Intrinsically photosensitive retinal ganglion cells

Photosensitive ganglion cells are a type of neuron in the retina of the mammalian eye, where they form a third class of photoreceptors in addition to rods and cones. They were discovered at the beginning of the 1990s. In contrast to the other ganglion cells of the retina are independently sensitive to light. They contain the pigment melanopsin photo.

Function

Compared with rods and cones, the photosensitive ganglion cells respond more slowly to the presence of light. They form a small proportion ( 1-3% ) of the ganglion cells of the retina. Their function is not the image or pattern recognition, but a stable perception of the surrounding brightness. They meet at least three main functions:

• By providing information about the duration of day and night, they play an essential role in the entrainment ( synchronization ) of the circadian rhythm ( the clock of the body's circadian rhythm ) with the 24- hour light - dark cycle. About the tract retinohypothalamicus send brightness information directly to clock the circadian rhythm, the suprachiasmatic nucleus of the hypothalamus.

• Photosensitive ganglion cells are connected by nerves with other brain areas, including on the pretectal area of the epithalamus with adjacent regions of the midbrain that mediate reflex eye movements ( superior colliculus ) and adjusting the pupil size of the luminance control ( Edinger - Westphal nucleus). Thus, they are for the pupil light reflex and other reactions to changes in the ambient lighting conditions of importance.

• They are involved in the control and the acute photic suppression ( caused by light suppression ) of the release of melatonin from the pineal gland.

The photo pigment of the photosensitive ganglion cells, melanopsin is most excited by light in the blue region of the visible spectrum. The maximum sensitivity is about 480 nm wavelength.

Discovery

Discovered in 1991 Russell G. Foster, Ignacio Provencio and colleagues a photo receptor in mouse eyes, was neither attributable to the journal nor the swab type. It has been shown that this receptor was involved in the circadian rhythm, the 24 - hour rhythm of the biological clock. Foster was appointed in 2008 a Fellow of the Royal Society. Was published that such a significant discovery in a relatively little-known magazine, makes the skepticism clear what had for the scientific community of the existence of another photoreceptor - type first. Finally, the eye was 200 years examined in detail, so that, as Foster himself wrote, had to seem unlikely that another type of receptor could be gone unnoticed. The fact that the newly discovered cells contain melanopsin, was published by Provencio and colleagues in 2007.

Credentials

• Cell type
• Anatomy of the eye
• See
• Nervous tissue
• Chronobiology