Finals BIO part 1

• Curt Richter's research in 1922 hinted at the idea of self-generated cycles
• migratory birds and squirrels, demonstrate the need to anticipate environmental changes rather than solely responding to immediate stimuli.
• Migratory birds, for instance, start their journey to winter homes before their summer habitat becomes too cold,
• birds when to fly south for the winter
• This behavior suggests the presence of an internal rhythm, termed an endogenous circannual rhythm
• Endogenous means “generated from within.” Circannual comes from the Latin words circum, for “about,” and annum, for “year.”
• Endogenous ciracannual rhythym: A rhythm is generated from within the organism and operates on an annual or yearly cycle
• Circadian comes from “circum,” for “about,” and “dies,” for “day.”
• endogenous circadian rhythms lasting about a day
• Sunlight plays a role in reducing sleepiness
• Circadian rhythms extend beyond regulating waking and sleeping
• they influence various bodily functions such as eating and drinking, urination, hormone secretion, drug sensitivity, and more
• Circadian rhythms also impact mood
• between "morning people" or "larks" who wake up early, become productive quickly, and experience reduced alertness as the day progresses;
• evening people" or "owls" who warm up more slowly, peak in the late afternoon or evening, and often tolerate staying up late better than morning people.
• Age influences sleep preferences, with children tending to go to bed and wake up early.
• with older rats exhibiting optimal performance shortly after awakening,
• with younger rats who tend to improve performance as the day progresses.
• Our circadian rhythms generate a period close to 24 hours
• The stimulus that resets the circadian rhythm is referred to by the German term zeitgeber (TSITE-gay-ber), meaning “time-giver.
• Light is the primary zeitgeber for land animals.
• Blind individuals, lacking the primary zeitgeber of light, rely on alternative stimuli such as noise, temperature, meals, and activity to set their circadian rhythms
• Jet lag refers to the disruption of circadian rhythms caused by crossing time zones
• Shift Work: People with irregular sleep schedules, including pilots, medical interns, and shift workers, experience variations in sleep duration based on when they go to sleep.
• Night-shift workers, in general, face a higher risk of accidents compared to day-shift workers.
• The use of artificial lighting in buildings during night shifts, typically in the range of 150–180 lux
• Curt Richter (1967) proposed this concept, emphasizing the clock's resilience to various forms of interference.
• The biological clock relies on a part of the hypothalamus known as the suprachiasmatic nucleus (SCN), located just above “supra” the optic chiasm
• The SCN is the primary regulator of circadian rhythms, particularly for sleep and body temperature.
• Damage to the SCN leads to erratic body rhythms
• The suprachiasmatic nucleus (SCN) independently generates circadian rhythms in a genetically controlled and unlearned manner
• The suprachiasmatic nucleus (SCN) is located just above the optic chiasm in the human brain
• The retinohypothalamic path, a branch of the optic nerve, extends directly from the retina to the SCN
• Mice with genetic defects destroying their rods and cones still synchronize their biological clocks with light cues.
• Blind mole rats, with minimal optic nerve axons and lacking typical visual structures, respond to light, resetting their circadian rhythms.
• The retinohypothalamic path to the SCN is influenced by a unique subset of retinal ganglion cells with melanopsin.
• Melanopsin containing ganglion cells respond directly to light and are mainly located near the nose in a non-uniform distribution
• The production of circadian rhythm, initially studied in insects like the fruit fly Drosophila
• n Drosophila, the genes period (per) and timeless (tim) play a crucial role in generating the circadian rhythm.
• These genes produce the proteins PER and TIM, which promote sleep and inactivity.