BPK 105 Study Guide - Final Guide: Cardiac Muscle, Skeletal Muscle, Sinoatrial Node
27 Apr 2018
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Modules 7 & 8 - Review Questions - Part 4
7. What are the major differences between the cardiac action potential and the skeletal
muscle action potential? What causes these differences, why is it important for how the
heart functions? [4 marks]
Refer to figure 12.14 in textbook.
- Prolonged action potentials (compare seconds)
- Longer refractory period
- Slow diffusion due to slow diffusion of Ca2+ into cell
- Different phases
- Cell to cell
- The prolonged action potential and refractory period allow cardiac
muscle to contract and relax almost completely before another
action potential can be produced. Also, the long refractory period in
cardiac muscle prevents tetanic contractions from occurring, thus
ensuring a rhythm of contraction and relaxation for cardiac muscle
Action potentials in cardiac muscle are prolonged compared to those in skeletal muscle and
have a depolarization phase, a plateau phase, and a repolarization phase.
Like action potentials in skeletal muscle and neurons, those in cardiac muscle exhibit
depolarization followed by repolarization. In cardiac muscle, however, a period of slow
repolarization greatly prolongs the action potential (figure 12.14). In contrast to action
potentials in skeletal muscle, which take less than 2 milliseconds (ms) to complete, action
potentials in cardiac muscle take approximately 200 to 500 ms to complete. In addition,
unlike in skeletal muscle, action potentials in cardiac muscle are conducted from cell to
cell.
The slow diffusion of Ca2+ into the cell is the reason the cardiac muscle fiber action potential
lasts longer than the action potentials in skeletal muscle fibers. The plateau phase ends, and
the repolarization phase begins as the Ca2+ channels close and many K+ channels open,
allowing K+ to move out of the cell.
Action potentials in cardiac muscle exhibit a refractory period, like that of action potentials in
skeletal muscle and in neurons. The refractory period lasts about as long as the plateau phase
of the action potential in cardiac muscle. The prolonged action potential and refractory
period allow cardiac muscle to contract and relax almost completely before another
action potential can be produced. Also, the long refractory period in cardiac muscle
prevents tetanic contractions from occurring, thus ensuring a rhythm of contraction and
relaxation for cardiac muscle. Therefore, action potentials in cardiac muscle are different from
Document Summary
Slow diffusion due to slow diffusion of ca2+ into cell. Also, the long refractory period in cardiac muscle prevents tetanic contractions from occurring, thus ensuring a rhythm of contraction and relaxation for cardiac muscle. Action potentials in cardiac muscle are prolonged compared to those in skeletal muscle and have a depolarization phase, a plateau phase, and a repolarization phase. Like action potentials in skeletal muscle and neurons, those in cardiac muscle exhibit depolarization followed by repolarization . In cardiac muscle, however , a period of slow repolarization greatly prolongs the action potential (figure 12. 14). In contrast to action potentials in skeletal muscle, which take less than 2 milliseconds (ms) to complete, action potentials in cardiac muscle take approximately 200 to 500 ms to complete. In addition, unlike in skeletal muscle , action potentials in cardiac muscle are conducted from cell to cell .
