What mechanisms are responsible for the following: a. Acetylcholine causes excit

Question

What mechanisms are responsible for the following: a. Acetylcholine causes excitation in the form of EPSP in the skeletal neuromuscular junction and inhibition in the form of slowed heart rate in cardiac pace maker cells? b. Adrenaline causes excitation that leads to increased heart rate and breathing capacity at the same time it causes inhibition and relaxation in the digestive system. c. Stimulating below the knee causes contraction of the extensor (quadriceps) muscles and relaxation in the flexor (hamstring) muscles. d. The reversal potential for the nicotinic acetylcholine receptor is around 0 mV. (Hint: Think of the potential for the ion allowed to pass through this ligand-gated receptor?) e. When the light is turned on the photoreceptor rods and cones undergo hyperpolarization and this hyperpolarization leads to excitation in both the bipolar and ganglion that receive signals from them. f. What is the neuronal basis for the observation that it is easier to tell where a sound is coming from than where a smell is coming from? g. Is it true that rods and cones have different thresholds and different distributions in the retina? (Yes or No). Explain your answer. h. Give an example of how the nervous system serves to control the internal homeostasis and another example of how it protects against outside dangers

Explanation / Answer

a. These two effects of acetylcholine are due to two different receptors: nicotinic and muscarinic.

Binding of acetyl choline to nicotinic receptor causes excitation in the skeletal muscles.

If acetylcholine binds to the muscarinic receptor, this interaction inhibits the adenylyl cyclase activity. The cAMP production leads to reduced activation of cAMP-dependent protein kinase; this reduces the heart rate, and contraction strength.

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