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Neurology > Sleep > Flashcards

Sleep Flashcards

1
Q

What is meant by brain rhythms?

A

The brain has evolved a variety of systems for rhythmic control – most striking example is our sleep/wake cycle.

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2
Q

Where do brain rhythms originate form?

A

The earth has a rhythmic environment – temperature, precipitation and daylight vary with the seasons.

In order to compete effectively and survive, an animal’s behaviour must oscillate with its environment.

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3
Q

What is the EEG?

A

The electroencephalogram (EEG) is a measurement of electrical activity generated by the brain and recorded from the scalp.

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4
Q

How does an EEG work?

A

Involves non-invasive electrodes placed on standard positions on the head – connected to amplifiers and a recording device.

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5
Q

What is the use of EEGs?

A

Today, the EEG is used primarily to help diagnose certain neurological disorders (e.g. seizures in epilepsy).

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6
Q

What does the EEG measure?

A

EEG measures the combined activity of a large number (1000s) of similarly orientated neurons.
EEG reflects summed post-synaptic activity of large cell ensembles.

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7
Q

What is required for a successful EEG to occur?

A

Requires synchronous activity across groups of cells.

The amplitude of an EEG signal depends upon how synchronous the activity of the neurons is.

When a group of cells is excited the tiny signals sum to generate a large surface signal.

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8
Q

What factor detrimentally affects an EEG result?

A

Timing is everything – the same amount of excitation can occur, but at irregular intervals resulting in a small summed signal.

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9
Q

How are EEG signals categorised?

A

EEG rhythms correlate with states of behaviours

EEG rhythms are categorised by their frequency range.

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10
Q

What are the common EEG rhythms associated with Sleep?

A

A high-frequency low-amplitude associated with alertness and waking (or dreaming…).

A low-frequency high-amplitude associated with non-dreaming sleep or coma.

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11
Q

What are the 2 ways synchronous brain rhythms are generated?

A

Via:

  • Pacemakers
  • Collective Behaviour
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12
Q

How do pacemakers generate synchronous brain rhythms?

A

Synchronous rhythms can be led by a central clock or pacemaker (e.g. thalamus).

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13
Q

What generates synchronous rhythms by collective behaviours?

A

Some rhythms of the cerebral cortex do not depend on a thalamic pacemaker – rely instead on collective interactions of cortical neurons themselves.

Synchronous rhythms can arise from the collective behaviour of cortical neurons themselves`

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14
Q

What is the major pacemaker of the body?

A

The thalamus, with its vast input to the cerebral cortex, can act as a pacemaker.

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15
Q

How does the thalamus produce synchronous brain rhythms?

A

Synaptic connections between excitatory and inhibitory thalamic neurons force each individual neuron to conform to the rhythm of the group.

Coordinated rhythms are then passed to the cortex by thalamocortical axons.

Thus, a relatively small group of centralised thalamic cells can compel a much larger group of cortical cells.

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16
Q

How does collective behaviour generate synchronous rhythms?

A

Excitatory and inhibitory interconnections of neurons result in a co-ordinated, synchronous pattern of activity.

This can remain localised or spread to encompass larger regions of the cortex.

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17
Q

What is the significance of brain rhythms?

A

Cortical rhythms parallel many interesting human behaviours

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18
Q

What are the functions of brain rhythms?

A

One plausible hypothesis is that most brain rhythms have no direct function – instead they are by-products.

However, even if brain rhythms don’t have a function, they provide us with a convenient window on the functional states of the brain.

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19
Q

What is sleep?

A

Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment.

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20
Q

What is the significance of sleep?

A

Sleep may be universal among higher invertebrates and perhaps amongst all animals (e.g. fruit fly Drosophila sleeps).
Prolonged sleep deprivation can be devastating to proper functioning.
However, we can stave off sleep… but not forever…

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21
Q

What are the functional states of the brain?

A
  • Wakefulness
  • Non-REM sleep
    Body capable of involuntary movement, rarely accompanied by vivid, detailed dreams.
  • REM sleep
    Body immobilised, accompanied by vivid, detailed dreams.
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22
Q

Outline the bodily changes that occur during Non-REM sleep

A
  • Temperature decreases
  • Heart rate drops
  • Breathing decreases
  • Brain energy consumption falls
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23
Q

How does the body respond in REM sleep?

A
  • Big temperature decrease
  • Irregular decreased heart rate
  • Irregular decreased breathing
  • Large increase in brain energy consumption
24
Q

How can we identify different stages of sleep?

A

EEG stages can be subdivided to indicate depth of sleep

Stages 1-4

25
Q

What is the initial stage of the sleep cycle?

A

Each night begins with a period of non-REM sleep.

26
Q

How often does the sleep cycle repeat in a night?

A

Sleep stages are then cycled throughout the night, repeating approximately every 90 minutes.

27
Q

How does sleep differ throughout the night?

A

As night progresses, there is a shift from non-REM to REM sleep.

28
Q

Why do we sleep?

A

No single theory of the function of sleep is widely accepted, although most reasonable ideas fall into two categories – theories of restoration and adaptation.

29
Q

What role does sleep have in restoration?

A

We sleep to rest and recover and to prepare to be awake again.

30
Q

How does sleep aid adaptation?

A

We sleep to protect ourselves (e.g. hide from predators) and to conserve energy.

31
Q

What is the neural mechanism of wakefulness?

A

During wakefulness, there is an increase in brain stem activity.

32
Q

Why is there increased brain activity during wakefulness?

A

Several sets of neurons increase rate of firing in anticipation of wakening and enhance the wake state (e.g. ACh, 5-HT, NE and histamine).

33
Q

How does brain activity differ in wakefulness and sleep?

A

Collectively, these neurons synapse directly brain regions including the thalamus and cerebral cortex.

Increase in excitatory activity suppresses rhythmic forms of firing in the thalamus and cortex present during sleep.

34
Q

How do neural mechanisms alter in sleep?

A

During sleep, there is a decrease in brain stem activity.

35
Q

Why is there decreased brain activity during sleep?

A

Several sets of neurons decrease rate of firing during sleep (e.g. ACh, 5-HT and NE).

36
Q

When does neural firing increase in sleep?

A

Cholinergic neurons in pons shown to increase the rate of firing to induce REM sleep.

37
Q

How do brain rhythms aid sleep?

A

Rhythmic forms of firing in the thalamus shown to block the flow of sensory information to the cortex.
However, other sleep-promoting factors also involved in promoting sleep…

38
Q

What are the 4 main sleep promoting factors?

A
  • Adenosine
  • Melatonin
  • Nitric Oxide
  • Inflammatory Factors
39
Q

How does adenosine promote sleep?

A

Adenosine receptor activation decreases heart rate, respiratory rate and smooth muscle tone (decreasing blood pressure).

40
Q

What is adenosine?

A

Adenosine is a building block for DNA, RNA and ATP.

41
Q

How are adenosine receptors manipulated to inhibit sleep?

A

Adenosine receptor antagonists (e.g. caffeine) promote wakefulness.

42
Q

What is melatonin?

A

Melatonin is a hormone secreted by the pineal body at night.

43
Q

How does melatonin promote sleep?

A

Over-the-counter medication for symptoms of jet-lag.

Shown to initiate and maintain sleep – role in natural sleep-wake cycle remains unclear.

44
Q

What is the role of Nitric oxide?

A

Nitric oxide (NO) is a potent vasodilator.
Decreases smooth muscle tone (decreasing blood pressure).
NO also stimulates adenosine release.

45
Q

How do inflammatory mediators aid sleep?

A

Sleepiness is a familiar consequence of infection (e.g. cold, flu).
Cytokines (e.g. interleukin-1) stimulates the immune system to fight infections.
Interleukin-1 levels shown to promote non-REM sleep –evidence for adaptation theory?

46
Q

What are circadian rhythms?

A

Almost all land animals coordinate behaviour according to circadian rhythms – the daily cycles of daylight and darkness that result from the spin of the Earth

47
Q

Why are rhythms so important for physiological function?

A

Most physiological processes also rise and fall with daily rhythms (e.g. temperature, hormone levels).

48
Q

Why are circadian rhythms so significant?

A

If cycles of daylight and darkness are removed from an animal’s environment, circadian rhythms continue.

49
Q

What determines the circadian rhythms?

A

Primary clocks for circadian rhythms are biological (“brain clocks”).

50
Q

What are ‘brain clocks’?

A

Environmental time cues (e.g. light-dark, temperature, humidity) are collectively termed zeitgebers.

51
Q

What is the consequence of having no ‘brain clock’?

A

It is quite difficult to separate a human from all possible zeitgebers – even inside a laboratory (e.g. people coming/going provide time cues).
Isolation studies are therefore best conducted in deep caves.

If humans are separated from all possible zeitgebers, they are said to be in a “free-running” state – internal biological clock of approximately 24.5-25.5 hours.

52
Q

What is the SCN?

A

The suprachiasmatic nucleus (SCN) is a small nucleus of the hypothalamus, located just above the optic chiasm.

53
Q

What is the role of the SCN?

A

It receives retinal innervation and synchronises circadian rhythms with the daily light-dark cycle.

54
Q

What happens when the SCN is removed from animals?

A

With no SCN, animals had fluctuating sleep and temperature - no pattern
SCN inhibition does not abolish sleep – animals will continue to coordinate sleep with light-dark cycles if they are present.

55
Q

What cells are responsible for sycnhronising the SCN to the circadian rhythms?

A

Retinal cells synchronising the SCN are not rods or cones – they are specialised photoreceptor cells expressing the photopigment melanopsin.

56
Q

How are melanopsin photoreceptors activated?

A

Photoreceptors expressing melanopsin are slowly excited by light and can detect changes in luminosity.

57
Q

How does melanopsin photoreceptor activation, synchronise the SCN?

A

Project directly to the SCN, inhibiting the production of melatonin by the pineal gland – melatonin involved in inducing the onset of sleep.

Neurology (20 decks)

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