Circadian Rythms

Circadian Rhythms

• a roughly 24 hour cycle that our body uses to regulate itself
• ex. hormone release and the sleep-wake cycles are regulated by the circadian clock
• How do we do this?
• ganglion cells in our retina detect light and darkness. These neurons project to the suprachiasmatic nucleus (SCN in hypothalamus) and use melatonin levels to tell the brain if there is light or not.
• high SCN activation during the day and low activation at night
• when SCN activation is low, it can no longer inhibit the pineal gland and the pineal gland will start producing melatonin

Pineal Body

• part of the brain that is activated SCN activity is low
• if its dark, pineal body secretes melatonin (a neurons-hormone) into bloodstream and CSF system
• if its light, pineal body is inhibited from secreting melatonin by the SCN

Sleep-Wake Cycle

• Sleep cycle
• activated by a single nucleus in the brain called VLPO
• VLPO tells all other brain structures to sleep
• ANALOGY: VLPO is the evil hypnotist
• activated by lack of sleep and circadian clock (daylight/darkness)
• Wake cycle
• SCN tells tuberomamillary nucleus (TMN) to turn on.
• TMN inhibits releases histamine to all areas of the brain including VLPO
• histamine inhibits VLPO which means the rest of the brain wakes up.
• ANALOGY: superhero TMN to the rescue! He slays VLPO.

Stages of Sleep

• Stage 1 = REM sleep. This is when we dream. Through each consecutive cycle, REM gets longer
• bodies movement is inhibited, but eyes are moving quickly - rapid eye movement (REM)
• Stage 2 + 3 = short wave sleep.
• Stage 4 = slow/long wave sleep.
• After you go through all the stages, you repeat them every 90 minutes or so. One 90 minute cycle is called an ultradian rhythm.

Things that use circadian rhythms

1. Sleep
2. Foot and water intake
3. Urine Production
4. blood pressure
5. Platelet Aggregation in the blood
6. Blood cell production
7. Temperature regulation
8. Hormone levels
9. Menstrual Cycle