Activity 39

Summary

In this detailed exploration, viewers dive into the various protective mechanisms of the brain. The video begins with a recap of past topics like the cranium and glial cells, specifically astrocytes, microglia, and the blood-brain barrier. It then transitions to new material on the meninges and cerebrospinal fluid (CSF), explaining their roles and differences between the protection of the brain and spinal cord. Key highlights include the dura mater's anatomy, ventricle system, CSF production and circulation, and the critical blood supply network. The importance of these protective measures is underscored with discussions on conditions like meningitis and hydrocephalus, highlighting potential complications. A comprehensive view of the brain’s protective systems is achieved through both discussion and supportive animations.

Highlights

• Explore the unique pairing of structural and fluid protection for the brain 🧠.
• Learn about the meninges and how they differ between the brain and spinal cord 🕸️.
• Discover the multi-role cerebrospinal fluid plays in brain health and protection 🌊.
• Dive into the ventricle system and learn how CSF circulates around the brain 🌀.
• Understand the vital role of blood supply and the protective Circle of Willis 🔄.
• Identify the potential dangers of conditions like meningitis and hydrocephalus 🚨.
• See how the blood-brain barrier helps protect against infections like bacterial meningitis 🛡️.

Key Takeaways

• The brain's protection involves combined structural and fluid-based systems like the cranium and cerebrospinal fluid 🧠💦.
• Cerebrospinal fluid serves as a cushion, providing chemical balance and buoyancy to the brain 🧬🌊.
• Blood supply is essential, with arteries like the internal carotid and vertebral playing critical roles in life support 🔴🩸.
• Conditions like meningitis and hydrocephalus highlight the importance of these protective systems 🚨.
• The Circle of Willis acts as a backup to maintain blood flow, but can be prone to dangerous aneurysms 🔄⚠️.

Overview

The episode starts by refreshing our memory on previous topics, tying them seamlessly with new learnings about the brain. The focus shifts smoothly from the structure of the cranium to deeper layers, detailing the brain's sophisticated protective measures. We revisit the meninges, comparing their protective features in both the brain and spinal cord, and learn about the central role of cerebrospinal fluid (CSF) in brain protection.

Key concepts around the enduring necessity of a stable blood supply are explained with clarity, highlighting the intricate Circle of Willis and its backup function for blood flow. The journey through the video explains the complexities of brain protection mechanisms, illustrated by conditions like meningitis and hydrocephalus, emphasizing the importance of maintaining these systems.

Even if science isn't your forte, you'll find this video not only informative but captivating. Jim Crimando provides insight into the brain's defense mechanisms in an engaging way, making sure you leave with a thorough understanding of why these systems are crucial. The episode wraps with further resources and encouraging viewers to dive into notes and supplementary videos for a richer learning experience.

Chapters

• 00:00 - 02:00: Introduction and Overview The chapter provides an introduction and overview of the brain, focusing on its protections. It refers back to previously covered material, including the bones of the cranium, glial cells like astrocytes, and the blood-brain barrier, emphasizing their protective roles. Microglia and meninges are mentioned as topics previously introduced, suggesting a review for those who need refreshment.
• 02:00 - 05:00: Brain Meniges and Differences from Spinal Cord The chapter revisits the topic of the meninges, focusing on their structure and spaces around the brain as compared to the spinal cord. It explores similarities and differences between the two. The chapter also delves into cerebrospinal fluid (CSF), discussing its production, purpose, and potential issues. Additionally, the importance of blood supply for brain protection and nutrient delivery is highlighted.
• 05:00 - 09:00: Dura Mater and Dural Folds This chapter discusses the protective layers surrounding the brain, focusing particularly on the dura mater and its folds. The transcript highlights the intricate routing for blood supply protection in this region. There are additional videos that complement this section by further exploring these protective structures, especially when analyzing the brain and its main protection, the cranium. After removing the cranial bones, the dura mater becomes visible, emphasizing its critical role in safeguarding the brain.
• 09:00 - 17:00: Ventricles and Cerebrospinal Fluid The chapter begins by discussing the protective layers of the brain, specifically focusing on the meninges—the dura mater, the arachnoid mater, and the pia mater. The dura mater is described as a thick, leathery outer coating that is continuous with the spinal cord. A deeper examination reveals differences in the structure, including what appears to be a slit in the dura mater, which the chapter hints at exploring further.
• 17:00 - 27:00: Blood Supply and Circle of Willis This chapter provides an overview of the blood supply to the brain, focusing on the Circle of Willis. It describes a coronal section of the brain, the structure of the cranium, and the meninges that surround the brain. While the meninges are similar to those of the spinal cord, this chapter also highlights the distinct differences between them. It discusses the characteristics of the dura mater, arachnoid mater, and pia mater, and introduces the concept of dural sinuses and their role in the brain's structure and function.
• 27:00 - 33:00: Aneurysms and Strokes The chapter 'Aneurysms and Strokes' begins with an examination of dural folds and the structural differences between the brain and spinal cord. It is noted that the brain lacks an epidural space, which is present in the spinal cord and is filled with adipose tissue for protection. Instead, in the brain, there is a direct transition from the cranium to the dura mater.

Activity 39 Transcription

• 00:00 - 00:30 all righty righty hey folks let's get started we're getting into the brain now this section is going to cover are the protections of the brain and some that we've already kind of covered from prior material we did the cranium remember all the bones of the cranium we did that a long time ago we did glial cells remember astrocytes and a blood-brain barrier and all the protective roles microglia and so kind of refer back to that take a look at that if that's not too fresh for you we also had started on meninges we did that with the spinal
• 00:30 - 01:00 cord we looked at the three layers of the meninges and some of the spaces and so we're gonna be kind of returning to that because that's it's similar but different around the brain and so we'll take a look at that and then we're going to look at the cerebrospinal fluid the CSF how it's produced where it's produced what's it for what happens if there's something goes wrong so we'll take a look at that or also look at the blood supply that's an important protection not only to supply the brain with oxygen and nutrients but there's
• 01:00 - 01:30 some interesting routing to protect that blood supply so those are some things we're gonna be looking at in this section there are also a couple of additional videos below here down here that will tie into this a couple of extra videos that I'll talk about a little bit later when we're looking at the brain obviously the protection a main protection for the brain you've got the cranium we kind of saw that we did the skeletal system and you remove that now you can see the dura the dura mater
• 01:30 - 02:00 the thick kind of leathery coating and that is continuous with the spinal cord dura mater and so you can see that outer coating there the dura and as you again you remove the dura you'll start to see the deeper layers of the meninges kind of this arachnoid and then the slick layer right on the surface that membrane that Pia mater and we start to see some differences you can almost see right here there's a difference it looks like there's like a like a slit in the dura so we're gonna take a look at that in
• 02:00 - 02:30 this view this is a coronal section of the brain and you got the cranium here and the meninges around the brain are very similar to what we saw with the spinal cord very similar we have the dura mater the arachnoid mater we have the PIA mater but there are some very distinct differences and we're going to look at those differences we'll look at the dural sinuses what those are we'll look at the dura mater itself is very
• 02:30 - 03:00 different we'll look at what they form called dural folds so we're gonna look at some of these differences right now we'll start off with you look at the cranium and then you get right immediately to the dura there is no epidural space around the brain remember with the spinal cord you had the epidural space and it was kind of filled without a pose for protection well there is no epidural space there is no adipose layer here see you go right from the
• 03:00 - 03:30 bone to the dura you can see the dura has 2 layers ok so that's a little different - we have a periosteal dura and that forms the periosteum of the inner cranium and that's the kind of the superficial part of the dura and then you have a deeper layer of dura called the meningeal dura the meningeal layer and so both of those two layers together form the dura so that's a little different than what we saw around the
• 03:30 - 04:00 spinal cord now sometimes there are locations where the two layers of dura separate and there is this sort of a space in between them and so when we look at that space in between them that is a dural sinus the dural sinuses the space between the meningeal dura and the periosteal dura this one for example is called the superior sagittal sinus anatomically it's telling you exactly where it is superior very high and
• 04:00 - 04:30 sagittal right on the midline the dural sinuses are filled with venous blood and that venous blood is being drained out of the brain so as blood leaves the brain it is collected into these large dural sinuses we can also see that parts of the meningeal dura form these deep folds those are the dural folds the one in this example is called a falx cerebri that Steve sent it's one example
• 04:30 - 05:00 of a dural fold a dural fold is an extra sort of like a flap or like a like a wall it separates large portions of the brain so you can see that dura kind of folding in down to separate the two hemispheres here so those are some of the differences between the meninges of the of the brain and the spinal cord other than that everything else is the same you still have the arachnoid subarachnoid subdural you still have the
• 05:00 - 05:30 pia so everything else is pretty much the same so as we look at the dura from the exterior and again it's a thin leathery coating pretty tough it's a tough mother you can see for example if we remove parts of the dura you've got that dural sinuses you got a dural fold here and a dural ful here and then in between that dural sinus and that's where blood is being collected from the
• 05:30 - 06:00 brain and then it eventually leaves the brain through the jugular vein now this is an example of the dearl fold again right on the midline the midsagittal great in that sagittal you got the big fold of dura that separates the two hemispheres of the cerebrum so there's a real literally a wall of separation between the two hemispheres of the brain now I'm going to take a look at what's
• 06:00 - 06:30 going on inside the brain with some of the spaces the brain is a is not a solid organ there are large fluid filled spaces those are the called the ventricles you can see these large fluid filled ventricles here you have two lateral ventricles okay those are large long hook shaped ventricles and then you've got in the middle a third ventricle and those are connected together the two lateral ventricles connect into the third ventricle which
• 06:30 - 07:00 is right smack in the middle of the brain and then that connects down to a little canal into the fourth ventricle and you can see the fourth ventricle right at the base of the brain now this is a on anterior view kind of showing the relationship you got the two lateral ventricles those are deep in the cerebrum they are connected to the third ventricle which is a slit like very skinny slit like ventricle connects down
• 07:00 - 07:30 through the little canal to the diamond-shaped fourth ventricle the fourth ventricle then you can see connects down into the central canal of the spinal cord there's also some exit points out of the fourth ventricle and that'll get us into the subarachnoid spaces around the brain now the ventricles are filled with cerebral spinal fluid and cerebral
• 07:30 - 08:00 spinal fluid is actually produced in the ventricles each of the ventricles has a choroid plexus and the choroid plexus our blood vessels that secrete this fluid cerebrospinal fluid it's it's almost like a like a filtered form of blood plasma the function of cerebrospinal fluid is to provide some chemical stability for the brain tissue and the spinal cord tissue it helps provide electrolyte balance pH balance
• 08:00 - 08:30 it provides almost like an interstitial tissue just a soaking of the tissue and it's a constantly produced and cycled through so we've got chemical stability we've got some protection it acts almost like a like a almost like a protective layer so when like if you get banged in the head or something you've got this fluidy cushion that's so that the brain doesn't smack up against the inside of
• 08:30 - 09:00 the cranium you have this little layer of fluid that acts as a protective layer it also provides buoyancy the cerebrospinal fluid can provide buoyancy for the brain itself your brain kind of floats in the cranium it's a very very soft organ if you didn't have cerebrospinal fluid it would kind of squeeze self by its own weight and kind of prevent its own growth and development so by having it it's like you know
• 09:00 - 09:30 having having somebody in water if you're lifting a person out of water it's easier to lift them if they're in the water they seem lighter and so that's kind of what the whole point of the the buoyancy effect of CSF is it it allows the brain to kind of float and not crush itself by its own weight the tsuba spinal fluid is produced and secreted from blood into the cerebral spinal into the ventricles and you can see it des flows from the lateral ventricle into the third ventricle from
• 09:30 - 10:00 the third ventricle down the cerebral aqueduct into the fourth ventricle each of the ventricles keeps adding more and more CSF and then at the fourth ventricle it exits into the subarachnoid spaces through these apertures MTG aperture lateral apertures and then it also goes from the fourth ventricle down into the central canal once its leaves the fourth ventricle you're now in the
• 10:00 - 10:30 subarachnoid space around the brain and the subarachnoid spaces surround the brain and spinal cord and and it's a circulation so this goes all the way down the spinal cord into the caudal region and comes all the way back up and eventually returns at these points here that's a very superior point of the dura we have these arachnoid where they're the arachnoid villi these arachnoid
• 10:30 - 11:00 villi are like wicks they wick up they soak up the cerebrospinal fluid and return it to venous blood so this is a dural sinuses has venous blood and the CSF is being soaked back into it so for real simplistic view CSF is produced by the choroid plexus and the ventricles goes around down and around out to the
• 11:00 - 11:30 subarachnoid spaces and returns to blood through the arachnoid villi or the arachnoid granulations and so it's a constantly circulating fluid it's continually produced from blood plasma it circulates around the brain and spinal cord and then is reabsorbed back into blood we have a total production of about a half a liter a day and you can see with cerebral spinal fluid it's a very very clear watery fluid it's it's like an ultra
• 11:30 - 12:00 purified form of blood plasma there's no should be not a lot of protein in there not like blood plasma proteins if there are problems in the brain if there's infection or a disease sometimes the cerebrospinal fluid can have abnormal components in this case you can almost see it like a little reddish tinge and so removing cerebrospinal fluid in order to test it is commonly done in certain diseases to
• 12:00 - 12:30 see what's happening inside the brain what materials might be there in that cerebral spinal fluid meningitis is an example of that where you have an infection there's an infection within the CMS remember your blood-brain barrier should normally work to keep bacteria and viruses out but sometimes they're able to pass that barrier if an infection in the brain is due to bacteria it's referred to as septic meningitis or bacterial meningitis that
• 12:30 - 13:00 is a very serious form of meningitis that is lethal form untreated it's very commonly it's lethal and it's diagnosed by testing the cerebrospinal fluid and looking to culture it to see if there's any bacteria normally you should not have any bacteria in your CSF if you have the signs of meningitis which include things like nauseousness if you have intense headache if you have a lot
• 13:00 - 13:30 of pain in your neck where you can't touch your chin to your chest and you have an intense headache that usually means there's a lot of pressure building up and so that's one of the things that you look at it plus a fever and so if they suspect that they will draw us through the spinal fluid out if there's nothing there that they see they might be result of a viral infection they refer to that as a septic meningitis aseptic meningitis is a less serious form it's still very painful still very you know it's not comfortable
• 13:30 - 14:00 at all but it's usually not fatal usually with that kind of viral infection you will get over it in a week or so but you'll be miserable but you have to know the difference in treating it if it's bacterial you have to get antibiotics right away so it's usually diagnosed by testing the cerebrospinal fluid and remember we talked about immediate spinal cord you obtain CSF through a lumbar puncture now I remember
• 14:00 - 14:30 you go into the lumbar region because the bones are big easier to get a needle through and that needle has to go through the epidural space through the dura into that subarachnoid space and then you draw out the cerebrospinal fluid so that is the lumbar puncture sometimes called just a spinal tap in order to get that CSF out and with the meningitis this is an example of bacterial meningitis you can see all of the abscess all throughout the surface
• 14:30 - 15:00 of the brain you can see the dura here the door has been cut and reflected back to expose the surface of the brain and this is obviously extremely serious as this is obviously post mortem and you can see that all of the spread of the abscess bacteria and again that's that's bacterial infection bacterial meningitis so as a circulation occur as though there can also be problems in the circulation if there's an obstruction
• 15:00 - 15:30 for example lateral ventricles to the third ventricle the way to get out is only through this little cerebral aqueduct if this cerebral aqueduct is blocked or let's say there's a developmental problem where it's too small it doesn't allow enough drainage that can result in a blockage of CSF flow and that can result in hydrocephalus hydrocephalus is this accumulation of fluid Suba spinal fluid in the ventricles of the brain and
• 15:30 - 16:00 in an infant that can cause an enormous and a swelling within the brain you can see the cranium because remember the fontanel's are not fully ossified yet we can see that the brain the cranium continues to expand and grow and fill with fluid and that puts an enormous amount of pressure on the brain tissue itself can cause an enormous amount of damage to the brain tissue and that's a result of this obstruction if you have a
• 16:00 - 16:30 blocked aqueduct or you can't get drainage out the CSF just builds up in the brain in an infant you would see bulging of the cranium it's this where to occur because of an in a problem and an adult obviously you wouldn't see the spreading of the other fontanel's because but this time the cranium as an adult would be fully sutured and closed the pressure would simply build up and it would cause an enormous amount of damage and obstruction to the to the blood flow to the brain in an infant
• 16:30 - 17:00 when this happens often times you have to surgically insert a shunt surgically an insert a bypass tubing to drain that CSF out of those ventricles and bypass the obstruction and then that drain goes into their V into a vein that returns the fluid back to their blood supply and here is an infant for example it has a shunt installed surgically implanted in order to drain that goes down into the
• 17:00 - 17:30 neck and into the subclavian vein and so that's going to stay there to continually drain CSF as the baby grows and develops eventually the tissue begins to grow around and it's not in the hair begins to grow you don't really see it as obvious as the baby grows so that is hydrocephalus there's another video down here take a look at that that also shows the cerebral spinal fluid the flow it's kind of a good animation
• 17:30 - 18:00 sometimes seeing it animate it helps so take a look at that video also right now we're going to take a look at the blood supply to the brain your brain is obviously an extremely important organ in the body and it has a very high demand for or for blood your brain weighs about two percent of your body two percent of your body weight is your brain but it takes twenty percent of your blood oxygen and
• 18:00 - 18:30 so it's really kind of taking a lot of oxygen in order to keep the nervous system to keep the brain functioning so we have two main sets of arteries that supply blood to the brain that is the internal carotid arteries right and left on each side you can see right here and then the vertebral arteries which kind of come up the back of the neck here you've got the memory in the cervical vertebrae you've got those transverse foramina well there is the vertebral arteries passing through
• 18:30 - 19:00 them and then they're going to enter through the foramen magnum the internal carotid arteries enter through the carotid canals now your brain needs a constant supply of oxygen there is no storage of oxygen in the brain remember when we talked about muscle you had myoglobin you well you there's no myoglobin for the brain you need a constant supply of oxygen and if you
• 19:00 - 19:30 decrease the supply of oxygen to the brain for even just a few seconds that can cause loss of consciousness lack of oxygen to the brain for even five to ten seconds will cause unconsciousness that's what the like it if you watch like the Ultimate Fighter or MMA they do it they do a choke out it's really not choking what they're doing is compressing they're compressing the internal carotid artery and if you get a good compression on that artery for five or ten seconds lights out okay that
• 19:30 - 20:00 person will be unconscious lack of oxygen to the brain for a couple of minutes can result in in death in the nerve tissue will will will die and so it's extremely sensitive to oxygen levels and so we we have to have a very good and protected blood supply to the brain this is an inferior view of the brain and we can see those two main routes you've got the two internal carotid arteries and the two vertebral arteries and when we look at the brain
• 20:00 - 20:30 itself this is sort of brain we're gonna take a look at this area right in the brain and kind of focus in on where those arteries enter the brain here is those two internal carotid arteries here is a two vertebral arteries and again here's our spinal cord you can see the gray matter and as we as we enter we're coming through the foramen magnum we're getting into the brain here those two vertebral arteries will eventually join at the base of the brain to form the basilar artery and
• 20:30 - 21:00 though as you can see branches coming off to feed the base of the brain you can also see the internal carotid arteries here the right and left they also join together with the basilar artery and they also join together with each other and you can see that right here this entire circle is called the Circle of Willis or the cerebral arterial circle and this is actually an
• 21:00 - 21:30 anatomical backup supply normally blood entering the right side stays on the right side and blood entering the left side stays on the left side but if there is a slight reduction of blood from one side here on the right blood entering the left can cross from the cross to the other side and then feed the other side of the brain this is sort of a sort of a back up it's an adaptation to protect
• 21:30 - 22:00 the blood supply in case there's a reduction in one side there is a video down here take a look at that video again and it'll talk about the arterial supply we just mentioned it'll mention the it'll show you the circle Willis it also talked about drainage the venous drainage it'll mentioned URLs I know Susannah don't focus too much on the venous side the drainage focus more on the arterial blood supply because that's what we're
• 22:00 - 22:30 going to be looking at that's kind of what were you focusing here this is actually an angiogram this is a an angiogram of the brain this is where they inject radiopaque dye into the blood supply into the arterial let's apply and through imaging you can see the radiopaque dye shows up on this image and this is a great image because it shows the basilar artery here and then it shows the internal carotid arteries here and as soon as they enter
• 22:30 - 23:00 the brain you can see the Circle of Willis how all those arteries joined together and you can also see how the internal carotid branches and feeds off each side you can see the arteries branching and going to the front remember under normal conditions blood entering the right or the left side stays on the right or the left side it doesn't cross over only if you have a reduction and you can see that best in
• 23:00 - 23:30 this view in this view the blood the radiopaque dye was injected only into one side only into one artery and you can trace that artery all the way up internal carotid artery and you can see that it stays it doesn't cross over to the other side so blood entering this side stays on this side to feed that side of the brain you can also see here the internal carotid artery it's pretty
• 23:30 - 24:00 cool II remember when we were looking at the skull a lot of times you couldn't get a stick through that hole the internal carotid for other crowded foramen and you can see that it kind of turns turns again kind of hairpin turns so there's a lot of turns and twists in this portion of the artery and all those turns and twists actually can create
• 24:00 - 24:30 weaknesses there's a large amount of pressure in these arteries and when they're connected in like t-bone intersections here that can create weaknesses and that's what we see in this view here we see aneurysms forming and an aneurysm is a weakening of a blood vessel begins to bulge out in this artery you can see the wall has weak it's kind of like a tire like a bald spot on a tire once it begins to get weaker it begins
• 24:30 - 25:00 to bulge more which weakens it more and the most of the aneurysms in the brain you can see the anterior communicating artery is 30% just that artery there the posterior the back half the Circle of Willis 25% over half of all aneurysms in the brain occur around the circle of the Willis so it's a good adaptation to have for a backup route but the cost of that is you're
• 25:00 - 25:30 you're having more aneurysms in those areas because of the pressure and then connections between the the arteries so when these aneurysms occur they can be very dangerous because they can rupture the aneurysm itself is a weakening of that blood vessel wall when it ruptures that's our hemorrhage or our stroke and you can see in this case there's a rupture that occurred here I think we
• 25:30 - 26:00 use the same image when you looked at the motor tracts if this is a motor tract coming from the cortex down through the white matter and then out this stroke this hemorrhage cerebral vascular hemorrhage can wipe out and destroy large parts of the brain here and so that's what happens when it when a blood vessel ruptures it's referred to as a stroke or a cerebral hemorrhage leading up to that is often the aneurysm
• 26:00 - 26:30 all right well I finishes up this section I remember there is a couple of extra video let's take a look at those remember to review the questions that are down here and also the text reading as you do these videos always remember take notes refer to those notes when you're doing your post activity review and remember all reviews should be done by midnight Friday