Sensory Physiology Flashcards
Visual light spectrum ranges from?
- 750nm Red
to
- 400mn Blue
What does the visual system detect?
- Light stimulus = Electromagnetic waves
What type of light can the eye distinguish?
1) Brightness
2) Wavelength (Color)
Pathway of light stimulus ?
1) Light tranduced by photoreceptors (Retina)
2) Carried to the CNS by axons of the retinal ganglion cells (Optic Nerve)
3) To the Thalamus
4) Projects to the visual cortex
What is the anatomy of the eye that provides protection?
1) Orbit
2) Eyelashes
3) Eyebrows
4) Eyelids
Lacrimal gland provides what property to the eye?
- Secretes tears
- Provides lubrication
What does the nasolacrimal duct function as?
- Drainage into the nasal cavity
What are the two chambers of the eye?
1) Aqueous Humor
(Anterior - Iris - Posterior Chamber - in front of lens)
2) Vitreous Chamber (Behind the lens)
What is located in the aqueous humor and what is its function?
- Low protein
- Plasma like fluid
- Supports the lens
What is located in the Vitreous chamber and its function?
- Behind the lens
- Clear, gelatinous matrix
(Vitreous body) - Maintains shape of eyeball
What alters the shape of the lens?
- Cilliary body/muscles
- Bends incoming light to focus on retina
What is the function of the pupil?
- Controls the amount of light allowed to enter
What determines the eye color?
- Iris pigment
Function of the Canal of Schlemm?
- Drains the aqueous humor (Anterior and Posterior)
- Controls the pressure
Why is the optic disc called the blind spot?
- No photoreceptors
- Where the optic nerve exits the eye
What helps to maintain the pressure, shape and consistency of the eyeball?
- Vitreous humor & Sclera
What is a transparent continuation of the sclera?
- Cornea
What reduces the reflection of the incoming light and helps to sharpen the image?
- Choroid (Pigmented)
What is the function of the Cilliary body?
- Dilates or Constricts the pupil
Where are the rods and cones located in the eye?
- Retina (Photoreceptors)
What is the function of the Macula?
- Center of visual field
- A lot of photoreceptors
- Most acute vision
- lateral to the optic disk
What is the function of the Fovea?
- Largest concentration of Cones (Color Photoreceptors)
- Center of the Macula in the Retina
Does the anatomic axis determine vision?
T of F
- False
- Because it lands in the optic disk, blind spot
Where does the visual axis land?
- Fovea Centralis
- Where the most photoreceptors are located
How does the eye converge light to a focal point on the retina?
- The convex lens is rounded
- Provides clear vision
How does the eye scatter light?
- The concave lens is pulled flat tight
What happens in near vision?
- Lens curvature increases (Rounded) Convex
- Accommodation reflex
What happens in distance vision?
- Lens curvature decreases (Flattened) Concave
- Accommodation reflex
What does the Accommodation reflex help with?
- Adjustment of the lens shape to keep objects focused
What controls the accommodation reflex?
- Cilliary muscles that pull or release the inelastic ligaments (Zonules) which act on the lens
What are the Zonules?
- Inelastic ligaments that are directly connected to the lens
- Help control the shape of the lens
What CN controls the Cilliary muscles?
- CN 3
Oculomotor
What causes the lens to flatten out?
- Long vision (Concave)
- Relaxed Cilliary muscles
- Zonules ligaments pulled tight
What causes the lens to round out?
- Short vision (Convex)
- Contracted cilliiary muscles
- Zonules ligaments relaxed
How do you test accommodation in a pt?
- Finger test
- Test CN 3 function
Define Presbyopia? (Doesn’t have to be pathological)
- Loss of accommodation
- Lost as we age
- Starts diminishing at 10 y/o
- 50% lost by age 40
- Almost 100% by age 60
Define Emmetropia?
- Normal vision
Define Hyperopia?
- Far Farsightedness
- Can not see short distances
- Focal point falls behind the retina
How do you correct hyperopia?
- With a Convex (Flattened) Lens
Define Myopia?
- Near nearsightedness
- Can not see long distances
- Focal point falls in front of the retina
How do you correct myopia?
- With a concave lens
Define Astigmatism?
- Abnormally curved of flattened corneas or eyeball
- Too short of too long
- Caused image distortion
What is the function of the Retina?
- Converts light energy into electrical signals
Where does the most acute vision occur?
- Fovea & Macula regions of the Retina
T of F
The Optic Nerve and the Retina are both part of the CNS?
- True
- Both outgrowths of the brain
What is the only part of the CNS that can be imaged directly noninvasive?
- Retina
- Good way to help monitor Neurodegenerative changes
What is the main link of transmission between Rods and Cones to the Ganglion cells?
- Bipolar cells
What other cells besides Bipolar cells help to process visual input?
- Amacrine Cells
- Horizontal cells
Pathway of vision includes?
1) Rods and Cones
2) Bunch of Processing cells
3) Ganglion cells
4) Ganglion cell Axons
5) Through retina avoiding Macula
6) Through the optic disc
7) Leave the eye Optic Nerve
Where does the light first hit when it enters the eye?
- Pigmented cells (Epithelial cells) with tentacles
- Prevent scattering of light
Where are the photoreceptors located on the retina which are involved in phototransduction?
- Outer
- Inner
- Basal segments of the Retina
What is the function of rod cells?
- Only Monochromatic vision (NO COLORS)
- Not located on Fovea
- Contain Rhodopsin
- Low threshold to low intensity light
- Low acuity
- Night vision
What is the function of Cone cells?
- Color vision (Three pigments, Red, Green, Blue)
- High threshold to high intensity light
- High acuity
- Day vision
- Present on the Fovea
How many layers of cone pigments are there?
- Three layers of membrane infoldings (Like pockets)
- Blue 450nm
- Green 500nm
- Red 700nm
What are the layers of phototransduction on a molecular level?
- Pigmented epithelium
- Outer segment
- Inner segment
- Synaptic Terminal
What is the function of the Pigmented layer?
- Absorbs extra light
- Prevents light distortion
What is the function of the Outer segment?
- Where the Rod and Cones transduce light in the membrane disks?
- Rod cell disk have Rhodopsin active
Retinal + Opsin = Inactive
What is the function of the inner segment?
- Metabolic functions and ATP Syn
What is the function of the synaptic terminal?
- Synapse of the Rod and Cone cells with the bipolar cells
Who are the main players in the phototransduction process?
- Rods and Cones
- Rhodopsin (Active)
- Transducin
- cGMP
- Cyclic Nucleotide Gated (CNG) membrane channels
- Neurotransmitter (Glutamate)
- Light
In darkness what are the active players?
- Opsin + Reinal (Inactive Rhodopsin)
- cGMP high
- CNG and K+ channels open
- Membrane potential @ 40mV
- Ca2+ sensitive channels open
- Glutamate continuoulsy being released into Rod / Bipolar cell synapse
What does light do to rod cells?
- Bleaches activates Rhodopsin (Seperates Opsin and Retinal)
- Activates rod cells (Hyperpolarization)
- Glatamate secretion decreases
What happens during the recovery phase of light transduction?
- Light stimulus gone
- Retinal combines with Opsin (Rhodopsin) recycled
- Increase in Glutamate release
True of False
More light increases the releases of more Glutamate?
- False
- Less light increases glutamate release and seperates Retinal and Opsin
T of F
All optic nerve axons cross over the Optic Chiasm?
- False
- Only certain ones
Where does light from the temporal visual fields project?
- Nasal retina fibers
Where does light from the nasal visual fields project?
- Temporal retina fibers
What do right visual fields stimulate?
- Left half of each retina
- Transmitted to the Left hemisphere
What do left visual fields stimulate?
- Right half of each retina
- Transmitted to the right hemisphere
What visual fibers cross at the optic chiasm?
- Nasal retina fibers
- Process Light from the temporal fields
T or F
Temporal retina fibers cross at the optic chiasm?
- False
- Project to the same side that its being projected from
- L Temporal = L Hemisphere
- R Temporal = R Hemisphere
Where does light from the left visual field project?
- Right side of the brain
Where does light from the right visual field project?
- Left side of the brain
What defines the binocular zone?
- Objects seen by both eyes = 3D
- Overlap area
Objects seen with only one eye?
- Fall outside the binocular zone
- 2D
