Muscle Contraction

Exercise 1: The effects of nerve stimulation

Objective:

To explore the motor and sensory effects of electrical stimuli on a student volunteer, using the nerves of the forearm.

Exercise2: Twitch response and recruitment

Objective:

To measure the muscular twitch response to nerve stimulation, and to show recruitment in the twitch response as the stimulus strength increases.

Exercise3: Summation and tetanus

Objectives:

To demonstrate the effects of changing the interval between paired stimulus pulses, and to observe a short titanic contraction.

Results of Experiment2:

Table1: The effects of varying stimulus strength on twitch force.

Stimulus (mA) | Response (mV) |

0.0 | 0.00 |

0.5 | 0.00 |

1.0 | 0.00 |

1.5 | 0.00 |

2.0 | 0.00 |

2.5 | 0.00 |

3.0 | 0.00 |

3.5 | 0.00 |

4.0 | 0.00 |

4.5 | 2.90 |

5.0 | 5.33 |

5.5 | 6.18 |

6.0 | 17.09 |

6.5 | 31.64 |

7.0 | 38.56 |

7.5 | 52.03 |

8.0 | 55.12 |

8.5 | 53.99 |

Questions:

1. Did you get a measurable twitch with a stimulus of 0mA?

No measurable twitch with a stimulus of 0mA.

2. What was the smallest current required to produce a contraction (the threshold current)?

Based on table1, the smallest current required to produce a contraction is 4.5mA.

3. What was the smallest current required to produce the maximum (largest) contraction?

From the table1, the smallest current required to produce the maximum contraction is 8.0mA

4. What happened to the number of fibers contracting as the current was raised from threshold to that required to produce a maximal contraction?

The numbers of fibers contracting have shown an increasing trend from the threshold down to the maximal contraction.

5. Why does varying the stimulus strength affect the twitch force?

This is because when varying the stimulus, the action potential is produced. Different degree of action potential caused by vary stimulus will result in different response of contraction. Hence, varying...