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Schematic diagram of pupillary light reflex neural pathway. Left direct light reflex involves neural segments 1, 5, and 7. Segment 1 is the afferent limb, which includes the retina and optic nerve. Segments 5 and 7 form the efferent limb. Left consensual light reflex involves neural segments 2, 4, and 7. Segment 2 is the afferent limb.
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.
Pupillary light reflex — a reduction of pupil size in response to light. Rectoanal inhibitory reflex - a transient relaxation of the internal anal sphincter in response to rectal distention. Rooting reflex — turning of an infant's head toward anything that strokes the cheek or mouth. Righting reflex - a proprioceptive reflex
An opsin absorbs a photon (a particle of light) and transmits a signal to the cell through a signal transduction pathway, resulting in hyper-polarization of the photoreceptor. Rods and cones differ in function. Rods are found primarily in the periphery of the retina and are used to see at low levels of light. Each human eye contains 120 million ...
Cones work at high light levels (during the day but also during driving at night in the headlamp spotlight). Rods take over at twilight and night. The y-axis has logarithmic scaling. A minor mechanism of adaptation is the pupillary light reflex, adjusting the amount of light that reaches the retina very quickly by about a factor of ten. Since ...
The visual system is organized hierarchically, with anatomical areas that have specialized functions in visual processing. Low-level visual processing is concerned with determining different types of contrast among images projected onto the retina whereas high-level visual processing refers to the cognitive processes that integrate information from a variety of sources into the visual ...
Pupillary reflexes, particularly the pupillary light reflex, are a powerful diagnostic tool often employed in clinical and emergency medical practice. A lack of equal consensual pupillary constriction to a light stimulus, especially a Marcus Gunn pupil , can be indicative of optic nerve damage, brainstem death, or optic tract damage in between.
The ability of the rodless, coneless mice to retain a pupillary light reflex was suggestive of an additional photoreceptor cell. [11] In the 1980s, research in rod- and cone-deficient rats showed regulation of dopamine in the retina, a known neuromodulator for light adaptation and photoentrainment. [3]