APK 2105C Lecture Notes - Lecture 43: Myocyte, Exercise Ball, Motor Unit
16 Jun 2018
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Department
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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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