(7) ENDOGENOUS PACEMAKERS AND EXOGENOUS ZEITGEBER Flashcards
(12 cards)
What endogenous pacemakers
○ What are they?
§ Internal body clocks that regulate biological rhythms
□ Eg the SCN on the sleep wake cycle
What is the SCN
○ The (Suprachiasmatic Nucleus) SCN
§ What is it?
□ The main endogenous pacemaker
□ Tiny cluster of nerve cells
Where is the SCN
§ Where is it?
□ In hypothalamus
□ Above optic chiasm
What does the SCN do
§ What does it do?
□ Even when eyes are shut
® SCN gets info on light from optic nerve
□ Light can penetrate eyelids
□ Special photoreceptors in eye transfer signals to SCN
□ If endogenous clock is running slow:
® Morning light automatically shifts clock ahead
® So in synchrony with outside world
□ SCN sends signal to pineal gland
What does the pineal gland do
§ The pineal gland:
□ Contains light sensitive cells
□ Melatonin production stopped when light sensed
□ Melatonin production starts when light falls
□ This induces sleep
Talk abt chipmunk research into ENDOGENOUS PACEMAKERS (including EVAL)
§ Chipmunks
□ Procedure:
® 30 chipmunks had SCN removed
® Released into the environment
□ Findings:
® Lesioned chipmunks = disrupted sleep/wake cycle
® Killed by predators as did not have enough sleep
□ Conclusion:
® SCN is responsible for sleep
□ Evaluation:
® Criticism
◊ Ethical issue - all chipmunks killed
◊ Extrapolation - humans are not hamsters
Talk abt hamsters research into ENDOGENOUS PACEMAKERS (including eval)
§ Hamsters
□ Procedure
® Bred mutant hamsters with 20 hour cycle
® Took SCN cells from mutant hamsters, transferred to normal hamsters
□ Findings
® Showed disruptive sleep/wake cycle
□ Conclusion
® Shows SCN determined by sleep/wake cycle
□ Evaluation
® Criticisms
◊ Ethical issue - not very nice for hamsters
◊ Extrapolation - humans are not hamsters
Talk about kneecaps research into endogenous pacemakers
§ Kneecaps
□ Campbell and Murphy:
® Procedure
◊ Shone light on back of 15 participants knees
® Findings
◊ Sleep/wake cycle deviated by 3 hours
® Conclusion
◊ Skin receptors all over body rather than just in SCN
® Evaluation
◊ RLA - blind people
What are exogenous zeitgebers
○ What are they?
§ External environmental cues that affect biological rhythms
□ Eg light on the sleep wake cycle
What is entrainment
○ Entrainment:
§ Cues in the environment reset the biological clock every day
Talk about light in relation to exogenous zeitgebers
○ Light:
§ Resets the internal body clock each day
§ Malanopsin is critical to this cycle
□ Protein
□ Detects natural light
□ Sends signals to SCN
How to train a baby to sleep using exogenous
○ How to train a baby to sleep:
§ Until 6 weeks
□ Sleep/wake cycle is random
§ By 16 weeks:
□ Most babies = entrained
□ Because:
® Schedules and social cues
◊ Eg meal times and bed times
§ Also applies to adults
□ Conforming to local sleep/eat times trains sleep/wake cycle
® Good for jet lag
