Your Autonomic Nervous System - The ESSENTIALS 🐧

Summary

This script delves into the autonomic nervous system (ANS), explaining its relationship with the entire nervous system and its control by the midbrain, limbic system, and spinal cord areas. It clarifies the ANS's complexity, involving many neurons and ganglia, and distinguishes between the sympathetic and parasympathetic divisions, highlighting their roles in 'fight, flight, freeze' responses and 'rest and digest' functions, respectively. The script also explains the unique adrenal sympathetic pathway, which releases hormones directly into the bloodstream to enhance the sympathetic response.

Takeaways

• 🧠 The autonomic nervous system (ANS) is a part of the nervous system that includes the sympathetic and parasympathetic divisions and is controlled by the midbrain, including the limbic system, amygdala, hypothalamus, medulla, and pons.
• 🌐 The ANS is connected to the rest of the nervous system, with the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system including sensory and motor pathways.
• 🏃‍♂️ The somatic motor system controls skeletal muscles and is simpler with a single neuron connecting to the muscle, unlike the autonomic motor system.
• 🤔 The ANS can be confusing due to the complexity of neurons and ganglia involved, as well as the vocabulary used to describe its components.
• 🔍 Autonomic motor neurons are more complex, with two neurons involved and the presence of ganglia, which are collections of nerve cell bodies outside the CNS.
• 📏 The length of preganglionic and postganglionic neurons depends on the location of the ganglia in the body; if the ganglion is close to the target, the preganglionic neuron is long and the postganglionic is short, and vice versa.
• 🛌 The parasympathetic division, known as the 'rest and digest' system, originates from the midbrain, medulla, pons, and sacral region of the spinal cord, with ganglia located near the effector organs.
• 💨 The sympathetic division, associated with the 'fight, flight, or freeze' response, originates from the thoracic and lumbar regions of the spinal cord, with paravertebral ganglia running along the spinal cord.
• 🔴🔵 The terms 'sympathetic' and 'parasympathetic' reflect the historical development of understanding these systems rather than their actual functions.
• 📦 Ganglia in the ANS act as relay stations, integrating and modifying signals, allowing effector organs to work in a coordinated manner, unlike the independent control required by the somatic motor system.
• 🚨 The adrenal sympathetic pathway is unique, with preganglionic fibers synapsing directly onto the adrenal medulla, releasing epinephrine and norepinephrine into the bloodstream to enhance the fight, flight, or freeze response.

Q & A

What is the autonomic nervous system (ANS)?

The autonomic nervous system is a part of the peripheral nervous system that controls involuntary actions such as heartbeat, blood flow, and digestion. It is comprised of two divisions: the sympathetic and parasympathetic systems.

What is the role of the CNS in the context of the ANS?

The CNS, which includes the brain and spinal cord, is the central part of the nervous system that processes sensory input and coordinates motor output. It is connected to the ANS through the motor or efferent pathways that control involuntary functions.

What are the two divisions of the ANS and what do they control?

The two divisions of the ANS are the sympathetic and parasympathetic systems. The sympathetic division is associated with the 'fight, flight, or freeze' response and is active during stress, while the parasympathetic division is known as the 'rest and digest' system, active during rest and non-stressful activities.

What is the difference between somatic motor neurons and autonomic motor neurons?

Somatic motor neurons control skeletal muscles and there is only one neuron in the efferent pathway. Autonomic motor neurons, on the other hand, are part of the ANS and involve a more complex pathway with two neurons and ganglia, which are collections of nerve cell bodies outside the CNS.

What are ganglia and why are they important in the ANS?

Ganglia are collections of nerve cell bodies located outside the CNS. They are important in the ANS because they allow for the integration and modification of signals, enabling the targets to work as a team and respond to the body's needs in a coordinated manner.

What are preganglionic and postganglionic neurons?

Preganglionic neurons are the neurons before the ganglion in the ANS, and postganglionic neurons are the neurons after the ganglion. The terms distinguish the parts of the autonomic pathway based on their location relative to the ganglia.

Why is the terminology of the sympathetic and parasympathetic divisions considered confusing?

The terminology is confusing because the names 'sympathetic' and 'parasympathetic' reflect the historical development of the knowledge rather than the actual functions of the divisions. 'Sympathetic' comes from the Greek meaning 'together with feeling or suffering,' and 'parasympathetic' means 'beside or near the sympathetic nerves.'

What is the adrenal sympathetic pathway and how does it differ from the other ANS pathways?

The adrenal sympathetic pathway is a special part of the sympathetic division where preganglionic fibers synapse onto cells in the adrenal medulla, causing the release of epinephrine and norepinephrine directly into the bloodstream. This pathway does not involve a postganglionic neuron or a ganglion and is part of the body's fight, flight, or freeze response.

How do the locations of the ganglia affect the length of preganglionic and postganglionic neurons?

If the ganglion is close to the target organ, the preganglionic neuron is long, and the postganglionic neuron is short. Conversely, if the ganglion is close to the spinal cord, the preganglionic neuron is short, and the postganglionic neuron is long.

What are the primary effects of the parasympathetic division?

The primary effects of the parasympathetic division relate to activities when the body is at rest or during normal, non-stressful activities, such as digestion, salivation, and lacrimation (tear production).

What are the primary effects of the sympathetic division?

The primary effects of the sympathetic division are associated with the body's stress response, including increased heart rate, blood pressure, and pupil dilation, which are crucial for survival during fight, flight, or freeze situations.

Outlines

00:00

🧠 Autonomic Nervous System Overview

This paragraph introduces the autonomic nervous system (ANS) and its relationship to the entire nervous system. It explains the structure of neurons and the concept of neurocrines, including neurotransmitters. The video aims to clarify the ANS's role, its control mechanisms, and the confusion surrounding its divisions. The CNS and PNS are outlined, with a focus on the autonomic motor neurons, which are divided into sympathetic and parasympathetic branches. The control centers for the ANS, including the midbrain, limbic system, and specific areas like the amygdala, hypothalamus, medulla, and pons, are identified. The complexity of the ANS is attributed to the numerous neurons and ganglia involved, with ganglia being collections of nerve cell bodies outside the CNS.

05:03

🛡️ Sympathetic and Parasympathetic Divisions

The second paragraph delves into the specifics of the sympathetic and parasympathetic divisions of the ANS. The sympathetic division, associated with the fight, flight, or freeze response, originates from the thoracic and lumbar regions of the spinal cord and has paravertebral ganglia, resulting in short preganglionic and long postganglionic neurons. In contrast, the parasympathetic division, known as the rest and digest system, originates from the midbrain, medulla, pons, and sacral spinal cord, with ganglia located near effector organs, leading to long preganglionic and short postganglionic neurons. The vocabulary and historical development of these terms are highlighted as potential sources of confusion. The paragraph also explains the function of ganglia as relay stations for integrating and modifying signals, allowing for coordinated responses to stress. Lastly, the adrenal sympathetic pathway is introduced, where preganglionic fibers directly synapse with the adrenal medulla to release hormones like epinephrine and norepinephrine into the bloodstream, enhancing the sympathetic response.

Keywords

💡Autonomic Nervous System (ANS)

The Autonomic Nervous System is a part of the peripheral nervous system that controls involuntary actions, such as heartbeat and respiration. It is central to the video's theme as it discusses the structure and function of the ANS, its relationship with the central nervous system, and how it is controlled by the midbrain and other areas.

💡Neurocrine

Neurocrine refers to molecules like neurotransmitters that are released from neurons and have an effect on other cells. In the context of the video, neurocrines are part of the communication process within the ANS, highlighting the chemical messengers that facilitate the system's responses.

💡Sympathetic and Parasympathetic Divisions

These are the two main divisions of the ANS. The sympathetic division is associated with the 'fight or flight' response, while the parasympathetic division is linked to 'rest and digest' activities. The video explains their contrasting roles and how they are controlled and function within the body.

💡Ganglion

A ganglion is a collection of nerve cell bodies located outside the central nervous system. The video describes ganglia as integral to the ANS, serving as relay stations for signals, allowing for coordinated responses among various targets in the body.

💡Preganglionic and Postganglionic Neurons

These terms refer to the neurons before and after the ganglion in the ANS. The video explains the significance of their positions, with preganglionic neurons being long or short depending on the ganglion's location, and postganglionic neurons being short or long accordingly.

💡Midbrain

The midbrain is a part of the brain involved in controlling the ANS, particularly through the limbic system and other areas like the amygdala, hypothalamus, medulla, and pons. The video emphasizes its role in regulating the ANS's responses to various stimuli.

💡Somatic Motor Division

The somatic motor division controls skeletal muscles and is used as a point of comparison in the video to the autonomic motor neurons. It illustrates the difference in complexity and control between voluntary muscle actions and the involuntary responses of the ANS.

💡Fight, Flight, or Freeze

This term describes the body's stress response, which is primarily managed by the sympathetic division of the ANS. The video discusses how this response is activated in situations of danger or stress, highlighting the importance of the sympathetic division in survival.

💡Rest and Digest

This phrase is used to describe the primary function of the parasympathetic division, which is to maintain body functions during non-stressful, resting states. The video contrasts this with the 'fight, flight, or freeze' response of the sympathetic division.

💡Adrenal Sympathetic Pathway

This is a unique pathway in the ANS where preganglionic fibers synapse directly onto the adrenal medulla, causing the release of epinephrine and norepinephrine into the bloodstream. The video explains how this pathway enhances the sympathetic division's effects, playing a crucial role in the body's stress response.

Highlights

Introduction to the autonomic nervous system (ANS) and its relationship with the entire nervous system.

Explanation of the CNS, including the brain and spinal cord, and the peripheral nervous system with sensory and motor pathways.

Differentiation between somatic motor neurons controlling skeletal muscles and autonomic motor neurons.

The autonomic nervous system is composed of the sympathetic and parasympathetic divisions.

Control of the ANS by the midbrain, limbic system, amygdala, hypothalamus, medulla, and pons.

The complexity of the ANS due to the involvement of many neurons and ganglia.

Comparison of somatic motor pathways with one neuron to autonomic motor pathways with two neurons and ganglia.

Definition and role of preganglionic and postganglionic neurons in the ANS.

The anatomical location of ganglia affecting the length of preganglionic and postganglionic neurons.

Historical development of the terms sympathetic and parasympathetic and their current meanings.

The parasympathetic division as the 'rest and digest' system with its origins in the midbrain, medulla, pons, and sacral spinal cord.

The sympathetic division, formerly known as 'fight or flight', now includes 'freeze', with origins in the thoracic and lumbar spinal cord.

The role of ganglia in allowing targets to work as a team and integrate signals in the ANS.

The contrast between the coordinated action of ganglia in the ANS and the individual control in somatic motor pathways.

The adrenal sympathetic pathway, where preganglionic fibers synapse onto adrenal medulla cells releasing epinephrine and norepinephrine.

The enhancement of the sympathetic division effects by epinephrine and norepinephrine released into the blood.

Recommendation for further learning with a video on neurocrines and receptors for the ANS pathways.

Closing remarks and call to action for viewers to engage with the content.

Transcripts

This will be the essentials of your autonomic nervous system.

I am assuming some general knowledge here; that you know the structure

of a neuron, that you're familiar with this term neurocrine, which

includes neurotransmitters as well as some other molecules.

In this video, I want to talk about the relationship of the ANS with respect to

the entire nervous system, like how does it fit, what controls it, why is it so

confusing, and what are the divisions.

What are they and what do they do?

All right, first of all, what's the relationship between the

autonomic division and the rest of the nervous system?

Okay, so here's the nervous system.

We've got the CNS.

That includes the brain and the spinal cord.

Then we have the peripheral nervous system.

We have the sensory or afferent pathways and the motor or efferent pathways.

Sensory or afferent coming into the CNS, motor or efferent going out from the CNS.

Okay, on the motor side we have the somatic motor that refers to neurons

that control skeletal muscles.

Okay, I'm going to use them as a point of comparison for the autonomic motor

neurons okay, because these people are more comfortable and familiar

with, but what we're talking about today are autonomic motor neurons.

The autonomic nervous system, which is comprised of two divisions, the

sympathetic and parasympathetic, and that's what we're going to focus on today.

Next, what controls the ANS?

We're talking about primarily the midbrain, including the limbic

system, especially the amygdala, the hypothalamus, the medulla, and the pons.

Why is it so confusing?

I'm going to say because there are too many neurons involved, and also ganglia.

Students hate ganglia.

Okay, so we're going to compare this to the somatic motor division as promised.

Somatic motor pathways include one somatic motor neuron that

synapses onto skeletal muscle.

You have experience with this.

You can control your skeletal muscles.

There's only one neuron in the efferent pathway, and that just makes sense.

Students get the somatic motor division.

Autonomic motor neurons, as you can see, are a little more complicated.

First of all, there are two instead of one.

And what is this thing, OK?

This is a ganglion, plural ganglia.

And a ganglion is a collection of nerve cell bodies that lie

outside the central nervous system.

And you see them here.

All of these yellow things, these are all ganglia.

These are collections of nerve cell bodies.

What they're for, we will get to in just a little bit.

The ANS is also confusing because the vocabulary itself is confusing.

Let's go back to this.

So we've got to be able to identify these neurons.

We have the neuron before the ganglion and we have a neuron after the ganglion.

Okay.

But we got to be more science- y than that.

So we're going to call this a preganglionic neuron and

a postganglionic neuron.

Now there are two main options here, depending upon where

the ganglion is in the body.

Option one is if the ganglion is close to the target.

In that case, the preganglionic neuron is long and the

postganglionic neuron is short.

However, we have other ganglia that are close to the spinal cord, in which

case, The preganglionic neuron is short, but the postganglionic neuron is long.

It just depends on where the ganglia are actually located.

So let's get into the divisions because this will make more sense.

We have the parasympathetic division and the sympathetic division.

The vocabulary is confusing as well.

Sympathetic comes from the Greek, syn meaning together and pathos

meaning feeling or suffering.

So early anatomists like Galen, oh hi, believed that nerves allowed

organs to work in sympathy or in coordination with each other.

Now, later, more nerves were discovered that seemed to work

in parallel or alongside the already named sympathetic nerves.

So they were called parasympathetic, which literally means beside

or near the sympathetic nerves.

These names really reflect the historical development of this knowledge rather

than, like, what they actually do.

So understandably, the terms are confusing.

So here you see the sympathetic nerves in red and the parasympathetic nerves

in blue.

What do the divisions do?

Let's talk about the parasympathetic division first.

This is known as the rest and digest system.

The preganglionic neurons here originate in the midbrain,

the medulla, and the pons.

As well as the sacral region of the spinal cord.

So you might see this referred to as the craniosacral division.

The ganglia are located either in or near the effector organs.

So that means the preganglionic neurons are going to have to

be long and the postganglionic neurons are going to be short.

So we can symbolize it this way.

The primary effects of the parasympathetic division include all kinds of things

that relate to what the body does when you are at rest or during

normal, non stressful activities.

The sympathetic division used to be known as the fight or flight response.

Now we have added "freeze".

So fight, flight, or freeze.

Preganglionic neurons here originate in the thoracic and the

lumbar regions of the spinal cord.

So you might see this referred to as the thoracolumbar division.

The ganglia are paravertebral.

So break that down.

Para means beside or near.

So think about words like parallel or paramedic.

So these ganglia, as you see here, run right along the spinal cord.

So what does that mean?

The preganglionic axons are short and the postganglionic axons will be long.

So sympathetic pathways will look like this.

The primary effects include all the things that happen to your

body when you are under stress.

So think about things that are extremely important for your survival.

That's what the sympathetic division is about.

So we've got the parasympathetic.

and the sympathetic.

But what are the ganglia for?

I promised you this.

To answer that, we want to think about how the targets work.

Ganglia allow for targets to work as a team.

They're more like relay stations where signals can be integrated and modified.

Some people think about it like a postal distribution center.

Let's think about fear.

Okay, so I looked up what most students are afraid of.

Top fears.

Ready?

So here they are.

Let's take the top two, fear of failure and fear of public speaking.

Think about what happens to your body when you're placed in a situation like, you

know, taking a test or giving a speech.

What happens to you, and more importantly, when do those things happen?

And hopefully you get that when you're in a fight, flight, or freeze

situation, Everything mobilizes together.

So if you're walking across the street, you turn and you see a bus,

your body goes into survival mode.

And all of the targets get that information instantaneously.

Let's compare that with somatic motor pathways.

The somatic motor division, which, remember, controls skeletal muscle, you do

not want your effectors to work as a team.

Think about fine motor control.

If you're playing a harp or you're doing a surgery, you want to be able to control

those individual muscles of your hand.

This is not a team effort.

So ganglia here would make no sense.

So again, ganglia allow targets to act in a coordinated way, something

that the somatic motor division

would not want.

Okay, there's one more pathway.

It's the adrenal sympathetic pathway.

So the adrenal glands, by the way, that just means near the kidneys, they're

strange glands because the cortex, the outer part, is a proper gland,

but the medulla, the meaty inside part, that's modified nervous tissue.

So preganglionic fibers synapse onto cells In the adrenal medulla, which then release

neurocrines into the blood, most of it is epinephrine, some of it is norepinephrine.

Epinephrine used to be called adrenaline, and norepinephrine

used to be called noradrenaline.

You will notice that these effects basically enhance the sympathetic

division that we already talked about.

So it's part of that fight, flight, or freeze system.

You see that there is no post ganglionic neuron.

There is no ganglion here.

Instead, we have a preganglionic neuron that synapses into the adrenal

medulla, which releases epinephrine and norepinephrine into the blood,

and those will bind to receptors on targets throughout the body.

How about quizzing yourself?

What do you remember about the parasympathetic division, the

sympathetic division, and the adrenal sympathetic division?

If you're still here and you want more, I'm going to recommend this

video, which actually goes into all of the neurocrines and all of the

receptors for all of these pathways.

As always, I hope that was helpful.

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