Question

9.         Discuss the mechanism(s) by which heart rate and strength of contraction are impacted by sympathetic activation (6 pts)?

10. Discuss the reflex that regulates changes in blood pressure through the activation of baroreceptors (8 pts).

12.       Compare and contrast action potentials in myocardial cells and P cells with respect to mechanism and function (12 points).

Answer 1

9.The sympathetic nerve activation releases the hormones catecholamines-epinephrines and norepinephrin at neuromuscular junction of cardiac nerves.Norepinephrin minimizes the repolarization period and accelerates the depolarization and contraction.Further it accerleate the heart rate and mycocardial contractility.

10. Baroreceptor are located at the carotid sinus and aortic arch and act as a mechanoreceptor.It sense the changes in tension of the arterial wall.Once the blood pressure increases, the coupling of sympathetic nerve inhibition and parasympathetic activation baroflex increases the blood pressure reduction.The parasympathetic activation leads to relex bradycardia in order to minimise the blood pressure in turn sympathetic inhibition leads to decrease in peripheral resistance.

11. Action potential in myocardial cells - These are slow and brief action potentials and produces in AV and SA nodes.The action potential produced by L type calcium channels.These cells depolarize and move towards threshold to generate action potential.

Action potential in P cells - These action potentials are produced in working cells and Purkinje cells.They contain long and fast action potential.It lacks spontaneous depolarization to threshold in order to produce action potential.The action potential in P cells initiated by large sodium current produced by opening of sodium voltage gated channel.