lecture 9 Flashcards
what is light?
light is composed of photons - particles of energy, emitted from atoms, that travel through space as wave
what is the light spectrum?
visible light for humans (390-750nm) is part of the electromagnetic spectrum
what are the 2 ways we see objects?
with 1. emission
and 2. reflection - light source emits light rays and hits object to reflect off of it
what is the pigment epithelium
provides nutrients to photoreceptors from the choroid (blood supply)
The Pigment absorbs excess photons
Involved in the visual transduction cycle
- In cats the pigment epithelium is called tapetum
- It doesn’t absorb pigment but reflect
- Reason why cats have good night vision
what is phototransduction
turning absorption of light into neural signal
(visual pigment absorbs light, which results in a change in the membrane potential)
how do we see objects?
example: flower
Flower goes through cornea (exterior layer), pupil (a hole that expands), Iris (colorful part of eye that contains pigment), and lens (focuses light and this turns the photo upside down)
Flower hits the retina (in retina everything is upside down)
some point in visual cortex the image gets flipped again
what are Rods and cones
respond to light that makes up the image of an object on the retina
what is pigment
something that absorbs light
whats the process of photoreceptors and phototransduction
In the dark there’s no photons and sodium channels are opened in photoreceptors, photoreceptors release NT (glutamate) in dark
In the dark: net depolarization
In light: hyperpolarization (more negative) in photoreceptors
what is the difference between rods and cones
Cones:
Daytime vision
Color vision
High spatial resolution
Fovea - ONLY CONES, primates and raptors only species with fovea
Rods:
Nighttime vision
Low spatial resolution
In peripheral vision only we only have rods
Absent in the fovea
Rods are activated in scotopic vision (night time vision)
do we have more rods or more cones in the retina
10x more rods
connection with cones?
cones in phobia have one to one connection
1 cone = 1 bipolar cell
connection with rods?
1 rod = sends to many bipolar cells (which means we perceive the output as larger).. this is why rods have low spatial resolution
many rods =
what determines spatial resolution?
convergence
where is vision formed
in the retina
why is Left visual field → right hemisphere and Right visual field → left hemisphere
LVF hits the:
Temporal portion of right retina
Nasal portion of left retina
RVF hits the:
Nasal portion of right retina
Temporal portion of left retina
Nasal retina projects contralaterally to LGN
Temporal retina projects ipsilaterally to LGN
(contralateral cross at “optic chiasm”)
what are the 2 most prevalent neurodegenerative diseases of photoreceptors
Retinitis pigmentosa - genetic disease, diagnosis is young, you will go completely blind, 1 in 4000
AMD - later diagnosis, lose foveal vision, 1 in 9, rods die first then cones
what are the 2 ways Vision restoration work
- sub retinal prosthesis..
Current prosthesis maximize contrast, but this isn’t reflective of natural scene statistics, patients can see zoomed in and contrasted version of a scene
2.Photoreceptor regeneration
Some vertebrates are capable of CNS regeneration (mitosis)
Muller glia cells (primary glia of the retina) reprogram to become neural progenitors (or stem cells) (this makes it capable of mitosis in adulthood and restore any lost cells)
What spectrum does visible light fall on, what are some other waves on this spectrum?
Visible light is a part of the electromagnetic spectrum. Some waves that are faster than the visible
spectrum are UV and Xray’s, while some slower waves are AM and FM radio waves. Some
animals have cones that are responsive to UV such as bees.
whats the visible light for humans
Visible light for Humans (390 - 750nm)
