Chapter 9 - Wakefulness And Sleep

Question 0

What is the endogenous circadian rhythm?

Answer 0

Your urge for sleep depends partly on the time of day, not just how long you have been awake for. Human wake-sleep rhythms are based on a 24 hour schedule

Question 1

What is the endogenous coir annual rhythm?

Answer 1

A bird generates a rhythm that prepares it for seasonal changes

Question 2

What does circadian rhythm effect?

Answer 2

Sleep-wake, eating, drinking, urination, secretion of hormones, sensitivity to drugs. Eg. Normal temperatures fluctuate over the course of the day. . We also have circadian rhythms in mood. Studies have shown that positive mood increases from waking to late afternoon, the a slight decrease til bed. Our most pleasant mood is at 5pm and our least at 5am. But remember we are all different. Not everyone is a morning person. Age can also impact on our rhythms with a child Going to bed early and getting up early, whilst a teen will stay up later and get up later.

Question 3

Describe how we reset our circadian rhythms.

Answer 3

We run on a 24 hour clock but. Need to reset out internal clock. Light is critical for resetting. The stimulus that resets the circadian rhythm is referred to as zeitgeber. Light is the dominant zeitgeber for land animals. Other zeitgebers include exercise, arousal, meals, the temp of the environment. Social stimuli, that is other people, are weak zeitgebers. Even when we try to set our wake-sleep cycles by the clock, sunlight has its influence. Eg daylight savings puts everyone out.

Question 4

What is a zeitgebers?

Answer 4

It is a stimulus that resets the circadian rhythm

Question 5

Describe the zeitgebers used by blind people.

Answer 5

Some use noise, temp, meals and activity. They obviously can’t use light and if they get out of sync, they can experience insomnia at night and sleepiness during the day.

Question 6

What is jet lag?

Answer 6

A disruption of circadian rhythms due to crossing time zones. The mismatch between internal circadian clock and external time can cause sleepiness during the day, sleeplessness at night, depression and impaired concentration.

People find it easier to adjust to crossing time zones going west than east because most people find it difficult to go to sleep before the body’s usual time.

Question 7

Adjusting to jet lag is often stressful. Explain the impacts of the stress.

Answer 7

Stress elevates blood levels of the adrenal hormone cortisol. Studies have found prolonged elevations of cortisol to damage neurons in the hippocampus (important for memory)

Question 8

Describe the impacts of shift work

Answer 8

Many workers don’t fully adjust to shift work. They are often groggy on the job, sleep poorly during the day, their body temp peaks during the day instead of at night when they are working. In general they have more accidents.

People adjust best if they sleep in a very dark room and work under very bright lights

Question 9

What is the suprachiasmatic nucleus or SCN?

Answer 9

Hit is part of the hypothalamus, just above the optic chasm. The SCN provides the main control of the circadian rhythms for sleep and body temp (although several other brain areas generate local rhythms). After damage to the SCN, the body’s rhythms become erratic. The SCN generates circadian rhythms itself in a genetically controlled, unlearned manner.

Question 10

How does light reset the SCN?

Answer 10

The SCN is located just above the optic chiasm. A small branch of the optic nerve, known as the retinohypothalamic path, extends directly from the retina to the SCN. Axons of that path alter the SCN’s settings. Most of the input to that path does not come from normal retinal receptors. 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. They respond to light slowly and turn off slowly when light ceases. Therefore they respond to the overall average not instantaneous light changes.

Question 11

How does the SCN operate in blind people?

Answer 11

Many people who are blind because of damage to the rods and cones nevertheless have enough input to the melanopsin containing ganglion cells to entrain their waking and sleeping cycle to the local pattern of sunlight.

Others may have no input from the visual cortex can have light sensitive excitation in the thalamus.

Question 12

How does the suprachiasmatic nucleus produce the circadian rhythm?

Answer 12

Researchers found in flies, 2 genes known as period and timeless produce the proteins PER and TIM. The concentration of these 2 proteins, which promote sleep and inactivity, oscillates over a day based on oscillation feedback over the day from several neurons.

Early in the morning, the messenger RNA levels responsible for producing PER and TIM start at low concentrations. They increase during the day. As TIM and PER increase, they feedback to inhibit the genes that produce the messenger RNA molecules. Thus, during the night, the PER and TIM concentrations are high but the RNA concentrations are decreasing.

By the next morning, PER and TIM protein levels are low, the flies awKen and the cycle starts again. Light activates a chemical that breaks down the RIM protein, thereby increasing wakefulness and synthesises the internal clock to the external world.

Mutations in the genes producing PER proteins lead to alterations of sheep schedules

Question 13

What is melatonin?

Answer 13

The SCN regulates waking and sleeping by controlling activity levels in other brain areas, including the pineal gland (an endocrine gland located just position to the thalamus). The pineal gland releases the hormone melatonin, which influences both circadian and circanual rhythms. The pineal gland secretes melatonin mostly at night, making us sleepy at that time. When people shift to a new time zone and start following a new s heddle, they continue to feel sleepy at their old times until, the melatonin rhythm shifts. Melatonin secretion secretion starts to increase about 2 or 3 hours before bedtime.

Note- those with damage to the pineal gland can stay awake for days.

Question 14

What is sleep?

Answer 14

A state that the brain actively produces, characterised by decreased response to stimuli. It is possible to awaken a sleeping person

Question 15

What is a coma?

Answer 15

An extended period of unconsciousness caused by head trauma, stroke or disease. A person in a coma has a low level of brain activity throughout the day.

Question 16

What is a vegetative state?

Answer 16

Someone in this state alternates between periods of sleep and moderate arousal. At no time does the person show an awareness of the surrounds. Breathing is more regular and a painful stimuli produces at least an automatic response of increased heart rate, breathing and sweating. They probably have some cognitive activity. This can last for years or months

Question 17

What is a minimally conscious state?

Answer 17

It is a stage higher than vegetative state with occasional, brief periods of purposeful actions and a limited amount of speech comprehension. This can last for months or years.

Question 18

What is brain death?

Answer 18

There is no sign if brain activity and no response to any stimulus. Drs wait 24 hours with no brain activity before announcing brain death, at which point most people feel that it is ethical to remove life support.

Question 19

What do they use to measure brain activity during sleep?

Answer 19

EEG

Question 20

What is a polysommograph?

Answer 20

A combination of EEG and eye movement records

Question 21

What are alpha waves?

Answer 21

These are characteristic of relaxation. They have a frequency of 8 to 12 per second

Question 22

What are sleep spindles?

Answer 22

Waves of 12-14Hz. They a bursts that last at least half a second. Sleep spindles result from oscillating interactions between cells in the thalamus and the cortex.

Question 23

What is a K-complex?

Answer 23

It is a sharp wave associated with temporary inhibition of neuronal firing.

Question 24

What are the prominent features of stage 2 ?

Answer 24

Sleep spindles and K-complexes

Question 25

What happens in stage 1 ?

Answer 25

The EEG is dominated by irregular, jagged, low voltage waves. Overall brain activity is less than in relaxed wakefulness but higher than other sleep stages. The cortex receives a great deal of input, much of it at high frequencies. Nearly all neurons are active

Question 26

Describe stages 3 and 4.

Answer 26

Heart rate, breathing rate and brain activity decrease, while slow, large amplitude waves become more common. Stages 3 and 4 constitute slow wave sleep (SWS). Slow waves indicate that neuronal activity is highly synchronised. By stage 4 sensory input to the cerebral cortex is greatly reduced.

Question 27

What is paradoxical sleep?

Answer 27

In the 1960s Jouvet discovered a period of sleep where the brain activity is high but the body is relaxed. It is a period of deep sleep in some ways but light in others. In humans it has since become to be known as REM sleep but as many animals do not move their eyes, it is still referred to as paradoxical sleep in animals.

Question 28

What is Rapid Eye Movement (REM) sleep?

Answer 28

Periods of rapid eye movements, high brain activity and high relaxation during sleep. Originally referred to as paradoxical sleep.

Question 29

What happens during REM sleep?

Answer 29

The EEG shows irregular, low voltage fast waves that indicate increased neuronal activity. Postural muscles are more relaxed than at any other time. Erections, heart rate, blood pressure, and breathing rates are more variable than at any other stage of sleep. Facial twitches, eye movements. The other stages a known as non-REM (NREM) sleep.

Question 30

Describe the sleep pattern.

Answer 30

When you fall asleep you start at stage 1, then 2, 3, 4, this should take an hour, then you go back again, 4, 3, 2, REM. the sequence repeats with each cycle lasting about 90 mins. Early in the night 3, and 4 predominate. Towards morning, REM occupies an increasing percentage of the time. The amount of REM depends on the time of day rather than how long you have been asleep for.

Question 31

Describe REM dreams.

Answer 31

REM dreams are more likely than NREM dreams to include striking visual imagery and complicated plots, but not always. REM and dreams usually Overlap but they are not the same thing.

Question 32

What happens if you cut through the midbrain?

Answer 32

It decreases arousal by damaging the reticular formation.

Question 33

What is the reticular formation?

Answer 33

A structure that extends from the medulla into the forebrain. Some neurons ascend into the brain whilst others descend into the spinal cord. Those that ascend are well suited to regulate arousal.

Question 34

what would happen if the reticular formation was damaged?

Answer 34

decreases arousal.

Question 35

What is the pontomesencephalon?

Answer 35

it is part of the reticular formation that contributes to cortical arousal. These neurons receive input from the sensory systems. Their axons extend into the forebrain, releasing acetylcholine and glutamine, which excite cells in the hypothalamus, thalamus, and basal forebrain. it therefore maintains arousal during wakefullness, increases arousal in response to new or challenging tasks. Stimulation awakens a sleeping individual or or increases the alertness of an already awake person.

Question 36

What is the locus coeruleus?

Answer 36

a small structure in the pons, usually inactive, especially during sleep, but it emits burst of impulses in response to meaningful events, especially those that produce emotional arousal. Axons from the locus coeruleus release norepinephrine widely throughout the cortex having a huge influence. Anything that stimulates the locus coeruleus strengthens the storage of recent memories and increases wakefulness.

Question 37

How does the hypothalamus influence arousal?

Answer 37

the hypothalamus has several axon pathways that influence arousal. 1. releases histamine neurotransmitter which produces excitatory effects throughout the brain. 2. mainly from the lateral and posterior nuclei of the hypothalamus releases a peptide neurotransmitter called orexin 3. Other pathways from the lateral hypothalamus regulate cells in the basal forebrain. Some of the axons from the basal forebrain release acetylcholine

Question 38

Describe the effects of histamine.

Answer 38

Histamine is an excitatory neurotransmitter. Cells releasing histamine are active during arousal and alertness, less active just before sleep and upon waking. Antihistamines create drowsiness so the new non-drowsy versions do not cross the blood-brain barrier very well, thus reducing the drowsiness.

Question 39

Describe the functions of orexin.

Answer 39

orexin is a peptide neurotransmitter. The axons releasing orexin extend to the basal forebrain and other areas where they stimulate neurons responding to wakefulness. Orexin is not necessary for waking but it is for staying awake, especially towards the end of the day. The level of orexin rises throughout the day and remains high when monkeys are kept awake beyond their bedtime. It dropped as soon as the monkeys went to sleep. Drugs that block orexin receptors increase sleep and procedures hat increase orexin lead to wakefulness and alertness.

Question 40

Describe the basal forebrain and arousal.

Answer 40

It is just anterior and dorsal to the hypothalamus. Axons extend to the thalamus and the cerebral cortex. Some of these axons release acetylocholine which tends to increase arousal. Acetylochine is released during wakefulness and REM sleep but not during slow-wave sleep.

Question 41

How does GABA relate to sleep?

Answer 41

GABA is the brain’s main inhibitor. It is responsible fore sleep. During sleep body temperature, and metabolic rates decreaase, as doe neuron activity. Active neurons continue to fire close to their usual rate and neurons in the brain’s sensory areas continue to respond to sounds and other stimuli. We remain unconscious because GABA inhibits synaptic activity. Because sleep depends on GABA mediated inhibition, it can be local within a brain eg dolphins only have half a brain asleep at a time. This helps to explain sleep walking and lucid dreams. The pons sends out inhibitors during sleep to stop the body from moving. Sometimes, if woken suddenly, the pons will take a moment to respond and you may find yourself temporarily paralysed.

Question 42

Describe what happens during REM sleep.

Answer 42

Activity increases in the pons (which triggers the onset of REM sleep), and the limbic system (which is important for emotional responses). Activity decreased in the primary visual cortex, the motor cortex, and the dorsolteral prefrontal cortex, but increased in parts of the parietal and temporal cortex. There are high amplitude waves called PGO waves (pons-geniculate-occipital). Waves are detected first in the pons, then the geniculate of the thalamus, then the occipital cortex

Question 43

Describe the relationship between serotonin, acetylcholine and REM sleep.

Answer 43

Acetylcholine is important for wakefulness and REM sleep. Serotonin and norepinephrine interrupts REM sleep.

Question 44

why dow sleep?

Answer 44

we have evolved inhibitory processes in the brain to force us to become less aroused and less alert.

Question 45

what is the function of sleep?

Answer 45

We rest our muscles,decrease metabolism, rebuild proteins in the brain, reorganise synapses and strengthen memories. People who don’t get enough sleep have trouble concentrating and become vulnerable to illness, especially mental illness. Inadequate sleep is a major cause of accidents by workers. Driving whilst sleep deprived is the same as alcohol influenced. People working inAntarctica during the winter sleep poorly and feel depressed. sleeplessness activates the immune system as if you were ill.

Question 46

What was the original function of sleep?

Answer 46

hypothesis that it was originally to conserve energy. Sleep conserves energy during inefficient times when activity would be wasteful and possibly dangerous. During sleep the temp decreases to save more energy. Muscle activity decreases saving more energy. Animals increase their sleep when there are food shortages. Grazing animals that need to eat for many hours sleep less. animals who need to be wary of predators get little sleep. Some animals can go for periods of time with no sleep without being sleep deprived eg migratory birds eat during the day and fly during the night.

Question 47

explain hybernation

Answer 47

animals decrease their body temp to just above the environment. brain activity declines, neuron cell bodies shrink and dendrites lose their branches. Hibernation retards the ageing process. it is a period of relative invulnerability to infection and trauma.

Question 48

Explain the relationship between sleep and memory

Answer 48

learning something just before sleep can help with memory. Sleep also helps people to reanalyse their memories. A nap that includes REM sleep can improve problem solving. Patterns that occur in the hippocampus are repeated during sleep but often faster. The amount of hippocampal activity during sleep correlated highly with the subsequent improvement in performance. Studies show that the brain often replays daily experiences but this can be done backward as well as forward. One way for sleep to strengthen memory is to weed out less successful connections and strengthen other synaptic connections.

Question 49

Explain how sleep spindles relate to memories

Answer 49

Sleep spindles are waves of activity that mostly occur in stage 2. They indicate an exchange of information between the thalamus and cerebral cortex. Sleep spindles increase in number after new learning.

Question 50

Explain the functions of REM sleep.

Answer 50

one third of a life is spent sleeping. one fifth of sleep is REM sleep. The species with the most total sleep time also have the highest percentage of REM sleep. In humans infants get more sleep and more REM sleepThe amount of NREM varies less amongst individuals and species. REM and NREM sleep may be important for consolidating different types of memories. NREM (verbal learning), REM (learned motor skills) but this doesn’t explain why people on antidepressants have decreased REM without incurring memory problems. Another hypothesis is that REM simply gets more oxygen to the corneas of the eyes. This makes sense as most of the REM happens late into the sleep but why do those on antidepressants not have defective corneas?

Question 51

Explain the activation-synthesis hypothesis

Answer 51

a dream is the brain’s effort to make sense of sparse and distorted information. Dreams begin with periodic bursts of spontaneous activity in the pons (PGO waves). The cortex uses the info from the waves and combines it with what ever else is happening and tries to make a story that makes sense of the info. One criticism is that the theory’s predictions are vague.

Question 52

Explain the Clinico-anatomical hypothesis

Answer 52

Like the other theory, this theory emphasises that dreams begin with arousing stimuli that are generated within the brain combined with recent memories and any information the brain is receiving from the senses. However, this theory puts less emphasis on the pons, PGO, or REM sleep. It regards dreams as thinking that takes place under unusual conditions. Som of the brain areas are geting very little input so that other areas are free to generate images without constraints or interference. Activity is suppressed in the prefrontal cortex thus we can not remember a dream ad we lose track during the dream. Meanwhile activity is high in parts of the parietal lobe, the visual cortex (the visual imagery of the dream), hypothalamus, amygdala (emotions and motivation).Hard to prove.