Final: Sensory Systems: Eyes Slides Flashcards
What is the stimulus for eyes?
Light (have light-sensitive photoreceptors, that have pigment that senses light)
What are the layers of the eye (outer to inner)?
Fibrous, vascular, neural
What does each layer of the eye do (general)?
Fibrous: outer layer that provides protection with its fibers
Vascular: middle layer; where blood vessels are (provide nourishment)
Neural: inner layer; convert light info to electrical activity
Parts of fibrous layer
Cornea and sclera
Sclera function
Muscle attachment; allows precise movement of eyeballs without needing to move whole head
Sclera structure and location
Majority of outer layer; white part of eye
Cornea structure and location
On top of colored part of eye; thick, transparent membrane; convex
Cornea functions
Protection but more importantly, corrects vision: convex shape corrects for distortion caused by movement of light through different medias (air then liquid)
Parts of vascular layer (6)
Ciliary muscles (smooth), iris, pupil, zonular fibers, lens, choroid
Choroid structure and function
Dark, pigmented layer to concentrate light (contains blood vessels)
Zonular fiber function
Hold lens in place
Ciliary muscle function
Accommodation: allows objects to be focused on retina no matter how near or distant they are (perfect camera that immediately adjusts) - changes shape of lens
Pupil function
Opening for light to enter (covered by cornea)
What type of muscles are ciliary muscles?
Involuntary smooth muscle
When is the lens in each shape?
Flattened (ciliary muscles relax, zonular fibers tight): object is far
Rounded (ciliary muscles contract, zonular fibers loose): object is near
What is the iris?
Colored part of the eye, with pupil at center
How/when does pupil size change?
Dim light: radial smooth muscles contract, pupil dilates
Bright light: circular smooth muscles contract, pupil constricts (smaller)
What happens in the neural layer?
Transduction: light converted to electrical activity, which is sent to the brain (neurons are here)
Retina function
Contains photoreceptors to receive light and send it to brain through optic nerve
Where is the highest density of photoreceptors?
Fovea centralis (high visual acuity)
Types of cells in retina (5)
Ganglion cells, amacrine, bipolar, horizontal, photoreceptors (rods and cones)
Ganglion cell function
Send signal to brain to be interpreted
Amacrine cell function
Support synapses between bipolar and ganglion cells
Horizontal cell function
Support/strengthen synapses between photoreceptors and bipolar cells
What’s the formula for sensation?
Need a receptor cell to synapse with neuron
Pathway after light hits photoreceptors (rods/cones)
Rods and cones form connections with bipolar cells/neurons - bipolar cells form connections with ganglion cells - ganglion cells send signal to brain
Difference between rods and cones
Rods: see B&W, more sensitive (extremely sensitive) to light, respond to low illumination
Cones: see more details (color), less sensitive to light (need a lot of light for stimulation), respond to high illumination
What do photoreceptors need to absorb light?
Pigment
Pigment-containing protein in rods
Rhodopsin (starts process of electrical activity)
Pigment-containing protein in cones
Photopsin
Which pigment do the proteins in rods and cones contain?
Retinal
Types of pigments in cones
Small (blue), medium (green), large (red) - size refers to wavelength
When are cones and rods depolarized?
When we CAN’T see (counter-intuitive)
When are cones and rods hyperpolarized?
When we CAN see
Cones/rods in the dark
high cGMP levels - Na+ channels open - Na+ influx causes depolarization - Ca2+ channels open - Ca2+ influx - NT (glutamate) release - graded potential in bipolar cells
What do Na+ channels in photoreceptors respond to?
Chemically gated; respond to cGMP (open with cGMP is high, closed when it’s low)
How does light induce chemical change in rods (start signal pathway)?
Retinal (pigment) changes chemical conformation - rhodopsin changes shape - activates transducin - alpha subunit translocates and activates phosphodiesterase - breaks down cGMP - Na+ channels close - hyperpolarization - no receptor potential, no NT release, no bipolar cell activity - brain IS getting signal
What is transducin?
Very similar to G protein - has three subunits; alpha subunit translocates and activates phosphodiesterase in photoreceptors
Rods/cones when exposed to light
low cGMP levels - Na+ channels closed - hyperpolarization - no NT release - no graded potential - nothing happens in bipolar cells - brain receives signal
Visual field
When you fixate on one point, what you can see without moving your head
Central vision
What you can see clearly in the visual field (in front of you)
Peripheral vision
Outer edges of vision; things still visible but no longer clear
Why is central vision clear?
Binocular vision: seeing things with both eyes visual fields overlap
Where in the thalamus do visual signals go?
Lateral geniculate nucleus
General neural pathway of vision
Nasal/temporal retina - optic nerve - optic chiasm - optic tract - lateral geniculate nucleus - visual cortex
Which side of brain do nasal retina signals (from both R and L) go to?
Left side
Which side of brain do temporal retina signals (from both R and L) go to?
Right side
Macular degeneration
Lose central vision, but not peripheral vision
Two optic nerves meet to form ____ _____
Optic chiasm
What forms optic tracts?
Some axons cross to opposite side of brain
