L10 - Circadian Rhythms Flashcards
what are BIOLOGICAL RHYTHMS?
BIOLOGICAL RHYTHMS are CYCLICAL CHANGES in PHYSIOLOGICAL SYSTEMS. They EVOLVED because the ENVIRONMENTS in which ORGANISMS LIVE have CYCLICAL CHANGES e.g day/night, summer/winter etc.
There are THREE TYPES of BIOLOGICAL RHYTHMS
what are the THREE TYPES of BIOLOGICAL RHYTHMS? ICU
(I) Infradian Rhythms
(C) Circadian Rhythms
(U) Ultradian Rhythms
what are CIRCADIAN RHYTHMS?
CIRCADIAN RHYTHMS are any CYCLE that LASTS 24 HOURS
NEARLY ALL ORGANISMS possess a BIOLOGICAL REPRESENTATION of the 24 HOUR DAY
These OPTIMISE an ORGANISM’S PHYSIOLOGY and BEHAVIOUR to best MEET THE VARYING DEMANDS of the DAY/NIGHT CYCLE
how do CIRCADIAN RHYTHMS WORK?
CIRCADIAN RHYTHMS are DRIVEN by the SUPRACHIASMATIC NUCLEI (SCN) in the HYPOTHALAMUS
This PACEMAKER must CONSTANTLY BE RESET so that our BODIES are in SYNCHRONY with the OUTSIDE WORLD
NATURAL LIGHT acts as an EXOGENOUS ZEITGEBER because it PROVIDES the INPUT TO THIS SYSTEM, setting the SCN TO THE CORRECT TIME in a PROCESS CALLED PHOTOENTRAINMENT.
The SCN then uses this information to COORDINATE ACTIVITY of CIRCADIAN RHYTHMS throughout the body
how does the SLEEP-WAKE CYCLE WORK? - PT 1
LIGHT and DARKNESS are the EXTERNAL SIGNALS that determine when we feel the NEED TO SLEEP and when we WAKE UP
This rhythm DIPS and RISES at DIFFERENT TIMES of the day so that the STRONGEST SLEEP DRIVES occur BETWEEN 2-4AM and 1-3PM
The RELEASE OF MELATONIN from the PINEAL GLAND is at its PEAK during the HOURS OF DARKNESS. MELATONIN INDUCES SLEEP by INHIBITING the NEURAL MECHANISMS that PROMOTE WAKEFULNESS. LIGHT SUPPRESSES the PRODUCTION OF MELATONIN
how does the SLEEP-WAKE CYCLE WORK? - PT 2
SLEEP and WAKEFULNESS are also under HOMEOSTATIC CONTROL. When we have been awake for a long time HOMEOSTASIS tells us that we NEED TO SLEEP because of the AMOUNT OF ENERGY USED UP DURING WAKEFULNESS.
This HOMEOSTATIC DRIVE FOR SLEEP INCREASES GRADUALLY THROUGHOUT THE DAY, reaching its MAXIMUM IN THE EVENING
CIRCADIAN RHYTHMS KEEP US AWAKE as long as there is daylight prompting us to SLEEP AS IT BECOMES DARK. The HOMEOSTATIC SYSTEM tends to make us SLEEPIER THE LONGER WE HAVE BEEN AWAKE REGARDLESS of whether its night or day. The INTERNAL CIRCADIAN RHYTHM will MAINTAIN A CYCLE of 24-25 HOURS, EVEN WITHOUT NATURAL LIGHT
+ PRACTICAL APPLICATIONS (EVALUATION OF CIRCADIAN RHYTHMS)
+ One PRACTICAL APPLICATION of circadian rhythms is CHRONOTHERAPEUTICS. The TIME THAT PATIENTS TAKE MEDICATION is very IMPORTANT for TREATMENT SUCCESS
It is essential that the RIGHT CONCENTRATION of drug is released in the TARGET AREA of the body AT THE TIME the drug is MOST NEEDED.
E.g the risk of HEART ATTACK is GREATEST DURING EARLY MORNING HOURS after waking. Medications have been developed that are taken BEFORE THE PERSON GOES TO SLEEP but are NOT RELEASED until the VULNERABLE TIME of 6AM.
- CZIESLER ET AL (EVALUATION OF CIRCADIAN RHYTHMS)
- RESEARCH on CIRCADIAN RHYTHMS has NOT ISOLATED PEOPLE from ARTIFICIAL LIGHT, because it was believed that ONLY NATURAL LIGHT AFFECTED CIRCADIAN RHYTHMS
However, MORE RECENT RESEARCH SUGGESTS this MIGHT NOT BE TRUE. CZIESLER ET AL ALTERED PPS CIRCADIAN RHYTHMS DOWN TO 22 HOURS and UP TO 28 HOURS by using ARTIFICIAL LIGHT ALONE
- INDIVIDUAL DIFFERENCES (EVALUATION OF CIRCADIAN RHYTHMS)
- There are INDIVIDUAL DIFFERENCES in the LENGTH OF CIRCADIAN RHYTHMS. One RESEARCH STUDY found that CYCLES CAN VARY from 13 to 165 HOURS
- MORE INDIVIDUAL DIFFERENCES (EVALUATION OF CIRCADIAN RHYTHMS)
- ANOTHER INDIVIDUAL DIFFERENCE in CIRCADIAN RHYTHMS is WHEN INDIVIDUALS REACH THEIR PEAK
‘morning people’ prefer to RISE EARLY and GO TO BED EARLY whereas ‘evening people’ prefer to RISE LATE
- ARCTIC REGIONS (EVALUATION OF CIRCADIAN RHYTHMS)
- Studies of INDIVIDUALS who LIVE IN ARCTIC REGIONS, where the SUN DOES NOT SET IN SUMMER MONTHS, show NORMAL SLEEPING PATTERNS DESPITE THE PROLONGED EXPOSURE TO LIGHT
This suggests that there are OCCASIONS where the EXOGENOUS ZEITGEBER of LIGHT may have VERY LITTLE BEARING on our INTERNAL BIOLOGICAL RHYTHMS
