Ganglion Cells Discussion
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What is ganglion cells explain briefy.
A ganglion cell is a cell found in a ganglion. Examples of ganglion cells include:
Retinal ganglion cell (RGC) found in the ganglion cell layer of the retina
Cells that reside in the adrenal medulla, where they are involved in the sympathetic nervous system’s release of epinephrine and norepinephrine into the blood stream
Cells of the sympathetic ganglia
Cells of the parasympathetic ganglia
Cells of the spiral ganglia
Ganglion cells are the final output neurons of the vertebrate retina. Ganglion cells collect information about the visual world from bipolar cells and amacrine cells (retinal interneurons). This information is in the form of chemical messages sensed by receptors on the ganglion cell membrane. Transmembrane receptors, in turn, transform the chemical messages into intracellular electrical signals.
These are integrated within ganglion-cell dendrites and cell body, and ‘digitized’, probably in the initial segment of the ganglion-cell axon, into nerve spikes. Nerve spikes are a time-coded digital form of electrical signalling used to transmit nervous system information over long distances, in this case through the optic nerve and into brain visual centers.
Ganglion cells are also the most complex information processing systems in the vertebrate retina. It is a general experimental truth that an organism as a whole cannot behaviorally respond to visual stimuli that are not also detectable by individual ganglion cells. Different cells become selectively tuned to detect surprisingly subtle ‘features’ of the visual scene, including color, size, and direction and speed of motion. These are called ‘trigger features’. Even so signals detected by ganglion cells may not have a unique interpretation. Equivalent signals might result from an object changing brightness, changing shape, or moving. It is up to the brain to determine the most likely interpretation of detected events and, in the context of events detected by other ganglion cells, take appropriate action.
Ganglion cell axons terminate in brain visual centers, principally the lateral geniculate nucleus and the superior colliculus. Ganglion cell axons are directed to specific visual centers depending of the visual ‘trigger features’ they encode. The optic nerve collects all the axons of the ganglion cells. In man this optic nerve bundle contains more than a million axons.