Special Senses II Flashcards
What is the role of the lens?
Accomodation
What flattens the lens?
Suspensory ligaments (ciliary muscle relaxes)
Lens flattening = near or far vision?
Far
Ciliary muscle contraction does what to the lens? What is the for?
Lens assume a more spherical shape
–near vision
The ciliary muscle of the eye contracts in response to what type of stimulation?
Parasympathetic
What is presbyopia?
Near point of vision recedes
True or false: the optic tract is part of the PNS, and is myelinated by schwann cells
False– part of the CNS, myelinated by oligodendrocytes
Round lens = contracted or not ciliary muscle?
Contracted
What are the three processes that occur while looking at a near object?
- Accommodation
- Convergence of visual axes
- Pupils constrict
What are the cells in the RPE that spread out horizontally?
Horizontal cells
Amacrine cells
What is a scotoma?
Visual field defect
Where are the rods and cones in the RPE?
In the back
What are the cells the the rod/cones connects to?
Bipolar cell, then
Ganglion cell
Do we regenerate rods?
No, but we renew them
What are the cells that are involved in scotopic vision (rods or cones)?
Rods
What are the cells that are involved in phototopic vision (rods or cones)?
Cones
What is the function of Vit A?
Part of the rod pigment rhodopsin
What is the only cell in the retina, beside rods and cones, that can sense light? What pigment do these cells contain? Purpose?
intrinsically photosensitive retinal ganglion cells contain melanopsin; seem to measure overall light intensity
What is the MOA of retinal detachment?
Vitreous seeps behind the retina, causing suffocation of the RPE.
Does the optic disk have photoreceptors? How about the fovea?
Fovea= yes, duh
Optic disk = no
Why is the foveola an avascular zone?
You can’t see through blood vessels
Where is the maximum number of rods?
Parafoveally
What is meant by the term meso topic?
Using both rods and cones
How many types of pigments are there in cones?
3
What is the symptom of Vit A deficiency?
Night blindness
What happens in the dark to rods and cones?
Na and Ca channels are held open by cGMP, to depolarize by constantly leaking K
What happens in the light to rods and cones? (3)
- Na+ / Ca++ channels close
- photoreceptor hyperpolarizes as K+ leaves cell
- decrease in release of neurotransmitters
Photoreceptors hyperpolarize or depolarize to light?
Hyper polarize
What is the molecular change that occurs with rod bleaching? How does it get back?
11-cis retinal goes to all trans retinal
Chaperones bring it back to cis
Why is the eye affected in MS?
Oligodendrocytes; not schwann cells
The retina is form by evagination of what part of the embryological brain?
Diencephalon
The axons of what cells make up the optic nerve and tract?
Ganglion cells
Do rods, bipolar cells, or ganglion cells have action potentials?
Only ganglion cells
What happens to neurotransmitter release from rods as they are exposed to light?
Less is released
Why do off-center ganglion cells fire less than on-center ones?
To give better contrast
Where does processing of light information first occur?
In the retina (contrast bit)
Why do you not need action potentials in the retina?
Distances are so short
Processing of information makes use of what type of potentials -
Graded (receptor and synaptic)
What is the neurotransmitter released by photoreceptors?
Glutamate
What is a receptive field in the visual system?
the area of retina from which the neuron can be influenced.
What are the places that the optic tract ends up in?
Hypothalamus
LGN
Superior colliculus
What is the nucleus involved in the pupillary light reflex? What are the CNs involved?
CN II–EWN(x2)–CN III
Review the pathways of CN II as per neuroanatomy, if you do not recall them!
LGN
The top part of the visual field is processed in which part of the occipital cortex?
Inferior
The lower part of the visual field is processed in which part of the occipital cortex?
Superior
Where are Meyer’s loop found?
From LGN, sweeps through the temporal lobe, to the calcarine suclus
Look at slide 38 and make some notecards offa that.
Should be review anyways
Lesion of Meyer’s loop = ?
superior – quadrant anopsia contralateral to lesion of
Meyer’s loop
Inflammation of the optic disk can produce what type of opia?
Central Scotoma
What parts of the eye register movement vs visual acuity and color perception?
Different ganglion cells
What are the two main visual pathways from the striate cortex to higher order visual areas?
Dorsal stream
Ventral stream
What is the function of the dorsal stream?
analysis of motion and relative positions of objects in visual scene
What is the function of the ventral stream?
high-level form vision and object recognition
What is the part of the brain that links all the hemi fields together?
Corpus callosum
What is prosopagnosia?
Inability to identify faces
What is cerebral akinetopsia?
Inability to see motion
Which cone type sense short wavelengths (red, green, or blue)?
Blue
Which cone type sense middle wavelengths (red, green, or blue)?
Green
Which cone type sense long wavelengths (red, green, or blue)?
Red
True or false: you can differentiate colors based on input from a single cone
False–
What causes red-green color blindness?
Loss of either red or green cones
What happens if you are missing both red and green cones?
Color blindness
What is Monochromatopsia?
have either one cone or no cones.
What are the charts that test for color blindness?
Ishihara charts
Genes for the red and green cones pigments are on what chromosome?
X
What chromosome is the blue cone on?
7
Rhodopsin gene is on which chromosome?
3
What are the monocular depth cues?
How big the image on the retina is
What is sensory fusion?
fixate both eyes on one point so that left and right images fall on corresponding positions in the two retinas
What causes strabismus?
Failure of the eyes to fixate on the same point
What is amblyopia?
Suppression of vision from the strabismus eye causing loss of vision
