Eyeballs Flashcards
What is the sclera?
White of the eye
How does the eye move in orbit?
3 extra ocular muscles
What are the two parts of the lens?
Aqueous humor and vitreous humor
What is the aqueous humor?
Nourishes cornea and is watery
What does the vitreous humor do?
Keep eye spherical, is 80% of the eyeball, and has phagocytic cells that remove debris
What is the choroid?
The capillary bed that provides blood to the photoreceptors
What is visual acuity?
Ability to distinguish two points that are close to each other (depends on space of photoreceptors)
Where do photoreceptors sit?
Pigment epithelium
What does the pigment epithelium do?
Reduces backscatter and renews photopigments and phagocytoses photoreceptor disks
What is the reflective layer beneath the photoreceptor layer?
Tapetum lucidum (causes eye shine)
Are there more rods or cones?
Rods (18x more)
What is contained in the membranous disks of photoreceptors?
Opsins
What photopigment is contained in rods?
Rhodopsin
Are cones or rods more sensitive to light?
Rods are 1000x more sensitive
What type of photopigment do cones have?
3, one for each color (blue, green, red)
What does scotopic mean?
Darkness lightning, relies on rods
What does photopic mean?
Daytime lighting, mostly cones
What photoreceptor is 100% present in the fovea
Cones
What is the ratio of photoreceptors to ganglion cells in the fovea?
1:1
What type of vision is the fovea best at seeing?
High rest vision
Are there more rods or cones in the peripheral retina?
Rods
What type of lighting is the peripheral retina best at seeing?
Dim light
How is a visual pigment molecule formed? (The components)
A chromophore (11-cis retinal) and an opsin
Why is 11-cis retinal important
It changes shape when hit with light
What is an opsin?
A GPCR
Are rods depolarized or or hyper polarized in the dark?
Depolarized, steady Na+ flow inside
What are the Na+ channels in the rods gated by?
CGMP, produced by guanylyl cyclase
What happens when light hits the photoreceptors
Rhodopsin is stimulated, activates transducin, transducin actives PDE, PDE turn cGMP into GMP, Na+ leaves the cell and causes the cell to be hyperpolarized
What receptors are on ON bipolar cells?
mGluR6, causes depolarization when glutamate isn’t present
What receptors are on OFF bipolar cells?
AMPA receptors, causes hyperpolarization when glutamate is present
What do horizontal cells do?
Inhibit the center photoreceptor with GABA-like NTs (only when glutamate hits the horiz cells)
What is the emphasis of contrasting light and dark edges called?
Luminance contrast
What are the 3 types of ganglion cells?
M-type, P-type, nonM-nonP type ganglion cells
What are some characteristics of M cells?
Larger receptive fields, APs are faster, low rest vision contribution, fires via transient bursts
What are some characteristics P cells?
Smaller receptive fields, high res vision contribution, fire sustained APs
What are the % populations of each of the retinal ganglion cells?
90% P-type, 5% M-type, 5% nonM-nonP type
What are the color opponents combinations?
Blue/Yellow and Green/Red
What are the Retinal ganglion cells that respond to sunlight and aid circadian rhythms?
IpRGCs
What is the opsin in ipRGCs?
Melanopsin
What is the optic chiasm?
A partial decussation of the optic nerves
What crosses the optic chiasm? Temporal or Nasal?
Nasal
Where to ganglion cell axons terminate?
LGN (located in thalamus)
What does the Suprechaismatic nucleus (SCN) of the hypothalamus do?
Controls circadian rhythms
Where is the pretectum? What does it control?
Between thalamus and midbrain, controls pupil size
What does the superior colliculus do?
Orients eye towards new stimuli, basically moving ur eye towards something the brain finds interesting
What’s the difference between visual field and hemifield?
Visual field is the entire region ur eyes see straight ahead, the hemifield is the imaginary halves of ur vision
What side of the brain does the left hemifield project to?
Right
What side of the brain does the right hemifield project to?
Left
What would a lesion to the left optic nerve do?
No vision in left periphery
What would a lesion in the left optic track do?
No vision in the right hemifield
What would happen if you lesion the optic chiasm?
All periphery would be lost
How many layers are there in the LGN?
6
What layers are ipsilateral in the LGN?
2, 3, and 5
What layers are contralateral in the LGN?
Layers 1,4, and 6
What layers in the LGN are M-type?
1 and 2
What layers in the LGN are P-type?
3-6
Are M-type or P-type ganglion cells sensitive to differences in wavelength?
P-type
What is the Primary Visual Cortex?
V1
What area in the retina is overrepresented in V1?
Central retina (aka fovea)
What is the breakdown on the 6 (really 9) layers of V1?
Layer 1
Layer 2
Layer 3
Layer 4A
Layer 4B
Layer 4Ca
Layer 4Cb
Layer 5
Layer 6
Which layer is the primary recipient of LGN afferents?
4C
What is contained in layer 4C?
Spiny Stellate cells which make connections within the cortex
What layers are pyramidal cells found in?
Layer 3, Layer 4B, Layer 5, Layer 6
What do the pyramidal cells do in V1?
Send axons OUT of V1
Which sub layer in Layer 4C are M-cell LGN neurons?
Alpha
Which sub layer in Layer 4 are P-type LGN neurons in?
Beta
What are the intra-cortical connections?
Layer 4Ca -> Layer 4B & Layer 4Cb -> Layer 3
Which neurons are binocular?
Most neurons outside of layer 4C
What is the word for being able to recognize depth perception?
Stereopsis
Where do Layer 2, 3, and 4B project to?
Other cortical areas
Where does Layer 5 project to?
Superior colliculus and pons
Where does Layer 6 project to?
Back to the LGN
What is a neuron being more sensitive to one orientation called?
Orientation selectivity
What are subsets of cells that are sensitive called? ____ selective
Direction
What type of neuron is synonymous for being direction selectivity?
M-type (think: motion)
What is the dorsal stream meant for?
Navigation, directing eye movements, motion perception (basically movement, M-type cells)
What is the ventral stream for?
Facial recognition, shape and colors, and potentially visual perception and visual memory (P-type cells)
