Muscle Lab

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LAB 6: Skeletal Muscle Physiology

Electrical Stimulation
1. Complete the following statements by filling in your answers on the appropriate lines below. A motor unit consists of a (a) and all the (b) it innervates. Whole muscle contraction is a(n) (c) response. In order for muscles to work in a practical sense, (d) is the method used to produce a slow, steady increase in muscle force. When we see the slightest evidence of force production on a tracing, the stimulus applied must have reached (e) . The weakest stimulation that will elicit the strongest contraction that a muscle is capable of is called the (f) . That level of contraction is called the __(g)__ . When the (h) of stimulation is so high that the muscle tracing shows fused peaks, (i) has been achieved.


2. Name each phase of a typical muscle twitch, and, on the following line, describe what is happening in each phase.










3. Explain how the PhysioEx experimental muscle stimulation differs from the in vivo stimulation via the nervous system. (Note that the graded muscle response following both stimulation methods is similar.)

4. What are the two experimental ways in which mode of stimulation can affect the muscle force?

Explain your answer.

Isometric Contraction
5. Identify the following conditions by choosing one of the key terms listed on the right. Key:
__________is generated by muscle tissue when it is being stretched. a. Total force

__________requires the input of energy.b. Resting force

__________is measured by recording instrumentation during contraction. c. Active force

6. Highlight the correct response in the parentheses for each statement.

An increase in resting length results in a(n) ( increase / decrease ) in passive force.

The active force initially ( increased / decreased ) and then ( increased / decreased ) as the resting length was increased from minimum to maximum.

As the total force increased, the active force ( increased / decreased ).

7. Explain what happens to muscle force production at extremes of length (too short or too long). (Hint: Think about sarcomere structure.)

Muscle too short:

Muscle too long:

Isotonic Contraction
8. Assuming a fixed starting length, describe the effect resistance has on the initial velocity of shortening, and explain why it has this effect.

9. A muscle has just been stimulated under conditions that will allow both isometric and isotonic contractions. Describe what is happening in terms of length and force.



10. Select the condition from column B that most correctly identifies the term in column A. Column A Column B
_______1. muscle twitch a. many cells responding to one neuron _______2. wave summation b. affects the force a muscle can generate _______3. multiple motor unit summation c. a single contraction of intact muscle _______4. resting length d. recruitment

_______5. resistance e. increasing force produced by increasing stimulus frequency _______6. initial velocity of shortening f. muscle length changing due to relaxation _______7. isotonic shorteningg. caused by application of maximal stimulus _______8. isotonic lengthening h. weight

_______9. motor unit i. exhibits graded response
_______10. whole muscle j. high values with low resistance values _______11. tetanusk. changing muscle length due to active...
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