Sleep and Arousal

Question 1

What are the 2 major ascending arousal pathways?

Answer 1

1) Ach projections from pontine tegmentum to thalamus (wakes up thalamus)
2) Noradrenergic projections from locus coeruleus (brainstem) to cortex

Histaminergic projections from tuberomamillary nucleus of hypothalamus to cortex

Orexin projections from lateral hypothalamus to brainstem nuclei

Dopamine from vPAG in midbrain

Serotonin projections from raphe nucleus (brainstem)

Question 2

Why is orexin so important to waking up?

Answer 2

Orexin does not talk directly to the cortex, but it does project to the nuclei in the brainstem and hypothalamus that do talk to the cortex. As such, without orexin, there is no signal transduction to the cortex about waking up.

Question 3

Describe the descending pathways that are sleep promoting

Answer 3

Ventrolateral preoptic hypothalamus –> projects to all nuclei that promote arousal and inhibit them with GABA and Galanin

Question 4

Monoaminergic brainstem neurons that promote wakefulness […] the VLPO neurons resulting in […]

Answer 4

Inhibit

Arousal

Question 5

Orexin neurons of the lateral hypothalamus […] the monoaminergic neurons resulting in […]

Answer 5

Activate

Arousal

Question 6

GABAergic/Galanin neurons in the VLPO […] the brainstem monoaminergic neurons and the LH orexin neurons resulting in […]

Answer 6

Inhibit

Sleep

Question 7

Acetylcholine is released from the […] to wake up the […]

Answer 7

pontine tegmentum

thalamus

Question 8

Histamine is released from the […] to wake up the […]

Answer 8

Tuberomamillary nucleus of hypothalamus

Cortex

Question 9

Dopamine is released from the […] to wake up the […]

Answer 9

vPAG

Cortex

Question 10

Serotoin is released from the […] to wake up the […]

Answer 10

Raphe nucleus

cortex

Question 11

Norepinephrine is released from the […] to wake up the […]

Answer 11

Locus coeruleus

Cortex

Question 12

Orexin is released from the […] to wake up the […]

Answer 12

Lateral hypothalamus

Nuclei of brainstem and hypothalamus involved in arousal

Question 13

The ascending and descending pathways of arousal and sleep promotion are not turned on at the same time. How does the brain know when to turn one on and the other off?

Answer 13

Light hits retina –> information about whether it is light or dark out goes to suprachiasmatiac nucleus of hypothalamus via retinohypothalamic tract –> SCN projects to dorsal medial hypothalamus which then turns one pathway on and the other off

Question 14

What is the role of the suprachiasmatic nucleus in the formation of melatonin?

Answer 14

SCN communicates with pineal gland via superior cervical sympathetic ganglion. When it is light out, the SCN inhibits the pineal gland and inhibits the release of melatonin. When it is dark out, the SCN is not acting on the pineal gland so the pineal gland can make melatonin.

Question 15

What does melatonin do in the brain?

Answer 15

Feedsback on and regulates the SCN and thus drives the circadian rhytmicity of the body

Question 16

How does brain wave activity change during the following stages of arousal:

• Awake
• Sleep - stage 1
• Sleep - stage 2
• Sleep - stage 3
• Sleep - stage 4
• Sleep - REM

Answer 16

Amplitude increases and frequency decreases as you move from stage 1 - 4. In REM sleep, brain activity appears similar to when awake.

Question 17

What stage of sleep do sleep spindles appear and what are they?

Answer 17

Stage 2

Generated by thalamus and thought to “veto” sensory output from thalamus to cortex during sleep

Question 18

What neurotransmitter(s) regulate REM sleep?

Answer 18

REM sleep begins when pontine cholinergic neurons become active. Raphe nucleus and locus coeruleus neurons are not yet active. REM sleep ends when cholinergic neuron activity decreases and monoaminergic neuron activity increases

Question 19

Why do we experience atonia (lack of muscle tone) during sleeping?

Answer 19

Because the locus coeruleus projects down to the spinal cord and those projections keep our muscles from moving while we dream