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Cell and Systems Biology
Course Code
Richard Stephenson

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low grade matter, less energy in grass. dont' get
sleep not ime coz need to eat to maintain enough e
hypotheszed, rel b/w mr and body size. implied slee
p had sth to with mr or energy met.
Regular sleep itself doesnt involve much of a redu
ction in MR but really depends on the perspective.
Hamster- nocturnal
Polyphasic. In this hamster, overnight, typical ul
trasian periodcity in MR asstd with ultradian osci
llation in body temps. Based on what we know from
other studies, these ultradian rhythms in oscillat
ion of MR were asstd with oscillations in activity
so the dips in metabolism were asstd with periods
in time when the animals were mainly asleep and t
hese peaks in metabolism asstd with activity. Hams
ters pretty active when awake but also we can see
even when they're asleep MR is fairly high and the
saving ast with sleep of MR is not all that great
. In little animals like this, the savings are mor
e important in large animals such as ourselves. Th
e bigger the animal, the less important sleep is f
or energy conservation; mainly as a result of the
fact that large animals have greater thermal inert
ia and are much less stressed as a result of that
by the thermoregulatory system. So depends on pers
One area where its become obvious that energy cons
ervation is important is a situation in which ener
gy availability and/or the energy cost of living a
sstd with env conditions such as cold gives rise t
o a behaviour appearing to be exaggertaion on NREM
sleep, this is an example of an animal that under
takes daily torpor such as daytime when these are
asleep most of the time. If you place animals in c

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onditions where food is limited and ambient temp i
s low, 12c for ex, and esp if you simulate winter
conditions by having rel short day which influence
s mel release and infl overall endocrine function,
then that elicits that torpor behaviour. Many sma
ll rodents, birds do this. Under stress conditions
like this, many small animals like this find it h
ard to survive under these conditions for many hou
rs in one go w/o eating if they maintain a normal
MR. Hummingbrids in a rel cool env basically starv
e to death if they have to go thru the entire nigh
t at a normal MR. They have such a high mr anyways
b/c of their small body size and so this places t
hem on the edge of survival. So they evolved this
torpid condition, they enter here everyday. We can
see unlike the situation where they go in to slee
p in the night, where their MR falls a bit, and th
eir body temp falls a bit, in the torpid state bod
y temp falls precipitously to rel low levels and t
heir MR follows suit. Enormous savings. So the que
stion is is this an extension of sleep or this a d
ifferent situation altogether? Does it tell us any
thing about sleep at all? Other species that dont
necessarily have dialy torpor will sometime instea
d have a seasonal behaviour referred to hibernatio
n. More intense that torpor and the torpic bouts t
end to last more than just a few hours. During hib
ernation, these bouts are seasonal. As seen, these
hibernation bouts last for many days. More extrem
e in that body temp tends to fall further than it
does during torpor. MR also falls to very low leve
ls. Overall savings greater than daily torpor. The
se animals have periodic increases in their body temp (euthermic intervals) or arousals where bod
y temp comes back up to the normal levels and MR i
ncreases as a result of that each time. There's a
big overshoot in metabolism that follows and thats
the cost that occurs in association with rewarmin
g these animals. It cost them a fortune! Its a mys
tery, then, as to why they'd do this. It was assum
ed they do this in order to eat and pee etc but as
later seen, most of them actually spend their tim

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e sleeping during this period when they warm up ag
ain. They using up vast energy doing so. There's a
clue there that maybe hibernation and sleep are n
ot necessarily the same thing. Infact these warmin
g periods cost them about 80% of the total energy
cost over the hibernation season. So they'd save h
ell lot of energy if they didn't do this. But it s
eems like they are doing it because they have to.
We see body temp rising and falling over the hiber
nation bouts. The tmp rises to normal levels durin
g these rewarming periods and falls to rel low lev
els (close to ambient temp). These hibernating ani
mals do like to keep their body temp just slightly
above the ambient temp. These animals, just becau
se they allow their body temps to fall like this,
doesn't mean they've lost control of it. This is a
regulated reduction in body temp. We can see this
by looking at MR. What we can see is MR going up
and down periodically and not by alot. These chang
es in MR are asstd with changes in temp. This is t
he temp regulation at work, making sure that this
body temp stays at the same level just above the a
mbient temp. You can see that env rose a little he
re, the temp reg system kinda kicked in to make su
re it doesnt sort of fall down to alot. If the env
temp goes down below 0, then these animals will r
aise their MR to keep their body temp up or close
to 1 or 2c usually. So its a active temp reg syste
m in a cold brain. You take your brain and cool it
down to 10c. It wouldnt work! Same thing with a r
at; the nuerons will switch off b/c of the cold. S
omething unique about hibernating animals keeps th
e vital stuff going. One of the things that keeps
on going is the circa clock and this arousal behav
iour is regualted in part by the circa timing system.
So the decrease in body temp is important for energ
y savings for 2 reasons:
There's a direct affect on the MR called the q10 a
ffect. Cells in a bag of chemical reactions. The a
mt of energy in the system dictates how fast the r
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