Ch. 10.4 Neurons at Different Levels of the Visual System Have Very Different Receptive Fields Flashcards
What is a receptive field?
Consist of the stimulus region and the features that excite or inhibit the cell. (see ch. 8)
At their resting potentials both rod and cone photoreceptors steadily release what synaptic neurotransmitter?
Glutamate
What effect does light have on photoreceptors?
hyperpolarization causing them to release LESS glutamate (because at resting they are always releasing glutamate)
What effect does dark have on photoreceptors?
depolarization causing them to release MORE glutamate (because at resting they are always releasing glutamate)
Does the neurotransmitter glutamate always trigger the same response in BIPOLAR cells?
It depends on the type of glutamate receptor the bipolar cell has. Increase of glutamate depolarizes one group of bipolar cells (off-center bipolar cells) but hyperpolarizes (on-center bipolar cells) another group - These groups differ in their receptive fields. Less glutamate has the opposite affect: on-center bipolar cell depolarize and off-center bipolar hyperpolarize.
What is a on-center bipolar cell?
On-center bipolar cells are excited by turning ON light in the center of its receptive field. They are excited because they receive LESS glutamate causing depolarization. The depolarization causes an increase of transmitter to be released to the ganglion cell.
What is a off-center bipolar cell?
Off-center bipolar cells are excited by turning OFF light in the center of its receptive field. They are excited because they receive MORE glutamate causing depolarization. The depolarization causes an increase of transmitter to be released to the ganglion cell.
What are on-center ganglion cells?
A ganglion cell that depolarizes when light turned on to the center of the cell’s receptive field.
The stimulated on-center ganglion then produce action potentials to report ‘light’ to higher visual centers.
What are off-center ganglion cells?
A ganglion cell that depolarizes when light is turned off (decreased light)
The stimulated off-center ganglion then produce action potentials to report ‘dark’ to higher visual centers.
What effect does glutamate (released by bipolar cells) have on ganglion cells?
Glutamate always depolarizes the ganglion cells.
Bipolar cells and ganglion cells have two basic types of retinal receptive fields. What are they?
On-center/off-surround and off-center/on-surround
What does on-center/off-surround mean
This refers to a concentric receptive field in which the center excites the cell of interest while the surround inhibits it.
What does off-center/on-surround mean
This refers to a concentric receptive field in which the center inhibits the cell of interest while the surround excites it.
What is LGN
Lateral geniculate nucleus (part of the thalamus)
What do you know about the LGN?
- Most ganglion cell axons synapse in the LGN
- It has 6 main layers
a. 4 dorsal (outer) layers called the parvocellular (relatively small cells)
b. 2 ventral (inner) layers called magnocellular (relatively large cells) - All layers have concentric receptive fields.
- The LGN neurons discriminate wavelengths
- Neurons from the LGN send their axons to V1 (primary visual cortex)
What did David Hubel and Torsten Wiesel find out about the V1 neurons?
That visual cortical neurons require more specific stimuli - more elongated bars of light (rather than the spots of light needed in the ganglion cells and LGN neurons). They found that V1 neurons respond best to lines or bars in a particular position and at a particular orientation in the visual field. Some required movement.
What are simple cortical cells?
Also called bar detector or edge detector. They respond best to an edge or a bar that has a particular width and a particular orientation and location in the visual field.
What are complex cortical cells?
They respond best to a bar of a particular size and orientation anywhere within a larger area of the visual field.
What is spatial-frequency filter model?
A model of pattern analysis of visual stimuli. Analyzing the number of light-dark (or color) cycles that the stimulus shows per degree of visual space.
What is ocular dominance slabs?
A slab of visual cortex in which the neurons of all layers respond preferentially to stimulation of one eye
What is orientation column
A column of visual cortex that responds to rod-shaped stimuli of a particular orientation.
