Functional neuroanatomy of the neurological examination: Cranial...
Transcript of 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
Fig 10.5 Thomson and Hahn,
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???
Fig 10.9 Thomson and Hahn,
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
Fig 10.8 Thomson and Hahn,
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
Fig 13.8 Thomson and Hahn
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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
Fig 10.6 Thomson and Hahn,
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
Fig 8.8 Thomson and Hahn
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Fig 8.1 Thomson and Hahn
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
Fig 8.2 Thomson and Hahn
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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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Fig 8.5 Thomson and Hahn
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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Fig 8.9 Thomson and Hahn
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
Fig 8.10 Thomson and Hahn
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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Fig 10.15 Thomson and Hahn
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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Fig 10.17 Thomson and Hahn
Auditory pathway in the brain
Fig 10.18 Thomson and Hahn
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
Fig 10.2 Thomson and Hahn
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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