VBMS 212 Neurology Quiz 4

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EYE: Outpouching of Diencephalon
- tf not strictly a peripheral nerve
- Outer Layer is optic cup
~~-- pigmented epithelium of retina
- Inner Layer
~~-- 9 layers of retina

Light travels through all layers of retina except outer befor reaching photo receptors
EYE PHOTORECEPTORS: Photoreceptor resting membrane potential in dark
- -40 mV (vs normal cell -70 mV)
- tf less polarized than other neurons
- high # of Na channels are open in dark
- constant release of Glutamate NT to bipolar cells
- tf bipolar cells are kept hyperpolarized

When light reaches photo receptors
- photopigments work through second messenger system to CLOSE Na channels
- tf photoreceptor cells HYPERPOLARIZE
- tf photoreceptor cells stop releasing glutamate NT
- tf bibolar ganglion cells depolarize
~~-- generate AP
- Retinal Ganglion cells are stimulated by AP of bipolar cells

Sudden change of Contrast generates increased activity than adjacent regions
- tf PROCESSING OCCURS IN RETINA
EYE OPTIC DISK: Retinal Ganglion Cells send axons over surface of retina to optic disk

Slightly ventro lateral to anatomical centre of retina (eyeball)

Blind spot

Start of Optic Nerve

Start of Myelenated Axons from retinal ganglion cells
- myelenation via OLIGODENROCYTES
~~-- ie NOT peripheral nerve
EYE OPTIC NERVE: Properly a TRACT
- travels caudally to optic chiasm
- crosses over in chiasm
~~-- species variablity
- travels laterally around thalamus
EYE OPTIC CHIASM: Animals and some Birds with laterally placed eyes
- 100% crossover of optic fibres

Mammals with Rostrally placed eyes
- Binnocular Vision
- amount of crossover is INVERSELY PROPORTIONAL to amount of BINOCULAR vision
- primates have 50% crossover
- cats 65% crossover
- dogs 75% crossover
- large animals 80 - 90% crossover

Retinal location determines which fibres cross over
VISUAL FIELD: View seen by two eyes when looking straight ahead
- divided into left and right visual fields
~~-- midline to lateral edge of what eye sees

Lateral portion of one side of visual field viewed by
- medial part of retina of ipsolateral eye
- lateral part of retina of contralateral eye

Light from one side of Binnocular visual field is viewed by
- medial part of retina of ipsolateral eye
- lateral part of retina of contralateral eye
VISUAL FIELD CROSSOVER: Visual field is viewed on opposite side of brain (occipital cortex)
- tf axons that view visual field of one side have to cross to the other
- tf axons of medial retina of the eye ipsolateral to the side of visual field cross over
- tf axons of the lateral retina of the eye contralateral to the side of the visual field do not
RETINAL AXONS THREE POTENTIAL TARGETS: Lateral Geniculate Nucleus
- dorsal caudal thalamus

Rostral Folliculus
- dorsal midbrain

Pretectal Area
- midbrain
EYE LATERAL GENICULATE NUCLEUS: Afferents from optic chiasm to Lateral Geniculate Nucleus in Dorsal Caudal Thalamus

Efferents from Geniculate nucleus travel to Occipital Cortex

Patterns of synapses remain the same as visual field patterns in retina

Retino Topic Map identical in
- Retina
- Geniculate Nucleus
- Occipital Cortex

Retinotopic Map is area of conscious vision in visual cortex
EYE ROSTRAL FOLLICULUS: Dorsal portion of mid brain

Afferents from optic tracts

Some processing of Unconscious vision
- Blind Sight

Coordinates head and eye movements in response to invountary visual stimuli
EYE SALLADE: Function of Rostral Colliculus

Movement of eye when object appears in visual field
- rapid movement to look and focus
- tf outputs from rostral colliculus to CN III, IV, VI
- highly coordinated movement
EYE SMOOTH PURSUIT: Function of Rostral Folliculus

Eyes smoothly follow moving object in visual field

Outputs from rostral colliculus to
- CN III, IV, VI
- Cervical Spinal cord
~~-- enable turning of head
EYE PRETECTAL AREA: Mid Brain
- Parasympathetic Nucleus of CN III
- Preganglionic axons CN III Parasympathetic Nerves
~~-- synapse in Cilary Ganglion near eye
~~-- post ganglionic neurons enervate smooth muscle of Iris

Controls Pupil size in response to light

Both left and right pretectal areas send axons to both left and right parasympathetic nuclei of CN III
- tf light in one eye will will cause both pupils to contract
~~-- Direct or Consensual Response
EYE DIRECT RESPONSE: Reflex of Pretectal Area

Contraction of Iris of Eye receiving light
EYE CONSENSUAL RESPONSE: Reflex of Pretectal Area

Contraction of Iris of BOTH eyes when one eye receives light
ANISOCORIA: Pupils of different size
MIOSIS: Small Pupil
MYDRIASIS: Large Pupil
VISUAL ACUITY COMPARED TO HUMAN: Dogs and Cats
- 1/6

Horses
- 1/3

Birds of Prey
- 3x
COLOUR VISION: Depends on number of different colour pigments in retina

Humans
- trichromatic

Cats
- trichromatic

Horses, Dogs, Ruminants
- dirchromatic
- red discriminated from blue/green
- less discrimination at blue end of spectrum
~~ inablility to differentiate blue/green/yellow
BLINDNESS: Hard to detect in animals
- less reliance on vision

Test Via
- strange environment
- drop cotton balls in visual field
~~ look for tracking eye motion
- Menace Reaction
MENACE REACTION: Normal response to looming object is BLINKING
- may also pull head away
- may also retract eyeball

Afferents same as conscious vision
- CN II
- synapse in Lateral Geniculate Nucleus
~~ thalamus
- neurons from LGN synapse in visual cortex
- neurons from visual cortex synapse in
~~ Nucleus of CN VII
~~--rostral medulla
~~ Cerebellum
- neurons from cerebellum synapse in
~~ Nucleus of CN VII
- motor efferents from
~~ Nucleus of CN VII

Learned response
- tf absent in very young animals

Habituates if Repeated
- tf may have to touch eye to stimulate

Avoid Air Movement
- will stimulate corneal sensory afferents
- Opthalmic branch of CN V
~~ corneal reflex is NOT learned
LESIONS IN MENACE REFLEX 7: Peripheral
- Retina
- CN II
- CN VII

Central
- Cortex
~~ motor cortex
~~ visual cortex
- Cerebellum
- Medulla
~~ Nucleus CN VII
- Brainstem
~~ between Thalamus and
~~-- Cerebellum
~~-- Nucleus CN VII
VESTIBULAR SYSTEM NAME THE COMPONENTS: Bony Labyrinth
- cavity in petrous temporal bone

Membranous Labyrinth
- membrane lined
- filled with endolymph
- contains sensory system

SEMICIRCULAR CANALS
- 3 with bases terminating in
~~ CHRISTA AMULARA containg
~~-- CUPULA
~~-- HAIR CELLS
~~-- CN VIII

UTRICLE
- large recepticle containing
~~-- MUCULA
~~-- HAIR CELLS
~~-- OTOLITHS
~~-- CN VIII

SACCULE
- large recepticle containing
~~-- MUCULA
~~-- HAIR CELLS
~~-- OTOLITHS
~~-- CN VIII
CHRISTA AMPULARUS: Detects Rotational Acceleration of Head

Cupula
- Gelatenous structure
- exposed to endolymph of semicircular canal

Hair Cells
- cilia protrudes into Cupulla
- basal surface in close contact with neurons of CN VIII
- bending of cilia inibits or excites neurons CN VIII

Inertia of fluid causes it to remain stationary when head rotates
- tf fluid resists motion of Cupula, displacing it in opposite direction of rotation
~~-- tf hair cells are bent in opposite direction of rotation
~~--~~ excitation/inhibition of neurons

When acceleration ceases
- fluid catches up
- Cupula is restored to normal position
~~-- tf hair cells are starightend
~~--~~ tf neither excitation or inhibition of neurons

Momentum of fluid causes it to keep moving when motion of head stops
- tf fluid displaces Cupula in same direction as rotation
~~-- tf hair cells are bent in same direction as rotation
~~--~~ inhibition/excitation of neurons
UTRICLE AND SACCULE: Detects Linear Acceleration of Head

Detects Static Position of Head

Mucula
- oriented horizontally and vertically
- Gelatenous membrane lined with otoliths
- exposed to endolymph of Utricle or Saccule

Hair Cells
- cilia protrudes into Mucula
- basal surface in close contact with neurons of CN VIII
- bending of cilia inibits or excites neurons CN VIII

Inertia of fluid causes it to remain stationary when head moves
- tf fluid resists motion of Mucula, displacing it in opposite direction of motion
~~-- tf hair cells are bent in opposite direction of motion
~~--~~ excitation/inhibition of neurons

When acceleration ceases
- fluid catches up
- Macula is restored to normal position
~~-- tf hair cells are starightend
~~--~~ tf neither excitation or inhibition of neurons

Inertia of fluid causes it to keep moving when motion of head stops
- tf fluid displaces Mucula in same direction as motion
~~-- tf hair cells are bent in same direction as motion
~~--~~ inhibition/excitation of neurons

Otoliths apply force to gel of Macula
- tf gravity displaces cilia of hair cells
- excitation/inhibition of neurons of CN VIII
VESTIBULAR NEURONS 7 TRENDY DESTINATIONS: Are Sensory
- tf cell bodies external to brain

Some axons synapse
- DIRECTLY in Vestibulocerebellum

Most neurons synapse in
- Vestibular Nucleus

Axons of Vestibular Nucleus Neruons
- travel in spinal cord
~~ VESTIBULOSPINAL NEURONS
~~ stimulate Ipsolateral Extensor muscles
- travel to Vestibulocerebellum
- travel to Motor Nuclei
~~ CN III
~~ CN IV
~~ CN VI
~~ ie Extrinsic Eye Muscles
- travel to Thalamus
~~ conscious perception of orientation
- travel to Vomition Centre
~~ in Medula
VESTIBULAR SYSTEM 3 FUNCTIONS AND MECHANISM: Coordinates
- Head
- Eye
- Trunk
During movement and at rest

Nystagmus
- aka Normal, Jerk, Vestibular
- flicking motion of eyes to maintain direction during head movement

Vestibulocollic (Neck) Reflexes
- maintains orientation of head during trunk manipulation
- via Neck Muscles

Works on balance of inputs from left and right vestibular apparati
- symetry is critical for proper functioning
VESTIBULAR SIGNS BLURT THE BASIC MECHANISM TELL ME THE TYPES: Any lesion that affects one side of system more than the other produces Vestibular Signs

Abnormal Postures and Movement
- head
- body

Abnormal Eye Movements
- Nystagmus
VESTIBULAR SIGNS POSTURE AND MOVEMENT FOUR FAILINGS: Head Tilt
- not axial head turn
- attempts to equalize asymetrical inputs from vestibular apparati
- animal perceives that correctly oriented head is tilted
- response of Vestibulocollic reflex
- Tilt is TOWARDS side of lesion
~~ in most cases

Falling
- reduction of extensor excitation on side of lesion
- tf falls to side of lesion

Rolling
- Combination of
~~ Extreme Head Tilt
~~ Extensor Weakness
- roll is attempt to right self
- extensor weakness causes roll to side of lesion

Circling
- technically form of falling
- towards side of lesion
- SMALLER than Cortical circling
VESTIBULAR SIGNS NYSTAGMUS NORMAL: Movement of eyes when head is moving
- flicking motion of eyes

As head turns vestibular nucleus of
- direction of turn
~~ depolarizes
~~ is STIMULATED
- opposite to direction of turn
~~ hyperpolarizes
~~ is INHIBITED

Slow Phase of Nystamgus
- eyes move SLOWLY in OPPOSITE direction to turn of head
- maintains direction of visual field

Fast Phase of Nystagmus
- eyes move RAPIDLY WITH direction of turn
- causes eyes to "catch up" with position of head

Visual Stimuli can override Nystagmus
- ie Smooth Pursuit
NYSTAGMUS 3 FORMS: Horizontal

Vertical

Rotary
VESTIBULAR SIGNS NYSTAGMUS ABNORMAL: aka Spontaneous or Resting

Abnormal Nystagmus occurs when head is STATIONARY

Results from imbalance of inputs from Vestibular Apparati
- inputs are reduced on side of lesion
- same effect as TURNING head to side OPPOSITE to lesion
- tf SLOW movement of eyes IN direction of lesion
- tf RAPID movement of eyes OPPOSITE to direction of lesion
VESTIBULAR SIGNS NYSTAGMUS ABNORMAL HOW IS IT NAMED: Named according to direction of FAST PHASE

ie OPPOSITE to side of lesion

ie if lesion on Left
- Resting Right Nystagmus
VESIBULAR SYSTEM DISEASE SIGNS WHICH ONE IS MANNA FROM HEAVEN WHAT IS TRICKY ABOUT THEM: Peripheral
- Labyrinth and CN VIII
- Eye Movement
~~ Mainly Horizontal Nystagmus
~~ Rarely Rotory Nystagmus
- Postural
~~ Head Tilt
~~ Falling
~~ Rolling
~~ Circling
- all towards side of Lesion

CENTRAL
- Brain Stem and Cerebellum
- Eye Movement
~~ VERTICAL Nystagmus
~~ Horizontal Nystagmus
~~ Rarely Rotory Nystagmus
- Postural
~~ Head Tilt
~~ Falling
~~ Rolling
~~ Circling
- all towards side of Lesion

Vestibular System is highly ADAPTIVE
- tf kvestibular signs may disappear within a few days
- Persistence in Rats
~~ least rolling
~~ moderate Nystagmus
~~ Most Head Tilt
- Visual System Aids Compensation
~~ tf Blindfold animal with intermittent or resolved signs
- ie Old Dog Vestibular Disease
~~ idiopathic
~~ resolves without treatment
VESTIBULAR DISEASE CAUSES: Peripheral
- Ear Infections
~~ progress from outer ear through middle to inner ear
~~ in dogs and cats may also induce Horners disease
~~-- sympatetic trunk runs through middle ear on way to eye
- Idiopathic
~~ ie Old Dog Vestibular Disease
- Trauma
- Tumors
- Iatrogenic
~~ aminoglycosides Antibiotics
~~-- toxic to hair cells
~~-- vestibular and hearing
~~-- permanent damage

Central
- any lesion of
~~ Vestibular Cerebellum
~~ Medulla
~~-- vestibular nuclei occupy a large portion of the medulla
- tumors
- inflammation
ALCOHOL INDUCED BED SPINS TELL JOE ALL ABOUT IT: Semicircular canals detect rotational acceleration

Normally not effected by gravity

Cupula is stationary when no head motion

Acute Alcohol Toxity
- affects cupula directly
- causes cupula to become bouyant
~~ tf cupula floats up into endolymph
~~-- tf cupula becomes SENSITIVE TO GRAVITY

When cupula is sensitive to gravity
- laying down causes it to move bending cilia of hair cells
~~ simulates rotary motion of head
~~-- results in rotary nystagmus
AUDITORY SYSTEM TRANSMISSION OF MECHANICAL ENERGY: External Ear

Tympanic Membrane

Middle Ear
- Malleus
- Incus
- Stapes
~~ Vestibular (Oval) Window of Cochlea
AUDITORY SYSTEM CONVERSION MECHANICAL ENERGY TO ELECTRICAL ENERGY: COCHLEA mostly divided by BASILAR MEMBRANE

Vibrations transmitted to VESTIBULAR WINDOW create waves in endolymph

Waves in endolymph create motion in Basilar Membrane

Basilar Membrane contains HAIR CELLS

CILIA of Hair Cells protrude into gelatenous TECTORIAL MEMBRANE which is adjacent to Basilar Membrane

Motion in Basilar Membrane creates movement relative to Tectorial Membrane
- tf Cilia of Hair Cells are bent
- tf hyperpolarization/depolarization

Basilar Membrane does not extent into Cupula (at end) of Cochlea
- tf waves in endolymph can travel to other side of Basilar Membrane relieving pressure
~~ tf higher energy efficiency

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