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Encyclopedia > Horizontal cell
Plan of retinal neurons.

Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the retina. Image File history File links Gray882. ... Image File history File links Gray882. ... Human eye cross-sectional view. ...

## Contents

There are three basic types of horizontal cells, designated HI, HII and HIII. The selectivity of these three horizontal cells, towards one of the three cone types, is a matter of debate. According to studies conducted by Boycott and Wassle neither HI cells nor HII cells were selective towards S,M, or L cones. By contrast, Anhelt and Kolb claim that in their observations HI cells connected to all three cone types indiscremenantly, however, HII cells tended to contact S cones the most. They also identified a third type of horizontal cell, HIII, which was identical to HI but did not make contact with S cones. Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ...

The HII cells also make connections with rods, but do so far enough away from the horizontal cell's soma such that they do not interfere with the activities of the cones.

They span across cones and summate inputs from them all to control the amount of GABA released back onto the photoreceptor cells, which depolarizes them. Their arrangement together with the on-centre and off-centre bipolar cells that receive input from the photoreceptors constitutes a form of lateral inhibition, increasing spatial resolution at the expense of some information on absolute intensity. The eye is thus more sensitive to contrast and differences in intensity. Gaba may refer to: GabÃ¢ or gabaa (Philippines), the concept of negative karma of the Cebuano people GABA, the gamma-amino-butyric acid neurotransmitter GABA receptor, in biology, receptors with GABA as their endogenous ligand Gaba 1 to 1, an English conversational school in Japan Marianne Gaba, a US model... Photoreceptor cells are contained in the retina and are responsible for transducing, or converting, light into signals that can be ultimately transmitted to the brain via the optic nerve. ... As a part of the retina, the bipolar cell exists between photoreceptors (rod cells and cone cells) and ganglion cells. ... simply; your nose receives messages from the environment sending them to the olfactory centre which is present in the cerebrum the largest part of brain: then you either smell a good smell or a bad smell stink with parts of seconds. ...

## Functional Properties

When light is shone onto a photoreceptor, the photoreceptor hyperpolarizes and reduces the release of glutamate, when this happens, horizontal cells reduce the release of GABA, which has an inhibitory effect on the photoreceptors. This reduction of inhibition leads to a depolarization of the photoreceptors. We therefore have the following negative feedback

Illumination$to$photoreceptor hyperpolarization$to$horizontal cell hyperpolarization$to$photoreceptor depolarization

One proposed theory for facilitation by the horizontal cells proceeds as follows. Assume we have 11 photoreceptors, one hyperpolarizing (H) bipolar cell, and one horizontal cell. All ten photoreceptors connect to the horizontal cell, and the middle photoreceptor (Pm) connects to the bipolar cell. The surrounding cells, which represent the outer receptive field, will be designated Po then we can explain an off-centre arrangement as follows. If light is shown onto the Pm then

1. Pm is activated by light and therefore hyperpolarizes
2. Pm reduces release of glutamate
3. Reduction of glutamate depolarizes the H bipolar cell
4. Reduction of glutamate hyperpolarizes the horizontal cell and it reduces release of GABA
5. Since Pois still releasing glutamate, reduction in GABA is marginal

If the light is shone onto the surrounding area then

1. Po is activated and therefore hyperpolarizes
2. Po reduce release of glutamate
3. Reduction of glutamate hyperpolarizes the horizontal cell
4. Horizontal cell reduces release of GABA
5. Reduction of GABA depolarizes photoreceptors
6. Po not affected since they are strongly being hyperpolarized by activation
7. Pm is affected and therefore depolarizes
8. Pm releases glutamate
9. H Bipolar cell is hyperpolarized

To explain diffuse light, then we consider both cases together, and as it turns out, the two effects cancel each other out, and we get little to no affects

Photoreceptors are light-sensitive proteins involved in the function of photoreceptor cells. ... As a part of the retina, the bipolar cell exists between photoreceptors (rod cells and cone cells) and ganglion cells. ... This article or section is incomplete and may require expansion and/or cleanup. ... A Ganglion Cell (or sometimes called a gangliocyte) is a type of Neuron located in the retina that receives visual information from bipolar cells; its axons give rise to the optic nerve. ...

Results from FactBites:

 Journal of Vision - Receptive field structure of H1 horizontal cells in macaque monkey retina, by (10768 words) The horizontal cells of mammalian retinas, such as those in cat and rabbit, are also extensively coupled and consequently have uniformly large receptive fields (Mills and Massey, 1994; Bloomfield, Xin, and Persky, 1995). H1 horizontal cell receptive fields were characterized by measuring their responses to drifting sinusoidal gratings as a function of spatial frequency, to flashing spots as a function of spot diameter, and to flashing annuli as a function of annulus inner diameter. In cat retina, increased cell density has not been correlated with a reduction in horizontal cell receptive field size as a function of decreasing retinal eccentricity (Lankheet et al., 1990, 1992; Nelson, 1977), a correlation that is very strong in primate retina.
 Webvision: Physiology of Horizontal Cells (2854 words) During the horizontal cell response to light, the trans-membrane potential increases or 'hyperpolarizes', from ~-30 mV in darkness to -40 to -70 mV in the presence of the light stimulus. The inference from such models is that signals in cell bodies of either the A or B type horizontal cells are expected to reflect only the local synaptic inputs from cones while signals in axon terminals of the B-type horizontal cells are expected to reflect only the local synaptic inputs from rods. Horizontal cells are affected by light stimuli over a much wider area than one might suppose based on the lateral extent of process arborization, or 'dendritic field'.
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