rhythms of sleeping of waking

• Endogenous rhythms refer to the body's ability to generate its own rhythm of waking and sleeping
• Endogenous circannual rhythm is a rhythm that prepares migratory birds for seasonal changes
• Animals also produce endogenous circadian rhythms that last about a day
• Humans generate 24-hour wake-sleep rhythms that can be modified only slightly
• Naval personnel on submarines generate rhythms of alertness and body chemistry averaging about 24.3 to 24.4 hours
• If individuals go without rhythms of waking and sleeping, they feel sleepier as the night goes on but more alert as morning arrives
• The stimulus that resets the circadian rhythm is called zeitgeber, with light being the dominant zeitgeber for land animals and humans
• Other zeitgebers include exercise, arousal, meals, and temperature of the environment
• The onset of light resets the biological clock, even in constant light or darkness
• Blind people may set their circadian rhythms by noise, temperature, meals, and activity
• Jet lag is a disruption of circadian rhythms due to crossing time zones, leading to sleepiness, sleeplessness, depression, and impaired concentration
• Adjusting to jet lag can be stressful and may lead to elevated cortisol levels, which can damage neurons in the hippocampus
• Most people find it easier to adjust to crossing time zones going west than east
• Shift workers, like pilots and doctors, may experience irregular sleep patterns and difficulty adjusting their circadian rhythms
• Morning people ("larks") awaken early and peak in productivity early, while evening people ("owls") warm up more slowly and peak in the late afternoon or evening
• Melatonin, a hormone produced by the Pineal Gland, regulates sleep and increases secretion 2 to 3 hours before regular bedtime
• The brain generates its own rhythm, known as the biological clock
• The biological clock mechanism is robust and remains steady despite lapses or deprivations
• The superchiasmatic nucleus (SCN) is the main driver of rhythms and is part of the hypothalamus
• Even a single SCN cell can maintain the circadian rhythm
• Lights affect the SCN through the retinohypothalamic path, a small branch of the optic nerve
• Melanopsin, special ganglion cells found near the nose, play a role in this process
• The reaction to light is slow and vision is towards the periphery
• The biochemistry of the circadian rhythm involves gene placement from mRNA coding to DNA
• Production and concentration levels of PER and TIM vary at day and night
• Alterations in sleep schedules may result in a circadian rhythm shorter than 24 hours