SLE2/ MODULE 6- Motor Units ANATOMY Flashcards
motor unit consists of what
-motor neuron
-its axon
-all the muscle fibers that it innervates
according to Enoka + Fuglevand (2001), the motor unit (MU) is…
the last common pathway of the nervous system to the muscle
as force increases + is maintained…
motor unit spikes occur
-if the force is maintained for a short period of time, we do not see changes in amplitude, quantity, or space between each of the spikes
motor unit
the basic functional unit of the nervous system and muscle that produces movement
where are the alpha motor neurons that innervate a muscle clustered
in a motor nucleus
how is the motor nucleus arranged
longitudinally along several spinal segments
what does the medial motor unit innervate
axial muscles (of the trunk + head)
what does the lateral motor unit innervate
appendicular muscles (of the arms + legs)
proximal muscles are ____
ventrolateral
distal muscles are ____
dorsolateral
immunolabeling of human spinal cord
what happens to choline acetyltransferase (AcAT)
it is synthesized in the cell body + transported to the motor endplates
describe the study of immunolabeling of human spinal cord
-a method to look at the axons of neurons traveling within the brachial plexus
*the reason we are looking at brachial plexus in this study is because that is the location responsible for dexterous control of the human arm + hand movements
*the researchers were interested specifically in neurons related to arm/hand movements
*this was the first study that was able to define what contribution from our neurons is sensory vs motor
*aim of this protocol was to look at whether the neurons were related to sensory/motor information
*it was done through an immunolabeling technique
anatomical data obtained from 9 heart beating organ donors (16-65 yrs)
total axon counts in brachial plexus
349,876 +/- 43,226 axons
anatomical data obtained from 9 heart beating organ donors (16-65 yrs)
% of motor axons
6.35 +/- 0.44%
anatomical data obtained from 9 heart beating organ donors (16-65 yrs)
how many motor neurons innervate hand muscles via the median + ulnar nerves
1,700
the control of voluntary actions by the nervous system is accomplished by modulating the activity of ____
relatively few motor neurons
given only 6% of neurons are motor neurons…
94% are sensory
-tells us nervous system must emphasize sensory information
-when there is motor information, it is done by very few neurons
parts of gastroc (3)
-lateral head
-medial head
-soleus (underneath)
when injected, ____ neurons lit up in white
RELATED
-random but isolated, not in one specific location
skeletal muscles range from ____ MUs to ____ MUs
10 MUs to 1500 MUs
motor unit size
a MU may contain 10-15 fibers (extraocular muscles) up to 500 fibers (gastrocnemius)
how many fibers does a MU of extraocular muscles contain
10-15
how many fibers does a MU of gastrocnemius contain
500
motor unit territory
a MU may occupy a large portion of the muscle
-its fibers are intermingled with fibers from other motor units
all or none principle
all of a MUs fibers work in unison
when the axon reaches the muscle…
it branches + innervates from a few fibers up to several thousand muscle fibers
myofibril
muscle fibers
muscle spindle conveys information to CNS through ____
afferent/sensory nerve fibers
-info aout changes in muscle length
the muscle force that a MU can produce largely depends on ____
innervation number
3 things related to how much force is produced
-innervation number
-fiber area (has to do with how many contractile proteins are lying in parallel vs in series)
-specific tension (amount of force produced for a given area of muscle)
more innervation = more/less parts of muscle involved = more/less force output
-more parts of muscle involved
-more force output
how many muscle fibers did biceps brachii have associated with each axon
750 muscle fibers
as motor units become bigger…
the more muscle fibers they innervate
motor units turn on in what order
from smallest to largest
smaller/larger motor units have more force
larger
glycogen-depletion technique
- isolate + activate a SINGLE motor unit
- image the activated muscle fibers
distribution of fibers
MU territory
which term is most closely related to the territory of a motor unit?
a) motor nucleus
b) muscle fiber
c) motor neuron
d) muscle unit
e) muscle space
d) muscle unit
