Gastrointestinal Smooth Muscle Worksheet

Activity of Gastrointestinal

Smooth Muscle Worksheet

INTRODUCTION

Give a brief description in your own words of the objectives and aims of this practical.

The aims of this practical was to understand how the nerves of the autonomic nervous system affect the

spontaneous relaxation and contraction of the gastrointestinal tract by experimenting through the release

of neurotransmitters, also to by mimicking the actions of neurotransmitters using specific drugs that target

these neurotransmitter's receptors. Also, to observe and further the research such drugs that can

interfere with the ability of the autonomic nervous system.

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.

When unstimulated, the rabbit ileum contracts and relaxes at a constant rate; however when the Rabbit

Ileum is stimulated; there is a noticeable drop in the amplitude of the contractions. This is due to the

higher voltage, which mean there will be a inhibition and greater reduction in the amplitude of the

contractions.

2) What is the frequency of the regular spontaneous contractions of the ileum? What causes these spontaneous contractions?

The rate of the spontaneous contractions of the ileum is approximately 20 contractions per minute, these

are caused by the pacemaker cells by the cajal cells which create action potentials spontaneously.

 Attach a copy of your experimental recordings showing the response to stimulating the nerves with the maximal voltage at both 5 Hz and 50 Hz.

3) Explain the effect of altering stimulus frequency on the response of the ileum to nerve stimulation.

The effect that increasing stimulus frequency meant that the response of the ileum showed a greater

release of neurotransmitters which means that there was a greater inhibition of contractions. A decrease

in stimulus frequency mean there was a greater response of more contractions.

B. MIMICKING THE ACTION OF THE AUTONOMIC NERVOUS SYSTEM USING DRUGS

 Attach copies of your experimental recordings showing the response of the ileum to the direct addition of noradrenaline and of acetylcholine to the tissue bath.

1) What was the final bath concentration of noradrenaline you used? Briefly describe the response of the ileum to the direct addition of noradrenaline.

The final bath concentration of noradrenaline was 0.149µM. The response of ileum to the direct addition

of the noradrenaline was an instant inhibitory (decrese) in response of the amplitude of the contractions of

the rabbit ileum.

2) What was the final bath concentration of acetylcholine you used? Briefly describe the response of the ileum to the direct addition of acetylcholine.

The final bath concentration of acetylcholine was 0.149µM. The response of ileum to the direct addition of

the acetylcholine was an excitatory response as the amplitude shifted upwards, but no large change in

the range,this is due to the increase of concentration of calcium ion (ca 2˖) the contractions of the ileum.

2) Since an inhibitory response to nerve stimulation was observed in all (or most) of the tissues studied in the practical, how is differential control (i.e., both inhibition and excitation) of gut contraction achieved in the body? Is it always inhibitory in vivo? What happens in the intact animal?

In the animal, the response of the ANS at the time, with contract as result of parasympathetic response or

will relax due to the sympathetic response in the gastrointestinal tract. The inhibitory response to nerve

stimulation relies on the predominant branch of the autonomic nervous system which occurs due to the

foremost populace of nerves present.

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?

Phentolamine blocks the adrenoreceptors, hence causes a large decresed inhibitory response in the

rabbit ileum, the immediate drop in amplitude is due to the blocking of alpha receptors, thus

noradrenaline becomes unable to activate these receptors as noradrenaline acts of alpha receptors

mostly.

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?

A reason that could account for the fact that the test concentration of phentolamine only partly

Blocked the inhibitory response is that the concentration of phentolamine was insufficient to block all the