Chapter 9

Chapter 9 - Chapter 9- Wakefulness and Sleep 9.1- Rhythms...

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Chapter 9- Wakefulness and Sleep 9.1- Rhythms of Waking and Sleeping Researchers first thought sleep had to do with external stimuli Curt Ritcher made the idea of self-generated rhythms of 24 hrs Endogenous cycles Endogenous circannual rhythm - the idea that our internal mechanisms prepare the body for seasonal changes Endogenous circadian rhythms - daily rhythms o Mammals have circ. rhythms for: sleep, eating, urinating, secretion of hormones, etc. o Differ among different individuals urge to sleep depends on time of day in addition to just internal stimuli humans generate wake-sleep rhythms o our body temp is colder when we sleep (36.7 C) vs. 37.2C during the day o sleep later until 20 yrs old, then you sleep earlier in night What evidence indicates that humans have an internal biological clock? o People who have lived in an environment w/ a 24hr schedule in dark have diff than light-dark schedule Setting and Resetting Biological Clock We adjust our internal workings to stay in phase with the outside world Light is critical for resetting our bio clock! Free-running rhythm - a rhythm that occurs when no stimuli reset or alter it o Ex: circadian rhythm Stimulus that resets the circ. rhythm is the German zeitgeber, meaning “time- giver.” Light is the dominant zeitgeber for land animals If blind, the circadian rhythm is set by meals, noise, temp, etc. or produce the free-running rhythm—which creates problems if it isn’t in phase with the clock Jet Lag - a disruption of circ rhythm due to crossing of time zones o Easier to adjust when going east west; we phase-delay our circ rhythm. ( phase- advance if going east) o Cortisol is an adrenal hormone elevate due to stress levels after jet lag Prolonged increase of cortisol=damage of neurons in hippocampus Shift Work- ppl. who sleep irregularly their duration of sleep depends on when go to sleep o Working at night does NOT change the circadian rhythm Mechanisms of the Biological Clock Biological clock depends on part of the hypothalamus called the superachiasmatic nucleus (SCN) –it’s just above the optic chiasm o SCN provides the main control of the circ rhythms for sleep and body temp. o If SCN is damaged, the body’ rhythms are less consistent and NOT synchronized o If SCN is disconnected from brain, it will still control the circ rhythm of body How light resets the SCN o A branch of the optic nerve, retinohypothalamic path , extends from retina SCN But most input does NOT come from normal retinal receptors
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The path comes from a special population of retinal ganglion cells that have their own photo pigment, melapsonin , unlike the ones found in rods or cones They respond to light even though they don’t get any input from rods/cones They respond to light slowly and turn off slowly when light ceases Biochemistry of the Circadian Rhythms
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This note was uploaded on 10/24/2011 for the course PSB 2000 taught by Professor Glendenning during the Fall '08 term at FSU.

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Chapter 9 - Chapter 9- Wakefulness and Sleep 9.1- Rhythms...

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