Download Exercise : Refractory period of cardiac muscle

Refractory period of cardiac muscle
Learning Objectives
At the end of the practical, the student should be able to:
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Define Refractory Period?
Differentiate between absolute and relative refractory periods?
Explain what is a cardiac cycle?
Determine the extent to which it is possible to re-stimulate cardiac
contraction during a cardiac cycle?
Refractory Period
Definition:
The period that follows effective
stimulation, during which excitable tissue
fails to respond to a stimulus of threshold
intensity.
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Absolute Refractory Period.
Relative Refractory Period.
Absolute Refractory Period:
During the absolute refractory period, a second stimulus (no matter how strong)
will not excite the muscle fiber.
Relative Refractory Period:
During the relative refractory period, the
muscle fiber can respond only to a
strong stimulus.
Cardiac Cycle
Definition:
A complete contraction and relaxation episode in the heart.
The cardiac cycle consists of:
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A Systolic Phase and
A Diastolic Phase.
One complete cardiac cycle forms
the common "lub-dub" pattern
recognized as the heart beat.
Exercise : Refractory period of cardiac
muscle
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The aim is to determine the extent to
which it is possible to re-stimulate
cardiac contraction during a cardiac
cycle.
• To be performed only if time allows and
instructed to do so.
• If you are using the ADInstruments
Bridge Amp please use this 'Zero
Bridge Amp' link to correct for any
residual offset voltage again.
Procedure
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Connect the positive and negative BNC connectors of the Animal Nerve
Stimulating Electrode to the analog Outputs on the Power Lab.
• Check that the number of pulses
in the Stimulator panel is set to 1.
• Click Start to begin recording.
• Gently place the tips of the
stimulating electrode on the
surface of the frog heart.
• By clicking the Stimulate button
on the Stimulator panel, attempt
to elicit a second contraction from
the frog heart at each of the
points in the cardiac cycle
illustrated in the figure below.
• Approximate points during the
cardiac cycle at which you should
attempt to stimulate the heart.
Stimulator Panel
• The Stimulator panel allows the control of the voltage (current in some
experiments) of a pulse, the number of pulses and the interval between pulses
applied to a tissue.
• In some experiments a Stimulate button may be visible. This allows the control
of stimulation independently from sampling.
Stimulate Button
• The Stimulate button is only available while recording. It allows the user to
stimulate at any time during a recording. Stimulation can be halted by clicking
the Stop button in the
LabTutor Data Panel.
Analysis
• In the table, enter "yes" if stimulation resulted in an extra
contraction (extra-systole) with a stimulus delivered at the
point in the contraction cycle or "no" if it did not.