Week 1 Flashcards
how are neurons charged?
what happens when depolarized?
what happens when hyperpolarized?
-70 millivolts (mV) on the inside
depolarized=excited, decrease in membrane potential, Na channels open and Na rushes
hyperpolarized=inhibitory, increase in membrane potential, becomes more negative inside
4 major types of neural circuits:
1) diverging
2) converging
3) negative feedback loop
4) lateral inhibition
2 main purposes of diverging neuron circuits:
1) redundancy
2) complexity: Each channel may analyze information in a different way or send information to different locations. (A diverging circuit allows for the separation of information within a signal)
How are midget bipolar cells an example of diverging neuron circuits:
1 foveal cone diverges to many midget bipolar cells (4)
•2 bipolar cells are responsible for very fine details and color. They also carry opposite color signals. If one is sensitive to long wavelengths (i.e. red light), other turned on by green.
•Other 2 deal with large targets, prefer moving stimuli, and get rid of color information.
•One of the above pairs is activated when the light is on; the other is activated when the light is off.
How can ganglion cells be an example of diverging neuron circuits:
1 magno bipolar cell diverges to many magno ganglion cells
2 different outputs from these cells:
1) Magno cells go to the magno layers of LGN (sensory information = perception)
2) Send second axon sent to superior colliculus (orienting reflex = head/eye coordination))
***= Faster response to a moving object (able to look at object before we are conscious of it). Due to parallel circuits.
give an example of how cones can be converging neuron circuits:
Many Conesconverge to 1 Magno Bipolar cells (Motion)
- Motion information is received form 10-15 cones
- Allows for more sensitivity but at the cost of precision
- One responds when it gets dark, the other responds to light
give an example of how rods can be converging neuron circuits:
rods: 400-600 Rods > 20-25 Bipolar cells > 1 Ganglion cell
- 20-25 rods converge on a single bipolar cell
- 20-25 bipolar cells converge onto a ganglion cell (may occur indirectly, but they will summate
* *very sensitive, but has poor acuity.
what is the main benefit of negative feedback loops?
Negative feedback loops provide temporal sharpening of information (shortens length of time for response).
what is the main benefit of lateral inhibition?
Occurs with negative inhibition and sharpens boundaries- using same cells and practically the same method as negative feedback.
*Allows edges to be enhanced so you can better see the world
Give 3 examples of lateral inhibition in visual pathway:
1) Horizontal cells: Inhibit receptors on the synaptic endings of the photoreceptor to turn down the response.
2)Amacrine cells: Turn down the response at the synaptic endings of the bipolar cells.
3) B/w Striate Cortex and the LGN: ~25% of the LGN is composed of interneurons that provide feedback
~1/3 of the optic radiations are running back to the LGN.
receptive field of a neuron:
Receptive field means the visual field for that cell
what are the 5 physiological types of ganglion cells?
(1) Boundary Detectors
(2) Movement-gated, dark convex boundary detectors
(3) Moving or changing contrast detectors
(4) Dimming detectors
(5) Inverse function of log luminance responders
Boundary Detectors ganglion cells make up what % of GCs? respond to?
size of retinal field?
~45%
- responds only to moving border
- small receptive fields (2°-3°)
*appearance: One level constricted field, Small dendritic tree
Movement-gated, dark convex boundary detectors ganglion cells make up what % of GCs? respond to?
size of retinal field?
~45%
- Retinal bug detector
- receptive field about 3-5 deg
*appearance: Many-level E dist’n, Longer stem for dendritic tree
Moving or changing contrast detectors ganglion cells make up what % of GCs? respond to?
size of retinal field?
~5%
- sensitive to both moving boundaries and stable boundaries only if contrast of the boundary is changed
- primarily tuned to big objects
- 7°-11° receptive fields
*appearance: Many level H dist’n: , Distinctively two trees (big part of retina)
