Visual System Flashcards
Pupil Function
changes the amount of light that enters the eye
Ciliary Muscle Function
contractions alter the curvature of the lens
Lens Function
convex lensbends light to focus it on the retina
Fovea
region of sharpest vision
Optic Disk Function
blind spot, no photoreceptors but where the optic nerve and blood vessels leave the eye
Photoreceptors function
transduce light energy into an electrical signal
- neurons collect the electrical signals to be transmitted along the optic nerve
Light Refraction
2/3’s at the cornea
1/3 at the lens
Lens Manipulation
- Relaxed ciliary muscles
- lens is flat
- distant objects focused - Contracted ciliary muscles
- lens is rounded
- closer objects focused
Presbyopia
loss of lens accommodation due to loss of lens elasticity
Neural Cells of the Retina
- Rods/Cones
- Bipolar Neurons
- Ganglion sensory neurons
Rods and Cones
sensory cells
- convert light energy into electrical signals
- only create graded potentials
Bipolar Cells
connect rods and cones to ganglion cells
- process and integrate info
- converge signals from several photoreceptors
Ganglion Cells
Transmittint Cells
- carry info along the optic nerve
- produce AP
Fovea Receptive Field
- small receptive field
- each photoreceptor has its own ganglion cell
Periphery Receptive Fields
- larger receptive fields
- many photoreceptors converge onto one ganglion cell
Pigment Epithelium Function
- absorbs extra light and prevents reflection
Photoreceptor Outer Segment
- light transduction using membrane disks
Photoreceptor inner segments
- major organelles
- photopigment synthesis and ATP production
Membrane Disks
- light detection
1. rhodopsin
2. conopsin
Rod Function
- low light / night vision
- rhodopsin is the signal transducer
- light hyperpolarizes the cell
Cones Function
- sharp vision and color vision
- 3 types of cones with different photopigments for a different color (red/blue/green)
- light hyperpolarizes the cell
Rhodopsin Details
- Opsin is the GPCR
- Retinal is the visual pigment
- Light hits rhodopsin and turns cis-retinal into trans-retinal
Rods Phototransduction
G Protein = Transducin
- activates Alpha protein which breaks down cGMP
Rod phototransduction in darkness
1) cGMP is high because there is no light to initiate breakdown
2) CNG channels are open, allowing Ca/Na to enter, depolarizing the cell to -40mV
3) nt glutamate is released
Rod phototransduction in light
1) Rhodopsin activated, breaks down cGMP
2) no Ca/Na entrance, cell hyperpolarizes
3) decreased glutamate release
4) adjacent bipolar/ganglion cells are excited
