Question

Contractility in the ventricle can be increased through:

A. Negative ionotropic influences such as parasympathetic stimulation of Ca2+ influx

B. Positive ionotropic influences such as sympathetic stimulation of Ca2+ influx

C. Positive ionotropic influences such as Ach released from the vagus nerve

D. Negative ionotropic influences such as drugs that mimic the effects of NE

E. None of the above

Answer 1

Positive ionotropic effect helps to pump more blood from the ventricle (increased cardiac output) and increase contractility of the ventricular musculature. The net effect of this positive ionotropic influences is the increase in intracellular Ca2+, This increase in stored Ca2+ in the sarcoplasmic reticulum helps to increase the contractility power of the ventricle of the heart. Sympathetic activity due to positive ionotropic effect also increases, this sympathetic drive enhances more sodium and Calcium ion in the heart muscle that actually enhances the ventricular contractility. So that option B is correct option.

Option A is incorrect because, Negative ionotropic influences decreases the myocardial contractility and cardiac output. this is the condition when the cardiac failure will happen. and parasympathetic stimulation in heart does not stimulate Ca2+ influx, it actually release acetylcholine neurotransmitter from the nerve terminal that decrease the ventricular contractility.

Option C is incorrect because, Ach (acetylcholine) releases from the vagus nerve terminal after vagal stimulation by parasympathetic nervous system,that decrease the heart activity and slow the ventricular contractility. This parasympathetic action does not occur in positive ionotropic influences.

Option D is incorrect because Drug that mimic NE (Norepinephrine) does not show negative ionotropic effect. This negative ionotropic influences does not increase the ventricular contractility of the heart.

So, Option B is correct.