Contraction of Cardiac Muscle Worksheet

Contraction of Cardiac Muscle Worksheet

Introduction

Give a brief general description, in your own words, of the aims of this practical.

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Experimental Preparation and Set-up

Briefly describe, in your own words, the experimental preparation and set-up used in this practical. 

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Experimental Results (and Discussion)

Experiment 1:  Length-Tension Curve

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Figure 1. The effect of altering muscle length on the force of contraction in toad cardiac muscle.

Table 1. The effect of muscle length on passive and active tension in isolated toad cardiac muscle.

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Figure 2. The effect of altering muscle length on active and passive tension in toad cardiac muscle.

(1) Explain how this length-tension relation in the isolated strip of toad cardiac muscle relates to the function of the whole toad heart in the animal.

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Experiment 2:  Varying Stimulus Strength

(2A) Briefly describe what you observed when you gradually increased the stimulus voltage (was the size of the contraction dependent on the voltage level?).

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(2B) Briefly explain how action potentials spread from one cardiac muscle cell to the next.

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(2C) Where is the electrical activity of the mammalian heart normally initiated?

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Experiment 3:  Effect of Extracellular Calcium on Active Tension

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Figure 3. The effect of altering the extracellular calcium concentration on the force of contraction in toad cardiac muscle.

Table 2. The effect of altering the extracellular calcium concentration on the active tension in isolated toad cardiac muscle.

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Figure 4. The effect of altering the extracellular calcium concentration on active tension in toad cardiac muscle.

(3A) Explain the effect of altering the extracellular calcium concentration on the force of contraction (active tension).

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(3B) What would you expect to happen to the contractions if the calcium concentration in the bathing solution was reduced to zero? Explain why.

*Please note that you were unable to completely remove all Ca2+.

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