Activity of Gastrointestinal Smooth Muscle Essay

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INTRODUCTION
Give a brief description in your own words of the objectives and aims of this practical.
The aim of this practical is to investigate how the autonomic nervous system (ANS) affects the motility in the gastrointestinal tract, by experimenting with the release of neurotransmitters.

A. RESPONSES TO NERVE STIMULATION
 Attach a copy of your experimental recordings showing a period of spontaneous contractions and the response to stimulating the nerves at 20 Hz with both a voltage that produced only a modest response and the voltage that produced the maximal response.

1) Briefly describe the response of the ileum when it is unstimulated and during stimulation of the nerves.
It is shown that
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Is it always inhibitory in vivo? What happens in the intact animal?

C. BLOCKING AUTONOMIC NERVOUS SYSTEM TRANSMITTER TARGETS
Effect of phentolamine on the responses to nerve stimulation and added transmitter substances
 Attach copies of your experimental recordings showing the response of the ileum to nerve stimulation and to the direct addition of noradrenaline and acetylcholine, in the presence of phentolamine.

1) What was phentolamine’s main effect? How does it produce this effect?

2) What two explanations could account for the fact that the test concentration of phentolamine only partly blocked the inhibitory responses to noradrenaline and nerve stimulation?

3) How would you design an experiment to distinguish between these two possibilities?

4) In some tissues there may be a reversal of the response to nerve stimulation in the presence of phentolamine (i.e. excitation instead of inhibition). Explain how this could occur.

5) Sometimes phentolamine also reduces the effect of acetylcholine. What important drawback to the use of drugs as tools for investigating physiological mechanisms does this illustrate?

Effect of atropine on the responses to nerve stimulation and added transmitter substances
 Attach copies of your experimental
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