The activity of the heart depends on intrinsic properties of cardiac muscle and on neural factors. Thus, a. vagus nerve stimulation of the heart reduces heart rate, b. sympathetic nerve stimulation of the heart decreases time available for ventricular filling, c. sympathetic stimulation of the heart increases its force of contraction, d. all of the above.

Video transcript

Hi, everybody. Let's look at our next question. It says which of the following is not an intrinsic control of arteriolar smooth muscle in the systemic circulation. A metabolic controls. B myogenic controls, C neural and hormonal controls or D both A and B. So let's walk through what our question is asking us. So it's talking about arterial or smooth muscle and the systemic circulation. So this would refer to the fact that the walls of the arteries can expand or say dilate or contract and this will affect how much blood can flow through. So it can decrease or increase blood flow. And we're talking about two types of control over this contraction and dilation. Extrinsic and intrinsic. So we can think of exterior and interior. Intrinsic control would be control by the specific tissue or area that's being controlled. So basically auto regulation, whereas extrinsic control would be mechanisms that act from outside on an organ or tissue. So, extrinsic versus intrinsic. So our question says which of the following is not an intrinsic control. So it's looking for extrinsic control. So choice A gives us metabolic control. This would be in response to the oxygen needs of different tissues. And when there's greater demand for oxygen, greater amounts of oxygen being used up, the arterial walls can expand to allow more blood flow to an area that needs it. Well, this would be intrinsic control. The arterial walls themselves are responding to this. So choice A is not going to be our answer. And choice B is myogenic controls. Myogenic controls would be how the arteries respond. So response to changes in blood pressure. So as blood pressure changes, that arterial walls respond by expanding or contracting to keep blood flow constant. Well, this is also an intrinsic control and therefore not our answer because it's the walls themselves responding to these changes in blood pressure. Well, A and B neither our answers. So of course, choice D which is both A and B will not be our answer. And we've arrived by elimination at choice C neural and hormonal controls. And these are indeed extrinsic factors. So it involves commands coming from the nervous system or from hormones. So they act from outside the arterial walls themselves. So the answer choice that is not an intrinsic control of arterial or smooth muscle and the systemic circulation. Choice C neural and hormonal controls. See you in the next video.