Endogenous Pacemakers Flashcards
What’s the difference between endogenous and exogenous?
Endogenous — having an internal source of origin
Exogenous — originating from outside of the body
What is the primary example of endogenous pacemakers and what is it made of?
SCN is an endogenous pacemaker that is a tiny cluster of nerves found in mammals, one in each hemisphere.
Where is the SCN found and what % of light info does it receive from the eyes?
It is just above the optic nerve cross (optic chiasm and receives 10% info from eyes.
Why is the SCN known as the ‘master clock’ ?
The cells in the SCN synchronise together and then synchronise other neurons in the rest of the body.
What makes SCN an endogenous pacemaker?
As it is used to control the rest of the body
Why is the rest of the body not very good at keeping rhythm?
They don’t have good access to light information.
What did Ralph (1990) do regarding hamsters? (2 things)
He bred hamsters to have a 20-hour circadian rhythm, then surgically removed the SCN and transplanted it into another hamster.
He also swapped the SCN from normal hamsters into the 20-hour mutant hamsters which started following a 24-hour rhythm.
What are the two weaknesses animal study problems?
What is the strength?
— humans and animals are similar but very different
—circadian rhythms in humans are more complex
— it would be unethical to remove a human SCN so animal studies are important for this
What were the two findings from Morgan’s (1995) study with hamsters? What do they suggest about the SCN?
The new hamsters had the same 20-hour circadian rhythm.
The mutant hamsters which had received the SCN from normal hamsters, and started following a 24-hour rhythm.
Suggests the SCN is the endogenous pacemaker controlling the circadian rhythm.
Define endogenous pacemaker
These are internal mechanisms that govern biological rhythms, i.e the circadian sleep-wake cycle.
What are the Three R’s of animal studies?
- refine (the technique)
-reduce (the number) - replace (with a lower level of animal on the hierarchy of being)
What did Decoursey et al. (2000) do regarding SCN’s and what were the three groups, (chipmunks)
What did they find?
They removed the SCN from 30 chipmunks, 24 had no operation with SCN intact, and 20 were intact controls.
Found SCN removed group were more active at night and much more likely to be eaten by predators.
Define endogenous pacemaker
These are internal mechanisms that govern biological rhythms, i.e the circadian sleep-wake cycle.
Who did Folkard (1996) study and what did the ppt volunteer to do?
They studied a university student, Kate Aldcroft, who volunteered to spend 25 days in a controlled lab environment, she had no access to external light cues.
What were the 2 findings from Folkard’s (1996) study whilst studying the university student?
— her body temperature had remained at a 24-hour rhythm
—however, her circadian rhythm had extended to 30hours, with sleep sometimes lasting 16 hours.
What do the findings from Folkard’s (1996) study with the university student suggest ?
Suggests that while the SCN doesn’t control the circadian rhythm, it is influenced by an exogenous zeitgeber (daylight)
What did Green and Gillette (1982) record and find from this? What does the finding support?
They recorded the electrical activity in the SCN using electrodes, and found that the SCN has a pattern of activity that repeats itself over 24.5 hours.
Supports the idea the SCN is an endogenous pacemaker.
Where is the pineal gland located and what info does it receive?
It is located towards the posterior of the human brain and gets info about the level of light from the SCN
What hormone does the pineal gland release and why?
It releases melatonin when the light levels are low that are entering the eyes.
What is Melatonin’s role and how does it do this?
Melatonin makes us feel sleepy by decreasing (inhibiting) the activity of areas in the brain that makes us feel awake.
