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Transducin (G t) is a protein naturally expressed in vertebrate retina rods and cones and it is very important in vertebrate phototransduction. It is a type of heterotrimeric G-protein with different α subunits in rod and cone photoreceptors. [1]
Leydig cells may grow uncontrollably and form a Leydig cell tumour. These may be hormonally active, i.e. secrete testosterone. These may be hormonally active, i.e. secrete testosterone. The function of Reinke crystals is unknown, but they appear in the case of Leydig cell tumours. [ 5 ]
Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells (rods and cones) in the vertebrate retina.A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve.
The prevailing theory of how simple and complex cells interact is that cells in the lateral geniculate nucleus stimulate simple cells, and simple cells in turn stimulate complex cells where then a combination of complex cells create depth perception. [1] [7] [10] Three different cell types exist: far cells, near cells, and tuned zero cells.
A hypercomplex cell (currently called an end-stopped cell) is a type of visual processing neuron in the mammalian cerebral cortex.Initially discovered by David Hubel and Torsten Wiesel in 1965, hypercomplex cells are defined by the property of end-stopping, which is a decrease in firing strength with increasingly larger stimuli.
The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of ...
Hormones that stimulate its production depend on the cell type and include luteinizing hormone (LH), ACTH and angiotensin II. At the cellular level, StAR is synthesized typically in response to activation of the cAMP second messenger system , although other systems can be involved even independently of cAMP .
The eye begins to develop as a pair of optic vesicles on each side of the forebrain at the end of the fourth week of pregnancy. Optic vesicles are outgrowings of the brain which make contact with the surface ectoderm and this contact induces changes necessary for further development of the eye.