Question

26. How is the action of ACh different in cardiac cells than it is in skeletal muscle cells?

Answer 1

26.

Acetyl choline is produced by the parasympathetic nerve endings of the SA node which are brought by Vagus nerve. Parasympathetic nerve reduces heart rate and strength of contraction to bring it to normalcy whenever it goes up.

Ach attches to the Ach receptors in the skeletal muscle , the Na channels open and activates the skeletal muscle to contract. So, in skeletal muscle, the Ach neurotransmitter is a stimulator.

In the case of cardiac muscle, it binds to a different receptor and inhibits the cardiac muscle. ACh is released from the vagus nerve endings and it reduces the cardiac muscle activity.

Parasympathetic nervous system has two different types of receptors called Muscarinic receptors, M2 and M3 receptors. The M2 receptors are present in the atria and in nodal tissues of the heart but not present in ventricles. When M2 receptor is activitated by binding of ACh neurotransmitter, it slows down the process of depolarization and also slows the conduction of the cardiac impulse across the atrioventricular node. The activation of the M2 receptors additionally also reduces the strength of cardiocyte contraction. These changes brought will reduce the cardiac output by reducing the heart rate and the stroke volume.

This is how Acetyl Choline binds to M2 receptor on the cardiac muscle and reduces the heart rate to normalcy and also reduces the strength of muscle contraction.