in this video we're going to highlight some of the cytoarchitecture of the nervous system and we'll start off with some quick definitions since scientists insist on giving similar structures different names depending on whether they're in the central nervous system or peripheral nervous system I'm dr. Catherine Moore the histology wizard during development we know that neurons migrate to specific areas and then they coalesce in groups so in the central nervous system we call those groups of neurons nuclei while in the P NS we call them ganglia and to confuse things even more groups of neurons in the enteric nervous system are also called plex I and as with many terms there are exceptions most notably the basal ganglia of the CNS bundles of axons are called tracts in the CNS and nerves in the P NS and the CNS also has regions that have specific layers of neurons principally in the cortex and the retina now we're going to look at some of the structures that we can see with basic histological stains and we'll start with the P NS and peripheral ganglia those collections of neuronal cell bodies here in this cartoon of a cross-section of the spinal cord I've labeled a peripheral nerve a sympathetic ganglion which is ventral and lateral to the spinal cord and this ganglion contains cell bodies of neurons that deliver information to the body about stress and danger and are responsible for our familiar flight or flight response and this is a ganglia of the autonomic nervous system I'm also showing a sensory ganglion that transmits afferent signals from peripheral receptors into the CNS because this ganglion has inputs inputs into the spinal cord it's called the dorsal root ganglia and these ganglia are covered by connective tissue capsules and they contain the cell bodies of pseudo unipolar neurons so these neurons have one axon that acts like both an axon and a dendrite and they actually lacks synapses now each neuron is surrounded by Schwann cells and just to make things more complicated these are sometimes called satellite cells but don't confuse these with satellite cells in skeletal muscle which are actually stem cells now enteric ganglia or plex eye are small groups of neurons that are in the digestive tract and they go all the way from the esophagus to the rectum examples are shown here with a and B in this intestinal H&E stained image now note that they look kind of wavy and pale and they're gonna look a lot like peripheral nerve this entire enteric nervous system by the way is often classified part of the parasympathetic branch of the autonomic nervous system but more recent work really is consistent with this being an entirely separate system that is essentially can act on its own to regulate gut motility now disruption of or lack of these nuclei can lead to digestive motility disorders such as a kaliesha where swallowing is quite difficult or hirschsprung disease which can result in megacolon peripheral nerves contain axons of both sensory and motor neurons and again these are associated with Schwann cells and the larger nerves are myelinated here I have a longitudinal Hz section and these nerves have a very pale appearance paler than smooth muscle and they're kind of wavy and note that these are axons so all those nuclei that you see are actually Schwann cell nuclei peripheral nerves actually contain three types of connective tissue covering and shown here both in this cartoon of a peripheral nerve and also in this H&E section the innermost covering is called the n donor iam this is thin connective tissue that has reticular fibers secreted by Schwann cells and the n donor iam surrounds an individual axon and its associated Schwann cells now single axons then bundled together into fascicles and the peri meriem surrounds each fascicle this connective tissue layer is thicker and it contains modified fibroblasts and you'll often actually see blood vessels and a few immune cells within the perineum finally the epineurium is the outer covering of large nerves and this is dense irregular connective tissue and it can actually be continuous with the capsule of a ganglion so those are our three connective tissue layers so now let's move on to the CNS CNS has two main components based upon where neuronal cell bodies are found gray and white matter here I've shown you a transverse or cross section of the spinal cord in this case it's stained with nissl stain and remember the stains rough endoplasmic reticulum and DNA and RNA so for the most part it marks the gray matter which is going to contain the neuronal cell bodies contains also dendrites and synapses now the white matter contains axons both myelinated and unmyelinated and there are a few cell bodies but not many white matter contains axons both myelinated and unmyelinated and only a few cell bodies and because there are so many axons in myelin this area actually appears white and fresh specimens now both white matter and gray matter contain astrocytes oligodendrocytes and microglia now the brain is organized in much the same way in this nissl stain section of cortex you can see both white and gray matter but recall that the cell bodies seen in the white matter here are not neurons but glial cells the gray matter of the cortex and cerebellum in Retton are then further organized into layers of neurons but we can't really see these using standard H&E or Nissel stains now in addition to the neurons and glia the parenchymal of the nervous system there are several other important CNS support tissues I want to touch on today the meninges are a set of connective tissue layers that provide protection for the brain cerebral spinal fluid or CSF is produced in ventricles and it bathes and cushions the cells of the brain and the brain can Taine's these ventricles that are lined with ependymal cells and that they communicate with the central canal that extends into the spinal cord so we're going to briefly review the meninges the outermost layer of the meninges is the dura mater and this layer is attached to the skull and it's actually separated from vertebral bones by a space called the epidural space which contains a little bit of loose connective tissue while the side facing the brain is very smooth and lined with mesothelioma dura has blood vessels and sympathetic nerve fibers as well the next two layers are often considered as a unit and they're called the leptomeninges which just means thin meninges and they serve to enclose the CSF a little bit like a sandwich so you think about that top piece of bread which is going to be the arachnoid mater and its outer surfaces adjacent to the dura then parts of its inner surface are going to protune in almost finger-like projections called trabeculae and these will actually contact the Pia mater the space between those two red line is called the subarachnoid space and it with CSF which flows through that space it flows down to the spinal cord up to the top of the brain and eventually returns to the blood through more protrusions of the arachnoid called arachnoid villi and finally our Pia mater is a loose connective tissue that faces the arachnoid contains a lot of blood vessels and nerves more importantly it covers the surface of the CNS and is lined by a membrane made up in part from astrocytes so those are the three layers now I just mentioned the ependymal cells of the central canal so let's take a closer look at these cells here's a image close-up of the central canal the spinal cord and if we zoom in even further you can appreciate the cells lining that canal these cells are actually derived from neural epithelium and they are either ciliated columnar cells or they're cuboidal cells that have extensive micro villi and these cells are important in helping with production of the CSF they actually help move fluid from the capillaries into the ventricles to form CSF but they also can help move metabolic waste now the larger structure that produces and regulates the composition of the CSF is the choroid plexus which i've shown here with a cartoon schematic and also in an H&E stain the choroid plexus is formed by extensions of the pia mater covered in ependymal cells and these extensions then push into the ventricles and they're closely associated with capillaries fluid then moves from the capillaries into the ventricles aided by the micro villi and cilia of those ependymal cells now the final structure I'll describe today is the blood-brain barrier the CNS does require blood supply it has to maintain a very high metabolic rate but at the same time it needs to be protected from toxins and other things carried in the blood so to accomplish these goals the capillaries in the brain are specialized to have limited access and this is primarily due to tight junctions between the capillary endothelial cells so most capillaries in the body are what we call fenestrated that is the end of Theal cells have spaces between them that allow a few substances to move back in forth in and out of the blood and in contrast capillaries that form the blood-brain barrier have tight junctions that seal these spaces so that substances have to pass via the cells that is via trance I ptosis across those endothelial cells which greatly restricts access other important components of the blood-brain barrier are the end feet of astrocytes and very specialized cells called parasites for more details on capillaries the blood-brain barrier and parasites watch my video on the vasculature of the cardiovascular system now with that we'll wrap up our review of the cytoarchitecture of the nervous system be sure to check out like and comment on my other videos suggestions and topics always welcome thanks for stopping by