The Muscle System
Exam 3 Extra
Supplemental Instruction
Iowa State University
1. Fill in the diagram at right and answer the
pertaining questions:
Leader: Cody
Course: AN S 214
Instructor: Dr. Selsby
Date:
2. What is the name of the neurotransmitter
released at the NMJ?
Acetylcholine Ach
3. What kinds of channels will open on the
sarcolemma?
voltage-gated ion channels
4. What major enzyme is present within the
synaptic cleft? What is its function?
Acetylcholinesterase-removes Ach from
receptors
5. What is the significance of the junctional
folds?
Increase surface area for Ach to bind to
receptors
6. What kinds of receptors are located in the
junctional folds?
Ligand-gated ion channels
7. What kinds of channels do they open?
Na+ channels and K+ channels
8. What does this ion exchange initiate?
Action Potential
9. How do we repolarize the sarcolemma to get back to our original state?
Close Na+ channels, open K+ channels
Supplemental Instruction
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10. Fill in the blanks and name structures A-D in the diagram below, illustrating the process
of excitation-contraction coupling:
11. What kinds of channels are located at A? Describe the consequences of their activation.
Ligand-gated ion channels, influx of Na+, outflow of K+
12. Draw the path of the end plate potential along the sarcolemma. What structure does it
enter?
T-Tubule
13. What is the effect of the spreading potential on the structure labeled C? D? Draw an
arrow symbolizing any structural changes.
Voltage-sensitive tubule protein (electron-dense feet) change shaperelease Ca2+
14. What particles are stored within the structure labeled B? What happens as a result of the
conformational change to structure D?
Ca2+, Terminal cisternae release Ca2+
15. What kinds of channels are located at B? Why do the intra-SR ions flood the cell?
Calcium channels, to bind to troponin for muscle contraction
16. What is the effect of these ions in the sarcoplasm?
Bind to troponin
17. What pump, by active transport, will pump calcium back into the SR?
Serca
18. What is the affect of Parvalbumin? Help bring calcium to serca
Calsequestrin? Helps bind calcium, to pump against gradient
19. Number the following 1-6 in the order that they occur during a muscle contraction.
5
ADP and Pi are expelled from the myosin head, allowing it to return to the relaxed
90º state.
1
The myosin head is in the relaxed state, at 90º. Bound to it is an ATP molecule.
3
Myosin heads bind to the now exposed binding sites on actin.
4
The flexion of a relaxing myosin head pulls its attached actin strand in towards the
center of the sarcomere.
2
ATP on the myosin head is cleaved into ADP and Pi, forcing myosin heads into the
high energy, 'cocked', position.
6
The myosin head binds an ATP molecule, allowing it to release actin.
20. How is acetylcholine moved away from receptors and the neuromuscular junction?
Enzyme acetylcholinesterase
21. What happens if there is no longer an action potential? What happens to the electron
dense feet?
No more calcium, they’ll close
22. What happens to the release of calcium?
Stops
23. What happens to troponin and tropomyosin?
Unbinding calcium, troponin releasing
tropomyosin, tropomyosin covers back-up
the myosin binding sites on the actin
24. Illustrate the actin-myosin interactions
responsible for the observed tension potential in
the blank boxes of the diagram to the right:
25. The amount of force generated by a muscle
fiber is dependent on the degree of overlap
between the actin and myosin subunits within
the sarcomere. When there is ____Excesive_
overlap, the ___actin___ strands become a
physical obstruction to each other, and
__myosin_____ begins to butt into the Z-disks. When there is _____too little____
overlap, too few myosin heads are able to form __cross bridges______, decreasing the
amount of force generated.
26. What are the 3 phases of a twitch and what event is correlated with each?
 Latent period; events of E-C coupling
 Period of contraction; cross bridge
formation
 Period of relaxation; calcium reentry into
SR, tension declines to zero
27. Label the diagram to the right’s axis and
identify which line belongs to Type I and
Type II fibers:
28. Which of these phases differ in length for
fast and slow twitch muscle?
Period of contraction, period of relaxation
29. Why is contraction faster in fast twitch
than in slow twitch muscle?
Rate at which ATP is hydrolyzed
30. Why is relaxation faster in fast twitch than in slow twitch muscle?
Calcium is reabsorbed faster
31. Which type of muscle is primarily used for sustained levels of exercised? Type I
Short bursts of activity? Type II
32. What type of muscle fiber would you expect to find in a 'natural sprinter'? Type II
A 'natural marathon runner'? Type I
33. On the blank diagrams below, fill in the changes in tension that occur with multiple
stimuli for both unfused and fused tetany. Use arrows to indicate stimuli and a line to
track the change in muscle tension:
UNFUSED TETANY
FUSED TETANY
34. How do these two types of tetany differ in frequency of stimulus?
Unfused: lower frequency fused: high frequency
35. How do these two types of tetany differ in amount of calcium released?
36. Which type of tetany can/cannot occur under normal physiological conditions?
fused
37. Define threshold stimulus (illustrated in
the figure to the right):
The stimulus at which the first observable
contraction occurs
38. What accounts for the gradual increase in
contractile strength?
Strength of stimulus increases
39. What happens if the stimulus is below
threshold?
No contraction
40. What happens when the stimulus reaches maximal strength?
No further increase in contractile strength
41. Name and define the two main types of muscle contractions discussed in class.
 ____isotonic__: muscle length changes and moves the load

_____isometric_____: produces force, but muscle neither shortens or lenthens
42. What are the two sub-types of isotonic contractions? Define each.
 Eccentric contractions: generate force as it lengthens

Concentric contractions: muscle shortens and does work
43. T/F: Muscles never push, they only pull.