The retinohypothalamic tract is a photic input pathway involved in the circadian rhythms A circadian rhythm is a roughly-24-hour cycle in the biochemical, physiological or behavioral processes of living entities, including plants, animals, fungi and cyanobacteria . The term "circadian", coined by Franz Halberg, comes from the Latin circa, "around," and diem or dies, "day", meaning literally " of mammals Mammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.[1] The origin of the retinohypothalamic tract is the intrinsically photosensitive Retinal Ganglion Cells Photosensitive ganglion cells, also called photosensitive Retinal Ganglion Cells , intrinsically photosensitive Retinal Ganglion Cells (ipRGC) or melanopsin-containing ganglion cells, are a recently discovered type of nerve cell in the retina of the mammalian eye which, unlike other retinal ganglion cells, are intrinsically photosensitive. This (ipRGC), which contain the photopigment melanopsin Melanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary light reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of G-protein-coupled receptor. The axons of the ipRGCs belonging to the retinohypothalamic tract project directly to the suprachiasmatic nuclei The suprachiasmatic nucleus, or nuclei, , a tiny region on the brain's midline in a shallow impression of the optic chiasm, is responsible for controlling endogenous circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions over a 24-hour period via the optic nerve The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibers are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system and the optic chiasm The optic chiasm or optic chiasma is the part of the brain where the optic nerves (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.[2][3] The suprachiasmatic nuclei receive and interpret information on environmental light, dark and day length, important in the entrainment In chronobiology, entrainment of a circadian system is the alignment of its own period and phase to the period and phase of an external rhythm. A common example is the entrainment of endogenous circadian rhythms to the daily light-dark cycle. Of the several possible cues, called zeitgeber (German for time-giver, synchronizer), which can contribute of the 'body clock'. They can coordinate periferal 'clocks' and direct the pineal gland The pineal gland is a small endocrine gland in the vertebrate brain. It produces melatonin, a hormone that affects the modulation of wake/sleep patterns and photoperiodic (seasonal) functions. It is shaped like a tiny pine cone (hence its name), and is located near to the center of the brain, between the two hemispheres, tucked in a groove where to secrete the hormone melatonin Melatonin (pronounced /ˌmɛləˈtoʊnɪn/ ), also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring hormone found in animals and in some other living organisms, including algae. Circulating levels vary in a daily cycle, and melatonin is important in the regulation of the circadian rhythms of several biological functions.
References
- ^ Gooley JJ, Lu J, Chou TC, Scammell TE, Saper CB (2001). "Melanopsin in cells of origin of the retinohypothalamic tract". Nat. Neurosci. 4 (12): 1165. doi The Digital Object Identifier System is a managed system for persistent identification of content-related entities on digital networks . These entities may be content items (digital files, physical objects, abstract works), or any related entities in a content transaction (e.g. licenses, parties, etc.). "DOI" is sometimes used to mean:10.1038/nn768. PMID 11713469.
- ^ from the retina to the optic chiasm, the ipRGC axons follow the same path as the axons of “regular” RGCs A retinal ganglion cell is a type of neuron located near the inner surface (the ganglion cell layer) of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells. Retinal ganglion cells collectively transmit visual information from the retina to several regions in (i.e. RGCs that are not intrinsically photosensitive)
- ^ Afifi, A.K.; Bergman, R.A. (2005-Jan-28) (paperback). Functional Neuroanatomy (2nd ed.). McGraw-Hill. p. 271. doi The Digital Object Identifier System is a managed system for persistent identification of content-related entities on digital networks . These entities may be content items (digital files, physical objects, abstract works), or any related entities in a content transaction (e.g. licenses, parties, etc.). "DOI" is sometimes used to mean:10.1036/0071408126. ISBN 9780071408127. http://www.mhprofessional.com/product.php?cat=116&isbn=0071408126&cat=116.
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Categories: Eye Categories: Visual system | Head and neck | Sensory organs | Facial features | Sleep physiology Categories: Sleep | Physiology | Neurophysiology | Circadian rhythms |
