Effects produced by the parasympathetic branch of the ANS include...

Question

Effects produced by the parasympathetic branch of the ANS include (a) dilation of the pupils, (b) increased secretion by digestive glands, (c) dilation of respiratory passages, (d) increased heart rate, (e) increased breakdown of glycogen by the liver.

Accepted Answer

Hi everybody. Our next question says the pupillary reflex which leads to the dilation of the pupils in darkness is mediated by a sympathetic nervous system. B, parasympathetic nervous system, C central nervous system or D autonomic nervous system. Well, this is a seemingly simple looking question which actually is a little bit complicated to think about. Um we know that dilation of the pupils is controlled by muscle movement. There are muscles that dilate and contract the pupils. So usually when we think of muscle movement, we think of the semantic nervous system and there are movements of the eye that are controlled by the somatic system that would be voluntary movements, like raising your eyelids or moving your eyeballs back and forth to track movement or look in a certain direction. But in the case of something like contraction and dilation of pupils, this is autonomic control. Since it's not necessarily a voluntary action, you want your pupils to expand, dilate and contract in response to light or darkness. As our question is saying here, uh and pupil dilation and contraction is also part of arousal and wakefulness. So that kind of falls under autonomic control. So that's where we start with a sort of complicated issue. So that might make us want to choose choice d autonomic nervous system. However, we need to remember that the autonomic nervous system has those two divisions. And as you can see, we have choice A and B sympathetic and parasympathetic. So we can go ahead and eliminate choice d autonomic nervous nervous system. Because even though this is the overarching control of this reflex, it's not as specific an answer. We also want to look at choice c the central nervous system, this reflex does involve the central nervous system because the signals go to the hypothalamus of the brain and then get sent out to the motor nerves. But you wouldn't say that the central nervous system directly mediates this response. It's sort of the coordinator, but it receives signals from and sends messages to the peripheral nervous system. So that's why CNS isn't correct because it's a mediator or excuse me, I should say it's a coordinator, not a direct mediator. So now we just have to remember, are we looking at the sympathetic or parasympathetic nervous system? Well, even this is a little more complicated than it seems because the dilation reflex or the pupil darkness reflex or pupillary dark reflex is controlled differently from the pupillary light reflex. So the pupillary dark reflex is controlled by this sympathetic nervous system. The pup pupillary light reflex where the pupil contracts in response to light. So we'll put contraction, under light reflex and dilation, under dark reflex, the light reflex is controlled by the parasympathetic nervous system. So that's even, you know, a rather complicated thing if we think this through logically, though it does make sense because dilation of the pupils in response to darkness, but also it's a response to stimuli that might be dangerous. So loud noises can make the pupils dilate as can sensations like a pinching sensation. And if we recall that the sympathetic nervous system is fight or flight dilating, the pupils allows the ice to take in more light and more visual stimuli. So it would be an appropriate response in a dangerous or stressful situation. Because while we often think about the skeletal muscles needing to be ready to run or fight, the sympathetic nervous system also involves just activating a general heightened awareness of the surroundings and pupillary dilation is a part of that. So our answer here will be choice a the sympathetic nervous system and we can rule out choice b the parasympathetic nervous system as that controls the contraction of the pupils in response to light. So once again, the pupillary reflex or specifically the pupillary dark reflex, which leads to the dilation of pupils in the darkness is mediated by choice. A the sympathetic nervous system. See you in the next video.

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Effects produced by the parasympathetic branch of the ANS include (a) dilation of the pupils, (b) increased secretion by digestive glands, (c) dilation of respiratory passages, (d) increased heart rate, (e) increased breakdown of glycogen by the liver.

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