Review Questions
1. In relaxed muscle, the myosin-binding site on actin is blocked by ________.
2. According to the sliding filament model, binding sites on actin open when ________.
3. The cell membrane of a muscle fiber is called ________.
4. Muscle relaxation occurs when ________.
5. During muscle contraction, the cross-bridge detaches when ________.
6. Thin and thick filaments are organized into functional units called ________.
Click here to return to Chapter 39
1. How would muscle contractions be affected if skeletal muscle fibers did not have T-tubules?
Solution: Without T-tubules, action potential conduction into the interior of the cell would happen much more slowly, causing delays between neural stimulation and muscle contraction, resulting in slower, weaker contractions.
2. What causes the striated appearance of skeletal muscle tissue?
Solution: Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell cause the entire cell to appear striated.
3. How would muscle contractions be affected if ATP was completely depleted in a muscle fiber?
Solution: Without ATP, the myosin heads cannot detach from the actin-binding sites. All of the “stuck” cross-bridges result in muscle stiffness. In a live person, this can cause a condition like “writer’s cramps.” In a recently dead person, it results in rigor mortis.
Library Info and Research Help | reflibrarian@hostos.cuny.edu (718) 518-4215
Loans or Fines | circ@hostos.cuny.edu (718) 518-4222
475 Grand Concourse (A Building), Room 308, Bronx, NY 10451