NPB 100 Lecture 16

NPB 100 Lecture 16 - Lecture 16 -Construction of receptive...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 16 -Construction of receptive fields -Lateral inhibition -Projection of ganglion cells -Retinal topic maps -Guidance system that operates to form retinal topic maps -Organization of mammalian visual system -Receptive fields are places in the visual space where you can apply a stimulus and generate a response from the cell -tend to be quite a small area since there are millions of ganglion cells in the eye -people thought receptive fields would be simple in structure and that large scale illumination over the whole visual space would be an effective way of stimulating ganglion cells; but this is not true! -receptive fields will be small with an area in the center that if you shine a light there, the cell will be excited; whereas, if you shine a light outside of that area, the cell would be inhibited -general shape tends to be circular -a central area with one kind of response and the surrounding area with another kind of respond -can also be inhibitory center and excitatory surround -this is called center surround antagonism -characteristic of ganglion cells’ receptive fields -receptive fields of ganglion cells that are driven by cones -can find ones that are positive for say blue light and inhibited by red light -center surround antagonism and color contrast -how does this come about? -1 to 1 ratio of 1 receptor driving 1 bipolar cell occurs only in the fovea -fovea: part of the eye with the highest visual acuity
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
-elsewhere in the retina, there are several photoreceptors converging on each bipolar cell, and several bipolar cells converging onto each ganglion cell -there are horizontal cells that send their processes laterally and make inhibitory synapses at the bipolar cells and the photoreceptors; the horizontal cells get their input from the photoreceptors -at the outer end of each bipolar cell, there is this convergence of synapses , some inhibitory and some excitatory, that are interacting on that particular cluster of neurons that come together at that point -the input from the photoreceptors uses glutamate, they are all excitatory -the inhibitory synapses use GABA, all the horizontal cells are GABAnergic -when the photoreceptor is in the dark, transmitting light, it is exciting the horizontal which feedbacks and inhibits the photoreceptor directly, and which also inhibits the bipolar. The output from the bipolar then is a mixture, a synthesis, of excitation from photoreceptors and inhibition from the bipolar. It is constantly under 2 opposing forces. -let’s considered what happens when only one photoreceptor is illuminated -the photoreceptor gets hyperpolarized due to illumination, it stops releasing transmitter, reduces the excitation on the bipolar, and it also reduces the inhibition from the horizontal cell. Because the bipolar is normally excited in the dark, it stops releasing NT and the ganglion cell turns off (this is an off ganglion
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/15/2010 for the course NPB NPB taught by Professor Bales during the Winter '09 term at UC Davis.

Page1 / 6

NPB 100 Lecture 16 - Lecture 16 -Construction of receptive...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online