Amacrine cell
Encyclopedia
Amacrine cells are interneuron
Interneuron
An interneuron is a multipolar neuron which connects afferent neurons and efferent neurons in neural pathways...

s in the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.

Overview

Amacrine cells operate at the inner plexiform layer
Inner plexiform layer
The inner plexiform layer is an area of the retina that is made up of a dense reticulum of fibrils formed by interlaced dendrites of retinal ganglion cells and cells of the inner nuclear layer. Within this reticulum a few branched spongioblasts are sometimes embedded....

 (IPL), the second synaptic retinal layer where bipolar cells and retinal ganglion cells form synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

s. There are about 40 different types of amacrine cells, most lacking axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....

s. Like horizontal cell
Horizontal cell
Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the retina of mammalian eyes. They help integrate and regulate the input from multiple photoreceptor cells...

s, amacrine cells work laterally affecting the output from bipolar cells, however, their tasks are often more specialized. Each type of amacrine cell connects with a particular type of bipolar cell, and generally has a particular type of neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

. One such population, AII, 'piggybacks' rod bipolar cells onto the cone bipolar circuitry. It connects rod bipolar cell output with cone bipolar cell input, and from there the signal can travel to the respective ganglion cells.

They are classified by the width of their field of connection, which layer(s) of the stratum in the IPL they are in, and by neurotransmitter type. Most are inhibitory using either GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...

 or glycine
Glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...

 as neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

s.

Functionality

Relatively little is known of the functional roles of the amacrine cells. Amacrine cells with extensive dendritic trees are thought to contribute to inhibitory surrounds by feedback at both the bipolar cell, and ganglion cell levels. In this role they are considered to supplement the action of the horizontal cells. Amacrine cells give much more input to M (Magnocellular) ganglion cells than to P (Parvocellular) ganglion cells.

Other forms of amacrine cell are likely to play modulatory roles, allowing adjustment of sensitivity for photopic and scotopic vision. The AII amacrine cell (also known as the Rod amacrine cell) is a mediator of signals from rod cells under scotopic conditions.

See also

  • Photoreceptor cell
  • Horizontal cell
    Horizontal cell
    Horizontal cells are the laterally interconnecting neurons in the outer plexiform layer of the retina of mammalian eyes. They help integrate and regulate the input from multiple photoreceptor cells...

  • Bipolar cell
  • Ganglion cell
    Ganglion cell
    A retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...


External links

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