Lecture 14 visual auditory vestibular Flashcards
What are the 3 layers of eye tissue?
Sclera/Cornea
Choroid w/ blood vessels and cillary body
Retina (inner most) w/ visual neurons
What is the function of the pupil?
Controls the amount of light
What is the function of the lens?
Accommodates for near objects
The fovea only has _______ (rods/cones) and has the _______ (lowest/highest) visual acuity and the smallest _______
Cone receptors
Highest
Visual field
Where is the blindspot in your eye?
Optic disc
What layer of the retinal structure contains melanin to decrease background scattering of light?
Outer pigmented layer
The inner layer of the retinal structure contains 3 neuron chains responsible for phototransduction, what are they?
Photoreceptors
Bipolar cells
Ganglion cells
Release of neurotransmitter by ________ result in generation of action potential in the ganglion cells of the retina
Photoreceptors
R
Cone receptors vs Rod receptors
Cone- Low light sensitivity, small receptive field, color (day-vision)
Rod- High light sensitivity, large receptive field, black and white (night-vision)
Ganglion cells of the retina synapse w/ the ________ resulting in visual perception
Optic Nerve
Rod receptors see in….
Black and white
Cone Receptors see in…
Color
What cells in the retina generate action potentials as 1st order neurons
Ganglion Cells
What are the two kinds of interneurons found in the retina?
Horizontal cells - Photoreceptors <–> Bipolar cells
Amacrine Cells - Bipolar <–> Ganglion Cells
What do the bipolar cells in the retina do?
Transfer info to the ganglion cells
What is the pathway for phototransduction?
Photoreceptor -> Bipolar Cell -> Ganglion Cell -> Optic nerve
Where are the 2nd order neurons for visual perception found?
Inside the lateral geniuclate body found in the thalamus
Identify these optic radiation fibers coming from the lateral (what visual fields are they for?)
- Fibers for the superior quadrants (inferior visual field)
- Fibers for the inferior quadrants (superior visual fields)
Where is the Primary Visual Cortex located?
In the occipital lobe along calcarine fissure
The upper part of the visual cortex is called the _____ and is for….
cuneus
for lower quadrant of both eyes
The lower part of the visual cortex is called the _____ and is for….
Lingula
Upper quadrant of both eyes
How is the Primary Visual Cortex organized?
Retinotopically organized
1 central region for the fovea
3 peripheral regions in each of the upper and lower part of the visual cortex
Which nerve fibers cross the optic chiasm? Nasal or temporal?
Nasal
Note: Don’t get confused because nasal fibers are not the ones that actually see the nose, they actually look out and away from the nose.
What makes up 1 hemi-visual field?
1 optic tract consisting of Ipsilateral temporal n fibers and contralateral nasal n fibers
In the visual association cortex, also called ____________, the ventral stream does what?
Occipito-temporal cortex
Perception of form, high spatial
resolution and visual acuity
In the visual association cortex, also called ____________, the Dorsal stream does what?
Parieto-occipital cortex
Motion, high temporal resolution
The dorsal stream goes to the…
The ventral stream goes to the….
Dorsal- Parietal Lobe
Ventral- Temporal Lobe
Pupillary reflexes are controlled by what areas of the brain?
Pretectal area and superior colliculus
The posterior parietal cortex is for…
Visually guides movement
Note: part of the Dorsal Stream
The occipital temporal region is for…
Visual identification of objects
Note: part of the ventral stream
The visual image is _____ and ____ when projected onto the retina
Inverted and reversed
Image from a monocular zone (meaning can only be seen with one eye) is projected where?
To the ispilateral nasal hemi-retina
Note: Images in binocular zone are projected to both hemiretinas on both sides
Vestibulo-ocular reflex
Keeping eye position stable during head mvmts to keep environment from visually bouncing
Optokinetic reflex
Use of visual info to stabilize images during slow head mvmts
Eye movements can be classified as either conjugate or divergence…
Conjugate- Eyes move in same direction
Convergence/Divergence - Opposite directions
What kind of eye movement does reading use?
saccades
Velocity of saccades…
Velocity of slow eye movements…
Up to 700 degrees/sec
Up to 100 degrees/sec
What stimulates the VOR
What stimulates the Optokinetic reflex?
VOR- head movement
Optokinetic reflex- moving visual stimuli
What reflex allows eyes to follow large objects in visual field
Optokinetic reflex
In Vestibulo-occular reflex… Eyes automatically move same
distance/speed in ________
direction to head mvmt
Opposite
Where is the horizontal gaze center?
Where is the vertical gaze center?
Horizontal- Paramedian pontine
Vertical- Rostral interstitial nucleus
Note: These are both of the gaze centers in reticular formation in the midbrain
What nerve controls both the VOR and optokinetic reflex
Vestibular nerve
NOT optic nerve
What does the Medial longitudinal fasciculus do for vision?
Coordinates activations of B neural
circuits
In general, What part of the brain controls eye movement?
Forebrain
Lesions at the superior colliculus can cause…
Lesions here increase latency and reduces accuracy, frequency and velocity of saccades
The frontal eye field in the forebrain is connected to the ___________ Paramedian pontine reticular formation both directly and indirectly by the _____________
Contralateral
superior colliculus
The “Frontal Eye Field” of the forebrain controls what?
Contralateral saccades and smooth pursuit
The basal ganglia controls the _________ of eye movement, whereas the cerebellum controls the __________ of eye movement
Basal ganglia - Proper initiation of eye mvmts
(Via the occulomotor and prefrontal loop)
Cerebellum- Execution of eye movement
(Via the Vestibulocerebellum and
spinocerebellum (vermis))
Lesion to R optic N causes…
Loss of vision in R eye
Lesion to optic chiasm causes…
Bitemporal (heteronomous) hemianopsia
Lesion to R optic tract causes…
L homonymous hemianopsia.
Lesion to R Meyer’s loop causes…
L superior homonymous quadrantanopsia
Lesion to R V1 Causes…
L homonymous hemianopsia with macular
sparing.
► Ossicles: malleus, incus, stapes
► Muscles: tensor tympani (V3), stapedius (VII)
These are all a part of the….
Middle ear
Organ of Corti includes hair cells that
get bent initiating _________________ which activates the cochlear N of cranial N 8
Mechanoelectrical transduction
What part of the ear vibrates in response to sound?
Tympanic membrane
What is the “hollow, coiled structure filled
with fluid – membranous labyrinth” in the ear
Cochlea
What causes hair cells to depolarize and activate cochlear nerve endings?
Basilar membrane and embedded hair cells to vibrate, causing Hair cells to bend against attached and immobile tectorial membrane,
- Sound waves hit tympanic membrane, causing
- _________________ to move, causing
- Membrane at opening to cochlea to move/vibrate, causing
- Fluid in ___________ to move, causing
- ____________ and embedded hair cells to vibrate, causing
- Hair cells to bend against attached and immobile tectorial membrane,
causing - Hair cells to depolarize and activate cochlear n endings
Ossicles
Cochlea
Basilar Membrane
What lobe is the primary auditory cortex found in?
Temporal
In the ascending auditory pathway, the cochlea gives information to the….
Auditory nerve (CN 8)
What cranial nerve is afferent for the pupillary light reflex
which is efferent?
afferent- CN 2
Efferent CN 3
Major Auditory pathway:
Cochlear nerve -> Auditory nerve -> brainstem auditory centers -> ________________ -> primary auditory cortex (temporal lobe)
Medial genticulate body of thalamus
Sound localization is due to parallel arrangement of..
Cochlea and medial+lateral superior olives
The superior colliculus is for…
the inferior colliculus is for…
Superior- vision
Inferior- Auditory
- Primary Auditory Cortex
- Secondary Auditory Cortex
What does the secondary auditory cortex do?
Compares sound with memories and categorizes them
What does wernicke’s area do?
Comprehend speech
wernicke’s area
B ear aural cues for sound localization are processed in _________________
Superior medial and lateral olives AND nuclei of lateral leminiscus
Primary Auditory cortex functions
supporting basic auditory
functions (frequency discrimination, sound
localization, primitive processing of communication
sounds)
How is the primary auditory cortex organized?
Tonotopically
What is the organ of corti?
Layers of hair cells that transmit info to the cochlear nucleus
What is this structure and what’s inside of it?
Ampullae
Crista (contains supporting cells and sensory hair cells)
The membraneous lambyrinth is filled with _________ fluid
endolymph
How many semicircular canals are there?
3
True or false: when the head is still, hair cells inside of the semicircular canals are still firing
true
When head is still, hair cells have baseline rate of firing
When head starts or stops turning, the cupula and
hair cells bend causing increase/decrease in firing
depending on direction of bending
If head is moving at steady rate, hair cells in
endolymph catch up to head mvmt and return to
baseline firing
Only active during acceleration/deceleration of
rotational head mvmts
What are the 2 functional pairs of semicircular canals?
L anterior/R posterior
R anterior/L posterior
X shape
Because they have the same axis of rotation so they work as a functional pair
What happens if a functional pair of SCC are not reciprocal?
impaired postural control, eye mvmts,
and/or nausea can occur
What are the Utricle and saccule (otolithic organs)?
membranous sacs that respond to linear
acceleration/deceleration and head
position relative to gravity
Each Utricle and saccule have a ____________ that contain supporting cells and hair cells with otoconia (calcium carbonate crystals)
Macula
Note: Linear mvmt of head displaces the
otoconia that then move gelatinous
substance and hair cells to stimulate or
inhibit firing of neurons, depending on
direction of mvmt
What Vestibular Anatomy is responsible for rotational movements?
What is responsible for linear movements?
Rotational- Semicircular canals
Linear movements- Otolithic organs
What lobe of the cerebellum received vestibular info from Vestibular nuclei in pons and medulla which comes from the vestibular nerve?
flocculonodular lobe (vestibulocerebellum)
How many vestibular nuclei are there and where are they found?
4 on each side on the junctions of the pons and medulla
Vestibulo-cervical reflex
Postural adjustments of head in response to activation of SCC
Vestibulo-cervical reflex uses what tract?
Medial vestibulospinal tract to medial vestibular nucleus
Vestibulo-spinal reflex
Postural and tone adjustments of body
The vestibulospinal reflex uses what tracts?
Lateral and medial vestibulospinal tracts (VST) and
reticulospinal tract (RST)
Vesibular spinal vs vestibulocervical reflex
Spinal- Medial + Lateral vestibulospinal tracts + reticulospinal
Cervical- JUST medial vestibulospinal tract
The Medial longitudinal fasciculus connects to what?
B connections to extraocular eye muscles and superior colliculus
- crucial connection between different areas involved in coordinating eye movements and maintaining balance
Cerebello-thalamocortical pathways
► Lateral and superior vestibular nuclei
► Thalamus
► Near S1 facial area and posterior
parietal cortex
► Involved in perception of body
orientation in extrapersonal space
► Lesions of R posterior parietal
cortex cause altered perceptions
of personal and extrapersonal
space
What is the first order neuron of the vestibular pathway
vestibular ganglion (also called Scarpa’s ganglion)
What is the second order neuron of the vestibular pathway?
vestibular nuclei in pons/medulla
Note: Vestibulospinal tract is formed by these 2nd order neurons
Medial VST tract vs Lateral VST tract
ipsilateral lateral VST – tonic excitatory effect on extensors
B medial VST – influences neck muscles and head mvmt
(Medial VST tract gets information bilaterally in the pons/medulla)
Visual and vestibular cortices are _________________
Reciprocially inhibited/activated
When visual cortex is more active, vestibular cortex is inhibited and
vice versa
