Receptive Fields Flashcards
Which parts of the eye are responsible for focusing light on the retina?
Cornea and Lens
How do the cornea and lens help to focus light on the retina?
Bending the light so that it falls on the retina
Why does visual perception rely on rods at night?
Cones don’t work at night due to lower sensitivity
We only rely on the rods because it has very high sensitivity
Why do cones enable higher acuity vision?
Because there is less neural convergence and is able to pick up on the fine details
What is the ratio between retinal ganglion cells and photoreceptors?
1:126 (1 million : 126 million)
Are there more or fewer ganglion cells than photoreceptors?
Fewer
Because there are fewer ganglion cells, what do they do?
Ganglion cells must condense raw information from the photoreceptors
They aim to extract only important information from the retinal image
What happens in single-cell recording?
- Physiological approach
- An electrode is inserted into a neuron and it measures the electrical activity
- It measures the activity of a SINGLE neuron
How do neurons communicate with one another?
By sending electrical impulses that travel down the axon
What does single-cell recording measure?
It measures the activity of a SINGLE neuron
(change in voltage as the action potential/nerve impulse passes by)
As action potential passes down the neuron, there is a spike in voltage
True or False?
As action potential passes down the neuron, there is a drop in voltage
False
As action potential passes down the neuron, there is a spike (sudden increase) in voltage
The more excited the neuron is, what happens to the action potential?
The more the action potential will fire
What does the rate of firing neurons indicate?
How active that neuron is
True or False?
If you excite a neuron more, it increases the size of the action potential
False
If you excite a neuron more, it DOES NOT increase the size of the action potential
Instead, it fires more action potential (rate of firing AP increases)
Increased rate of action potentials indicates ….
Increased activity of the neuron
Often single cell recording from ganglion cells is performed on cats. Describe how the activity of the cells is measured
1) Electrode is inserted into the retina to measure the ganglion cell
2) Experimenters present different stimuli to the cat
3) Experimenters observe what effect each stimulus has on the activity of the ganglion cell
Before you present any stimuli, the ganglion cell is already active. What term is used to describe this cell activity?
Baseline activity from the cell
Through single-cell recording and presenting different stimuli, what do experimenters aim to measure?
Experimenters try to find a stimulus that changes the activity of that ganglion cell
How is ganglion cell response measured? List 9 steps
1) Present spots of light onto the retina
2) Observe whether the ganglion cells respond (through the rate of firing AP)
3) Find the spot of light that increases the activity of the ganglion cells
4) Map out an area on the retina where any light within that area causes an increase in the activity of the ganglion cell
5) Fill that area with light (this will increase AP)
6) Observe what happens when you place the light just outside that area
7) If the light is just outside, the ganglion cell activity will decrease in response relative to the baseline level
8) Map out a 2nd (larger) area that surrounds the 1st area where light within that outer region causes an inhibitory response
9) If you present a bigger spot of light in the 2nd area, you’ll get an even bigger decrease in response
What is an inhibitory response?
Hyperpolarisation
When the ganglion cell is responding less than it would be if there was nothing presented to the retina
When the ganglion cell is responding less than it would be if there was nothing presented to the retina
This is known as…?
Inhibitory response
The area on the retina which, when stimulated by light, elicits a change in the firing rate of the cell
This is known as…?
Receptive field of a cell
Define receptive field
The area on the retina which, when stimulated by light, elicits a change in the firing rate of the cell
When there is an increase in the ganglion cell’s response rate, this is known as…?
Excitatory response (depolarisation)
Higher rate of firing action potential per/sec