Set #4 (Lecture 20 + Textbook PGs 262-285 Study Guide)

Who incorrectly argued that sleep was a passive process?

Frederick Bremer.

How does the VLPO promote sleep?

By inhibiting wake-promoting regions, including the LC, raphe nucleus, and tuberomammillary body.

True or false: Rising adenosine signals sleep, and caffeine is an antagonist to adenosine.

True.

What brain structure secretes melatonin?

The pineal gland.

What does the passive theory of sleep propose?

Sleep occurs when there is not enough sensory stimulation to keep the brain awake.

What everyday conditions seem to support the passive view of sleep?

We usually reduce light, sound, movement, and uncomfortable sensory stimulation when going to sleep.

What does the active theory of sleep propose?

Sleep is actively produced by brain mechanisms rather than simply caused by a lack of stimulation.

Why were brain lesions and transections used to study sleep?

Researchers could damage or disconnect different brain areas and observe how sleep and wakefulness changed.

What two questions was Bremer trying to answer with his transections?

Which brain areas control sleep and whether sleep is an active or passive process.

What was Bremer's cerveau isolé preparation?

A mid-collicular transection that separated the forebrain from lower brain areas.

What happened after Bremer's cerveau isolé transection?

The cat appeared permanently asleep or comatose.

What major sensory systems remained available after the cerveau isolé transection?

Mainly vision and olfaction; much other sensory information could no longer reach the forebrain.

What was Bremer's encéphale isolé preparation?

A lower transection that separated the spinal cord from the brain.

What happened to sleep after Bremer's encéphale isolé transection?

The cat continued to cycle normally between sleep and wakefulness.

Why was the cat paralyzed after the encéphale isolé transection?

Descending motor signals from the brain could no longer reach the body.

What sensory information was mainly lost after the encéphale isolé transection?

Somatosensory information coming from the body.

How did Bremer originally interpret his transection results?

Believed sleep resulted from reduced sensory stimulation (less information reaching the brain from the senses).

Why is Bremer's passive interpretation now considered incorrect?

Later research showed that active neural systems control sleep and wakefulness.

What did Moruzzi and Magoun do to further test Bremer's passive theory?

They made a mid-pontine transection between Bremer's two transection locations.

What happened after Moruzzi and Magoun's mid-pontine transection?

The cats barely slept and remained awake most of the time.

How did the mid-pontine transection experiment with cats challenge the passive theory of sleep?

The cats remained awake even after sensory input was reduced, showing that less sensory input does not automatically cause sleep.

What major conclusion came from the work that challenged Bremer?

Sleep and wakefulness are actively controlled by brain mechanisms.

What does ARAS stand for?

Ascending reticular activating system.

What is the ARAS?

A neural system that activates the forebrain and helps maintain wakefulness.

Where does the Ascending Reticular Activating System (ARAS) originate and project?

Mainly in the brainstem and hypothalamus and sends signals throughout the forebrain to promote wakefulness (being awake and alert).

What happens when the ARAS is severely damaged?

Wakefulness is greatly reduced, potentially producing a nearly permanent sleep-like or comatose state.

Can strong stimulation briefly increase arousal after major ARAS damage?

Yes, but normal sustained wakefulness is greatly impaired.

What is the reticular formation?

A network of neurons in the brainstem that helps regulate wakefulness, attention, sleep, and arousal.

What did the discovery of REM demonstrate about the sleeping brain?

Sleep is not simply brain inactivity; the brain can be highly active during sleep.

What are FTG neurons?

Brainstem neurons with very long, widespread projections that can broadly influence brain activity.

Why are the widespread projections of FTG-like neurons important?

They allow a small group of neurons to influence the overall state of large portions of the brain.

What is a neuromodulator?

A chemical system that broadly changes the state or activity of neural networks rather than carrying one specific message.

How do neuromodulatory systems differ from specific sensory pathways?

They project widely and change overall brain state rather than transmitting one narrowly defined type of information.

Which three neurotransmitters were especially important in early research on sleep and arousal?

Acetylcholine, norepinephrine, and serotonin.

What neurotransmitter is used by important wake-promoting neurons in the brainstem and basal forebrain?

Acetylcholine (ACh).

What do PPT and LDT stand for?

Pedunculopontine tegmental and laterodorsal tegmental nuclei.

Where are the PPT and LDT located?

In the pons/midbrain region.

What neurotransmitter do the PPT and LDT use?

Acetylcholine.

What do the PPT and LDT help promote?

Wakefulness (being awake) and cortical activation (increased activity in the cerebral cortex).

What EEG pattern is associated with cholinergic wake activity?

Fast, desynchronized beta activity.

Where do cholinergic wake systems send information?

To areas including the thalamus, basal forebrain, and cerebral cortex.

What does LC stand for?

Locus coeruleus.

Where is the locus coeruleus located?

In the pons.

Why is the locus coeruleus called the "blue spot"?

It appears blue in unfixed brain tissue.

What neurotransmitter does the locus coeruleus release?

Norepinephrine/noradrenaline.

What is the locus coeruleus's major sleep-wake function?

Promoting arousal and wakefulness.

How widely does the locus coeruleus project?

Through several pathways that reach widespread areas of the brain and cerebral cortex.

Why can the locus coeruleus strongly influence overall brain state?

Its norepinephrine projections are extremely widespread.

What neurotransmitter is primarily associated with the raphe nuclei?

Serotonin (5-HT).

Where are the raphe nuclei located?

Along the midline of the brainstem.

What does "raphe" mean?

Seam.

About how many raphe nuclei are there?

About 8-9.

How widely do serotonergic neurons from the raphe system project?

Throughout much of the brain.

What can serotonin from the raphe system do to thalamocortical neurons?

Help activate them.

What are thalamocortical neurons?

Neurons that send information from the thalamus to the cerebral cortex.

Does serotonin have only one sleep-wake function?

No. Different serotonergic neurons can have different effects on sleep and wakefulness.

What does it mean that the serotonergic system is heterogeneous?

Different serotonin neurons can perform different functions rather than all doing the same thing.

What is an agonist?

A substance that activates a receptor or mimics a neurotransmitter's effect.

What is an antagonist?

A substance that blocks or interferes with a neurotransmitter's effect.

If a neurotransmitter promotes sleep, what would an agonist generally be expected to do?

Increase its sleep-promoting effect.

What would an antagonist of a sleep-promoting neurotransmitter generally do?

Block the neurotransmitter's sleep-promoting effects, potentially increasing wakefulness.

What major neurotransmitter systems help promote wakefulness?

Acetylcholine, norepinephrine, serotonin, orexin, and histamine.

What is orexin also called?

Hypocretin.

Where are orexin neurons located?

In the hypothalamus.

What is orexin's major sleep-wake function?

It promotes and stabilizes wakefulness.

How do orexin levels generally change while a person is awake and approaching sleep?

They rise during waking and decrease as sleep approaches.

How can an abrupt loss of orexin signaling relate to narcolepsy?

Loss of a wake-promoting signal can allow sleep or REM-related features to suddenly intrude into wakefulness.

What other hypothalamic chemical promotes wakefulness?

Histamine.

When is histamine activity especially associated with the sleep-wake cycle?

During wakefulness and alertness.

Why can antihistamines such as Benadryl cause sleepiness?

Blocking histamine signaling reduces a wake-promoting system.

What is the general role of monoamine systems in wakefulness?

Their widespread projections help maintain an alert, activated brain state.

Are there active brain mechanisms for both waking and sleeping?

Yes. Wake-promoting and sleep-promoting systems actively oppose each other.

Can drugs modify sleep and wakefulness by acting on neurotransmitter systems?

Yes.

What happens to sensory responsiveness during slow-wave sleep (SWS)?

Responsiveness to the environment decreases.

What happens to brainstem arousal activity during SWS?

It decreases.

What happens to thalamic and cortical firing during SWS?

Neurons fire together in a more coordinated rhythm (synchronized).

What EEG waves characterize SWS?

Delta waves.

Does slow-wave activity always occur throughout the entire brain simultaneously?

No. Slow-wave activity can occur locally in different brain areas.

What is localized sleep?

Some brain regions show sleep-like activity while other regions remain more active.

Can sleep spindles also occur locally rather than everywhere at once?

Yes.

What is unihemispheric sleep?

One cerebral hemisphere shows SWS while the other remains more active.

Why is unihemispheric sleep useful for marine mammals?

It lets them continue swimming, avoid obstacles, and surface to breathe.

What does VLPO stand for?

Ventrolateral preoptic area.

Where is the VLPO located?

In the hypothalamus.

What does the name ventrolateral preoptic describe about the VLPO's location?

It is toward the bottom and side and lies in front of the optic chiasm.

When is the VLPO especially active?

During slow-wave sleep.

What major inhibitory neurotransmitter does the VLPO release?

GABA.

What other inhibitory chemical is released by VLPO neurons?

Galanin.

Which wake-promoting areas does the VLPO inhibit?

The raphe nuclei, locus coeruleus, tuberomammillary nucleus, and other arousal systems.

What happens when the VLPO inhibits wake-promoting nuclei?

Wake activity decreases and sleep is promoted.

What does TMN stand for?

Tuberomammillary nucleus.

Where is the tuberomammillary nucleus located?

In the hypothalamus.

What neurotransmitter does the tuberomammillary nucleus produce?

Histamine.

Besides sleep regulation, what functions are associated with galanin?

Eating, learning, mood regulation, and neuroprotection.

What is the sleep-wake flip-flop mechanism?

Sleep-promoting and wake-promoting systems mutually inhibit each other.

What happens in the flip-flop system when the circadian system signals sleep?

The VLPO inhibits wake-promoting nuclei, allowing sleep to occur.

What happens in the flip-flop system when the circadian system signals waking?

Wake-promoting nuclei become active and inhibit the sleep-promoting system.

Which three wakefulness nuclei were emphasized in the sleep-wake flip-flop?

The raphe nucleus, locus coeruleus, and tuberomammillary nucleus.

What does mutual inhibition mean in the sleep-wake flip-flop?

The sleep and wake systems suppress each other, so one state dominates at a time.

Why is the sleep-wake system described as a flip-flop?

Because the brain can quickly switch between two opposing systems, one that keeps us awake and one that promotes sleep.