Neuronal Control of Smooth Muscle

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upon various canditions

Contraction amplitude pre-nerve stimulation Contraction amplitude with the maximum response to nerve stimulation Effect of nerve stimulation on the contraction amplitude (PLEASE SHOW YOUR CALCULATIONS)

Nerve stimulation

agonist addition? Maximum – Minimum

= 2.1 mV Maximum – Minimum

= 0.6 mV Express the effect of nerve stimulation as % change (from pre-nerve stimulation to maximum response to nerve stimulation):

= -71.4 %

DRUG A Maximum – Minimum

= 1.7 mV Maximum – Minimum

= 0.8 mV Express the effect of nerve stimulation as % change (from pre-nerve stimulation to maximum response to nerve stimulation):

= -52.9 %

DRUG B Maximum – Minimum

= 1.8 mV Maximum – Minimum

= 7.9 mV

Express the effect of nerve stimulation as % change (from pre-nerve stimulation to maximum response to nerve stimulation):

= 77.2 %

Phentolamine + Noradrenaline Maximum – Minimum

= 3.3 mV

Maximum – Minimum

= 2.7 mV

Express the effect of nerve stimulation as % change (from pre-nerve stimulation to maximum response to nerve stimulation):

= -22.2 %

Phentolamine + Acetylcholine Maximum – Minimum

= 3.4 mV

Maximum – Minimum

= 5.0 mV

Express the effect of nerve stimulation as % change (from pre-nerve stimulation to maximum response to nerve stimulation):

= 32 %

Phentolamine + nerve stimulation Maximum – Minimum

= 4.5 mV

Maximum – Minimum

= 3.5 mV

Express the effect of nerve stimulation as % change (from pre-nerve stimulation to maximum response to nerve stimulation):

= 29%

DISCUSSION (NO MORE THAN 500 WORDS – PLEASE JUST ANSWER QUESTIONS 1-5).

1) Referring to the relevant figure and table, briefly describe the response of the spontaneously contracting ileum to nerve stimulation. Was this response altered by increasing the voltage of nerve stimulation? If yes, why does increasing the voltage change the response to nerve stimulation?

Prior to nerve stimulation, the rate of contraction of the ileum remained constant, once the ileum was subjected to stimulation it resulted in a sympathetic response whereby the amplitude of contraction reduced significantly. When increasing the voltage, it was noted that the amplitude of contraction decreased. This occurs as increasing the voltage allows for action potentials to fire and release neurotransmitters as the voltage that is applied is at or above the threshold stimulus.

2) What was the frequency of the regular spontaneous contractions in your preparation (measured in contractions per minute)? What causes or initiates these spontaneous contractions? Why do you think autonomic nerve stimulation does not alter the rate of contractions in the ileum, whereas in the heart autonomic nerve stimulation alters the rate of contractions?

The rate of spontaneous contraction of the ileum was measured at approximately 25 contractions per minute. These spontaneous contractions are driven by the interstitial cells of the Cajal found in the gastric pacemaker region.

3) REFERRING TO THE RELEVANT TABLES AND FIGURES (i.e. your experimental results), explain how you have determined if Drug A or Drug B are noradrenaline or acetylcholine. In your response you must refer to the normal actions of these drugs on smooth muscle function in the gut.

When noradrenaline attaches to adrenoceptors, gut motility and secretion decreases and whereas when acetylcholine attaches to muscarinic receptors gut motility and secretion increases. We deduced that Drug A was noradrenaline and Drug B was acetylcholine. Referring to table _ figure_ it illustrates a reduction of 53% in amplitude suggesting that the contraction of the ileum has decreased, due to a sympathetic response thus will cause a decrease in gut motility hence it was determined that drug A is noradrenaline. Referring to table _ figure _ it shows a parasympathetic response with an increase of 77% in amplitude indicating that drug B is acetylcholine as an excitatory response will cause increase in motility and secretion in the gut.

4) Discuss how your experimental protocols have enabled you to determine if you are stimulating sympathetic or parasympathetic nerves. YOU MUST REFER TO THE RELEVANT FIGURES AND TABLES (i.e. your experimental results) in order to support your conclusions. . In your response you must refer to the normal actions of these drugs on smooth muscle function in the gut (including their effects on smooth muscle receptors). If your data analysis does not show any clear results - explain how you might alter your experimental protocols for future experiments.

Referring to table 1 and figure 1, it shows the isolated ileum being put through a range of voltages which resulted in a decrease in amplitude on the spontaneous contractions

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