Visual system Flashcards
What is the optic nerve?
Bundle of axons at the retina
What is the ability to focus light dependant on?
The refractive power of both the cornea and the lens, as well as the shape of the eye globe
What is hyperopia
Far sightedness, refractive power is insufficient for close objects
What it myopia
Near sightedness, refractive power is too strong for distant objects
What is the pupillary light reflex
Connections between the brainstem and retina that contract the pupil in response to light
Circular muscles
Decrease the pupil size
Radial muscles
Dilate the pupil
VIsual field
Amount of space viewed by the retina when the eye is straight ahead
Visual acuity
Ability to distinguish two nearby points
What determines visual acuity
Photoreceptor spacing and refractive power.
What is the direct pathway for signal transmission
Photoreceptors —-> Bipolar cells —–> Ganglion cells
What are the lateral connecting neurons
Amacrine cells and horizontal cells
What are the 4 segements of photoreceptors
outer, inner, cell body, synaptic termina
Photoreceptors convert…..
electromagnetic radiation to neural signals
What happens to membrane potential when exposed to light
Vm hyperpolarizes.
What is the “dark current”
A cGMP-gated Na+ channel that is open in the dark and closed in the light
How does the brain percieve objects in the visual field
A shift in Na+ sends a signal to the brain
During the dark current, what is released?
A steady release of neurotransmitter
What is rhodopsin made of?
Retinal and Opsin
Where is rhodopsin present
Membrane folds known as disks in the outer segment of rods
What does light convert 11-cis-retianl to?
all-trans-retinal (activated form)
What are rods best for?
Seeing in dim light
What are cones best for?
Seeing in normal daylight
What are “on” and “off” pathways
Bipolar and ganglion cells can detect increases and decreases in luminance
