Circadian Rythms Flashcards
What are biological rhythms
Cyclical changes in physiological systems which have evolved because the environments in which organisms live have cyclical changes e.g. day night summer winter… . There are three types, circadian, ultradian, infradian
What is the 24 hour circadian rhythm?
A biological rhythm, often known as the biological clock, that is reset by levels of light. It’s derived from Latin. Circa meaning about and dian meaning day
what organisms have a circadian rhythm and why?
Almost all organisms possess a biological representation of the 24hr day. These optimise an organisms physiology and behaviour to meet the varying demands of the day/night cycle
What is the circadian rhythm driven by
The suprachiasmaric nuclei (SCN), which is located in the hypothalamus. This pacemaker must constantly be reset so that our bodies are in synchrony with the outside world. Natural light provides the input into this system, setting the SCN to the correct time in a process known at photo entrainment. The SCN then uses this info to coordinate the activity of circadian throughout the body.
What is the sleep wake cycle?
Example of circadian rhythm, dictating whether an animal should go sleep or wake. Light is the primary input to this system, acting as the external cue for waking and sleeping. Light gets detected by the eye, which sends a signal, regarding the level of brightness, to the SCN. The SCN then uses this information to coordinate the activity of the circadian system. Sleep drive is the highest between 2 and 4am and 1-3pm
How else is sleep wake cycle controlled
It’s also controlled by homeostasis. When we have been awake for a long time, homeostasis tells our body to sleep because of the amount of energy used up in wakefulness. This drive increases throughout the day, reaching its maximum in late evening, when most people fall asleep
What is another circadian rhythm?
Body temp - body temp is at its lowest at 4:30am (36°) and it’s highest in early evening at 6pm (38°). Sleep normally occurs when core temp starts to drop and nearing the end of sleep, body temp starts to rise, promoting the feelings of alertness first thing in the morning.
Advantages of circadian
It has practical applications - chronotheraputics. The time that medication is taken is very important for treatment success. It is essential that the right concentration of drugs is released in the target area of the body at the time the drug is most needed. E.g. risk of heart attack is greatest during the early hours of the morning after waking. Medications have been developed so that they can take them before sleep, but not released until 6am
Also has research support - Siffre found that the absence of external cues such as light significantly altered his circadian rhythm. When he resurfaced from an underground cave with no lights or clocks he believed the date was a month earlier than it actually was, suggesting that his sleep wake cycle was increased by the lack of external cues, making us: believe the day was longer than it actually was, making him think fewer days had passed
Disadvantages circadian
It doesn’t account for individual differences in circadian rhythms. Duffy et al found that ‘morning people’ tend to go bed at 10pm and wake at 6am, whereas ‘evening people’ prefer to go bed at 1am and wake at 10am, demonstrating that there are individual differences in circadian rhythms and researchers should focus on these
It’s also found temp my be more important than light in determining circadian rhythms. Buhr et al found that fluctuations in temp set the timing of cells in the body and caused tissues and organs to become more active or inactive. He claimed that light levels are converted into neural messages that set the body’s temperature and these fluctuations can send powerful signals to our body clocks. Demonstrating that circadian rhythms are affected by many factors suggesting that a holistic approach is preferable
