functional neuroanatomy of the neurological examination
TRANSCRIPT
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Functional
neuroanatomy of
the neurological
examination:
Cranial nerves
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Chris ThomsonBVSc(Hons), Dip ACVIM (Neurol), Dip ECVN, PhD
VTH, IVABS, Massey University
Palmerston North, New Zealand
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The Neuro Exam
• Aim to assess:
1) Mentation/arousal and
behaviour
2) Posture and gait
Sensory function – proprioception,
tactile
Motor function – gait, spinal reflexes
Coordination
Balance
4) Cranial nerves
5) Visceral function
6) spinal pain-hyperpathia
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Fig 10.1 Thomson and Hahn
Dog brain, ventral aspect, cranial
nerves
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General principles
– Sensory, motor, or mixed
– Parasympathetic – CNN III, VII, IX, X
– Sensory links• reflex function
• sensory reception – somatosensory cortex, cerebellum
• Sensory nucleus – trigeminal sensory complex
– Nuclear arrangement in brainstem• Ξ to fragmented spinal cord columns
– Only one CN that is pure CNS
– Attachment mainly ventral/ventrolateral • except ???
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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 Muscles of facial expression
Salivary, lacrimal glands, taste, masticatory
muscle (which one?)
VIII Vestibulocochlear Pons/myelencephalon Hearing, balance
IX Glossopharyngeal Myelencephalon Swallowing, salivary glands, taste
X Vagus Myelencephalon Taste, swallowing, laryngeal, salivary glands,
parasympathetic to body viscera
XI Accessory Myelencephalon Laryngeal function, neck muscles
XII Hypoglossal Myelencephalon Tongue muscles
Cranial nerves, attachment and main functions
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Fig 1.7 Thomson and Hahn
Fig 10.2 Thomson and Hahn,
Functional CNN nuclear columns in the brainstem
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Vision –
CN II (p92)
• Optic nerve– Visible CNS
• Optic chiasm– Variable degree of cross over
• Herbivores 80-90%
• Cats 65%
• Inversely related to stereoscopic vision
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
• 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
Fig 10.8 Thomson and Hahn,
Pupillary light reflex pathway
Consensual reflex
affected by degree of
cross over
e.g. human versus
horse
Swinging light test
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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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Somatosensory input
from head
Fig 10.6 Thomson and Hahn, trigeminal sensory complex
Fig 10.6 Thomson and Hahn,
C7 spinal cord, TS
Afferents: CNN V, VII, IX, X
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Vestibular System
• Proprioceptors
– Hair cells
– Location • Membranous labyrinth
inner ear/petrous temporal bone
– Function to maintain posture
• Head, neck, trunk, limbs, eyes
• During rest and motion
• Anti-gravity function
Fig 8.8 Thomson and Hahn
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Fig 8.1 Thomson and Hahn
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How do hair cells function in
head equilibrium?
• Deflection of microvilli – 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– Detection by hair cells in semi-circular
canals
– Detect effect of acceleration in 3 planes
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Fig 8.2 Thomson and Hahn
Effect of gravity on macula of sacculus or utriculus
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Fig 8.3 Thomson and Hahn, effect of acceleration on SCD
– Head rotation
• Causes endolymph flow in 1+ 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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Fig 8.4 Thomson and Hahn– SC ducts are bilaterally paired
• e.g. Left anterior-right posterior
– Example: Turning head to left
-> flow of endolymph in opposite directions in paired ducts
• Stimulating from left side and inhibitory from right side
• Uneven neural input to each side of brain; head rotation is perceived
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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 Hahn
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Physiological Nystagmus
• Vestibulo-ocular reflex (VOR)
– Mechanism
• Slow phase – vestibular origin
• Fast phase – extraocular muscle stretching,
brainstem reflex activity
– Function
• Visual fixation during head rotation
• Example
– L head rotation -> R CN IV and L CN III
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Vestibular Function and Eyeball
Position
• Pathway– Vestibular apparatus -> VN -> MLF -> CN III, IV, VI
• Head and eyeball position coordinated
• Predator vs prey species
• Vestibular dysfunction– Strabismus
• Afferent vs efferent dysfunction
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Fig 8.9 Thomson and Hahn
Effect of vestibular lesions; uneven stimulation of VN at rest,
with decreased stimulation on side of the lesion
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Paradoxical
Vestibular
Disease
• Signs– Head tilt to opposite side
– Nystagmus (fast phase) to side of lesion
– Ipsilateral ataxia
and proprioceptive deficits
• Lesion location– Area of caudal cerebellar peduncle
Fig A21 Thomson and Hahn
TS through cerebellar
peduncles
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Paradoxical Vestibular Disease
Fig 8.10 Thomson and Hahn
Loss of inhibitory output to vestibular nuclei; XS stimulation
on side of the lesion
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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
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Fig 10.15 Thomson and Hahn
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Fig 10.16 Thomson and Hahn
Cochlear
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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-V???
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A curious fact about CN VIII
• It’s only an afferent nerve
– right?
• Olivocochlear reflex
– Protective
– Discriminative –
neutralises background
noise http://upsidedowndogs.com
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Other CNN nuclei (VII, IX, X, XI)
Solitary tract and nucleus – sensory input: taste, carotid sinus, thoracic and
abdominal viscera (p101)
•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
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Fig 10.19 Thomson and Hahn,
Innervation of the pharynx and
larynx
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Autonomic innervation of the head
• Parasympathetic = craniosacral
– Therefore CNN III, VII, IX, X
– Functions?
• Sympathetic = thoracolumbar outflow
– Therefore not via CNN, but via sympathetic
fibres from the cranial thorax
– Function?
– Dysfunction?
• See next section
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• Olfaction – CN I – Conscious perception
• Olfactory cortex of piriform lobe
• Connections with
– limbic system, hypothalamus, cerebrum
– olfaction stimulates memory, emotion and
behaviour
– Brainstem – olfaction stimulates autonomic
function
* *
Dog brains, XS
and horizontal
sections, MRI
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Fig 10.3 Thomson and Hahn,
Comparative anatomy CN I, dog and human brain
Dogs 100,000-1million time more sensitive than humans
Blood hounds 10-100million times more
(Wikipedia)