In this experiment the sciatic nerve is stimulated electrically with different voltages. The isometric tension developed by the gastrocnemius muscle is recorded.
You should select different voltages by clicking on these buttons on the stimulator panel to increase or decrease the stimulus voltage.
Task
You should stimulate the nerve with different voltages and measure the peak amplitude of the muscle contraction at each stimulus voltage.
Tabulate your results and then try answering the questions.
Volts
Question 1
If you were carrying out this experiment on a live preparation good experimental practice would dictate that different stimulus voltages were applied randomly. This is to ensure that the nerve will not anticipate the size of the stimulus.
When the muscle is removed from the body it rapidly fatigues and the tension generated by successive application of the same stimulus voltage will fall. by randomising stimuli and delivering a control stimulus at different times during the experiment you can monitor fatigue and make allowances.
When the muscle is removed from the body it rapidly fatigues and the tension generated by successive application of the same stimulus voltage will fall. by randomising stimuli and delivering a control stimulus at different times during the experiment you can monitor fatigue and make allowances.
Question 2
The duration of the muscle twitch is 150 -160 ms.
The duration of the muscle twitch is 7.5 - 8.0 division @ 20 ms/div. = 150 - 160 ms.
The duration of the muscle twitch is 7.5 - 8.0 division @ 20 ms/div. = 150 - 160 ms.
Question 3
The maximum tension developed in this experiment is 25g.
The maximum tension developed (stimulus voltages > 3.0) is 6.9 divisions @ 5g / div = 34.5g.
The maximum tension developed (stimulus voltages > 3.0) is 6.9 divisions @ 5g / div = 34.5g.
Question 4
The characteristics of the muscle twitch are similar in all muscles.
The duration of the twitch varies according to the type of muscle: in "slow fibres" the twitch may last over 150 ms, in "fast fibres" it may be less than 10 ms. Temperature also affects the duration of the twitch contraction.
The duration of the twitch varies according to the type of muscle: in "slow fibres" the twitch may last over 150 ms, in "fast fibres" it may be less than 10 ms. Temperature also affects the duration of the twitch contraction.
Question 5
A motor unit is the smallest functional unit of contraction in muscle.
A motor unit comprises a motor neurone and the muscle fibres it innervates. Each motor neurone branches and supplies several muscle fibres: thus activation of one motor neurone will activate several muscle fibres.
A motor unit comprises a motor neurone and the muscle fibres it innervates. Each motor neurone branches and supplies several muscle fibres: thus activation of one motor neurone will activate several muscle fibres.
Question 6
All motor units comprise a motor neurone whose branches innervate 5-10 muscle fibres.
This may be typical of motor units of muscles concerned with fine graded movements but in large muscles of the leg and back each motor neurone may innervate 120-170 muscle fibres.
This may be typical of motor units of muscles concerned with fine graded movements but in large muscles of the leg and back each motor neurone may innervate 120-170 muscle fibres.
Question 7
The muscle tension increases as the stimulus voltage applied to the nerve increases because more motor units are activated as the voltage is increased.
As the stimulus voltage is increased more nerve fibres and thus more and more motor units are activated. The amplitude of the contraction is proportional to the number of motor units which are activated.
As the stimulus voltage is increased more nerve fibres and thus more and more motor units are activated. The amplitude of the contraction is proportional to the number of motor units which are activated.
Question 8
An isometric contraction is one in which the muscle length changes but the tension remains constant.
This is the definition of an isotonic contraction. An isometric contraction is one in which the muscle tension changes but the length remains constant.
This is the definition of an isotonic contraction. An isometric contraction is one in which the muscle tension changes but the length remains constant.
DEMO
When the muscle is removed from the body it rapidly fatigues and the tension generated by successive application of the same stimulus voltage will fall. by randomising stimuli and delivering a control stimulus at different times during the experiment you can monitor fatigue and make allowances.
When the muscle is removed from the body it rapidly fatigues and the tension generated by successive application of the same stimulus voltage will fall. by randomising stimuli and delivering a control stimulus at different times during the experiment you can monitor fatigue and make allowances.