Functional neuroanatomy of the neurological examination: Cranial...

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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

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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?

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Fig 1.7 Thomson and Hahn

Fig 10.2 Thomson and Hahn,

Functional CNN nuclear columns in the brainstem

4Fig 10.1 Thomson and Hahn

Dog brain, ventral aspect, cranial nerves

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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

XII Hypoglossal Myelencephalon Tongue muscles

Cranial nerves, attachment and main functions

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To move both eyes to the right

requires stimulation of …

http://londonbeep.com/

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Vision –

CN II

• Optic nerve– Visible CNS

• Optic chiasm– 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

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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

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Visual

Reflexes

• Rostral colliculus

– Tectonuclear (bulbar) – extraocular muscles

– Tectospinal – cervical muscles

– Function???


Optic pathway and its connections

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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


Pupillary light reflex pathway

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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


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The menace response appears in

kittens / puppies by _______

weeks of age

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Somatosensory input from head

Fig 10.6 Thomson and Hahn, trigeminal sensory complex


spinal cord, XS; What level?

Afferents: CNN V, VII, IX, X

To the trigeminal sensory complex

• Mesencephalon

• Pons

• Myelencephalon

Projects to contralateral somatosensory cortex

Substantia

gelatinosa.

http://www.winslowvetmobile.com/

http://www.saltoftheearth.

What cranial nerve is being

assessed in these images?

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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


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X 3

Static equilibrium

Dynamic equilibrium

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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

Fig 18.7 Uemura

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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


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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

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What are the effects of vestibular nuclei stimulation?

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Vestibular nuclei connections

Fig 8.6 Thomson and HahnTo temporal lobe

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

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Effect of vestibular lesions; uneven stimulation of VN at rest,

What signs occur with abnormal

vestibular function?

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Distance penlight test: for subtle anisocoria and strabismus

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

27Fig 13.1 Thomson and Hahn

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Paradoxical Vestibular Disease

• Lesion in caudal cerebellar peduncle or flocculonodular lobe

• Loss of inhibitory output to vestibular nuclei;

• 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

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Hearing – CN VIII

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Mouse cochlea,

https://www.best.edu.au

SV

ST

Stria vascularis

BM

CD

Spiral

ganglion

Tortora, Fig 17-22

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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

http://vethospital.tamu.edu

What animal type?

Onset of hearing, deafness• Onset of hearing

– Kittens 5 days

– Puppies 14 days

• normal by 4-5 weeks

• Deafness

– 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

https://s-media-cache-ak0.pinimg.com https://upload.wikimedia.org

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Auditory pathway in the brain


Brainstem auditory evoked reflex

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)

VII ?

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What else can BAER be used for?

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A curious fact about CN VIII

http://upsidedowndogs.com

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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Other CNN nuclei (VII, IX, X, XI)

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

•Nucleus ambiguus – somatic efferent to larynx and pharynx


Recurrent laryngeal nerve damage can cause paralysis of

the ____ muscle and failure of glottal opening

Fig 10-20 Thomson & Hahn

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Fig 10.19 Thomson and Hahn, Innervation

of the pharynx and larynx

Dyce, Figs 4-12 (2) and 4-14 (5)

41Fig 10.21 Thomson and Hahn,

Which cranial nerves innervate the

following function of the tongue?

– Motor

– Sensory (touch)

– Taste

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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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