VISUAL SYSTEM Flashcards
What type of photoreceptor is most abundant at the FOVEA?
CONES
- avascular region
Which photoreceptor is found on the peripheral part of the retina, is monolithic, transient, and for low light?
RODS
Where do axons of ganglion cells converge to form the optic nerve?
OPTIC DISK
- blind spot
What is the visual pathway from the retina?
- Optic nerve
- Optic Chiasm
( nasal retina axons cross) - Optic Tract
- Lateral Geniculate
- Optic Radiations
- Visual Cortex (occipital lobe)
Which parts of the retina cross? Which don’t? Which project medially? Laterally?
- TEMPORAL PORTIONS of retina DO NOT cross
- medial vision - Nasal portions cross
- lateral vision
70% of the visual cortex comes from what region?
FOVEA
Which cells have: 1. Large cell bodies 2. Dense DENDRITES 3. LARGE receptive fields 4. Rapidly adapting 5. respond best to MOVEMENT Which photoreceptors are these cells composed of?
M-Type cells
(Magno-cellular)
- RODS!!!
(M=man is color blind)
Which cells have:
- Small cell bodies
- short DENDRITES
- SMALL receptive fields
- more in FOVEA
- respond best to COLOR & FINE DETAIL
Which photoreceptors are these cells composed of?
P-Type
(Parvo-cellular)
-CONES!!!
Where does perception begin? Where else does information enter the brainstem?
Primary Visual Cortex
(AREA 17 in the Calcarene fissure of Occipital Lobe)
ALSO:
- Pretectal Area (pupillary light reflex)
- Superior Colliculus (head & neck movements –> descending MLF)
For optic radiations, where do upper fibers travel? Lower?
upper = PARIETAL
lower = TEMPORAL
Upper optic radiations end up at which visual field? lower?
Upper = INFERIOR
Lower = SUPERIOR
Which fibers makeup Meyer’s loop?
LOWER optic Radiations
If you cut the RIGHT optic nerve, what is the result?
RIGHT EYE blindness
If you cut the OPTIC CHIASM, what is the result?
TUNNEL VISION
- Bilateral Hemianopeia
- lateral (nasal) vision is not functioning
If you cut the RIGHT optic TRACT, what is the result?
Homonymous Hemianopia in the LEFT
lose temporal vision of LEFT eye, and RIGHT nasal vision of RIGHT eye
If you cut the RIGHT MEYER’s loop, what is the result?
(lower fibers = SUPERIOR vision)
Left Homonymous Superior Quadrantanopia (upper)
PIE IN THE SKY!!!
If you cut the RIGHT Lateral Geniculate fibers, what is the result?
same as cutting the optic tract
- LEFT homonymous Hemianopia
lose left temporal field, and right nasal field
If you partially lesion the RIGHT Optic Radiation fibers, what is the result?
LEFT Homonymous INFERIOR Quadrantinopeia
If you lesion all the RIGHT Optic Radiation fibers (either stroke or car accident), what is the result?
Left Homonymous Hemianopeia with Macular Sparing
What is the direct reflex and the consensual reflex?
Direct = light shone into LEFT eye so pupil constricts
Consensual = RIGHT pupil constricts as a result to the light in the left eye
Why do both pupils constrict when light is shone into the Right eye?
Bilateral Connections to Edinger-Westphal nucleus by optic fibers
- in SUPERIOR COLLICULUS & PRETECTAL area
Which area is responsible for the pupillary right reflex?
PRETECTAL area
If the RIGHT optic nerve (CN2) is damaged, and light is shown into this eye what is the result? What if light is shined into the eye without the lesion?
NEITHER PUPIL constricts
(direct response lacking and consensual)
BOTH PUPIL constrict when shine light into opposite eye (consensual response & direct response in tact)
What is the result if light is shined into an eye with CN3 lesioned?
PUPIL in neither eye responds to the light (regardless of damaged eye)
What are the sympots of Horner’s syndrome? What has been lesioned?
- Meiosis
- Ptosis
- Anhydrosis
- lesion of Superior Cervical Ganglion
What are the 3 results in changing gaze to focus on a nearby object?
- Vergeance of eyes (contract medial recti)
- Ciliary muscle constrict (lens thickens since tension released on zonulr fibers)
- Constriction of both pupils (to reduce light and improve optical performance)
What is the corneal eye blink reflex mediated by?
- Free nerve endings in cornea
- Spinal Trigeminal (pain)Tract or Chief Sensory (touch)
- Interneurons
- Motor neurons in CN 7
- Orbicularis oculi
What distributes information from each cornea during the CORNEAL BLINK REFLEX bilaterally to Facial Motor Neurons?
Reticular Formation Interneurons
(relay station)
- eye blink is consensual = happen to both eye
The corneal blink reflex directly involves with 2 cranial nerves?
CNV1 (ophthalmic division)
CN 7 - Orbicularis Oculi
(CN 8 also, since responding to loud sounds can cause us to blink, CN 3 = respond to bright light)
Which layer of the primary visual cortex is most expanded?
IV
What are the 3 specialized hyper columns and their main functions?
- Orientation –> spatial (vertical, horizontal perception)
- Blobs –> color specificity
- Occular DOminance - LEFT vs RIGHT
Which cells are responsible for motion and spatial relationships or WHERE an object is?
MAGNOCELLULAR
Which cells are responsible for depth and form, stationary objects & shapes?
PARVOCELLULAR cells
- interblob = depth and form
- blob = color sensitivity
Which cortex (temporal or Parietal) is responsible for where an object is? What an object is?
Parietal (dorsal stream, non-color discriminative info) = WHERE
TEMPORAL (ventral stream from color & non) = WHAT AN OBJECT IS
What are the 2 ways to detect motion o an object?
- Image moves temporally across retina (eye =stationary)
2. Head & eyes move to fix image on FOVEA
Where is movements best represented?
Middle Temporal area of V5 (Medial Superior Temporal area)
If the head is not moving, what kind of detection is used?
TEMPORAL
How does the cortex perceive color?
Compares the differences in brightness & output, thus assigned a COLOR to that particular combo
What kind of color cones are missing in the fovea?
BLUE
How many cone systems does a human have?
3
Red
Bue
Green
On presentation to the emergency room, the pupillary light reflexes are tested on an unconscious patient. The direct response to stimulation of the right eye is normal, as is the consensual response. Both the direct and consensual responses are absent when light is shown in the left eye. Where is the deficit in this patient? Optic chiasm Right optic tract Left optic nerve Left oculomotor nerve Right calcarine sulcus
C) Left Optic N.
A 79-year-old woman complains to her physician that she is having trouble seeing. She has no previous history of visual problems. Visual field examination reveals a right, superior quadrantanopia. Ophthalmoscopic examination shows no abnormalities with the optic disc, retinal vasculature or signs of retinal detachment. Which one of the following represents the most likely location of the lesion in this woman?
a) Left lateral geniculate nucleus (inferior quadrantinopea)
b) Left Meyer’s loop
c) Left calcarine gyrus
d) Right Meyer’s loop
e) Right optic tract
B) Left Meyer’s Loop
. A visit to her physician confirms a partial visual loss, and MRI reveals a vascular lesion in the right hemisphere in the upper Calcarene sulcus. What deficits is the woman experiencing?
a) Left homonymous hemianopia
b) Left inferior quadrantanopia
c) Left superior quadrantanopia
d) Right inferior quadrantanopia
e) Right superior quadrantanopia
b) Left Inferior Quadrantanopia
