L10 - Homeostatic and Circadian Reg of Sleep

Question 1

What is process s

Answer 1

homeostatic factor

• increases during wakefulness exponentially
• represented as the amount of slow wave sleep. can’t measure this during wakefulness.
• the amount of SWS increases if they had a nap during the day, compared to if they napped in the morning, because more drive for slow waves.
• homeostatic factor gets greatest just before we go to sleep.

Question 2

What is process c

Answer 2

Circadian Factor
- sine way
- not a true sin wave though because it has a bit of a ‘blip’ in the middle of the day - post lunch dip.
-

Question 3

What is propensity?

Answer 3

How sleepy we feel, it’s the diff between the curves of PROCESS C AND PROCESS S

when the lines meet is where we usually wake

Question 4

What is some evidence for process s and process c independence?

Answer 4

• circadian oscillator can be phase shifted w/o affecting SWS
• during forced desynchrony protocol, ciradian and homeostatic processes are seperated.
• sleep that occurs during the normal wake period following a period of sleep dep still shows SWS rebound
• animals w a lesion in pacemaker cells still show homeostatic properties, but not circadian properties.

Question 5

What is forced desynchrony protocol

Answer 5

s

Question 6

Evidence against process s and c independence?

Answer 6

• in forced desynchrony protocol, interaction between circadian and homeostatic systems are often observed- the circadian cycle is a little diff when there is a high SWS drive/deprivation
• the circadian phase does slightly alter the amount of SWS
• Sleep dep reduces the phase setting ability of light.

Question 7

What is the hypnotoxin theory of slep?

Answer 7

CSF of sleep deprived dogs were injected into brains of well-rested dogs and induced sleep, even in the morning.

suggests that there is a hypnotoxin, chemical that makes us go to sleep and builds up as we’re awake. .

Question 8

What is adenosine’s relevance to sleep?

Answer 8

It’s thought to be the factor behind process s

• nucleoside that forms during the breakdown of ATP
• caffeine is an antagonist of the receptor.
• postulate that the brain adenosine increases in an activity dependent fashion.
• injection of adenosine induces SWS.
• cat adenosine levels in basal forebrain rise during prolonged waking and fall during sleep.
• broken down by adenosine deaminase. slow and fast acting forms
• there is a strong correlation between reported sleep need, SWS amplitude and amount and the form of adenosine deaminase someone has.

Question 9

What did Zeitzer find about adenosine?

Answer 9

• microdialysis probe in humans to measure adenosine
• normal sleep reduction in adenosine levels over night
• 38hr sleep dep - no rise in adenosine
• thalamic and hypothalamic regions showed no exponential increase, so maybe diff brain areas built up in diff ways???
• maybe microdialysis pores got blocked up so coudnt properly detect

Question 10

What is some evidence against adenosine and its role in sleep?

Answer 10

• adenosine receptors are in brain regions where we’d expect to increase wakefulness.
• dynamics of build up and decay don’t match process s
• extreme activity that increases adenosine should result in SWS increase - but not observed.

eg. zeitzer study

Question 11

What are some factors that could play a role in process s?

Answer 11

• Adenosine
• Cytokines
• Other sleep/immune factors

Question 12

How can cytokines have an effect on sleep?

Answer 12

• Associated with process s
• they are proteins produced by leukocytes and other cells functioning as intracerebral mediators
• can induce sleep if injected into animals.
• interleukin, interferon and alpha and tumour necrosis factor also been shown to promote sleep
• human conditions such as rheumatoid arthritis, where these build up have symptoms of sleepiness.

Question 13

What are the key properties of circadian rhythms?

Answer 13

1. persists w/o time cues
2. phase can be shifted by light and drugs
3. period can be entrained if near the intrinsic period
4. clock does not change with temperature.

• rhythm can be bserved in core body temp, metatonin and cortisol and other variables.

Question 14

How does body temp change with circadian rhythm?

Answer 14

• decreases at night, increases during wakefulness.

Question 15

What is the suprachiasmatic nucleus (SCN)?

Answer 15

the SCN contains a biological clock that governs circadian rhythms

• lesions disrupt the circadian rhythm
• SCN cells do not required direct neural connection to control circadian rhythms, but may do using chemical signals . —> can transplant it and it still works. dont need neural connections.

Hamster got SCN lesioned - drinking bouts were evenly spread throughout the day, instead of just at night (it’s nocturnal)

Question 16

How do SCN cells know the time?

Answer 16

the cells exhibit circadian rhythms in activity - glucose metabolism is mroe active during the day, and each cell seems to have its own clock (Seperate daily peaks).

• genes in SCN controls production of proteins that inhibit the production of the same gene (per & tim; at midday these reach highest levels, and through -ve feedback loop it inhibits further production)

time it takes for the protein to break down creates the 24 hr cycle.

Question 17

Describe SCN inputs

Answer 17

• melanopsin containing ganglion cells in the retina are light sensitive, and gets to the SCN through retinohypothamic tract.
• the intergeniculate leaflet of the lateral genicular thamaic nucleous is also a pathway for other environmental stimuli such as food and activity to set the biological clock.
• melatonin, produced endogenously

Question 18

What is melatonin?

Answer 18

It is secreted in the dark, by the pineal gland and has a slight hypnotic effect.

SCN gives info about light/dark –> info goes down interneurons to the spinal cord –> goes back to pineal gland to release/not release melatonin –> feeds back to SCN

Feeds back into the SCN to phase shift the circadian rhythm, but light is MUCH more efficient at phase shifting.