Neurons
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
Neurons can be classified in a number of ways. One of the earliest classifications is anatomical, according to which neurons can be unipolar, bipolar, or multipolar. Unipolar neurons have only one process emanating from the cell body. In the case of sensory neurons of the dorsal root ganglia (Figure 11.2), this single process divides at some distance from the cell body into two main branches that conduct APs from peripheral sensory receptors, past this branch point and into the spinal cord. On the other hand, most amacrine cells of the retina (Figure 7.1a) have dendrites and no axons. They neither generate nor conduct action potentials; instead they actively conduct synaptic signals through their dendrites to their target cells. Figure 7.1b illustrates a bipolar cell of the retina having an axon and a single dendrite on opposite ends of the soma. The axon of the dopamine-releasing neuron of the substantia nigra, which is a nucleus of the basal ganglia (Section 12.2.3), emerges from a dendrite up to 240 µm from the soma.
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Amacrine cells are interneurons located in the inner nuclear layer of the RETINA. They lack axons, but through their dendrites modify signal transmission from BIPOLAR CELLS to GANGLION CELLS. The input to amacrine cells comes from axons of bipolar cells as well as from dendrites of other amacrine cells. Their output is directed to ganglion cells, other amacrine cells, and axons of bipolar cells, thus forming complex feedback, feed-forward, and reciprocal networks. Amacrine cells use GABA, GLYCINE, ACETYLCHOLINE and DOPAMINE as neurotransmitters, and some of these transmitters are co-localized in the same cell.
Prenatal Cocaine Exposure and the Eye
Richard J. Konkol, George D. Olsen in Prenatal Cocaine Exposure, 2020
What is the disease mechanism that may have led to this abnormality? Dopamine is presumed to play a role in eye growth.22 Regulation of postnatal eye growth and refraction relies on a vision-dependent feedback mechanism. This mechanism appears to be located, at least in part, in the retina. Retinal amacrine cells containing dopamine seem to be implicated in a negative feedback loop that links ocular growth control to vision.22 If cocaine interferes with dopamine release or receptors, then it could play a role in affecting visual outcome by changing ocular growth.
The therapeutic effect of nano-zinc on the optic nerve of offspring rats and their mothers treated with lipopolysaccharides
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Eman Mohammed Emara, Hassan Ih El-Sayyad, Amr M Mowafy, Heba a El-Ghaweet
Lipopolysaccharides (LPS) are a toxic component in Gram-negative bacteria’s cell walls [1]. The hydrophilic core polysaccharide chain, the repetitive hydrophilic O-antigenic oligosaccharide side chain and the hydrophobic lipid portion that is known as lipid A are the three structural elements that make up the macromolecules of intact bacterial LPS [2]. The intrauterine infection brought on by bacterial LPS exposure causes preterm delivery, neurological damage and fetal inflammation in the retina and optic nerve, which manifests in their structure and neurochemistry. It also results in a decrease in tyrosine hydroxylase immunoreactive (TH-IR), dopaminergic amacrine cells and all of which can impair vision. When compared to control fetuses, myelin sheath thickness decreased in LPS-exposed fetuses at a critical time for optic nerve development [3]. According to several studies, LPS causes systemic inflammation and affects directly placental cells causing the release of pro-inflammatory mediators that activate microglia. In addition, astrocytes cause the production of cytokines in the developing fetal brain [4,5].
Effect of vitamin D deficiency on spatial contrast sensitivity function
Published in Clinical and Experimental Optometry, 2022
Other important retinal cells that assist in the regulation of visual processing are horizontal cells and amacrine cells. The lateral coupling of these cells plays an important role in visual acuity and contrast sensitivity formation by adjusting the receptive field sizes.20,21 The centre-surround organisation of receptive fields, in which the object (centre) and its background (surround) have different illumination signals is primarily regulated by bipolar cells.22 The large receptive fields of horizontal cells have been considered to form the surround of bipolar cells,23 and as a result of a light-induced increase in dopamine, uncoupling of horizontal cells leads to a reduced surround receptive field that is related with increased local contrast detection.24
Advances in Neuroscience, Not Devices, Will Determine the Effectiveness of Visual Prostheses
Published in Seminars in Ophthalmology, 2021
Bardia Abbasi, Joseph F. Rizzo
In the retina, visual signals emerging from over 90 million photoreceptors are processed by horizontal, bipolar, and amacrine cell circuits prior to activation of some complement of the 1.2 million RGCs whose axons comprise the optic nerve.65–67 Inner retinal processing by pre-RGC circuits provides spatial resolution, detection of color, motion and texture detection, light adaptation (across 8 log units of intensity), control of circadian rhythms, and saccadic suppression (to counter image degradation by larger eye movements).68–70 These processed data are then encoded among at least 15 subtypes of RGCs, each tiled across the retina with relatively little overlap, conveying distinct visual representations in parallel to the brain.70 The best-characterized RGC populations include midget cells (with small, center-surround receptive fields with high spatial sensitivity), parasol cells (with large, center-surround achromatic receptive fields with high temporal sensitivity), and bistratified cells (with blue-yellow center-surround receptive fields), which collectively comprise around 90% of RGCs in the primate retina.67,70,71 The major RGC classes are further divided equally between “ON” and “OFF” cells that respond antagonistically to the intensity of light.64
Related Knowledge Centers
- Anatomy
- Dendrite
- Eye
- Inner Plexiform Layer
- Interneuron
- Neurite
- Retina
- Synapse
- Retinal Ganglion Cell
- Retina Bipolar Cell