson and Hahn Effect of vestibular lesions; uneven stimulation of VN at rest, 24 What signs occur with abnormal vestibular function? Distance penlight test: for subtle anisocoria and strabismus

26 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 Paradoxical Vestibular Disease

Fig 8.10 Thomson and Hahn

• Lesion in caudal cerebellar peduncle or flocculonodular lobe • Loss of inhibitory output to vestibular nuclei; 28 • XS stimulation on side of the lesion 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 Hearing – CN VIII

30 Fig 10.15 Thomson and Hahn SV

CD Stria vascularis

BM

ST

Mouse cochlea, https://www.best.edu.au

Spiral ganglion

31 Tortora, Fig 17-22 http://vethospital.tamu.edu

Hearing – CN VIII

• Conscious hearing – auditory cortex, temporal lobe • Reflex function – Muscles of the middle ear What animal type? • 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

33 Onset of hearing, deafness

• Onset of hearing – Kittens 5 days – Puppies 14 days • normal by 4-5 weeks • Deafness – Conduction • Otitis externa/media

– Sensorineural https://s-media-cache-ak0.pinimg.com https://upload.wikimedia.org • 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 10.17 Thomson and Hahn I spiral ganglia, CN VIII Auditory pathway in the brain II cochlear nuclei III dorsal nucleus of trapezoid body IV ? (lateral lemniscus and nucleus) V caudal colliculus

VI ? (medial geniculate nucleus) 35 VII ? What else can BAER be used for?

36 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

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37 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 can cause paralysis of the ____ muscle and failure of glottal opening Fig 10.19 Thomson and Hahn, Innervation of the pharynx and larynx

Dyce, Figs 4-12 (2) and 4-14 (5) 40 Which cranial nerves innervate the following function of the tongue? – Motor – Sensory (touch) – Taste

41 Fig 10.21 Thomson and Hahn, 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?

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