Exam 3: Properties of Motor Units, Fiber Types, and Voluntary Control o
Muscle Force
Study online at https://quizlet.com/_c4tpg5
alpha motor neuron + axon + all innervat-
ed fibers
the smallest functional sub-division of
what is a motor unit
the neuromuscular system -> all or none
principal (an AP in the m.n. goes pro-
duces a contraction in all innervated
muscle fibers)
what are the two mechanisms for grading
1. recruitment of m.n.
muscle force voluntarily (choosing varia-
2. rate coding (firing frequency)
tions in strength)
1. either dissect a nerve down to the sin-
gle motor axon or using the ventral root
and dissecting that down to one axon to
keep it to only one m.n.
how do you study how the muscle fibers 2. electrostimulation at high frequency
of a single m.n. are distributed through- many times to completely fatigue the
out the muscle? muscle fibers
3. stain for glycogen stores
4. you look for the absence of glycogen
(because this gets depleted with com-
plete fatigue)
1. territory (how the muscle fibers of a
single motor unit distributed throughout
what are the properties of motor units the muscle)
2. innervation ratio
3. mechanics (types of m.n.)
the number of fibers innervated by a sin-
gle alpha neuron/motor unit.
bigger muscles have larger motor units
what is the innervation ratio?
the eyes have the smallest motor units
with maybe 2 fibers per alpha neuron bc
they don't even hold load besides the eye
itself
hands, for example, would be some-
, Exam 3: Properties of Motor Units, Fiber Types, and Voluntary Control o
Muscle Force
Study online at https://quizlet.com/_c4tpg5
where in between - less than legs, much
more than eyes
how does the innervation ratio control
a higher ratio -> higher tension
tension?
tested with twitch test and fatigue test
1. S - slow, non-fatigable (fatigue index
is 1 (high)), long contraction time, low
tetanic fusion frequency, no sag, small
innervation ratio, small fiber x-sectional
area, innervates slow oxidative fibers
2. FF - fast, fatigable (low fatigue index),
short contraction time, high tetanic fusion
frequency, has sag, large innervation ra-
tio, larger fiber x-sectional area, inner-
what are the mechanics/types of motor vates fast glycolytic fibers
units? 3. FR - fast, fatigue resistant (high fatigue
index), short contraction time but slow-
er than FF, high tetanic fusion but lower
than FF, sag present but less than FF,
innervates fast oxidative glycolytic fibers
-the decrease in force after hitting peak
force during isometric tetanus (in type FR
and FF motor units)
-even occurs during submax frequencies
what is sag -doesnt occur with slow motor unites
Muscle Force
Study online at https://quizlet.com/_c4tpg5
alpha motor neuron + axon + all innervat-
ed fibers
the smallest functional sub-division of
what is a motor unit
the neuromuscular system -> all or none
principal (an AP in the m.n. goes pro-
duces a contraction in all innervated
muscle fibers)
what are the two mechanisms for grading
1. recruitment of m.n.
muscle force voluntarily (choosing varia-
2. rate coding (firing frequency)
tions in strength)
1. either dissect a nerve down to the sin-
gle motor axon or using the ventral root
and dissecting that down to one axon to
keep it to only one m.n.
how do you study how the muscle fibers 2. electrostimulation at high frequency
of a single m.n. are distributed through- many times to completely fatigue the
out the muscle? muscle fibers
3. stain for glycogen stores
4. you look for the absence of glycogen
(because this gets depleted with com-
plete fatigue)
1. territory (how the muscle fibers of a
single motor unit distributed throughout
what are the properties of motor units the muscle)
2. innervation ratio
3. mechanics (types of m.n.)
the number of fibers innervated by a sin-
gle alpha neuron/motor unit.
bigger muscles have larger motor units
what is the innervation ratio?
the eyes have the smallest motor units
with maybe 2 fibers per alpha neuron bc
they don't even hold load besides the eye
itself
hands, for example, would be some-
, Exam 3: Properties of Motor Units, Fiber Types, and Voluntary Control o
Muscle Force
Study online at https://quizlet.com/_c4tpg5
where in between - less than legs, much
more than eyes
how does the innervation ratio control
a higher ratio -> higher tension
tension?
tested with twitch test and fatigue test
1. S - slow, non-fatigable (fatigue index
is 1 (high)), long contraction time, low
tetanic fusion frequency, no sag, small
innervation ratio, small fiber x-sectional
area, innervates slow oxidative fibers
2. FF - fast, fatigable (low fatigue index),
short contraction time, high tetanic fusion
frequency, has sag, large innervation ra-
tio, larger fiber x-sectional area, inner-
what are the mechanics/types of motor vates fast glycolytic fibers
units? 3. FR - fast, fatigue resistant (high fatigue
index), short contraction time but slow-
er than FF, high tetanic fusion but lower
than FF, sag present but less than FF,
innervates fast oxidative glycolytic fibers
-the decrease in force after hitting peak
force during isometric tetanus (in type FR
and FF motor units)
-even occurs during submax frequencies
what is sag -doesnt occur with slow motor unites
