LAB 9: Skeletal Muscle Physiology
1. Complete the following statements by filling in your answers on the appropriate lines below.
A motor unit consists of a ___1___ and all the ___2___ it innervates.
Whole muscle contraction is a(n) ___3___ response.
A ___4___ is the response of a muscle to a single, brief threshold stimulus.
When the frequency of stimulation is so high that the muscle tracing shows fused peaks, ___5___ has been achieved.
___6___ is the stimulus strength at which the first observable muscle contraction occurs
The phenomenon, called ___7___, brings more and more muscle fibers into play
1. _motor neuron___
2. _muscle fibers___
4. _Muscle twitch___
5. _complete tetanus___
6. _threshold stimulus___
2. Name each phase of a typical muscle twitch, and, on the following line, describe what is happening in each phase.
a. _Latent period___
_the first moments after stimulation when excitation contraction is occuring___
b. _Period of Contraction___
_the muscle shortens if the tension is great enough to overcome the load.___
c. _Period of Relaxation___
_Calcium ions is pumped back into sarcoplasmic reticulum and muscle tension decreases to baseline level.___
3. Identify the following conditions by choosing one of the key terms listed on the right.
_Passive force___ is generated by muscle tissue when it is being stretched
a. Total force
_Active force___ is produced during muscle contraction
b. Active force
_Total force___ is measured by recording instrumentation during contraction
c. Passive force
4. Highlight the correct response in the parentheses for each statement.
An increase in resting length results in a(n) ( increase / decrease ) in passive force.
As the total force increased, the active force ( increased / decreased ).
5. Explain what happens to muscle force production at extremes of length (too short or too long). (Hint: Think about sarcomere structure and actin and myosin interactions)
Muscle too short: _Muscle force produced is reduced and they lose their strength as they cannot contract.___
Muscle too long: _Muscle force production is reduced because of insufficient overlap of actin and myosin. There isn’t maximal cross bridge formation.___
6. Select the LETTER of the condition from column B that most correctly identifies the term in column A.
__C__ 1. Muscle twitch
_E___ 2. Wave summation
_B___ 3. Multiple motor unit summation
__F__ 4. Resting length
_D___ 5. Resistance
_I___ 6.concentric isotonic contraction (shortening)
_H___ 7. Eccentric isotonic contraction (lengthening)
_A___ 8. Motor unit
_G___ 9. tetanus
A. Many cells responding to one neuron
B. Affects the speed of a muscle contration
C. A single contraction of intact muscle
E. The addition of one twitch to another
F. Muscle length changing due to relaxation
G. Recording shows no evidence of muscle relaxation
H. The peak tension developed is less than the resistance
I. Changing muscle length due to active forces
7. What does this picture represent?
12. Name the indicated structures:
2. _I band___
3. _Z disc___
8. _T tubule___
9. SARCOPLASMIC RETICULUM
10. OPENINGS OF T-TUBULES
8. Name the indicated structures.
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