Parasympathetic Nervous System - Online Tutor, Practice Problems & Exam Prep

The parasympathetic nervous system, often referred to as the craniosacral division, promotes rest and digest functions, conserving energy through decreased heart rate and bronchiole constriction. It enhances gastrointestinal activity, facilitating digestion via increased peristalsis and secretion. Urination is encouraged through bladder muscle contraction and sphincter relaxation. Additionally, pupil constriction optimizes near vision. The vagus nerve, crucial for parasympathetic innervation, synapses close to target organs, ensuring efficient communication between preganglionic and postganglionic fibers, which are long and short, respectively.

Function of the Parasympathetic Nervous System

In this video, we're going to be talking about the function of our parasympathetic nervous system. So, just like we did for our sympathetic, I'm going to go over some of the physiological effects and talk about how it's going to be promoting those rest and digest functions. As a reminder, our parasympathetic system is going to be promoting restoration and the conservation of energy. It's going to be performing a lot of those kind of homeostatic restful functions. And some of the main examples of parasympathetic effects are going to include decreases in heart rate as well as a constriction of the bronchioles in the lungs, and both of those are going to conserve energy for our body.

In our gastrointestinal tract, things are going to get very exciting. We're going to start to see increased movement, increased secretion, as well as a relaxation of these sphincters, and that is going to promote food passing through that tract. So a lot of digestion happening there. In our bladder, what we're going to see is a contraction of the smooth muscle as well as a relaxation of the sphincter and combined those are going to promote urination. So, you know, if we're in our fight or flight situation, urination is not going to be a priority so that is why that is being handled by our parasympathetic system.

And then, finally, we're going to see a constriction of the pupil. And the purpose of that is, without getting into any eye anatomy in this lecture, when your pupil is constricted it actually creates a condition in your eye where it optimizes up-close vision. So here, you know, we're relaxed, we're calm, we don't have to be scanning the environment for danger or anything like that. So it's going to be promoting vision of objects that are close to you. This is not an exhaustive list, but these are kind of the main functions of the parasympathetic system and I will see you guys in the next one. Bye bye.

Parasympathetic Nervous System Example 1

Okay. So here we have a list of autonomic effects and we're going to be filling in for each one if it is the result of the sympathetic or parasympathetic division. Alright. So, a is increases activity to the gastrointestinal tract and that is going to be parasympathetic. Right? Our rest and digest system. So we'll put a p there. Alright. So b is vasodilation in skeletal muscles. So that is allowing more blood to get to our muscles, giving them more oxygen, more glucose, and that is a sympathetic response kind of gearing up our body for a potential fight or flight situation. And then c dilates pupils. What dilating the pupils does is allow more light to get into them and allows you to see better, essentially, which is a sympathetic response. Again, a nice evolutionary mechanism to help us scan the environment for threat. For d, we have constricting bronchioles and that is going to be parasympathetic. Right? With our parasympathetic, we're not gearing up to potentially, you know, run somewhere or fight someone. We don't have to be taking in a lot of oxygen and taking deep, deep breaths. Right? So that is a parasympathetic and if the parasympathetic is constricting them, we're going to have that opposite effect from our sympathetic dilating them. So, e is going to be a sympathetic effect. And then, f, decreased heart rate, that is going to be parasympathetic. Right? So we're nice, we're calm, we're relaxed, we're in a state of kind of relaxation and digestion. Right? So we don't need to have a really fast heart rate for that. Alright. So there you have it and I will see you guys in the next one. Bye bye.

Structure of the Parasympathetic Nervous System

Okay. So, let's get into the structure of our parasympathetic nervous system. Here, fibers are going to be arising from the brainstem and the sacral region. This is sometimes also called our craniosacral division. Arguably, the most important one of these nerves is our vagus nerve or cranial nerve 10. This nerve provides about 90% of parasympathetic innervation, so it is very important. They're all doing a great job. They're all important, but this is, like, the MVP.

And then what we find in this division is that many preganglionic fibers actually synapse in ganglia within their target organs. So they're actually synapsing within the effector organ rather than in ganglia outside of it. Sometimes they do synapse in external ganglia, and in this division, these are called terminal ganglia. These are ganglia where preganglionic fibers can synapse with postganglionic fibers. You can think of these as being functionally very similar to collateral ganglia. They serve the exact same purpose. It's a location where that synapse can take place. The difference is these terminal ganglia are very close to their target organs. So those collateral ganglia are certainly closer compared to that sympathetic trunk. Right? But these terminal ganglia are extremely close. The way I always think of this is I think of these terminal ganglia as being like that terminal stop or that final stop right before the ultimate destination of that organ because they're so close to each other.

What we find here is that the preganglionic fibers are of course very long because they're extending all the way from the spinal cord or the brainstem all the way to the effector organs. And then our postganglionic fibers tend to be very short, and you can see that here in our image. You can see our purple fibers are all very long and our green fibers are all very short. Again, those synapses are going to be taking place either within the target organs or in terminal ganglia very close to them. And you can see that our fibers are arising from the cranial nerves up here as well as the sacral nerves down here.

Alright? So that's the structure of our parasympathetic nervous system and I will see you guys in our next video. Bye bye.

Parasympathetic Nervous System Example 2

Okay. So this one reads, after getting in a car accident, Gordon's sacral nerves are severely damaged. Which of the following bodily functions do you think would be affected by this injury? So remember, the sacral nerves are going to be stemming from the sacrum way at the bottom of our spinal cord and they're going to be innervating some of the anatomically lowest organs in our body. So our genitals, our bladder, and portions of our large intestine. So looking at the choices here, it looks like c would fit that best. There's a good chance that Gordon's urinary bladder function would be impacted by this accident. Looking at a and b, both saliva production and blood pressure would be innervated by cranial nerves in our parasympathetic division. And looking at d, adrenaline production is something that we see in our sympathetic division. It is actually not something that we see in a parasympathetic division at all. So our answer here is going to be c.

In the parasympathetic nervous system, preganglionic fibers are ________ and postganglionic fibers are __________.

• A. Short; long.
• B. Short; short.
• C. Long; short.
• D. Long; long.

Here’s what students ask on this topic:

What are the main functions of the parasympathetic nervous system?

The parasympathetic nervous system primarily promotes rest and digest functions, conserving energy. Key functions include decreasing heart rate and constricting bronchioles to conserve energy. It enhances gastrointestinal activity by increasing peristalsis and secretion, facilitating digestion. In the bladder, it promotes urination through smooth muscle contraction and sphincter relaxation. Additionally, it constricts the pupil to optimize near vision, allowing for better focus on close objects. These actions collectively help maintain homeostasis and energy conservation during restful states.

How does the parasympathetic nervous system affect the gastrointestinal tract?

The parasympathetic nervous system significantly enhances gastrointestinal activity. It increases peristalsis, which is the movement of the digestive tract that propels food forward. It also boosts the secretion of digestive enzymes and fluids, aiding in the breakdown and absorption of nutrients. Additionally, the relaxation of sphincters in the gastrointestinal tract allows for the smooth passage of food and waste. These actions collectively facilitate efficient digestion and nutrient absorption, promoting overall digestive health.

What role does the vagus nerve play in the parasympathetic nervous system?

The vagus nerve, also known as cranial nerve 10, is crucial in the parasympathetic nervous system. It provides approximately 90% of parasympathetic innervation to various organs, including the heart, lungs, and digestive tract. The vagus nerve helps decrease heart rate, constrict bronchioles, and enhance gastrointestinal activity. It also plays a role in promoting urination and pupil constriction. By innervating these organs, the vagus nerve ensures efficient communication and coordination of parasympathetic functions, maintaining homeostasis and energy conservation.

What is the structure of the parasympathetic nervous system?

The parasympathetic nervous system, also known as the craniosacral division, consists of fibers arising from the brainstem and sacral spinal cord. Preganglionic fibers are long and extend to target organs, where they synapse with postganglionic fibers in terminal ganglia located very close to or within the target organs. The vagus nerve is a major component, providing extensive parasympathetic innervation. This structure allows for efficient and localized control of parasympathetic functions, promoting rest and digest activities in the body.

How does the parasympathetic nervous system promote urination?

The parasympathetic nervous system promotes urination by causing the contraction of the smooth muscle in the bladder wall and the relaxation of the internal urethral sphincter. This combination of actions facilitates the expulsion of urine from the bladder. During restful states, the parasympathetic system ensures that urination can occur efficiently, as opposed to during fight or flight situations where urination is not a priority. This helps maintain fluid balance and waste elimination in the body.