Circadian rythms in mammals

Abstract

Cirkadijani ritmovi su svi biološki procesi koji pokazuju endogene oscilacije kroz 24 sata. Reguliraju stanične, endokrine i neuralne procese. Ritam budnosti i spavanja je najbolje istražen cirkadijani ritam, pri čemu je spavanje definirano elektroencefalografskim snimkama i prema varijacijama u EEG valovima podijeljeno na 4 stadija i REM san. Unutrašnji cirkadijani sat sinkronizira se s osvjetljenjem okoliša putem retinohipotalamičkog trakta koji završava na stanicama suprahijazmatske jezgre, glavnog regulatora dnevno-noćnih ritmova u tijelu. Samo spavanje reguliraju mnogi dijelovi mozga, uključujući hipotalamus, talamus, retikularnu formaciju u produljenoj moždini i regije srednjeg mozga. Epifiza, koja kod brojnih kralješnjaka ima glavnu ulogu u regulaciji cirkadijanih ritmova, od manje je važnosti kod sisavaca. U tjelesnim stanicama postoji molekularni sat koji se temelji na transkripcijsko-translacijskim povratnim spregama i fosforilaciji njihovih komponenti. Uz poremećaje pomaka samog cirkadijanog ritma u odnosu na vanjske uvjete, vrlo su česti poremećaji vezani uz spavanje koji uključuju insomniju, hipersomniju i parasomnije. Poremećaji spavanja povezani su s neurodegenerativnim i psihičkim bolestima, iako je ta veza relativno slabo istražena. Problemi sa spavanjem nisu samo simptomi mnogih bolesti koji se trebaju liječiti odvojeno, već su elementarni dio patofiziologije čije daljnje proučavanje ima potencijala da razjasni patogenezu tih bolesti s ciljem unapređenja terapije.Circadian rhythms include all biological processes that display endogenous oscillation of about 24 hours. These rhythms regulate cellular, endocrine and neural processes. A well-known circadian rhythm is the sleep-wake cycle. Sleep is physiologically characterized by 4 stages and REM sleep, all of which have different EEG wave patterns. Body's internal clock is synchronized with environmental illumination via retinohypothalamic tract that leads to suprachiasmatic nucleus, the main regulator of circadian rhythms in the body. Sleep itself is regulated by numerous parts of the brain, including hypothalamus, thalamus, reticular formation in medulla and regions of midbrain. The pineal gland, which serves as the main clock in many vertebrates, has a less important function in mammals. Cells have their own molecular circadian clock which is based on transcriptional-translational feedback loops and phosphorylation of its components. Apart from phase shifts that characterize circadian rhythm disorders, a common problem in general population are sleep disorders which include insomnia, hypersomnia and parasomnias. Sleep disorders are linked to neurodegenerative and psychiatric disorders, but this connection hasn't yet been adequately clarified. Sleep problems aren't a mere symptom of many disorders that needs to be treated separately, but a core part of pathophysiology. Further research has the potential to clarify pathogenesis of these diseases and improve therapy for patients