Visual System Flashcards
What are the 10 layers of the retina?
- Inner limiting membrane – tight junctions of Muller cells
- Ganglion cell axons – form optic nerve at optic disc
- Ganglion cells – M‐type and P‐type cells
- Inner plexiform (synaptic zone) layer – synapses between bipolar and
ganglion cells (amacrine cells modulate output of bipolar cells) - Inner nuclear layer – cell bodies of bipolar, horizontal and amacrine cells;
nuclei of Muller cells - Outer plexiform layer – synapses between photoreceptors and bipolar cells
(horizontal cells modulate output of photoreceptors) - Outer nuclear layer – cell bodies of rods & cones
- Outer limiting membrane – tight junctions of Muller cells
- Photoreceptor layer – phototransduction by rods and cones
- Pigmented epithelium – metabolic support for tips of photoreceptors; absorb
stray photons of light
Are there action potentials in the rods and cones?
NO!
Where are the first action potentials of the retina?
In the axon of ganglion cells
What are characteristics of rods?
Highly sensitive and specialized for night vision
What are characteristics of cones?
Low sensitivity and specialized for daylight
What is the order of cells that light hits NOT at the fovea?
Ganglion Cells
Interneurons
Photoreceptors
What is special about the fovea in the retina?
There are only cones and NO RODS.
There is also only photoreceptors and NO blood vessels, interneurons or ganglion cells are present.
Describe the pathway from the retina to the visual cortex?
Optic nerve ->
Optic chiasm (axons from nasal retina cross here) ->
Optic Tract ->
Lateral Geniculate Nucleus (thalamus) ->
Optic Radiations (geniculocalcarine tract) ->
Visual Cortex
What are the 2 main classes of ganglion cells?
M-type: Large cell bodies and dense arborizations, 50 rods to 1 ganglion cell; large receptive fields; transient response to continuous light (rapidly adapting); respond best to movement and large objects; RODS
P-type: Small cell bodies, with 1:1 relation to cones; small receptive fields; more numerous near fovea; wavelength selective (color); respond best to color and fine detail (high acuity); CONES
What visual information enters the brainstem via the pretectal area?
Information for pupillary reflexes
What visual information enters the brainstem via the superior colliculus?
Information for head and eye movements
What are the optic radiations of the upper and lower fibers?
Upper Fibers - correspond to lower field of vision and are via the parietal lobe
Lower Fibers - correspond to the upper field of vision and is done via the Meyer’s Loop of the temporal lobe
What results in a lesion of the right optic nerve?
Blind Right Eye
What results in a lesion of the optic chiasm?
Bitemporal hemianopia - vision is narrowed
What results in a lesion of the right optic tract?
Left homonymous hemianopia - loss of both left fields
What results in a lesion of the fibers of the Meyer’s Loop in the right temporal lobe?
Left homonymous upper quadrantanopia (“Pie in the Sky” lesion) - loss of left upper quadrants in both eyes
What results in a lesion of the lateral geniculate body?
Left homonymous hemianopia - loss of both left fields
What results in a lesion of the optic radiation fibers?
Left homonymous lower quadrantanopia (macular sparing often present) - loss of lower left quadrants in both eyes
What results in a lesion of the calcarine sulcus?
Left homonymous hemianopia with macular sparing - like with optic tract and lateral geniculate but with macular sparing
What is the direct and consensual pupillary reflex?
The response of the illuminated eye is the direct reflex, the response of the unilluminated eye is the consensual response. Both pupils constrict due to the bilateral connections to the Edinger-Westphal nucleus by the optic fibers traveling through the brachium of the superior colliculus to the pretectal area.
What is the accommodation reflex?
It consists of vergence of the eyes (contraction of both medial recti muscles), ciliary muscle constriction (which causes the lens to thicken by releasing tension on the zonular fibers), and constriction of both pupils which improves optical performance and reduces light entering the eye due to greater reflectance from the nearer object.
Describe the pathway of the accommodation reflex.
Visual Cortex in Occipital Lobe -> Lateral Geniulate Nucleus in Thalamus -> Occulomotor Nucleus
What does optic nerve damage result in regards to the pupillary reflex?
It produces equal pupils, neither of which responds to light shone in the eye ipsilateral to the lesion, but both eyes respond normally to light shone in the contralateraleye.
What does occulomotor nerve damage result in regards to the pupillary reflex?
It causes a dilated ipsilateral pupil that does not respond to light shone into either eye. The contralateral eye will still respond to direct and consensual reflexes.
