Lecture 5 - 9/11/2009 Lecture 4 Circadian Rhythms: Control...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 9/11/2009 Lecture 4 Circadian Rhythms: Control of sleep-wake states Lecture 4 Circadian Rhythms • What are circadian rhythms • Brain Mechanisms of the circadian (biological clock) rhythms • Setting and resetting biological clocks • Two-process model of sleep-wake regulation Lecture 4 Circadian rhythms • What is a “circadian” rhythm? – “circa” = approximately circa” – “dies” = day dies” • Rhythms with an approximately 24-hr cycle 24length that are endogenous in origin (meaning generated within the body) 1 9/11/2009 Lecture 4 Circadian rhythms • All animals produce endogenous circadian rhythms. rhythms. • These internal mechanisms operate on an approximately 24hr cycle. • What do they do? – Regulate the sleep/wake cycle. – Also regulate eating & drinking, drinking, body temperature, hormone release (even urine volume) amongst others. Lecture 4 Circadian Rhythm: First demonstration • Jean Jacques d’Ortous de Mairan (1729): French geophysicist: • Studied leaf movements of a heliotrope plant across the 24hr period • Discovered the persistence of circadian rhythms in absence of external cues (e.g. light) Lecture 4 Circadian Rhythm: Human demonstration Zeitgeber = “time giver” • 1938: Kleitman and Richardson spent 6 weeks in Mammoth Cave, Kentucky (world's longest cave). • At the time, some scientists believed our sleep/wake rhythm was controlled by sunlight. • Examined what happened to their sleep/wake schedule in the total absence of light? light? 2 9/11/2009 Lecture 4 Circadian Rhythm: Human demonstration Zeitgeber = “time giver” • Richardson (younger) developed a +24hr day (between 26-28hr/”day”), with 269hr sleep periods • Kleitman (older) had a harder adjusting and stuck close to 24hr. http://www.time.com/time/magazine/rticle/0,9171,760040,00.html • Take home: Human circadian home: clock generates a rhythm slightly longer than 24 hours when it has no external cue to set it. Lecture 4 Circadian Rhythm: Human demonstration Zeitgeber = “time giver” Lecture 4 Example of a Circadian Rhythm Mean rectal temperatures for nine adults: adults: Body temperature reaches its low for the day about 2 hours after sleep onset; it reaches its peak about 6 hours before sleep onset. Fig. 9-2, p. 267 3 9/11/2009 Lecture 4 Rhythms of Waking and Sleep • Circadian rhythms differ between people (and animals) leading to different patterns of wakefulness and alertness. • Also change as a function of age. age. – Example: sleep patterns from childhood to late adulthood. adulthood. – Remember how early you used to wake up at the weekend as a kid! Lecture 4 Circadian Rhythms • What are circadian rhythms • Brain Mechanisms of the circadian (biological clock) rhythms • Setting and resetting biological clocks • Two-process model of sleep-wake regulation Lecture 4 Controlling the rhythms of Waking and Sleep • Mechanisms controlling circadian rhythms (and thus sleep/wake) include the following: 1. The Suprachiasmatic nucleus (SCN). 2. Genes that produce certain proteins. 3. Melatonin levels. 4 9/11/2009 Lecture 4 Rhythms of Waking and Sleep The Suprachiasmatic Nucleus (SCN) • The suprachiasmatic nucleus (SCN) is part of the hypothalamus and the main circadian regulator of rhythms including wake-sleep (and other rhythms e.g. temperature). • Very small (only 20,000 neurons) yet effects are enormous! Lecture 4 Rhythms of Waking and Sleep Melatonin • The SCN regulates waking and sleeping by controlling activity levels in other areas of the brain. • One of these routes is that the SCN regulates the pineal gland. • The pineal gland secretes melatonin (“Darkness Hormone”) Yeah yeah, why is this important? Lecture 4 Rhythms of Waking and Sleep • Melatonin secretion usually begins 2-3hr before bed. • Melatonin feeds back to reset the sleep-wake rhythms through its effects on the SCN i.e. signals light/dark (i.e. when we should sleep and wake) • Melatonin pills: Taken in the afternoon can phase-advance the internal clock (i.e. winding a clock forward), making you want to sleep. 5 9/11/2009 Lecture 4 Circadian Rhythms • What are circadian rhythms • Brain Mechanisms of the circadian (biological clock) rhythms • Setting and resetting biological clocks • Two-process model of sleep-wake regulation Lecture 4 Rhythms of Waking and Sleep • Purpose of the circadian rhythm is to keep our internal workings in phase with the outside world. • A zeitgeber (“time-giver”) is a term used to describe any stimulus that resets our circadian rhythm. • Light is the most import zeitgeber for resetting our circadian rhythms to 24hr, b/c it is the most reliable. (other include: exercise, noise, meals, and temperature). Lecture 4 Rhythms of Waking and Sleep • Jet lag: The disruption of the circadian rhythm due to crossing time zones. • How does it happen: Occurs due to a mismatch of the internal circadian clock and external time. • Characterized by sleepiness during the day, sleeplessness at night. 6 9/11/2009 Lecture 4 Rhythms of Waking and Sleep Leave New York at 7PM Arrive London at 7AM, which is 2AM New York • NYC-->London: So, when you fall asleep on the plane, you are woken when it is morning at destination in London, it is still 2AM back in NYC. • For every hour that your shift out of your time zone, it takes about one day to readjust (e.g. NYC-London = 5hr difference, hence 5 days to adjust) Lecture 4 Circadian Rhythms • What are circadian rhythms • Brain Mechanisms of the circadian (biological clock) rhythms • Setting and resetting biological clocks • Two-process model of sleep-wake regulation Lecture 4 TwoTwo-process model of sleep-wake regulation sleep• So, the general desire to sleep is subject to regulation by, and synchronization with, the circadian rhythm. • Thus, we commonly reach maximum sleepiness in the middle of the night, and minimum sleepiness at awakening. • This circadian factor or “process” (aka “Process-C”) is the “Processfirst (of two) governing sleep-wake rhythms. The other… sleep- ProcessProcess-C 7 9/11/2009 Lecture 4 TwoTwo-process model of sleep-wake regulation sleep• The Homeostatic (second) component of the two-stage model twostates that sleep is ALSO determined as a function of how long you’ve been awake. awake. ProcessProcess-C Lecture 4 TwoTwo-process model of sleep-wake regulation sleep• The Homeostatic (second) component of the two-stage model twostates that sleep is ALSO determined as a function of how long you’ve been awake. awake. • This component reflects the time that has elapsed since sleeping (known as “Process-S”). “ProcessProcessProcess-S Greatest urge to sleep = Greatest distance between Process-S and Process-C ProcessProcess- ProcessProcess-C • Take home: the longer your awake, the more you want to sleep! home: Lecture 4 TwoTwo-process model of sleep-wake regulation sleep- ProcessProcess-S ProcessProcess-C 8 9/11/2009 Lecture 4 TwoTwo-process model of sleep-wake regulation sleep• The Homeostatic (second) component of the two-stage model twostates that sleep is ALSO determined as a function of how long you’ve been awake. awake. • This component reflects the time that has elapsed since sleeping (known as “Process-S”). “ProcessProcessProcess-S ProcessProcess-C • Caffeine blocks the chemical adenosine which builds up, contributing to Process-S Process- Lecture 4 TwoTwo-process model of sleep-wake regulation sleep• Pulling the all-nighter: Feel really bad around 4-5AM all4• Start to feel better around 11AM due to Process-C Process• Feel utterly miserable at 11PM due to both Process-C and S Process- ProcessProcess-S ProcessProcess-C AWAKE Sleep Deprivation Explained Lecture 4 Lecture 4 - Summary • All living species, including humans, express circadian rhythms, which synchronize biological processes (e.g. wake-sleep) to a daily wakecycle, principally controlled by the suprachiasmatic nucleus (SCN). (SCN). • However, these endogenous (self-paced) circadian rhythms are not (selfprecisely 24hrs, and therefore need environmental cues (zeitgeber’s) (zeitgeber’s) to reset them to 24hrs, light being the most influential of these. • The SCN controls sleep-wake timing via several routes, including the sleeprelease of melatonin, which informs the brain of light and dark. melatonin, • But circadian rhythms are only part of the story in controlling when we wake and sleep, with a two-process (S and C) model proposed to twooffer a more accurately explanation. 9 ...
View Full Document

Ask a homework question - tutors are online