Chapter 14- Biological rhythms, sleep, and dreaming

Question 1

Diurnal

Answer 1

Humans and other primates are diurnal- active during the day. When animals sleep typically depends on when their predators or prey sleep

Question 2

Nocturnal

Answer 2

Active during dark periods

Question 3

Pineal gland

Answer 3

A secretory gland in the brain midline, the source of melatonin release

Question 4

Entrainment

Answer 4

The process of synchronizing a biological rhythm to an environmental stimulus.

Question 5

Free-running

Answer 5

Referring to a rhythm of behavior shown by an animal deprived of external cues about time of day. Behavior becomes free-running in continuous dim light.

Question 6

Circadian rhythm

Answer 6

Function that have a 24 hour rhythm- results in animals being active either at night or during the day. Rhythms may be behavioral, physiological, or biochemical, like thirst, body temperature, or hormone levels. All have biological origin.

Question 7

What is an endogenous clock, and how does it generate circadian rhythms?

Answer 7

A hamster placed in a dimly lit room continues to show a daily rhythm in wheel running despite the absence of day versus night, suggesting that the animal has an internal, biological clock. Even if the light is always dim, the animal can detect other external cues, like outside noises or temperature. However, in constant light or dark, the circadian cycle is not exactly 24 hours. Activity starts a few minutes later each day, so eventually the hamster is active when it’s daytime outside.

Question 8

Why are circadian rhythms beneficial?

Answer 8

Circadian rhythms synchronize behavior and body states to changes in the environment. The endogenous clock enables animals to anticipate an event, such as darkness, and to begin physiological and behavioral preparations before that event (in this case, before it gets dark).

Question 9

Phase shift

Answer 9

Normally, the internal clock is set by light. The shift of activity produced by a synchronizing stimulus is referred to as a phase shift

Question 10

In humans, which factors allow for entrainment?

Answer 10

Light (visual input), meals, sleep, job/class, activity (exercise). Several of these inputs are also regulated by a biological clock.

Question 11

Which region of the hypothalamus contains the biological clock?

Answer 11

The suprachiasmatic nucleus (SCN). Lesions confined to the SCN portion of the hypothalamus interfere with circadian rhythms of drinking and locomotor behavior and hormone secretion.

Question 12

What happens when the SCN is damaged?

Answer 12

If light/dark cycle maintained, no change in behavior. If only dim light, random behavior- animal will eat and sleep at random times

Question 13

In mammals, how does light information reach the SCN?

Answer 13

Retinal ganglion cells in the eye send their axons along the retinohypothalamic pathway, splitting off at the optic chiasm to synapse within the SCN. This is the pathway that carries information about light to the hypothalamus to entrain behavior.

Question 14

How do retinal ganglion cells work?

Answer 14

The retinal ganglion cells are sensitive to light themselves, without using special receptors. This is because the cells have a special photopigment called melanopsin. The retinal ganglion cells send their axons to the SCN, but other melanopsin containing retinal ganglion cells project to the brainstem, informing the brain about light to control pupil diameter. Melanopsin is most sensitive to blue light frequencies, which is why blue light has the largest effect on human circadian systems.

Question 15

Which 2 proteins are made by the SCN?

Answer 15

SCN makes two proteins called clock and cycle.

Question 16

How do the clock and cycle proteins work?

Answer 16

The two proteins bind together to form a dimer (a pair of molecules joined together). The dimer binds to the cell’s DNA to promote the transcription of two other genes (per and cry). The resulting per and cry proteins will dimerize as well, and inhibit the expression of the clock and cycle genes that began this process.

Question 17

What is the function of the clock and cycle mechanism?

Answer 17

SCN neurons use this mechanism to keep time approximately, and neurons communicate through their synapses to synchronize their activity and produce a constant period of about 24 hours, driving the circadian rhythm. The same molecular clock operates in almost every cell in the body, and they are all in sync as long as the SCN is intact.

Question 18

How does light entrain the molecular clock to the light-dark cycle?

Answer 18

The retinohypothalamic tract is used to get light information to the SCN. The retinal ganglion cells containing melanopsin detect light and release the neurotransmitter glutamate in the SCN. Glutamatergic synapses trigger a chain of events in SCN that promotes the production of per protein. When the animal’s photoperiod is shifted, the per production shifts the phase of the molecular clock.

Question 19

Do humans have an endogenous circadian clock?

Answer 19

Yes. In the absence of external cues, humans display a circadian rhythm of the sleep-wake cycle. External cues (lights, meals, jobs, alarm clocks) entrain our clock to a 24 hour period, the circadian clock encourages our brain to sleep at some times of the day and to remain awake at others. The free running period is slightly greater than 24 hours.

Question 20

How are brain potentials measured to define the different sleep stages?

Answer 20

Brain potentials recorded through EEGs provide a way to define, describe, and classify levels of arousal and states of sleep, supplemented by recording eye movements (with EOG) and muscle tension measurements (with EMG).

Question 21

2 classes of sleep

Answer 21

1. NREM- subdivided into 3 stages

2. REM

Question 22

Beta activity/desynchronized EEG

Answer 22

A fully awake person’s EEG is desynchronized as is a mix of multiple frequencies. It includes many fast frequencies and is of a low amplitude. This is called beta activity or desynchronized EEG.

Question 23

What is the pattern of electrical activity during stage 1 NREM sleep?

Answer 23

During relaxation as you’re about to go to sleep, regular and slightly slower oscillation occurs. This is called alpha rhythm. As you enter stage 1 sleep, there is smaller amplitude, irregular frequency, and sharp waves called vertex spikes. Stage 1 NREM sleep is accompanied by a slowing of heart rate and a reduction in muscle tension, and the eyes might roll around slowly.

Question 24

How long does stage 1 NREM last?

Answer 24

A few minutes

Question 25

NREM sleep is characterized by

Answer 25

Reduction in postural tension- opposed to REM where there is no postural tension at all

Question 26

How long does each sleep cycle last?

Answer 26

90-110 minutes

Question 27

Stage 2 NREM sleep

Answer 27

You can observe sleep spindles and K complexes. If woken up during the first 2 sleep stages, a person would deny that they’d been sleeping.

Question 28

Sleep spindles

Answer 28

Bursts of 12-14 Hz waves, occur during stage 2 NREM

Question 29

K complexes

Answer 29

Sharp negative EEG potentials that have a larger amplitude, observed during stage 2 NREM sleep.

Question 30

Stage 3 NREM sleep

Answer 30

Stage 3 sleep is defined by large amplitude, very slow waves called delta waves. It’s also called slow wave sleep. During SWS, neighboring cortical neurons tend to have synchronized activity, as if they were all “chanting” together rather than fulfilling different functions as they do in waking.

Question 31

REM sleep

Answer 31

A person will exhibit small amplitude, high frequency activity, similar to the brain activity of an individual who is awake. This is coupled with the complete relaxation of skeletal muscles. REM is also called paradoxical sleep, since the brain waves look awake, but the brainstem is profoundly inhibiting motor neurons and the skeletal muscles are therefore completely limp. During REM, we experience rapid eye movements, vivid dreams, and irregular breathing and pulse rates.

Question 32

What happens after a person reaches stage 3 NREM sleep?

Answer 32

It takes about 90 minutes to progress through the 3 NREM stages. Then, a person returns briefly to stage 2. After that, the person enters REM sleep.

Question 33

Can we repay sleep debt?

Answer 33

No. You won’t get the same benefits of sleep from only sleeping in on weekends that you would from sleeping 8 hours every night.

Question 34

How much do we sleep and when?

Answer 34

Young adults tend to sleep from 7-8 hours, and spend about half that time in stage 2 sleep. The last half of the night contains more REM sleep and less stage 3 REM sleep, with the last REM period before waking lasts 40 minutes. At puberty, the circadian rhythm shifts for most people, so they get up later in the day.

Question 35

When does most vivid dreaming occur?

Answer 35

Most vivid dreaming occurs during REM sleep. Dreams can occur during NREM too, but these dreams are more like thoughts (thinking about problems, etc). During REM sleep, dreams are more like a mental movie, and people can experience sights, sounds, smells, and actions.

Question 36

What are the functions of sleep? (4)

Answer 36

1. Sleep conserves energy
2. Sleep enforces niche adaptation
3. Sleep restores the body and brain
4. Sleep aids memory consolidation

Question 37

How does sleep conserve energy?

Answer 37

We use less energy when we’re asleep. During stage 3 sleep, we experience reduced muscle tension, lower heart rate, reduced blood pressure, and slower respiration, indicating a slower metabolic rate.

Question 38

How does sleep enforce niche adaptation?

Answer 38

Almost all animals are either nocturnal or diurnal. This is part of an ecological niche. For example, nocturnal animals like mice, are better at sneaking around in the dark and use hearing and smell to locate food. They sleep during the day so they are inactive while diurnal predators are awake.

Question 39

How does sleep restore the body and brain?

Answer 39

One function of sleep is the rebuilding or restoration of materials used during waking, like proteins. This is likely why most growth hormone release happens during SWS. The widespread belief that sleep helps us ward off illness is well supported by research. Sleep also restores the brain by allowing it to get rid of waste products. Glial cells remove toxins from the cerebrospinal fluid, and this removal occurs more quickly during sleep.

Question 40

How does sleep aid memory consolidation?

Answer 40

Participants tend to display better retention of material if they sleep between their learning period and a test- sleep helps with consolidation of memory. Sleep deprivation also makes people more susceptible to forming false memories. In addition, patterns of neuronal activity seen while a task is learned during wakefulness are recreated during subsequent NREM sleep, as if the brain is “rehearsing” the material. The memory consolidation function of sleep might involve determining which synapses are gained or lost.

Question 41

Which 4 neural systems interact during sleep?

Answer 41

1. Basal forebrain
2. Brainstem
3. Pons
4. Hypothalamus

Question 42

How does the forebrain generate slow wave sleep?

Answer 42

The basal forebrain generates SWS, and neural circuits within the basal forebrain regulate activity of GABA-ergic neurons that send their axons to other areas of the brain. It also inhibits the reticular formation

Question 43

Function of the reticular formation in sleep

Answer 43

The reticular formation is a brainstem structure- includes the medulla and the thalamus. It helps to promote wakefulness. It also sends signals to the basal forebrain- one function of the basal forebrain during sleep is to inhibit the reticular forebrain. Damage to this area promotes a constant sleep state.

Question 44

Function of the pons in sleep

Answer 44

The pons triggers REM sleep by sending signals to the basal forebrain. The subcoeruleus of the pons has been identified as having active neurons during REM sleep. The subcoeruleus inhibits motor neurons to keep them from firing by releasing inhibitory neurotransmitters GABA and glycine- the neurons are blocked from producing an action potential, so the muscles are completely flaccid.

Question 45

Hypothalamus function in sleep

Answer 45

Hypocretins/orexins are used as neurotransmitters, and send axons to the other 3 sleep centers and seem to coordinate them, enforcing the patterns of sleep. Normally, hypocretin keeps sleep at bay and prevents the transition from wakefulness directly into REM sleep.

Question 46

Sleep paralysis

Answer 46

Sleep paralysis is the temporary inability to move or talk just before falling asleep or just after waking up, and can be accompanied by hallucinations. It’s thought to be caused when the subcoreolus in the pons continues to impose paralysis for a short while after a person wakes up from a REM episode.

Question 47

Narcolepsy

Answer 47

Narcolepsy is attacks of sleep that occur during waking hours. People with narcolepsy enter REM in the first few minutes of sleep, and exhibit a disturbed pattern of sleep at night. With narcolepsy, hypocretin neurons in the hypothalamus degenerate, inappropriately activating the cataplexy (loss of muscle tone) pathway that is normally only activated during REM sleep.