L1-The Visual System Flashcards
What does the sensory system do?
Allows us to interface with the world.
List seven basic characteristics of the sensory system.
1) Specific for a type of energy
2) Transduce (convert) the energy into a code the brain understands
3) Filters the “flood” of information
4) Discriminates between intensities of energy
5) Responds reliably
6) Suppresses extraneous (irrelevant) information
7) Contributes to direction of attention and behavior
How are receptors spread around the body?
Receptors must be spread with density related to demand.
(i.e. spatial location of receptors must maximize knowledge of the world in an efficient manner and this topographic information must be understood by the brain)
What must receptors be able to respond to?
Receptors must be able to respond to stimulus intensity.
e.g. the visual system needs to be able to distinguish between light and dark.
What is the difference between anatomical vs physiological?
Anatomy refers to the internal and external structures of the body and their physical relationships, whereas physiology refers to the study of the functions of those structures.
What is the receptive field?
An area of space where stimulation results in a response.
(every receptor has one)
Describe the basic sensory visual processing pathway.
1) Photo(receptors) in retinal ganglion cells are transmitted through the optic nerve to the 2) Thalamus (Lateral Geniculate Nucleus/ LGN) which are transmitted through the optic radiations to the 3) visual cortex.
What side (left/right) of the visual field is projected by which side (left/right) of the hemisphere?
The right side of the visual field is projected by the left hemisphere of the brain while the left side of the visual field is projected by the right hemisphere of the brain.
Descsribe an owl’s eyes
tubes/cylinder rod-shaped eye
describe bees’ eyes
5 eyes, 2 large compound eyes (lots of tiny lenses that can detect shapes) and 3 simple or ocelli which detect light but not shapes
describe lizard eyes
have 4 cones (RGB+UV range) same in some birds and fish
describe rabbit eyes
located laterally, provide 360 view
What is the function of the visual system?
to detect, filer and process the visual scene into features which can be analyzed in parallel prior to binding or integration into a whole perception
What is the stimulus of the eye?
visible light, contrast and color
contrast - the ultimate reason we see anything because it allows us to distinguish objects from each other to perceive them.
What is the hub of the eye?
Retina
photoreceptors go to neurons of retina which have correlation with anatomy of optic nerve, LGN, visual cortex and is best regarded as an outgrowth of the brain?
What are the eye’s associated processes?
iris/pupil reaction to light level
fixation - extraocular muscles (looking at a stimulus)
accommodation (focusing by crystalline lens)
Sagittal or lateral plane
divides body/object into right and left side
transverse/ axial/ cross-sectional plane
divides body/object of regard into superior (upper) and inferior (lower) parts
coronal/frontal plane
divides body/object of regard into front and back parts
anterior/ rostral =
front
posterior/ caudal =
back
dorsal =
top
ventral =
bottom
lateral =
toward the side (R/L)
medial =
toward the midline
ipsilateral =
same side
contralateral =
opposite side
superior =
above
inferior =
below
proximal =
closer to origin of strucutre
(e.g. the elbow is proximal to the wrist)
distal =
further from origin of structure
(e.g. the wrist is distal to the elbow)
What are the three chambers of the human eye?
1) Anterior chamber
2) posterior chamber (smallest)
3) vitreous chamber (largest)
What are the three coats of the human eye?
1) internal nervous layer - retina
2) intermediate vascular pigmented layer - uvea, ciliary body, iris, choroid
3) external, fibrous layer - cornea, sclera
What are the four sections of the optic nerve?
1) intraocular
2) intraorbital
3) intracanalicular
4) intracranial
What is the function of the optic nerve?
it’s the anterior extension of the white matter of the brain. It carries nerve fibers that are the axons of the ganglion cell layer of retina to the lateral geniculate body then to the visual cortex.
- nerve fibers converge on the optic disk and exit through the lamina cribrosa
optic nerve fibers are (generally) *non-myelinated within the eyeball but are myelinated posterior to the disc - optic nerve consists of 500,000 to 1,200,000 axons of approx. 1um diameter
- axons comprising the optic nerve do not posses Schwann cells and can therefore not regenerate
Blood supply
- derived from ophthalmic artery via: branches of central retinal artery and short ciliary arteries
describe the internal layer (the retina (sensory layer))
1) photoreceptors are at the back of the retina
2) the retinal photoreceptors are our main interface with visual world
intervening structures of the eye must do one or more of the following to maintain homeostasis:
- nourishment
- waste removal
- protection
- transparency anteriorly
- sharp imagery
- pointing to item of interest in world (fixation)
- teaming with the other eye (binocularity)
What is the blind spot?
Rod and cone photoreceptors are differently distributed across the retina where there are 0 receptors at around 15 degrees from the fovea on the nasal side because that is where the optic nerve is located hence resulting in the blind spot.
