H8.1 Rhythms of waking and sleeping
Endogenous rhythms:
- endogenous circannual rhythm: a rhythm that prepares for seasonal changes
- endogenous circadian rhythms: last about a day. activity correlates mainly with your
circadian rhythm, and only secondarily with how long you have been awake.
Setting and Resetting the Biological Clock:
- Although circadian rhythms persist without light, your rhythm is not perfect. Unless
something resets it from time to time, it would gradually drift away from the correct time.
The stimulus that resets the circadian rhythm is referred to termzeitgeber
→ Light is by far the dominant zeitgeber for land animals, whereas the tides are
important for some marine animals.
→ other zeitgebers include exercise, arousal of any kind, meals, and the temperature of
the environment.
→ Social stimuli—that is, the effects of other people—are ineffective as zeitgebers,
unless they induce exercise or other vigorous activity.
- People at the eastern edge have a sleep midpoint about 30 minutes earlier than those at
the west, corresponding to the fact that the sun rises earlier at the eastern edge.
- Some blind people do set their circadian rhythms by noise, temperature, meals, and
activity. However, others who are not sufficiently sensitive to these secondary zeitgebers
produce circadian rhythms that are a little longer than 24 hours. When their cycles are in
phase with the clock, all is well, but when they drift out of phase, they experience
insomnia at night and sleepiness during the day.
- Jet lag: Most people find it easier to adjust to crossing time zones going west than east.
→ Going west, we stay awake later at night and then awaken late the next morning,
already partly adjusted to the new schedule. We phase-delay our circadian rhythms.
→ Going east, we phase-advance to sleep earlier and awaken earlier.
→ Adjusting to jet lag is often stressful. Stress elevates blood levels of the adrenal
hormone cortisol, and many studies have shown that prolonged elevations of cortisol
damage neurons in the hippocampus, a brain area important for memory.
- People adjust best to night work if they sleep in a very dark room during the day and
work under very bright lights at night, comparable to the noonday sun. Short-wavelength
(bluish) light helps to reset the circadian rhythm better than long-wavelength light does
- Among shift workers, morning people are most impaired when working the night shift
and evening people are most impaired when working the morning shift.
- Being a morning person or an evening person depends partly on age. It also depends on
genetics and several environmental factors, including artificial light. In low-tech societies
, without electric lights, people go to sleep about three hours after sunset, seldom awaken
during the night, and wake up at sunrise.
- Even beyond the teenage years, morning people report being happier than evening
people, on average, possibly because their biological rhythms are more in tune with their
9-to-5 work schedule.
- Morning type people tend to be more moral and honest in the morning, whereas evening
type people tend to be more moral and honest in the evening.
Mechanisms of the Biological Clock:
- The Suprachiasmatic Nucleus (SCN): generates circadian rhythms itself in a genetically
controlled manner. If SCN neurons are disconnected from the rest of the brain or
removed from the body and maintained in tissue culture, they continue to produce a
circadian rhythm of action potentials.
→ How Light Resets the SCN:
- A small branch of the optic nerve, known as the retinohypothalamic path, from the retina
to the SCN, alters the SCN’s settings. Most of the input to that path, however, does not
come from normal retinal receptors.
- The surprising explanation is that the retinohypothalamic path to the SCN comes from a
special population of retinal ganglion cells that have their own photopigment, called
, melanopsin, unlike the ones found in rods and cones. These special ganglion cells
receive some input from rods and cones, but even if they do not receive that input, they
respond directly to light.
- These special ganglion cells are located mainly near the nose, from which they see
toward the periphery.
- They respond to the overall average amount of light, not to instantaneous changes in
light. The average intensity over a period of time is, of course, exactly the information the
SCN needs to gauge the time of day.
- These ganglion cells respond mainly to short-wavelength (blue) light. For that reason,
exposure to television, video games, computers, and so forth, all of which emit mostly
short-wavelength light, tends to phase delay the circadian rhythm and make it difficult to
fall asleep at the usual time.
→ The Biochemistry of the Circadian Rhythm:
- several genes responsible for a circadian rhythm: period (abbreviated PER) and timeless
(TIM), produce the proteins PER and TIM. The concentration of these two proteins,
which promote sleep and inactivity, oscillates over a day, based on feedback interactions
among neurons.
- Early in the morning, the messenger RNA levels responsible for producing PER and TIM
start at low concentrations. As they increase during the day, they increase synthesis of
the proteins, but the process takes time, and so the protein concentrations lag hours
behind.
- As the PER and TIM protein concentrations increase, they feed back to inhibit the genes
that produce the messenger RNA molecules. Thus, during the night, the PER and TIM
concentrations are high, but the messenger RNA concentrations are declining
- However, in addition to the automatic feedback, light activates a chemical that breaks
down the TIM protein, thereby increasing wakefulness and synchronizing the internal
clock to the external world.
- Mammals have three versions of the PER protein and several proteins closely related to
TIM and the others found in flies. Mutations in the genes producing PER proteins lead to
alterations of sleep schedules.
- People with certain PER mutations have been found to have a circadian rhythm shorter
than 24 hours, as if they were moving about a time zone east every day. They
consistently get sleepy early in the evening and awaken early in the morning. Most
people look forward to days when they can stay up late
- People with an altered PER gene look forward to times when they can go to bed early.
Most people with this sleep abnormality suffer from depression
, → Melatonin
- The SCN regulates waking and sleeping by controlling activity levels in other brain
areas, including the pineal gland. The pineal gland releases the hormone melatonin.
- In all cases, it is released mostly at night. In diurnal animals like humans, it increases
sleepiness. In nocturnal animals, it increases wakefulness.
- In addition to regulating sleep and wakefulness, melatonin also helps control the onset of
puberty and bodily adjustments to changes of season
- Melatonin secretion starts to increase about 2 or 3 hours before bedtime. Taking a
melatonin pill in the evening has little effect on sleepiness because the pineal gland
produces melatonin at that time anyway. However, people who take melatonin earlier
start to become sleepy.
H8.2 Stages of Sleep and Brain Mechanisms
Sleep and Other Interruptions of Consciousness:
- Sleep is a state that the brain actively produces, characterized by decreased activity and
decreased response to stimuli.
- In contrast, coma is an extended period of unconsciousness caused by head trauma,
stroke, or disease. Someone in a coma has a low level of brain activity and little or no
response to stimuli.
- Someone in a vegetative state alternates between periods of sleep and moderate
arousal, although even during the more aroused state, the person shows no awareness
of surroundings and no purposeful behavior. Breathing is more regular, and a painful
stimulus produces at least the autonomic responses of increased heart rate, breathing,
and sweating.
- a minimally conscious state is one stage higher, with brief periods of purposeful actions
and a limited amount of speech comprehension. A vegetative or minimally conscious
state can last for months or years.
- Brain death is a condition with no sign of brain activity and no response to any stimulus.
Endogenous rhythms:
- endogenous circannual rhythm: a rhythm that prepares for seasonal changes
- endogenous circadian rhythms: last about a day. activity correlates mainly with your
circadian rhythm, and only secondarily with how long you have been awake.
Setting and Resetting the Biological Clock:
- Although circadian rhythms persist without light, your rhythm is not perfect. Unless
something resets it from time to time, it would gradually drift away from the correct time.
The stimulus that resets the circadian rhythm is referred to termzeitgeber
→ Light is by far the dominant zeitgeber for land animals, whereas the tides are
important for some marine animals.
→ other zeitgebers include exercise, arousal of any kind, meals, and the temperature of
the environment.
→ Social stimuli—that is, the effects of other people—are ineffective as zeitgebers,
unless they induce exercise or other vigorous activity.
- People at the eastern edge have a sleep midpoint about 30 minutes earlier than those at
the west, corresponding to the fact that the sun rises earlier at the eastern edge.
- Some blind people do set their circadian rhythms by noise, temperature, meals, and
activity. However, others who are not sufficiently sensitive to these secondary zeitgebers
produce circadian rhythms that are a little longer than 24 hours. When their cycles are in
phase with the clock, all is well, but when they drift out of phase, they experience
insomnia at night and sleepiness during the day.
- Jet lag: Most people find it easier to adjust to crossing time zones going west than east.
→ Going west, we stay awake later at night and then awaken late the next morning,
already partly adjusted to the new schedule. We phase-delay our circadian rhythms.
→ Going east, we phase-advance to sleep earlier and awaken earlier.
→ Adjusting to jet lag is often stressful. Stress elevates blood levels of the adrenal
hormone cortisol, and many studies have shown that prolonged elevations of cortisol
damage neurons in the hippocampus, a brain area important for memory.
- People adjust best to night work if they sleep in a very dark room during the day and
work under very bright lights at night, comparable to the noonday sun. Short-wavelength
(bluish) light helps to reset the circadian rhythm better than long-wavelength light does
- Among shift workers, morning people are most impaired when working the night shift
and evening people are most impaired when working the morning shift.
- Being a morning person or an evening person depends partly on age. It also depends on
genetics and several environmental factors, including artificial light. In low-tech societies
, without electric lights, people go to sleep about three hours after sunset, seldom awaken
during the night, and wake up at sunrise.
- Even beyond the teenage years, morning people report being happier than evening
people, on average, possibly because their biological rhythms are more in tune with their
9-to-5 work schedule.
- Morning type people tend to be more moral and honest in the morning, whereas evening
type people tend to be more moral and honest in the evening.
Mechanisms of the Biological Clock:
- The Suprachiasmatic Nucleus (SCN): generates circadian rhythms itself in a genetically
controlled manner. If SCN neurons are disconnected from the rest of the brain or
removed from the body and maintained in tissue culture, they continue to produce a
circadian rhythm of action potentials.
→ How Light Resets the SCN:
- A small branch of the optic nerve, known as the retinohypothalamic path, from the retina
to the SCN, alters the SCN’s settings. Most of the input to that path, however, does not
come from normal retinal receptors.
- The surprising explanation is that the retinohypothalamic path to the SCN comes from a
special population of retinal ganglion cells that have their own photopigment, called
, melanopsin, unlike the ones found in rods and cones. These special ganglion cells
receive some input from rods and cones, but even if they do not receive that input, they
respond directly to light.
- These special ganglion cells are located mainly near the nose, from which they see
toward the periphery.
- They respond to the overall average amount of light, not to instantaneous changes in
light. The average intensity over a period of time is, of course, exactly the information the
SCN needs to gauge the time of day.
- These ganglion cells respond mainly to short-wavelength (blue) light. For that reason,
exposure to television, video games, computers, and so forth, all of which emit mostly
short-wavelength light, tends to phase delay the circadian rhythm and make it difficult to
fall asleep at the usual time.
→ The Biochemistry of the Circadian Rhythm:
- several genes responsible for a circadian rhythm: period (abbreviated PER) and timeless
(TIM), produce the proteins PER and TIM. The concentration of these two proteins,
which promote sleep and inactivity, oscillates over a day, based on feedback interactions
among neurons.
- Early in the morning, the messenger RNA levels responsible for producing PER and TIM
start at low concentrations. As they increase during the day, they increase synthesis of
the proteins, but the process takes time, and so the protein concentrations lag hours
behind.
- As the PER and TIM protein concentrations increase, they feed back to inhibit the genes
that produce the messenger RNA molecules. Thus, during the night, the PER and TIM
concentrations are high, but the messenger RNA concentrations are declining
- However, in addition to the automatic feedback, light activates a chemical that breaks
down the TIM protein, thereby increasing wakefulness and synchronizing the internal
clock to the external world.
- Mammals have three versions of the PER protein and several proteins closely related to
TIM and the others found in flies. Mutations in the genes producing PER proteins lead to
alterations of sleep schedules.
- People with certain PER mutations have been found to have a circadian rhythm shorter
than 24 hours, as if they were moving about a time zone east every day. They
consistently get sleepy early in the evening and awaken early in the morning. Most
people look forward to days when they can stay up late
- People with an altered PER gene look forward to times when they can go to bed early.
Most people with this sleep abnormality suffer from depression
, → Melatonin
- The SCN regulates waking and sleeping by controlling activity levels in other brain
areas, including the pineal gland. The pineal gland releases the hormone melatonin.
- In all cases, it is released mostly at night. In diurnal animals like humans, it increases
sleepiness. In nocturnal animals, it increases wakefulness.
- In addition to regulating sleep and wakefulness, melatonin also helps control the onset of
puberty and bodily adjustments to changes of season
- Melatonin secretion starts to increase about 2 or 3 hours before bedtime. Taking a
melatonin pill in the evening has little effect on sleepiness because the pineal gland
produces melatonin at that time anyway. However, people who take melatonin earlier
start to become sleepy.
H8.2 Stages of Sleep and Brain Mechanisms
Sleep and Other Interruptions of Consciousness:
- Sleep is a state that the brain actively produces, characterized by decreased activity and
decreased response to stimuli.
- In contrast, coma is an extended period of unconsciousness caused by head trauma,
stroke, or disease. Someone in a coma has a low level of brain activity and little or no
response to stimuli.
- Someone in a vegetative state alternates between periods of sleep and moderate
arousal, although even during the more aroused state, the person shows no awareness
of surroundings and no purposeful behavior. Breathing is more regular, and a painful
stimulus produces at least the autonomic responses of increased heart rate, breathing,
and sweating.
- a minimally conscious state is one stage higher, with brief periods of purposeful actions
and a limited amount of speech comprehension. A vegetative or minimally conscious
state can last for months or years.
- Brain death is a condition with no sign of brain activity and no response to any stimulus.
