Lecture 46 4/30/24 Flashcards
How fast does light travel?
186,000 miles per second
Which cells are involved in vision?
-photoreceptor
-bipolar
-ganglion
What is contained in the outer portion of the photoreceptor cell?
membranous discs
Which protein is embedded in the membranous disc membranes?
rhodopsin
When are the Na+ channels in the outer portion of the photoreceptor cell open?
when it is dark
What does the influx of Na+ into the photoreceptor cell cause?
release of glutamate, an inhibitive neurotransmitter that prevents vision from functioning properly
What is cGMP?
molecule that keeps the Na+ channels open in the photoreceptors
What is retinal?
an aldehyde embedded within rhodopsin
What is 11-cis retinal?
the native form of retinal that makes rhodopsin very stable
What happens when a photon of light strikes rhodopsin?
11-cis retinal becomes all-trains retinal, and rhodopsin becomes active
What happens once rhodopsin is activated?
-causes the beta and gamma subunits to come off of the transducin molecule
-causes GDP to come off of transducin
-causes GTP to attach to the remaining alpha subunit of transducin
How does inactivated transducin differ from activated transducin?
inactivated:
-alpha, beta, and gamma subunits
-GDP
activated:
-alpha subunit only
-GTP
When does the PDE molecule become activated?
when alpha-GTP binds to the gamma subunits of PDE
What is the PDE molecule comprised of?
-one alpha subunit
-one beta subunit
-two gamma subunits
What is phototransduction?
process through which rhodopsin becomes activated, which in turn activates transducin and PDE
What is the role of activated PDE?
-hydrolyzes cGMP into 5’-GMP
-lack of cGMP leads to closure of Na+ channels
Where do the axons of the ganglion cells run?
to the brain
What must occur in order for an image to be seen?
every pixel of the image must be recreated on the retina
What is retinotopic organization?
if an image is created on the retina, it can be transduced all the way to the brain
What happens when an object is 20 feet or more away from the eye?
-light rays are essentially parallel
-cornea is able to recreate image on retina without additional assistance
What happens when an object is less than 20 feet away from the eye?
-light rays diverge, and the cornea is not strong enough to bring them back perfectly to produce an image
-the lens helps to adjust the light rays in order to produce the image
What happens with the lens when we look at a distant object?
-ciliary bodies are at rest and flattened
-ciliary zonules are taut
-lens is pulled into a flattened sphere and serves as a weak refractory surface
What happens with the lens when we look at a close object?
-ciliary bodies contract
-ciliary zonules have slack
-lens is able to form its typical sphere shape and serves as a strong refractory surface
What is accomodation?
process of going from distance to near vision and vice versa
