AnS214 SI Session 11
Wednesday, 2/17, 4pm
CQoD: "Clothes make the man. Naked people have little or no influence on society." --Mark Twain
A. Excitation-Contraction Coupling (EMC)
1) Acetylcholine, upon diffusion across the synaptic cleft, induces what kind of change on the sarcolemma?
How does this affect t-tubule proteins?
2) What effect do these changes have on terminal cisternae?
3) The leakage of Ca+ from the SR results in the opening of what channels?
The net effect is.....?
4) This excitation is 'coupled' to the contraction pathway by what event?
B. Contraction (EMC)
1) Number the following 1-6 in the order that they occur during a muscle contraction.
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.
Myosin heads bind to the now exposed binding sites on actin.
The flexion of a relaxing myosin head pulls its attached actin strand in towards the center of the sarcomere.
ATP on the myosin head is cleaved into ADP and Pi, forcing myosin heads into the high energy, 'cocked', position.
The myosin head binds an ATP molecule, allowing it to release actin.
2) For each of the above steps, illustrate the actions of the myosin heads.
1 → 2 / 2 → 34 → 5 / 5 → 6
C. Relaxation (EMC)
1) What actions take place at the end plate to initiate relaxation?
2) What actions take place on the myosin fiber to stimulate relaxation?
3) What actions take place within the cytoplasm to finalize relaxation?
D. Fast (II) and Slow (I) Twitch Fibers (EMC)
Label the diagram axis and identify which line belongs to type I and type II fibers.
1) What are the 3 phases of a twitch?
2) Which of these phases differ in length for fast and slow twitch muscle?
3) Why is contraction faster is fast twitch than in slow twitch muscle?
4) Why is relaxation faster in fast twitch than in slow twitch muscle?
E. Length-Tension Relationship (EMC)
1) Illustrate the actin-myosin interactions reponsible for the observed tension potential in the blank boxes.
2) 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 ______overlap, the ______strands become a physical obstruction to each other, and ______begins to butt into the Z-disks. When there is ______overlap, too few myosin heads are able to form ______, decreasing the amount of force generated.
3) Why does a contraction become 'easier' with progressive shortening of the muscle?
4) Human resting sarcomere length is considered 'sub-optimal'. By what % does resting length need to increase to generate the most possible force during contraction?