LAB 3 :)

Question 1

Fibers (cylindrical shaped cells) are bound together by…

Answer 1

connective tissue.

Question 2

Nerve cells that innervate skeletal muscle are called

Answer 2

somatic motor neurons.

Question 3

Somatic motor neurons have their cell bodies where?

Answer 3

Their cell bodies are located in the gray matter of the spinal cord and brain.

Question 4

Each muscle fiber is innervated by?

Answer 4

only one motor neuron nerve ending

Question 5

Can a single motor neuron innervate several muscle fibers?

Answer 5

Yes

Question 6

Electrical impulses generated and conducted by muscle fibers is usually weak or strong?

Answer 6

weak

Question 7

Since it is weak, explain how muscle fibers cause a big enough reaction to be detected by the surface electrodes?

Answer 7

Although the electrical impulse generated and conducted by each fiber is very weak (less than 100 microvolts), many fibers conducting simultaneously induce voltage differences in the overlying skin that are large enough to be detected by a pair of surface electrodes.

Question 8

The changes in amplitude of the recording indicate changes in what?

Answer 8

the amount of electrical activity at the level of the muscle fiber membrane.

Question 9

Depolarization triggers

Answer 9

contraction

Question 10

Muscle action potentials precede the _______________________…

Answer 10

contraction of the muscle fibers

Question 11

Is EMG a direct measure of muscle force?

Answer 11

NO!!!

Question 12

EMG is measured (prior/after) any force generating mechanism.

Answer 12

prior

Question 13

What is neuromuscular fatigue?

Answer 13

complex phenomenon that has been defined as the inability to maintain a given intensity of physical exertion, or of muscular contraction.

Question 14

Activation failure sites

Answer 14

CNS (failure to excie motor neuron due to changes in their cellular properties or afferent input altering function)

spinal cord (cortical commands)

neuromuscular junction (inefficient neuromuscular transmission)

sarcolemma (inability to equilibrate changes in ion concentration inside and outside the sarcolemma)

Question 15

Contractile failure site

WITHIN MUSCLE

Answer 15

Ca2+ (reduced calcium release)
Ca2+ uptake
Cross-bridge failure. (betweena ctin and myosin)

Question 16

EMG is a recording of electrical events at the level of the…

Answer 16

muscle fiber sarcolemma

Question 17

Why is EMG considered “index of activation”?

Answer 17

It can therefore be used as an index of activation because it is monitoring the level of activity from the last of the “activation sites”.

Question 18

FOR MAXIMAL: If EMG AND force both decline indicates what?

Answer 18

would indicate that decreased motor unit recruitment (i.e., activation failure; sites 1 to 4) is most likely the main cause of the declining force during this type of contraction.

Question 19

FOR MAXIMAL: What would signify contractile failure?

Answer 19

EMG constant (motor unit activation is sustained) and loss of force

Question 20

Data explains what about the submax test?

Answer 20

The data should enable us to determine why the difficulty increases with time, and will show how the rotation and summation of motor units allows us to maintain sub-maximal levels of force output for several minutes.

Question 21

Normally what happens for submax

Answer 21

Sub-maximal level of force production is constant, EMG increases substantially over time. This increase indicates that additional motor units are being recruited as the initial motor units (i.e., the motor units that were initially recruited) begin to experience fatigue and cannot, on their own, maintain the targeted level of force production.

Question 22

When theres a change of _______, both contractile and activation failure contributes to the fatigue.

Answer 22

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