To what extent would damaging the suprachiasmatic nucleus affect a person’s sleep-wake cycle, and why?

Question 1

main points

Answer 1

1) INTRO
2) SCN + sleep & SCN + environment
3) genes & sleep wake cycle
4) bilateral lesions of SCN & sleep wake cycle
5) basal ganglia & sleep wake cycle
6) behavioural stress & sleep wake cycles
7) homeostasis & sleep

Question 2

INTRO (3)

Answer 2

1) what is SWC? - biological rhythm; typically a circadian rhythm; zeitgibers
2) purpose - to optimise behaviour & physiology of the organism for functioning (Saper et al. 2004)
3) rhythms can run without any external cues - internal bio clock

Question 3

POINT 1 A + B

Answer 3

A) SCN - medial hypothalamic nerve cells that is the master circadian pacemaker
- Ralph et al. (1990)

B) how is the SCN entrained by light? - Provencio, (2011):
- retinohypothalamic tracts & melatonin

Question 4

POINT 2

Answer 4

Genes that control circadian rhythms

• Crane (2012): CLOCK & BMAL1 genes expressing oscillating genes
• Charrier (2017): melatonin controls expression of CLOCK & BMAL1

Question 5

POINT 3

Answer 5

Bilateral lesions of SCN & circadian rhythms
- Liu et al. (2012): - the circadian rhythm in sleep and wakefulness was completely eliminated in rats subjected to bilateral SCNX, but the amount of total daily sleep remained largely the same

Question 6

POINT 4

Answer 6

Basal Ganglia

• Qiu (2010): striatums’ lesions induced sleep & Nucleus accumbens’ lesions reduced sleep
• Lazarus et al. (2013):
  a) adenosine - Nac
  b) dopamine - striatopallidal fibres (striatum)

Question 7

POINT 6

Answer 7

Cano et al. (2008)

• VPLO activated sleep drives
• arousal system activated by stress
• • one was not able to overcome the other as they’re both strong influencers**

Question 8

POINT 5

Answer 8

homeostasis & sleep

• Gnocchi & Bruscalupi, (2017)
• peripheral organs express at least a partially self-sustained circadian oscillator
• brain itself possesses its own circadian oscillation in the expression of several genes that seems to be independent of the activity of the SCN,

Question 9

Conclusion

Answer 9

• The sleep – wake cycle would not be completely void with total damage to the SCN but it does have a strong influence
• There are other factors involved which will influence the sleep wake cycle: basal ganglia, stress behaviour, homeostasis & food availability

Question 10

dopamine & adenosine

Lazarus et al. (2013)

Answer 10

DOPAMINE (STRIATUM) (PREVENT)

• found highly in Striatopallidal fibres (striatum fibres)
• deletion of D2 receptors promotes sleep (bc striatum & dopamine = prevent sleep)
• sleep disorders i.e. narcolepsy are treated using dopamine agonists bc it prevents sleep

ADENOSINE (NAC) (PROMOS)

• found in high numbers in Nac
• caffeine blocks adenosine receptors (inc wakefulness)