Chapter 6c Flashcards
Biological Rythm
Biological rhythms :repeated biological processes that are regulated by
internal mechanisms
Circadian rhythm
Circadian rhythms are biological and behavioural changes that occur as part of a cycle that lasts around 24 hours. The sleep-wake cycle is a type of circadian rhythm. Eg The sleep-wake cycle is a 24-hour-cycle that is made up of time spent sleeping and time being awake and alert.
Ultradian rhythm
Ultradian rhythms are biological and behavioral changes that occur in a cycle that lasts less than 24 hours.: eg A sleep episode is the full duration of time spent asleep, from falling asleep until waking up. Throughout an individual’s sleep episode, an individual experiences sleep cycles. A sleep cycle is a repeated approximate 90-minute-period in which an individual progresses through stages of REM and NREM (stages 1–3) sleep. The number of sleep cycles an individual experiences in a sleep episode depends on an individual’s sleep duration. However, on average, there are usually around five or six sleep cycles during a typical sleep episode
SCN
The suprachiasmatic nucleus (SCN) is an area of the hypothalamus that is responsible for regulating an individual’s sleep-wake patterns. The SCN is made up of two nuclei that have approximately 10,000 neurons each and are located above the optic chiasm (the intersection of the optic nerve fibres between each eye). The SCN plays a key role in regulating our sleep-wake cycle by acting like an internal
body clock.
Regulate the sleep wake cycle by The SCN receives information from both external (prescience and absence of light) and internal (suppression and expression of particular genes known as clock genes) cues to help modulate the circadian rhythm.
Clock genes
When clock genes are expressed they produce clock proteins, whereas when they are suppressed, they do not produce clock proteins. Clock genes are expressed or suppressed at certain times during the 24-hour period, which generates and regulates the circadian rhythm. Clock genes operate via a negative feedback loop. This means that when there are low levels of clock proteins in the body, clock genes are translated into clock proteins. As levels of clock proteins increase in the body, the clock genes stop producing clock proteins and existing clock proteins are degraded. This then allows for clock genes to make more clock proteins that are degraded once again, therefore establishing the negative feedback loop. This process follows a 24-hour cycle of clock protein generation and degradation, which reflects our circadian rhythm of the sleep-wake cycle.)
Melatonin
The information from our internal cues and external cues dictate the messages that the SCN sends to the pineal gland, which is a gland in the brain responsible for the production and release of melatonin. Melatonin is a hormone released by the pineal gland typically at night- time to induce sleep as part of the sleep-wake cycle. The body produces melatonin naturally and usually in adequate amounts. At the onset of darkness in the evening, levels of melatonin start to rise (Grivas & Savvidou, 2007). At around 8 to 9pm, melatonin levels should reach a level that starts to induce a sense of calmness, which promotes sleepiness, leading to an individual naturally wanting to induce sleep at around 10 to 11pm. Melatonin peaks between 2 and 4am, when individuals are typically in the deepest sleep, before gradually declining over the night and before waking in the morning. Melatonin does not directly induce sleep, but rather promotes a state of calm and relaxation to help make it easier to fall asleep. Once melatonin is produced and released, it travels to all areas of the body via the bloodstream. The level of melatonin in the body helps to regulate the sleep-wake cycle. Melatonin levels are at their highest at night-time and lowest in the morning, therefore promoting sleep at night-time.
SCN sleep regulation process
steps summarise the process of the SCN regulating the sleep-wake cycle atnight-time:
1. The SCN receives external cues. The SCN also receives internal cues.
2. After receiving both internal and external cues, the SCN sends neural messages (signals) to the pineal gland to produce and release melatonin.
3. The pineal gland releases melatonin into the bloodstream, which promotes feelings of calm and relaxation, therefore promoting sleep.
