we're going to start discussing the nervous tissue cells found in the body there are two cells the neurons and the glial cells the neurons are the typical cells that are seen in the under microscopes there are these really large ones with three major parts to it those three major parts being the dendrites these are little extensions that stick off of the neuron the cell body which is where the nucleus and a majority of the organelles are found and then the axon the portion that sends the electrical signals the neurons make up around 20 percent of nervous tissue um nervous tissue cells and then the majority of the nervous tissue is going to be composed of neuroglial cells also known as glial cells in general when we talk about glial cells they're going to support and nourish neurons and they make up around 80 percent of the nervous system tissue now since we have these two major different types of cells in the nervous system we need to talk about terminology and go over a little bit of the definitions between the two so there's two major divisions the central nervous system and the peripheral nervous system and they're both going to take contain neurons and glial cells but we have to remember though is that the neurons are going to have three major parts dendrites and then the Somas or cell bodies so when we talk about neurons within the central nervous system what's going to happen is those neurons are going to be bundled together and when they become bundled together we're going to have all of the axons going to be bundled together in certain areas in all of the cell bodies are going to be bundled together in certain areas the axons when they are bundled together are going to be called tracks in the central nervous system the tracks will be myelinated which means that they will appear white or contain the myelon sheath on them which makes them white matter so in the central nervous system bundles of axons are going to be known as tracts well if the axons are bundled together then the cell bodies are going to need to be bundled together bundles of cell bodies in the central nervous system are known as nuclei now the neurons in the central nervous system are really going to have the same type of functionality as the neurons in the peripheral nervous system but the difference is going to be the names and these names are helping us determine what area we talk about if you hear the word track then you know that they're referring to somewhere in the brain of spinal cord if you hear the word nuclei you know the referring also somewhere in the brain or spinal cord the nuclei are going to be bundles of cell bodies where the tracks are going to be bundles of axons well we're still going to have bundles of accents of cell bodies in the peripheral nervous system but we're going to call that something else in the peripheral nervous system when we have bundles of axons we refer to those as nerves so what this picture shows you is it's showing you individual axons and they're all going to be bundled together and then all of these axons that get bundled together are going to be packaged into a larger structure that is known as the nerve now the same process is going to happen in the central nervous system I just don't have any pictures of that so we can see that we have individual axons here each of these dots is an individual axon and you can see that we're bundling all these axons together when we bundle all these axons together in peripheral nervous system it is known as nerves in the peripheral nervous system the nerves can be myelinated are non-myelinated so they may or may not contain white matter and then if we're bundling the axons together we're going to also bundle the cell bodies together and in the peripheral nervous system bundles of cell bodies are going to be known as ganglia so what this picture is showing us is it's showing us individual cell bodies so here is a nucleus of one cell body here's a nucleus of another cell body here's a nucleus of another cell body so we have hundreds of thousands of potential cell bodies all going to be bundled together in one area when we see this in the peripheral nervous system again it is known as a ganglia eight so if you hear the term ganglia you know that you're referring to the peripheral nervous system if you hear the word nuclei you're referring to the central nervous system but both the describing bundles of cell bodies if you hear the word tracts you're referring to the central nervous system if you hear the word nerves you're referring to the peripheral of the nervous system however they're both referring to bundles of axons so the terminology helps us distinguish the location in the body now before we can move on to actually understand how the nervous system sends signals and supports the neurons that do send the signal we need to understand the parts of the neuron so we're just going to go over the parts of the neuron now this is a specific type of neuron we're looking at that we'll discuss in a minute however all parts are going to be the same on different neurons the appearance just may change depending on the type of neuron we look at so the first part is going to be the dendrites the dendrites are cytoplasmic extensions that are going to receive information so we can see right here we have this Arrow going towards the axon so dendrites function is to receive information next we have the cell body also known as the Soma so you may hear the term Soma instead of cell body the Soma is going to be the area that contains the majority of the organelles obviously the nucleus is in the Soma we will have cytoplasm and mitochondria Golgi apparatus but some of the more important organelles are going to be the neurofibrils and the nasal bodies the neurofibrils will be found throughout the entire neuron and they're going to help with movement um of organelles they're going to help with division they're going to help with structure then also we have nasal bodies nasal bodies are rough ER within neurons if you can remember what rough ER does rough ER helps produce proteins well the nasal bodies do the same thing the nasal bodies will produce proteins that could potentially be packaged as neurotransmitters which means they're going to be chemical signals eventually now coming off of the cell body you are going to see a cone-shaped area we call this the Axon hillock so this cone-shaped area is the axon hillock and off of the hillock we have our initial segment of the axon so the axon hillocks the cone-shaped area and then the initial segments just the beginning of the axon the axon hillex important because the axon hillock is going to contain what we call the trigger Zone the trigger Zone is where new electrical signals or new action potentials will begin so the axon hillock contains the trigger Zone and this is where new action potentials will begin so the axon hillock leads to the initial segment which is going to be the beginning of the axon the axon's job is to send electrical signals now the axon can be long or short depending on the neuron in the body and at the end of the axon what you're going to see is these little extensions and these are known as the axon terminals terminal means n so these are the extensions at the end of the axon but you'll notice that those extensions end in a swelling these are known as the synaptic end bulbs it's within the end bulbs that we are going to see neurotransmitters packaged in vesicles which we've already discussed in the previous chapter chapter 10. now you'll notice in this particular picture this axon has material on it this is where we're going to see the nerve impulse jump over and it's jumping over areas called the Schwann cell now the Schwann cell is going to be a special cell that helps produce the myelon sheath which is a lipid protein covering now since it's a cell it's going to have a nucleus as you can see right here and it's going to have its own plasma membrane which we call the neurilemma so if you remember when we talked about the muscle cells they had sarcolemmas well Schwann cells are going to have neurilemmas so we can see that we have this white area this is the lipid protein covering that makes up the myelin sheath and then this outer layer just this outer layer right here is going to be the neurilemma which is actually the cell membrane of the Schwann cell what the Schwann cell does is when it myelinates it basically helps insulate the neuron and it's going to help the nerve impulses hop from this Gap to this Gap these gaps are known as the node of Ron Veer and we can have hundreds of gaps so we can have just a few gaps it depends on the length of the axon of the neuron now because neurons are going to be found in different areas of the body and because they're going to look different we're going to have different structural and functional classifications if you remember we talked about function already we can have Sensory neurons they're going to take information from the peripheral to the central nervous system it can also take information to the brain we're going to have as interneurons they're going to be the integrative or anal analyzing neurons those are only going to be found within the brain and spinal cord so the central nervous system and then we get a motor neurons these are going to take information away from the central nervous system or they can take information away from the brain so that's function but then we have structural depending on their looks so when we talk about structural the first thing we're going to talk about is how many projections do we have coming off of the Soma so if you remember let's go back to this picture real quick here's our Soma and then we have different projections coming off the Soma here we have lots of dendrites and then we have our axon so when we talk about structural we talk about how many projections come off of the Soma so our first one is a multi-polar notice that we have lots of dendrites coming off and then we have our Axon so would you say this is one two are lots of projections coming off the Soma if you said Lots then you're correct anytime you have lots of projections off the Soma it's going to be referred to as a multi-polar neuron you'll notice that we still have all the same areas we have the trigger Zone within the hillock axon myelin sheath can be present we have our axon terminals or synaptic end bulbs multi-polar neurons are going to be motor neurons so anytime you hear someone talk about multipolar they're referring to either motor neurons which is the majority or they could be referring to interneurons okay our next type is going to be a bipolar when you hear the word by what do you think of if you said two you're correct okay here we have one major dendrite that splits in branches and then we have our axon so we have one projection here and one projection here so that's 2 which tells us it's a bipolar neuron notice we sell the same parts we have our cell body our dendrites our trigger Zone which is the hillock our axon we have our terminal and our N Bulbs bipolar neurons are unique because they're only found in special senses such as your retina for vision your olfactory neurons your gustatory your taste neurons and then your auditory neurons so we only find bipolar neurons in special Senses eyes nose ears taste our next will be uni u9 means ones if you look here we have one projection off of the Soma and then it splits one end goes to the dendrites the other end is going to be the axon we still have the same Parts though we have our trigger Zone where the hillock will be this is what turns into the initial segment of the axon we have our axon Terminals and our N Bulbs unipolar neurons are going to be your Sensory neurons basically everything is set for special senses now what's unique is that if you think about some of these Sensory neurons that we've talked about or the sensory receptors we've talked about merkels meissners pacinian we've talked about pain receptors well all of those that we talked about are considered Sensory neurons unipolar so here is the Meisner detects touch basically that's your dendrites your dendrites will lead directly to your axon here's the merkels they also detect touch these are the receptors on the dendrites they lead directly to the axon pacinian deep touch deep pressure here's the basically the dendrites leads to the axon and then nociceptors these are for pain these are the dendrites they lead to the axon why would it be important to have these as unipolar instead of multi or bi well what we're skipping is we're basically skipping going through the integration area of the Soma so we're sort of having to go through three steps the dendrites the Soma and then the axon all we have to do is basically go directly from dendrites to axon we get to skip step two so this makes the sensor receptor much faster so think about if you put your finger on a hot stove you want to have a very quick reflex well the faster the sensory receptor the sensory receptors can communicate and send the signal the faster your reaction will be foreign now our next cells are going to be the glial cells neuroglia cells they're going to be a total of six that we're going to go over four of them will be in the central nervous system two of them will be in the peripheral nervous system now this picture that we're looking at right here is of the central nervous system remember the majority of the function of glial cells is to support and nourish the neurons