Refractory Period of the Heart

Ventricular muscle, unlike skeletal muscle, is incapable of any significant degree of summation of contractions, and this is a very good thing. Imagine that cardiac muscle were able to undergo a prolonged tetanic contraction. During this period, no ventricular filling could occur since filling can occur only when the ventricular muscle is relaxed, and the heart would therefore cease to function as a pump.

The inability of the heart to generate tetanic contractions is the result of the long absolute refractory period of cardiac muscle, defined as the period during and following an action potential when an excitable membrane cannot be re-excited. As described in Chapter 11, the absolute refractory periods of skeletal muscle are much shorter (1 to 2 ms) than the duration of contraction (20 to 100 ms), and a second contraction can therefore be elicited before the first is over (summation of contractions). In contrast, because of the long plateau in the cardiac-muscle action potential, the absolute refractory period of cardiac muscle lasts almost as long as the contraction (250 ms), and the muscle cannot be re-excited in time to produce summation (Figure 14-23).

In this and previous sections, we have presented various similarities and differences between cardiac and skeletal muscle. These were summarized in Table 11-6.

PART THREE Coordinated Body Functions

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART THREE Coordinated Body Functions

Tension developed

Tension developed

Muscle Contraction Refractory Period

FIGURE 14-23

Relationship between membrane potential changes and contraction in a ventricular muscle cell. The refractory period lasts almost as long as the contraction.

FIGURE 14-23

Relationship between membrane potential changes and contraction in a ventricular muscle cell. The refractory period lasts almost as long as the contraction.

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Responses

  • jasmin
    Why the refractory period a good thing for cardiac muscle?
    8 years ago
  • mezan tesmi
    Why beneficial for refractory period in cardiac muscle?
    8 years ago
  • fabiola
    Why would it be beneficial for cardiac muscle to have a long refractory period?
    8 years ago
  • bilbo
    Why is absolute refractory beneficial for the heart?
    8 years ago
  • renato
    Why would it be beneficial for cardiac muscle to have a long absolute refractory period?
    8 years ago
  • ennio
    What is the significance of the long refractory period to the function of the heart?
    8 years ago
  • Bodo Puddifoot
    Does absolute refractory period in the heart lasts till cardiac contraction?
    8 years ago
  • Freyja
    Why would a second contraction occur in the refractory period of the heart?
    7 years ago
  • yvonne
    Which muscle has a shorter absolute refractory period?
    7 years ago
  • raffaella li fonti
    Which muscle has a long refractory period and what is its contraction?
    7 years ago
  • GARRY
    What is absolute refractory period skeletal muscle?
    7 years ago
  • ALFRED STEVENSON
    What different functions result from from different absolute refractory period in muscles?
    7 years ago
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    7 years ago
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    7 years ago
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    7 years ago
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    7 years ago
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    What is The total refractory period of cardiac muscle?
    7 years ago
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    7 years ago
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    7 years ago
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    7 years ago
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    7 years ago
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    7 years ago
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    6 years ago
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    6 years ago
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    6 years ago
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    6 years ago
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    6 years ago
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    6 years ago
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    6 years ago
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    6 years ago
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    Why is it necessary for the refractory phase of a cardiac muscle to be longer than a skeletal muscle?
    6 years ago
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    What is the sigificance of refractory period in heart function?
    6 years ago
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    6 years ago
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    3 years ago
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    WHY IS CARDIAC MUSCLEIS LONGER THAN SKELETAL MUSCLES DURING REFACTORY PERIOD?
    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    3 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    2 years ago
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    1 year ago
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    1 year ago
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    1 year ago
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    1 year ago
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    1 year ago
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    1 year ago
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    1 year ago
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    1 year ago
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    1 year ago
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    11 months ago
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    11 months ago
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    11 months ago
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    11 months ago
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    11 months ago
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    10 months ago
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    10 months ago
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    10 months ago
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    10 months ago
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    9 months ago
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