Vision 2.2 [HY] Flashcards
What’s Sclera?
White of the eye
Choroidal vessels
two sets of blood vessels, supplied the eye with nutrients
Retina Vessels
complex intermingling
of blood vessels between the sclera and the retina
Retina
contains actual photoreceptors that transduce light into electrical information the brain can process.
Cornea
clear, domelike window in the front of the eye, which gathers and focuses the incoming light
Anterior Chamber
front of the eye, lies in front of the iris
Posterior Chamber
Between the iris and the lens
Iris
- colored part of the eye
- Two Muscles: dilator pupillae, which opens the pupil under sympathetic stimulation & constrictor pupillae, which constricts the pupil under
parasympathetic stimulation - continuous with the choroid
Choroid
vascular layer of connective tissue that surrounds and provides nourishment to the retina.
Ciliary Body
produces the aqueous humor that bathes the front part of the eye before draining into the canal of Schlemm
Lens
Lies right behind the iris and helps control the refraction of the incoming light.
Ciliary Muscle
As the muscle contracts, it pulls on the suspensory ligaments and changes the shape of the lens to focus on an image as the distance varies (called accomodation)
Vitreous Humor
transparent gel that supports the retina
Retina
- Back of the eye and is like a screen consisting of neural
elements and blood vessels. Its function is to convert incoming photons of light to electrical signals. - Part of CNS
Duplicity theory of vision
retina contains two kinds of
photoreceptors (Cones and Rods)
Cones
- Color vision
- Sense fine details
- requires far more light b/c each cone responds only to certain wavelengths of light
Rods
- more functional than cones
- highly sensitive to photons
- easier to stimulate than a cone cell
- can be stimulated by light of any color (unlike cones)
- Only sense light and dark
- Not great for detecting fine details b/c spread over a much larger area of the retina
- More rods than cones
Rhodopsin
- Reason for sensitivity of rods
- all rods contain only a single pigment type
Macula
- Central section of the retina
- has a high concentration of cones
Fovea
- the centermost region of the macula
- contains only cones
- Further away from fovea, rod concentration increases and cone decreases
- Where visual acuity is best
Optic Disk
- devoid of photoreceptors
- gives rise to a blind spot
Bipolar Cells
- Where rods and cones synapse directly & highlight gradients between adjacent rods or cones
How does photon travel in eye?
Rods & Cones in back of the eye -> action potentials Bipolar Cells -> Ganglion Cells -> Optic Nerve
Resolution relationship with ganglion
- More receptors on one ganglion the lower the resolution
- Fewer cones on single ganglion cell than rods
Amacrine and Horizontal Cells
- receive input from multiple retinal cells in the same area before the information is
passed on to ganglion cells. - accentuate slight differences between the visual information in each bipolar
cell - increase our perception of contrasts
Visual Pathway
- Visual information is processed contralaterally
- Nasal fibers cross at optic chiasm
- the temporal field of each eye
stimulates the nasal fibers of each eye
LGN of thalamus
some visual signals synapse with nerves that then pass through radiations in the temporal and parietal lobes to the visual cortex
- Has Parvo and Magnocellular cells
Superior Colliculi
- When nerve fibers skip the thalamus, go to Superior Colliculi in midbrain
- control some reflexive responses to visual stimuli and reflexive eye movements.
Parallel Processing
- brain’s ability to analyze information regarding color, form, motion, and depth simultaneously
- i.e. use independent pathways in the brain
Form
- Object and its boundaries
Parvocellular Cells
- In LGN
- Where neurons carrying information from the fovea and surrounding central portion of the retina synapse
- High spatial resolution: detect very fine detail
- Low Temporal resolution
Temporal Resolution
Ability to detect fast/moving objects
Magnocellular Cells
- In LGN
- high temporal resolution
- Good for detecting motion
- In periphery
Binocular Neurons
responsible for comparing the inputs to each hemisphere and detecting these differences.
Feature Detectors
- detects a very particular, individual feature of an
object in the visual field - Activated in parallel