Visual System Flashcards by Libby Sarra

what is the eye composed of

outer
middle
inner (retina) layers

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what is the thin watery fluid anterior to the lens and between the cornea

aqueous humor

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what fluid is in the anterior and posterior chambers

aqueous humor

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where is aqueous humor produced?

ciliary process in the posterior chamber

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how often is ah produced?

replaced every 2-3 hours/constantly produced

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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

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how is the ah replaced?

collects in the canal of schlemm before it enters the venous dranage of the sclera

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Thick, jelly-like semifluid found posterior to the lens, between the lens and the retina

vitreous humor

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what fluid is important for maintaining the shape of the eye/orbit

vitreous humor

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what is the only nerve that the arachnoid follows all along to its final destination?

CN II (optic nerve)

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considered extension of diencephalon/window to the CNS system

CN II

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white part of the eye

sclera

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clear portion of the eye anteriorly
nonadjustable lens of the eye

cornea

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does the cornea layer change shape

no, the lens underneath does

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what is the outer layer also known as

corneoclera layer

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In the adult eye the ______ become the sclera and the choroid which cover the posterior 5/6 of the eye.

meninges

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Sclera is continuous with _____ and the choroid is continuous with the _______

dura
pia-arachnoid

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what can an Opthalmoscopic examination show

specific changes due to increased intracranial pressure

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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.

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where does the pupillary constriction come from

Pupillary constriction is mediated by the parasympathetic component of CN III

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what contains the blood vessels and nerves

choroid

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pigmented portion and consists of smooth muscles for constricting and dilating the pupil

iris

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where is dilation of the eye mediated?

mediated by sympathetic neurons from spinal cord segments T1 and T2

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pertaining to a division of the autonomic nervous system originating from brainstem nuclei or the sacral spinal cord

parasympathetic

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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.

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