Question

Answer the following:

Describe the mechanisms by which acetylcholine affects heart rate.

Describe the mechanisms by which epinephrine affects heart rate.

Describe the mechanisms by which atropine followed by acetylcholine affects heart rate.

Epinephrine mimics the effects of which branch of the autonomic nervous system?

Compare the effect of acetylcholine on cardiac muscle with its effect on skeletal muscle. Can you explain the mechanistic basis for the difference?

Answer 1

1) Acetylcholinebisvtge neurotransmitter released by parasympathetic nervous system via vagus nerve at synapses with cardiac muscle cells.The acetylcholine binds to M2 receptors in the cells of cardiac muscle Ach hyperpolarises the SA nodal cells and decreases the rate of diastolic depolarisation.As a result ,rate of impulse generation is reduced which results in decresed heart rate- bradycardia.

2 ) Epinephrine is the neurotransmitter released by sympathetic nervous system at synapses with cardiac muscle cells.The epinephrine binds to beta 1 receptors on SA nodal cells epinephrine increases the heart rate by increasing the slope of slow daistolic depolaristion of cells in the SA node .It also activates latent pacemaker in A-V node and Purkinje fibers.

3) Acetylcholine causes bradycardia when atropine is given followed by Acetylcholine by as atropine is the anticholinergic drug blocks inhibitory effects of parasympathetic neurotransmitter acetylcholine on heart rate leading to tachycardia and improves Atrioventricular conduction by blocking muscuranic effects.

4) Epinephrine mimics the effects of sympathetic nervous system which is branch of autonomic nervous system.

5) Acetylcholine effect on Cardiac muscle.

Ach neurotransmitter released by PNS binds to musuarnic receptors just receptors in the heart it hyperpolarises the SA nodal cells and decreases the rate of daistolic depolaristion this results in reduction in heart rate bradycardia.

Acetylcholine effect on skeletal muscle

The Acetylcholine binds to acetylcholine receptorsbthatbis nicotinic receptors on the skeletal muscle fibers,it opens ligand gated sodium channels in the cell.Sodium ions then enter the muscle cell, stimulating muscle contraction.