SLE2/ MODULE 6- Motor Units ANATOMY

Question 1

motor unit consists of what

Answer 1

-motor neuron
-its axon
-all the muscle fibers that it innervates

Question 2

according to Enoka + Fuglevand (2001), the motor unit (MU) is…

Answer 2

the last common pathway of the nervous system to the muscle

Question 3

as force increases + is maintained…

Answer 3

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

Question 4

motor unit

Answer 4

the basic functional unit of the nervous system and muscle that produces movement

Question 5

where are the alpha motor neurons that innervate a muscle clustered

Answer 5

in a motor nucleus

Question 6

how is the motor nucleus arranged

Answer 6

longitudinally along several spinal segments

Question 7

what does the medial motor unit innervate

Answer 7

axial muscles (of the trunk + head)

Question 8

what does the lateral motor unit innervate

Answer 8

appendicular muscles (of the arms + legs)

Question 9

proximal muscles are ____

Answer 9

ventrolateral

Question 10

distal muscles are ____

Answer 10

dorsolateral

Question 11

immunolabeling of human spinal cord

what happens to choline acetyltransferase (AcAT)

Answer 11

it is synthesized in the cell body + transported to the motor endplates

Question 12

describe the study of immunolabeling of human spinal cord

Answer 12

-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

Question 13

anatomical data obtained from 9 heart beating organ donors (16-65 yrs)

total axon counts in brachial plexus

Answer 13

349,876 +/- 43,226 axons

Question 14

anatomical data obtained from 9 heart beating organ donors (16-65 yrs)

% of motor axons

Answer 14

6.35 +/- 0.44%

Question 15

anatomical data obtained from 9 heart beating organ donors (16-65 yrs)

how many motor neurons innervate hand muscles via the median + ulnar nerves

Answer 15

1,700

Question 16

the control of voluntary actions by the nervous system is accomplished by modulating the activity of ____

Answer 16

relatively few motor neurons

Question 17

given only 6% of neurons are motor neurons…

Answer 17

94% are sensory
-tells us nervous system must emphasize sensory information
-when there is motor information, it is done by very few neurons

Question 18

parts of gastroc (3)

Answer 18

-lateral head
-medial head
-soleus (underneath)

Question 19

when injected, ____ neurons lit up in white

Answer 19

RELATED
-random but isolated, not in one specific location

Question 20

skeletal muscles range from ____ MUs to ____ MUs

Answer 20

10 MUs to 1500 MUs

Question 21

motor unit size

Answer 21

a MU may contain 10-15 fibers (extraocular muscles) up to 500 fibers (gastrocnemius)

Question 22

how many fibers does a MU of extraocular muscles contain

Answer 22

10-15

Question 23

how many fibers does a MU of gastrocnemius contain

Answer 23

500

Question 24

motor unit territory

Answer 24

a MU may occupy a large portion of the muscle
-its fibers are intermingled with fibers from other motor units

Question 25

all or none principle

Answer 25

all of a MUs fibers work in unison

Question 26

when the axon reaches the muscle…

Answer 26

it branches + innervates from a few fibers up to several thousand muscle fibers

Question 27

myofibril

Answer 27

muscle fibers

Question 28

muscle spindle conveys information to CNS through ____

Answer 28

afferent/sensory nerve fibers
-info aout changes in muscle length

Question 29

the muscle force that a MU can produce largely depends on ____

Answer 29

innervation number

Question 30

3 things related to how much force is produced

Answer 30

-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)

Question 31

more innervation = more/less parts of muscle involved = more/less force output

Answer 31

-more parts of muscle involved
-more force output

Question 32

how many muscle fibers did biceps brachii have associated with each axon

Answer 32

750 muscle fibers

Question 33

as motor units become bigger…

Answer 33

the more muscle fibers they innervate

Question 34

motor units turn on in what order

Answer 34

from smallest to largest

Question 35

smaller/larger motor units have more force

Answer 35

larger

Question 36

glycogen-depletion technique

Answer 36

1. isolate + activate a SINGLE motor unit
2. image the activated muscle fibers

Question 37

distribution of fibers

Answer 37

MU territory

Question 38

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

Answer 38

d) muscle unit