What’s up, Taim talks med here. In this video  we’re gonna talk about the sympathetic nervous  

system. As you see from this brief diagram, the  sympathetic and the parasympathetic parts of our  

nervous system controls more or less all our  internal organs. Sympathetic being the fight  

or flight response, and parasympathetic  being the rest and digest response. And  

they’re both as you see here a part of the  autonomic nervous system, which again is  

the motor division of our peripheral nervous  system. So, in this video again, we’re going  

detailed into the sympathetic nervous system. And we’re gonna do that by first going through  

the general structures of the sympathetic, or  the autonomic nervous system in general. Just  

some basic concept that you need to know in order  to understand the sympathetic nervous system,  

like the different paravertebral and prevertebral  ganglia, pre and post synaptic neurons,  

which neurotransmitters are released, etc. Then we’re gonna cover the main highway for  

the sympathetic nervous system which is the  sympathetic trunk, or the sympathetic chain  

ganglia. And we’re gonna do that in two segments  by first covering the innervation of the head,  

neck and thorax, then the innervation of the  abdominal and the pelvic viscera. I’ll show  

you the relation between the different plexuses  in our abdominal and thoracic cavity. This is to  

understand the relation between ganglia, organs  and the plexuses. So, after you’ve watched this  

video, and understood everything regarding the  sympathetic nervous system, I’m gonna test you  

with a little quiz. You’re not escaping that one,  it’s a simple quiz to check if you paid attention. 

Let’s go ahead and begin with some terms. Now the  autonomic nervous system – so both the sympathetic  

and parasympathetic nervous system is made up of a  relay that includes two neurons. And when there’s  

a group of nerve cell bodies that are next to each  other within the actual central nervous system,  

the whole thing is called a nucleus, while a  group of nerve cell bodies that are located  

outside of the central nervous system is called  a ganglion. Alrgiht? That is the first thing I  

want you to understand. The second thing I want  you to understand is that this is pons, alright? 

Below it is the Medulla, then we got the spinal  cord. When we talk about the sympathetic ganglia  

in general, we divide those into two groups  based on their location. They can either be  

paravertebral ganglia located laterally to  the spinal cord. And we got some midline  

ganglia located in front of the vertebra  and the aorta, called prevertebral ganglia. 

The paravertebral ganglia run alongside  the spinal cord, and they’re interconnected  

forming a sympathetic chain of ganglia as you see  here. And this chain receives nerve fibers from  

the thoracolumbar area of the spinal cord. Some  sources write C8-L2, some sources say T1 to L2.  

Take it with a grain of salt, but you’re never  wrong when you say thoracolumbar region. Fibers  

may go up, down, synapse with nuclei at the same  level, or they may leave as splanchnic nerves and  

go synapse with the prevertebral ganglia. Alright,  this is the second thing I want you to understand.  

The third thing. The third thing I want you to  know about the autonomic nervous system is that,  

you know they can innervate the eye, the salivary  glands, cardiovascular, respiratory system,  

gastrointestinal system, urinary system and so on,  right? If we group them all together, and add the  

brain and the spinal cord here. The third thing  I want you to know is actually something I said  

earlier but the sympathetic nervous system  originate from the thoracolumbar region,  

giving off pre-ganglionic fibers to either  the paravertebral or prevertebral ganglia,  

to then give off postganglionic  fibers towards the target organ. 

Parasympathetic nervous system has two components.  A cranial part that consists fo cranial nerves,  

primarily the oculomotor, facial, glossopharyngeal  and the vagus nerve. And it has a sacral part. 

Notice what’s common for both the sympathetic  and the parasympathetic nervous system? 

They both have pre and post-ganglionic neurons. The preganglionic and postganglionic neurons  

release different neurotransmitters  and this is really important. 

The preganglionic neurons release  acetylcholine, and that’s why the preganglionic  

neurons are called cholinergic neurons. Acetylcholine binds to nicotinic receptors  

on the cell membrane of postganglionic neuron. Nicotinic receptors are ion channels that open  

when acetylcholine binds to them; and they allow  positive ions like sodium and calcium to cross the  

cell membrane, activating the postganglionic  neurons and initiating an action potential. 

Most postganglionic neurons in the sympathetic  nervous system are called adrenergic neurons  

because they release adrenaline and noradrenaline,  or catecholamines. There are postganglionic  

neurons that release acetylcholine as well in the  sympathetic nervous system to sweat glands for  

example, but postganglionic cholinergic neurons  are primarily related to the parasympathetic  

nervous system, while postganglionic adrenergic  neurons are primarily for the sympathetic  

nervous system, releasing catecholamines. Catecholamines activate the adrenergic  

receptors on the cells of the target organs. And there are two main groups of adrenergic  

receptors, alpha and beta receptors. So, we have alpha1 and alpha2, and beta1,  

beta2 and beta3, which are all g-coupled  receptors. G-proteins gets activated when  

catecolamines bind, which ultimately enable cells  to change, and that’s how the sympathetic nervous  

system creates change at the cellular level. I’ll  try to cover their function as we go through the  

scheme for the sympathetic nervous system. So that was the third thing that I wanted you  

to know. The fourth and last thing I want you to  understand before we dive into the actual scheme,  

is that if we take out a segment of the  spinal cord within the thoracolumbar area,  

you’ll see that the preganglionic fibers come  from the lateral horns of the thoracolumbar  

spinal cord segment. Preganglionic  fibers here are denoted in a dotted line. 

These axons leave the spinal cord through  the anterior nerve roots to reach the  

spinal nerve. Then they enter the white rami  communicantes to reach the sympathetic trunk 

When the preganglionic fibers are within  the sympatheic trunk, 4 things can happen. 

They can descend and synapse in  a lower paravertebral ganglion. 

They can ascend and synapse in  a higher paravertebral ganglion,  

which are usually the cervical parts. They can skip the sympathetic chain completely,  

and go all the way towards the prevertebral  ganglia. Once they pass through the sympathetic  

trunk, they may combine with fibers from other  levels to form something called a splanchnic  

nerve. So it’s the splanchnic nerves that  synapse on a prevertebral ganglia. So they  

can either go to pre-vertebral ganglia,  or directly towards the suprarenal gland. 

The fourth way is that they may synapse directly  in a paravertebral ganglion at the same level. 

Now what happens is, after synapsing inside  the ganglion, postganglionic fibers leave  

through the gray ramus communicans and  they re-enters the same anterior ramus,  

which it initially travelled through, to continue  with the spinal nerve, innervating all structures  

related to the branches of the anterior and  posterior rami of the same spinal nerve. 

These fibers can also combine with fibers  from other levels to form splanchnic nerves,  

which then pass onto the thoracic viscera. Same goes to the pre-vertebral ganglia. The  

postsynaptic fibers pass onto the abdomen and  pelvic viscera via a visceral motor nerve plexus. 

Alright, so that was the 4 major things that  I wanted you to keep in mind. The first thing  

being the difference between the word nuclei  and ganglion. The second thing being where the  

parasympathetic and sympathetic outflow  is located, and the difference between  

a pre-ganglionic and post-ganglionic fiber is.  Third thing being the anatomical relation between  

the sympathetic ganglia. They can either be  paravertebral as in the sympathetic chain,  

or prevertebral ganglia as in the celiac  ganglia, superior mesenteric ganglia,  

and so on. The fourth thing I want you to know  is that prevertebral fibers can do 4 things once  

they enter the sympathetic chain. They can go  down, up, leave towards the prevertebral ganglia,  

or they can synapse with cell bodies within the  ganglia at the same level. Alright. Finally,  

let us now make a scheme for the sympathetic  nervous system. Just remember that this is  

just a scheme, nothing that is topographically  correct. This is just to make it easier for you  

to remember. And keep in mind there are a lot  of variations to these things, two different  

sources may show you to different schemes.  I’ll just try to show you the general one. 

Alright. Now. Let’s cover the sympathetic trunk.  Here again we see Pons, Medulla and the spinal  

cord. Laterally to the spinal cord we see the  paravertebral ganglia, also called the sympathetic  

chain, or the sympathetic trunk. It receives it’s  sympathetic fibers from the thoracolumbar area,  

that’s T1-L2 but again take it with a grain of  salt. Sources also say C8 to L2, L3 region. When  

fibers reach the sympathetic trunk, they may  ascend and synapse with a nuclei located some  

segments above. They may decend. They may synapse  with nuclei at the same level, or they may leave  

the sympathetic trunk as preganglionic fibers. The sympathetic trunk is divided into cervical  

ganglia, which are three pairs usually. Thoracic  gangli, which are 10-11-12 pairs approximately,  

Lumbar ganglia, which are 4-5 pairs,  sacral ganglia, usually 4 pairs,  

and last ones are the coccygeal ganglia, they’re  often fused together to form gnalgion impar,  

which is the unpaired ganglion at the bottom. Now, let’s talk about the sympathetic innervation  

of the head, neck and thorax. Most of which  are innervated by the cervical ganglion. 

Now the cervical ganglion received fibers  from approximately T1-T4, and since it’s  

not adjacent to the thoracolumbar outflow, they  don’t have white rami communicans, only gray rami  

communicans. Kinda makes sense doesn’t it? Now, the cervical ganglia are divided into  

the superior cervical, which is the largest  one of them. Middle cervical ganglion, which  

is extremely small. It may be divided into 2-3  smaller parts, or sometimes it may be even absent.  

And we got the inferior cervical ganglia, which  is often fused with the 1st thoracic ganglion,  

to which then it’s called cervicothoracic  ganglion, or stellate ganglion. It’s a headache  

sometimes studying the sympathetic nervous  system, there are a whole lot of variations.  

But let’s start with the superior cervical first. The gray rami communicans of the superior cervical  

ganglion is going to continue into the rami of the  first 4 cervical nerves, innervating structures  

associated with those nerves, but what’s special  here is that the superior ganglion is going to  

give off the postganglionic internal carotid  nerve, which forms the internal carotid plexus  

around the internal carotid artery. From  here, these postganglionic fibers will go  

through the otic ganglion without synapsing with  it, then further on towards the eye and release  

norepinephrine. Now think about it logically,  in a fight or flight response, what is the eye  

gonna do in order to help in this situation?  Well you wanna be able to see all options that  

you have in a fight or flight situation right? So the pupils are gonna dilate. So norepinephrine  

si gonna act on the dilator pupillae muscle,  causing pupillary dilation, allowed more light  

to come in and give you possibility to see far. The norepinephrine is also gonna act on the  

ciliaris muscle, to flatten the lens,  allowing to focus on far vision aswell,  

this is called accommodation, so norepinephrine  here also helps with accommodation. 

Alright what else do we have from the internal  carotid plexus? We got a deep petrosal nerve,  

which carries sympathetic fibers into the  pterygopalatine ganglion and remember those  

are postganglionic fibers, they’re not  gonna synapse in these ganglia. These  

postganglionic fibers come from the superior  cervical ganglia. The deep petrosal nerve is  

gonna act on two places. It’s gonna act on the  blood vessels supplying the lacrimal glands,  

releasing norepinephrine, decreasing the blood  flow to decrease the lacrimation. Or it can act  

directly on the lacrimal gland decreasing the  lacrimation, decreasing the tear production  

basically. Other places is it can act also on  glands located in the oral cavity, nasal cavity,  

and the sinuses, specifically the maxillary  and sphenoid sinus. It’s gonna do the same  

here. Norepinephrine cause vasoconstriction,  decrease blood flow to these areas. It’s also  

gonna act on the salivary glands within the  oral cavity, to make a thick mucus production. 

So that is the branches associated with the  internal carotid plexus. Since we have an  

internal carotid nerve, we gotta have an external  carotid nerve as well, right? This one is gonna  

form a plexus around the external carotid artery. From here, we gonna have the sympathetic root  

going towards the submandibular ganglion, and  a Sympathetic root towards the otic ganglion,  

both providing sympathetic innervation to  primarily the major salivary glands, which  

are the parotid, submandibular and the sublingual  glands. Decreasing the mucus production there too. 

The superior cervical nerve aso give off  a laryngopharyngeal nerve which join the  

pharyngeal branches from the glossopharyngeal  and vagus nerves and form the pharyngeal  

plexus to basically provide motor, sensory and  sympathetic innervation to the pharyngeal area. 

Alright let’s do the middle cervical one. Remember  the middle cervical ganglion is extremely small  

and varies between the population. After receiving  its preganglionic fibers from the upper thoracic  

segments, it’ll give off gray rami communicans  towards 5th and 6th cervical nerves and supply  

structures associated with them. There are  gonna be fibers from the middle cervical,  

as well as from the inferior cervical  ganglion that’s going towards the thyroid  

and the parathyroid glands. Remember these glands  are under hormonal control from the pituitary  

gland. So sympathetic nerves act as vasomotor  nerves, not secretomotor, basically increasing  

blood flow to help produce more thyroid hormones  for energy during the fight or flight response. 

From the inferior cervical ganglion, we  got gray rami communcans that join the 7th  

cervical nerve and the 1st thoracic  nerve. Again there are variations,  

but the inferior cervical ganglion also give  off a vertebral nerve that travels towards the  

vertebral artery and forms a plexus around it. Other nerves we got here is a Superior cervical  

cardiac nerve, a middle cervical cardiac  nerve, and an inferior cervical cardiac nerve,  

which all go together towards the heart,  to help form the a cardiac plexus. So that  

was everything for the cervical ganglia. Now the thoracic ganglia all have gray rami  

communicans that join the intercostal nerves. But  what they also have are fibers that contribute  

to the sympathetic innervation of the thoracic  viscera. From approximately T2, T3, T4 and T5,  

we got thoracic cardiac nerves, which join in with  the cardiac plexus to help with the sympathetic  

innervation. Now, if you remember from the  anatomy of the heart, the heart has mainly  

two systems. It has a myocardial system, and a  conducting system. The sympathetic nerves are  

gonna act on both of them, what do you think is  gonna happen now? In a fight or flight response? 

The conducting system is composed of nodule  cells, right? The SA node primarily is the  

functional one. They function to regulate the  heart rate, so what’s gonna happen is that the  

sympathetic nervous system is gonna try to  increase the heartrate, so it has a positive  

chronotropic action. And we said the heart has two  main systems, the other one being the myocardium.  

You’re in a fight or flight response, you need  more blood to the body, and so you need the  

cardiac muscles to contract harder to increase  its cardiac output and again increase the blood  

pressure. So that’s the other thing that’s gonna  happen, it’s gonna increase the contractility,  

we call that positive inotropic effect. Alright. Now let’s add some more organs  

here. From around the same region, there’re  gonna be postganglionic fibers that’s’ gonna  

give sympathetic supply to the esophagus  and the bronchi, basically to help form  

the oesophageal plexus and the pulmonary plexus.  You don’t eat while you’re fighting or running,  

usually. So you’d wanna decrease the  peristalsis in the esophagus. That’s  

basically what the sympathetic innervation  here does. The respioratory system is opposite,  

you need oxygen during a fight or flight response,  so it causes bronchodilation, and vasoconstriction  

of the bronchial arteries to decrease the blood  flow and decrease the secretion of glands to help  

open up the airways as much as possible. So that was mainly what I wanted to talk  

about when it comes to the innervation of the  head neck and thorax. Let’s do the sympathetic  

innervation of the abdominal and pelvic viscera. There are two main things here that you need to  

remember. The first thing is that all nerves that  exit and supply the organs are called splanchnic  

nerves. Remember those are pre-ganglionic fibers.  They don’t synapse with the paravertebral ganglia  

at all. What they do, is that they exit and travel  towards the pre-vertebral ganglia. This is so  

important that you understand this concept. Here  you see a section of the abdominal aorta along  

with some plexuses aswell. The pre-vertebral  ganglions we have are the celiac ganglia,  

superior mesenteric ganglia, aorticorenal ganglia,  and the inferior mesenteric ganglia. These ganglia  

have postganglionic fibers that travel through  their plexuses to innervate specific organs. 

Again before we continue, there are  a whole lot of variations when it  

comes to the sympathetic outflow. Different  sources may give you different information,  

and to be fair they are all true. The reason  is many of these ganglia are interconnected,  

but let’s go through a very basic scheme. From approximately T5 to T9, we got preganglionic  

fibers called the greater splanchnic nerves,  that carry their fibers to the celiac ganglia.  

After synapsing, the celiac ganglia give off  postganglionic fibres that travel along the plexus  

on the arterial branches from the celiac trunk,  and they mainly provide sympathetic innervation  

to the upper organs here. So it goes to the liver  to promote glycogenolysis, we’re in a flight or  

flight situation so we need sugar. We’re breaking  down glycogen into glucose. Fibers will also go  

to the stomach and upper part of the duodenum  to inhibit peristalsis, and also increase the  

contraction of the pyloric sphincter. We really  don’t need our GI tract to be active at this  

moment, so the bile pathway is also inhibited.  The pancreas is also innervated here to basically  

help keep our blood sugar high, it’s going to  increase the glucagon and decrease the insulin  

production. Fibers can also go to the spleen. Now the spleen is ideally positioned within  

the circulatory system as a blood filter  to detect, respond to, and protect against  

blood-borne antigens. So it’s packed with  blood and lympocytes. In the spleen we got  

a non-lymphoid red pulp and a lymphoid white  pulp, and between them is a marginal zone,  

a transitional site from circulation to peripheral  lymphoid tissues. One important function of the  

marginal zone is to trap particulates and  initiate innate responses against them,  

or to initiate immune tolerance. The sympathetic  nerves here theoretically help regulate the  

immune activities within this system through  norepinephrine. I’m not sure to what extent it’s  

completely relevant to the overall sympathetic  response, but I’ll put my sources down in the  

description if you wanna read a bit more about it. Now. The greater splanchnic nerve can have a  

branch that comes off here and goes to the adrenal  medulla. What does that mean? That means that the  

adrenal medulla receives pre-ganglionic fibers  directly, and so these fibers go directly towards  

the chromaffin cells in the adrenal medulla, we  call these an ‘’intramural ganglia’’. And when  

the chromaffin cells are stimulated, it’s gonna  release norepinephrine and epinephrine directly  

into the bloodstream to have a widespread  strong effect on the whole body. Alright. 

From T10 and T11, we got the lesser splanchnic  nerve that primarily go to the superior mesenteric  

ganglion, which supplies things like the  ascending colon, cecum, the proximal 2/3  

of the transverse colon. The small intestine  and the distal duodenum. All to inhibit the GI  

system, again. Decrease peristalsis, decrease  absorption by constricting the blood vessels,  

and decreasing the secretion process. Then from T11, we got the least splanchnic  

nerve which may go to the aorticorenal ganglion.  Again there are lots of variations. Fibers from  

the lesser splanchnic nerve may go to the  aorticorenal ganglion. The least splanchnic  

nerve may go directly to the renal plexus.  Different sources might tell to different things,  

just keep those things in mind. But essentially  what’s important is that postganglionic fibers  

are gonna innervate the kidneys. Now what do  you want the kidneys to do in a fight or flight  

response? You don’t really wanna pee. So you cause  vasoconstriction of the blood flow to decrease  

the urine production within the kidneys. And,  remember we got a RAAS system, a renin angiotensin  

aldosterone system. So sympathetic response  help produce more renin from the kidneys to help  

increase the blood pressure. Fibers also go to the  ureter to decrease the peristalsis of the ureters. 

From the lumbar region, we got the lubar  splanchnic nerves going towards the  

inferior mesenteric ganglion. The inferior  mesenteric ganglion is the most inferior  

of the prevertebral sympathetic ganglia in the  abdomen. It’s a small ganglion and sometimes it  

may just be a loose collection of cells rather  than a defined ganglion. So some sources don’t  

even consider it as a ganglion, you might  find some sources write that preganglionic  

fibers synapse with cells within the plexuses  of this region, wether that may be the inferior  

mesenteric plexus or the intermesenteric  plexus. But the overall postganglionic  

supply is the same. And that is highlighted  here. Basically supplying the rest of the GI  

tract which is the descending colon, sigmoid,  the distal transverse colon and the rectum. 

Postganglionic fibers also go towards the smooth  muscles within the walls of the urinary bladder.  

Do you wanna urinate when you’re in a flight  or fight response? No. So it’s gonna decrease  

the contraction of the urinary bladder. And it’s  going to increase the constriction of the internal  

urethral sphincter to help keep the urine in. Then we got the genitals. So ovaries, uterus,  

and so on for the female. For male it’s  the penis, scrotum and so on. In male,  

the sympathetic response is gonna primarily  help with ejaculation. For female it will  

act on the uterus to primarily cause uterine  contractions. Not to go in too much detail. 

Lastly we have the sacral splanchnic nerve,  which may contribute to the innervation of  

organs around the inferior hypogastric plexus,  mainly the gonads. Remember I keep telling you  

this that there are a lot of variations when it  comes to this system, and different ganglia and  

fibers are interconnected between each other. The  last thing I wanna mention here is, something I  

haven’t mention here. But you see all of those  nerves in between the ganglia? Those are all  

the plexuses in the abdominal region that contain  autonomic nerves in general, so both sympathetic  

nerves and also parasympathetic fibers through the  vagus nerve. So for example, the celiac ganglia,  

how does it reach its target organs? Through  the celiac plexus. Which may be connected to  

the superior mesenteric ganglia as well. There is the superior mesenteric plexus,  

the inferior mesenteric plexus. In the pelvis  we have the superior hypogastric plexus and  

the inferior hypogastric plexus. We got the  intermesenteric plexus aswell. They contain  

cell bodies that act as postganglionic fibers.  And when these cell bodies are clustered,  

that is when we get those prevertebral ganglia.  And remember I told you the inferior mesenteric  

ganglion is sometimes scattered so much it’s  not even considered a ganglion. So some sources  

might write that fibers synapse with cells within  the inferior mesenteric plexus for example. But  

overall this is how the plexuses are arranged in  the abdominal and pelvic cavity. In the thorax you  

know you may have the pulmonary plexus, cardiac  plexuses, and also the esophageal plexuses. There  

are some other plexuses here aswell. But overall  that was mainly all I had for the sympathetic  

nervous system. I hope it made sense! Now, comes the fun part. Remember I  

told you that we got some important preganglionic  nerves coming from the thoracic lumbar and sacral  

region going towards the prevertebral ganglia?  What’s the name of those preganglionic fibers? 

10 points if you got that one correct. What about  here? What’s the 4 main branches that is given  

off from the superior cervical ganglion? And I’ll  reveal the answer now. Got those correct aswell?  

In that case you’ve grasped the most important  things that you need to know when it comes to  

the anatomy of the sympathetic outflow The next video is going to be about  

the parasympathetic nervous system. Thank you so much for watching another  

one of my videos. If you enjoyed, learned  something from it, please remember to like,  

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