APK 2105C Lecture Notes - Lecture 42: Motor Neuron, Motor Unit, T-Tubule

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Chapter 12, Lecture 3
Muscle Physiology
Mechanics of muscle contraction
o All muscle cells respond the same way to an AP
Despite variability in force and duration of whole muscle contractions
May need small, slow type of contraction
May need quick, strong contractionexplosive movement in
weight lifting
o The motor unit
One somatic motor neuron and all the muscle fibers it innervates
ONE somatic motor neuron
o May be attached to multiple muscle cells
There is only one synapse on each cells
o Individual cells are only activated by a single motor neuron
All myocytes will contract if the neuron fires every single time
The size of the motor unit = how many cells it innervates
o Muscle twitch = mechanical response of a
muscle cell, motor unit, whole muscle to a
single end plate potential
When all the cells contract at the
same time due to the firing of a
Reproducible, all or nothing event
If you provide the same
stimulus the exact same thing
will happen every time
One end-plate potential always leads
to the same amt of Ca released every
Latent period = when no force is
generated yetafter the stimulus
Time delay between the AP
and initiation of contraction
Time for ECC
o Time for AP to travel down T tubule and stimulate release
of Ca
Contraction phase = quick rise in tension
Crossbridge cycling is occurring
Cytosolic Ca levels are rising
Relaxation phase = slow decline in tension
Cytosolic Ca is returned to the SR
Number of crossbridges decline
Not all twitches are equal
There is variability in speed of
contraction and amt of force
Muscle may take longer to reach its
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