Neurophysiology 7: Vision (Lecture 81) Flashcards
Eyes that are binocular are indicative of?
Carnivores or predators
Have better depth perception
Eyes that are lateralized are indicative of?
Ruminants or prey
Have larger fields of vision
What are the three tunics/layers of the eye?
Fibrous
Vascular
Nervous System
Where are the photo receptors located?
On the back of the retina
Where is the visual blind spot?
Optic disk
Which part of the eye does the majority of the bending of the light?
Cornea
Does the cornea or lens refract more light?
Cornea refracts light more than the lens does
Light is _______ _____ and ____ on the retina
Upside down
Reversed
What are the layers of the retina?
- Pigament cell layer
- Photoreceptor layer
- Outer nuclear layer
- Outer plexiform layer
- Inner nuclear layer
- Inner plexiform plexus
- Ganglion cell layer
- Optic Nerve Layer
What is the function of the pigament cell layer ?
Absorbs light and prevents light scatter between photoreceptors
Convert trans-retinal to cis-retinal needed by photoreceptors
What is the Tapetem lucidum?
Reflective layer in choroid that increases light detection in dark conditions
Retinal pigment epithelium lacks melanin overlying tapetum
What are the two photoreceptors?
Rods and cone
What is the photoreceptors type of the rod? What is the function of this?
Rhodopsin
Absorbs light
What part of vision do rods aid in?
Night
Scotopic vision
Monochromatic vision
What part of vision do cones aid in?
Color, photopic, or day vision
What is the photoreceptors type of the cones?
Photopsins or iodopsins
How many photopsins do humans and primates have? How many do dogs have?
3 types in humans and primates
2 types in dogs, horses, and other domestic animals
How to stimulate action potential in rods and cones?
G-protein coupled receptors
In the dark, rhodopsin contains _________
Light absorption causes transformation to ________, which dissociates from opsin (bleaching reaction)
Cis-retinal
Trans-retinal
After bleaching, rhodopsin must be rebuilt for the rod to function. What is this process?
- Trans-retinal transported to pigmented layer and actively converted to cis-retinal
- Cis-retinal transported back into rod and combined with opsin
- Process is slow for rhodopsin—rods don’t function well in bright light
After bleaching, the process for cone photospins is similar to that of rhodopsins. BUT how does it differ?
THIS IS FASTER THAN THE PROCESS FOR RHODOPSIN
1.) more intense light needed for bleaching
2.) photopsin regenerates rapidly
Explain the phototransduction process.
- Conversion of cis->trans-retinal changes shape of G-protein
- PDE degrades cGMP
- CGMP gated Na+ channels
- Hyperpolarize the cell and decrease glutamate release
What is the first order neuron for the retinal pathway?
Bipolar cell
What is the 2nd order neuron for the retinal pathway?
Ganglion cells
Under what condition do rods work best? Why is this?
Rods work best in dim light/dark conditions
One photon of light can activate a rod, many needed to activate a cone
Why can one photon of light activate a rod, but you need many to activate a cone?
Due to greater sensitivity and amount of photo pigment in rods
Why are bipolar cells more likely to be activated by low levels of light?
Convergence of rods
Why is there less sensitivity of cone pathway to light?
One cone or just a few cones converge on one bipolar cell
What makes up a bipolar cell? (For rods)
Many rods converge
What is the pathway for conscious perception of vision?
Optic nerve -> optic chasm -> optic tract ->
Where is the lateral geniculate nucleus?
In the thalamus
What is the 3rd oder neuron in the conscious perception of vision pathway?
Lateral geniculate nucleus in thalamus
Each visual field represented in the ______ optic tract.
Contralateral
The closer together the eyes are, the more _____________________________,
The more input each eye gets from BOTH visual fields
Increased medial eye placement -> _____ _____ _______ ______ -> _______ _______ ________ _______
Increased binocular vision overlap -> decreased decussation at optic chiasm
(True/false) Visual input that crosses the midline before entering the eye does NOT need to cross the midline again.
True
Which species has more decussation: cat or horse?
A horse
Does a pupillary light response mean that the animal is visual in that eye?
No
(TRUE/FASLE) Having a pupillary light response does not guarantee that we have conscious perception of vision.
TRUE
What two fibers does the optic tract contain?
Pupillary light response
Vision fibers
Where is the pupillary light response located?
Is subcortical
Midbrain
What does anisocoria mean?
Different size pupils
More decussation = more ____ the eyes
Lateral
What type of response is the menace response?
Cortical response
Describe the menace reflex pathway
Menace reflex tests the retina -> optic nerve -> optic chiasm -> optic tract -> visual cortex -> facial nucleus in medulla
What is the vestibulo-ocular reflex?
Initiates compensating eye movement to keep vision fixed when head turns
CHICKEN VIDEO SLAY SLAYYYYY
Visual startle reflex pathway?
Rostral colliculus in midbrain -> decussation -> descends cord in the to spinal tract -> contraction of neck muscle to turn toward stimulus
