Visual System Flashcards
T/F: the eye is a globe that is filled with fluids
True
How many layers does the eye have?
Three
Outer layer, middle layer, and inner layer (retina)
Where are the vision receptors in the eye?
In the inner layer (retina)
What fluids are in the eye?
Aqueous humor and vitreous humor
What is aqueous humor?
Thin watery fluid anterior to the lens, between the lens and the cornea
Does aqueous humor contain nutrients for the cornea and the lens since the cornea and lens lack blood supply?
Yes
We cannot have blood supply in those areas because it needs to be clear so we can see through it
What is vitreous humor?
Thick, jelly-like semifluid found posterior to lens, between the lens and the retina
Why is vitreous humor important?
It is important for maintaining shape of the eye/orbit
And it also allows the eye to change shape to focus
What is the outer layer of the eye?
Sclera and cornea
Which outer part of the eye is the white part?
Sclera
What outer part of the eye is the clear part?
Cornea
T/F: The cornea is the non-adjustable “lens” of the eye
True
What portion of the middle layer contains blood vessels and nerves?
Choroid
What portion of the middle layer is the pigmented portion and consists of smooth muscles for constricting and dilating?
Iris
What mediates pupillary constriction?
Parasympathetic component of CN III
What mediates dilation?
Sympathetic neurons from T1 and T2
The lens is suspended behind the iris by what?
Zonula fibers
What is the ciliary body?
Contains involuntary muscles that vary the tension exerted on the lens by the zonula fibers
What is the function of the ciliary bodies?
The adjust the shape of the lens to make it more rounded, accommodation
Do we lose the ability to accommodate as we age?
Yes
It becomes hard to switch back and forth between focusing on things that are close to us and far away
What does the retina do?
It is the light sensing part of the eye
What is the retina an extension of?
Diencephalon
What are the different cell types in the retina?
Interneurons, bipolar cells, amacrine cells, and horizontal cells
What do the bipolar cells in the retina represent?
The optic nerve (CN II)
Rods are the photoreceptors for what type of vision?
Black, white and gray vision
Night vision
Cones are the photoreceptors for what type of vision?
Color vision
High visual acuity
T/F: the light has to travel through multiple layers to get to the receptive portion of the rods and cones
True
What are retina ganglion cells?
Most anterior cells of the retina
Axons of these bipolar cells form the optic nerve (CN II)
What is the process of stimulation of the rods and cones?
Rods and cones are stimulated by light
Once they are stimulated, graded receptor potentials are produced (little light gives little voltage change)
The excitation is passed on to other cells of the retina
When the retinal ganglion cells finally receive the excitation, AP generated if the stimulus is above threshold
Are there photoreceptors, ganglion cells, or other interneurons present at the optic disk?
No
This is where the axons of the ganglion cells leave the eye to form the optic nerve
What is the optic disk?
Natural blind spot
How big is the macula?
1 cm in diameter
Where is the macula?
Around the fovea
What is special about the macula and fovea?
It is an area rich in cones (no rods)
What is special about the fovea?
It is directly in line with the visual axis and is the region of highest visual acuity
What is special about the macula?
It provides sharp, straight-ahead vision that is needed for driving and reading small print
What is the central visual pathway?
Retinogeniculostriate pathway
Where does the retinogeniculostriate come from and lead to?
Retina to V1
What are the steps of the retinogeniculostriate pathway?
Retinal ganglion cells axons of CN II pass to the optic chiasm where some decussate and enter either the right or left optic tract
Most fibers in the optic tract terminate in the lateral geniculate nucleus of the thalamus
What are the steps from the eyeball to the brain?
Nerve, chiasm, tract, brain
What are the cortical connections from the lateral geniculate nucleus?
Fibers project through the internal capsule and become optic radiations
Projecting to the primary visual cortex either above or below the calcarine sulcus
Are projections from the lateral geniculate nucleus ipsilateral?
Yes, they only cross over in the optic chiasm
Is the lateral geniculate nucleus mapped?
Yes
What is the light reflex?
Bright light directed into one eye causes pupils of both eyes to constrict
Contraction of the pupillary constrictor muscles
What eye has the direct light response?
The eye that is stimulated
Which eye has the consensual light response?
The unstimulated eye
How does the light reflex happen?
AP from the retinal ganglion cells through CN II, optic chiasm, and optic tract to the superior colliculus
Two halves of the superior colliculus connected (communicating)
Parasympathetic component of CN III activated
Ciliary ganglion activated
Pupillary constrictor muscles activated
No cortical involvement
What is the accommodation-convergence reflex?
Adjustments of the lens by activation of the ciliary body to bring close objects into focus
Is there cortical involvement in the accommodation-convergence reflex?
Yes
What are the steps of the accommodation-convergence reflex?
After stimulus info reaches V1, impulses descend to the superior colliculus to activate preganglionic parasympathetic neurons
Activation of the ciliary ganglion follows
To cause smooth muscles of the ciliary body to round the lens for near vision
Is the accommodation-convergence reflex similar to the light reflex?
Yes
