Visual System Flashcards
what is the eye composed of
outer
middle
inner (retina) layers
what is the thin watery fluid anterior to the lens and between the cornea
aqueous humor
what fluid is in the anterior and posterior chambers
aqueous humor
where is aqueous humor produced?
ciliary process in the posterior chamber
how often is ah produced?
replaced every 2-3 hours/constantly produced
what can be a result of an inbalance in production and reabsorption of ah and intraocular pressure rises?
constricts blood flow to the retina
blindness can result
glaucoma
how is the ah replaced?
collects in the canal of schlemm before it enters the venous dranage of the sclera
Thick, jelly-like semifluid found posterior to the lens, between the lens and the retina
vitreous humor
what fluid is important for maintaining the shape of the eye/orbit
vitreous humor
what is the only nerve that the arachnoid follows all along to its final destination?
CN II (optic nerve)
considered extension of diencephalon/window to the CNS system
CN II
white part of the eye
sclera
clear portion of the eye anteriorly
nonadjustable lens of the eye
cornea
does the cornea layer change shape
no, the lens underneath does
what is the outer layer also known as
corneoclera layer
In the adult eye the ______ become the sclera and the choroid which cover the posterior 5/6 of the eye.
meninges
Sclera is continuous with _____ and the choroid is continuous with the _______
dura
pia-arachnoid
what can an Opthalmoscopic examination show
specific changes due to increased intracranial pressure
what is papilladema
swelling of the retinal veins and blurring of the margin of the papilla
the most important sing of increased intracranial pressure that can be seen during a routine neurological exam
papilla starts to protrude into the eye instead of remaining depressed when viewed 3-dimensionally.
where does the pupillary constriction come from
Pupillary constriction is mediated by the parasympathetic component of CN III
what contains the blood vessels and nerves
choroid
pigmented portion and consists of smooth muscles for constricting and dilating the pupil
iris
where is dilation of the eye mediated?
mediated by sympathetic neurons from spinal cord segments T1 and T2
pertaining to a division of the autonomic nervous system originating from brainstem nuclei or the sacral spinal cord
parasympathetic
pertaining to a division of the ANS originating from the lumbar and thoracic spinal cord
sympathetic
what is horner’s syndrome?
Transverse spinal cord lesion at T1 (to T2), result in constricted pupil (aka miosis), ptosis, facial anhidrosis
what types of syndrome can result in blue-gray iris because of failure to pigment
congenital syndrome??
thin guide ropes
zonula fiber
suspended behind the iris by zonula fiber (thin guide ropes) that are anchored in the ciliary body
lens
contains involuntary muscles that vary the tension exerted on the lens by the zonula fibers
ciliary body
Adjusting the shape of the lens to make it more rounded is called
accomodation
why is accommodation in our eyes important?
enables us to focus on near objects
when is the lens flatter?
objects that are further away
when is the lens rounded?
closer objects
a refractive error that makes it hard for middle-aged and older adults to see things up close.
loss of elasticity progresses rapidly after about age 45, and by age 60 accommodation is virtually lost
presbyopia
he light-sensing part of the eye
retina
extension of the diencephalon
retina
what cell types are in the retina?
interneurons, amacrine cells, bipolar cells (CN II cells) and horizontal cells
photoreceptors for black, white and gray vision and are important for night vision
rods
the photoreceptors for color vision and for high visual acuity
cones
what are the photoreceptors of the retina?
rods & cones
specialized receptors in the eye?
photoreceptors
do the superficial layers in the retina (between the light source and the photoreceptive endings) reduce visual sensitivity?
no because the layers of superficial cells don’t absorb/distort the light
most anterior cells in the retina
retinal ganglion cells
axons of these bipolar cells form the optic nerve (CN II)
retinal ganglion cells
what are stimulated by the light?
rods and cones
only rods and cones respond to light
true
Once light reaches rods and cones, what occurs?
graded receptor potentials are produced (more photons, more graded change (amplitude modulated) in receptor potentials)
The excitation is passed on to other cells of the retina
When the retinal ganglion cells finally receive the excitation, action potentials are generated if the stimulus is above threshold
describe the process of stimulation of rods and cones
once the stimulus (light) strikes rods and cones, stimulated and created receptor potential and with enough change triggers an action potential in the nerve, ap travels the pathway and gets info into the CNS and into the brain
where axons of the ganglion cells leave the eye to form the optic nerve
optic disk
natural blind spot
optic disk
region where no photoreceptors, ganglion cells or other interneurons are present
optic disk/natural blind spot
region of the retina about 1 cm in diameter
macula
what provides the sharp straight ahead vision that is needed for driving and reading small print?
macula as a whole
what is the area rich in cones and not rods?
fovea
directly in line with the visual axis and is the region of highest visual acuity
fovea
provides the sharp, straight-ahead vision that is needed for driving and reading small print
macula
How can we get poorer vision?
people with diabetes, genetics, other diseases, aging
About 80% of the fibers of the optic tract synapse in the ________
lateral geniculate nucleus.
Describe the Retinogeniculostriate pathway
Retinal ganglion cells axons of CN II pass to the optic chiasm where some decussate and enter either the left or right optic tract
Most fibers in the optic tracts terminate in the lateral geniculate nucleus of the thalamus
Fibers from the lateral geniculate nucleus project through the internal capsule and become the optic radiations
Projecting to the primary visual cortex (Brodmann’s area 17) either above or below the calcarine sulcus, in the cuneus or lingual gyrus respectively
Projections from LGN to area 17 are ipsilateral
overarching term for things that leave the thalamus and go to the cortex
thalamocortical projections
The visual cortex is also called
striate cortex
Lateral geniculate has ______ layers.
6
Ipsi fibers to layers ________ and contra fibers to layers _______
2,3,5
1,4,6
is everything mapped?
yes
what is the tectal pathway?
combined visual and reflex pathway
describe the tectal pathway
Some fibers of the optic tract synapse in the superior colliculus
Fibers from the superior colliculi project to the pretectal area and to the thalamus (to the pulvinar, a nucleus in the thalamus)
Retina to superior colliculus in the midbrain tectum
where do fibers from the pulvinar go?
Fibers from the pulvinar project on to the cortex (not primary visual cortex but other areas in the temporal lobe for abstract visual interpretation)
what is superior colliculi important for?
visual attention and detection of movement
It activates neurons of the tectospinal pathway to orient the head to a novel moving visual stimulus
relating to biologic variations or rhythms with a cycle of about 24 hours.
circadian rhythms
optic radiations going from lateral geniculate are in what lobe?
temporal
below calcarine sulcus
upper visual field
above calcarine sulcus
down visual field
right vf goes to
left brain
left vf goes to
right brain
can we have vision and auditory problems if we have a deficit to the temporal lobe?
yes, cortical deafness and blindness
what does conjugate eye movement mean?
both eyes move in the same direction
lenses round
accomodation
convergence
when it rounds the lens to see up close, both eyes come close to the nose (both medial rectus muscles pull and lr relaxes on both sides)
Does Bright light directed into one eye causes pupils of both eyes to constrict?
YES
consensual
- light that went to the other eye
direct response
- the one that went to the eye
describe the light reflex
Action potentials from retinal ganglion cells through CN II (optic nerve), optic chiasm and optic tract to the superior colliculus (tectal pathway)
Two halves of the tectum are connected by the posterior commissure
Parasympathetic component of CN III is activated
Ciliary ganglion activated
Pupillary constrictor muscles activated
No cortical involvement
why do physicians flash light into eyes with comas?
w/ cortical head injury, quick assessment that when they flash light in their eye there should be a bilateral reflex constriction and this is to see the BS and T1and T2 to make sure the BS is still in tact
what is the accomodation-convergence reflex
if i go to read something that is close, visual info goes to cortex and lets it know it is blurry, then sends info back out to accommodate and clear the vision
Adjustments of the lens by activation of the ciliary body to bring close objects into focus
After stimulus info reaches the visual cortex, impulses descend from V1 to the superior colliculus to activate the preganglionic parasympathetic neurons of the Edinger-Westphal nucleus
Activation of the ciliary ganglion follows
how do the smooth muscles of the ciliary body move for near vision?
rounded
how do the smooth muscles of the ciliary body move for far vision?
flattened
what happens during near vision?
as the eyes round to focus on a near object, the eyes converge due to contraction of the medial rectus muscles and pupils constrict to increase the definition of the image
CN III functions.
both eyes move in the same direction
conjugate eye movement
lenses round
accomodation
when it rounds the lens to see up close, both eyes come close to the nose (both medial rectus muscles pull and lr relaxes on both sides)
convergence
optic radiations going from lateral geniculate are in what lobe?
temporal
can we have vision and auditory problems if we have a deficit to the temporal lobe?
cortical deafness and blindness
below calcarine sulcus
upper vf
above calcarine sulcus
lower vf
left brain
right vf
right brain
left vf
