APK 2105C Lecture Notes - Lecture 43: Myocyte, Exercise Ball, Motor Unit

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Chapter 12, Lecture 4
Muscle Physiology
Force generation in whole muscles
o Force generation in individual fibers
Crossbridge formation
Frequency of stimulation
o Isometric muscle twitches are only all or none if the
frequency is low
Ensures that twitches are well separated in time
If you allow the force to come all the way back
down to 0 before sending another stimulation, you’ll
only be able to go as high as your last simulation
At 0, all of the Ca is back in the SR and no
crossbridge cycling is happening
o At higher frequencies of stimulation
Ca release from SR exceeds rate of Ca removal
If you send the next stimulation before it comes all
the way back down to 0, you’ll be able to go a little
higher than before because you started a little
higher
o Twitch treppe summation tetanus
Treppe
Potentially a
warming up
phase for the
myocyte as its
stimulated to
contract more
frequently
Ca is allowed
enough time to
get back into
the SR
o Tension returns to 0 between
stimulation
THIS IS NOT SUMMATION
Summation and tetanus
Force is not
allows to come
all the way
back down to 0
Summation
and tetanus
occur at
frequencies
which result in
overlap of
twitches
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