one of the exercise that I do in my in-person classes and with students is I challenge them to come up with the differences between a dendrite and an axon a dendrite versus an axon what are those differences I've actually made this an exam question in the past and where I asked students to tell me the differences between a dendrite versus an axon and they can draw them out they can write me an essay but one of the most effective waves that I've seen is when they take and label the characteristics of the dendrite and each time they label one they compare that to the axon and a lot of times students will write in what the dendrite has but then they leave the Hawks on blank and I don't know if that's because they don't know I don't know if they assume that I should assume that they know yet not all students know it can get quite complex so one of the things that I ask of them is to be complete to write in the characteristic of the dendrite and then tell me what that characteristic is like in the axon if it's the same or if it's different and how it's different and that can be quite challenging so let me read hash the dendrites in the axon real quick the dendrites are these kind of listening areas of a neuron or the soma I'll do a little some liner where is the axon is more like the mouth here I have some lips with some teeth here and should've drawn how I'm different but that's okay you get the idea I have the tongue in and this is the output and that this is the input the dendrite is the listening and the axon is the output end and between we have a soma okay now dendrites look a little bit like hot rod flames to me okay they're gonna be branching like so as they interact with neurotransmitters and other stimuli make that one look like a hot rod flame and they have these areas where they have receptors to receive those neurotransmitters we call these the end plates certainly in a muscle cell okay in axons they're gonna have these axon terminals and those the axon terminals can take on many different shapes they can widen up they can be bulbous one of my anatomy professors her area of study are these terminal blue tones or terminal buttons the axon terminals okay where the output is supposedly occurring now the axon itself I wanted to find to define three different types of axons and the first is type a a type-a axon is heavily myelinated and large diameter or radius a type a is going to look something like this an ape has conduction velocities of about 300 miles per hour very fast so type a is the most heavily myelinated and the fastest conducting so we're gonna see a little theme here the rate of conduction depends on two factors the degree of myelination and the diameter of acts on the degree of myelination and the axon diameter Tybee fibers are going to have a smaller diameter and less myelin they can conduct around 30 miles per hour I was just remember this thing in threes or the tens 300 miles per hour for type a and only 30 miles per hour for tight be much slower because less myelin less axonal diameter type C fibers are going to be unmyelinated and very thin radius or diameter okay they're gonna conduct around three miles per hour three miles per hour these are three different types of axons now we find type a in the sensory system and motor neurons now for type B and type C we're typically gonna find type B an autonomic nerve fibers and type C we also find in autonomic fibers when we went over the typical spinal nerve you might have wondered why one was called the gray ramus community and one what's called the white ramus communicants well the white ramus communicants carries Type B autonomic fibers into the sympathetic chain and type C fibers come out of that sympathetic chain they're unmyelinated they're gray in color okay now that we know some different types of axons and we know kind of the structure of the dendrite versus the axon what the heck are the differences what are the similarities and how do we articulate this well this is basically the process scientists went through to come up with a definition for an axon and I let students organically come up with that they'll say that dendrites are the input and axons are the output that's what scientists law originally but we now know that that's not always the case that can't always defined a dendrite versus an axon there's retrograde signaling that happens there an axon there's dendrites in the nasal mucosa that may communicate with the hypothalamus as output and game I students have come up to me with all sorts of studies that has helped me evolve my teaching a little bit this would be zero points this comparison because it's just wrong accurate would be to say that dendrites are generally the input and axons do output in general but not always is what that implies so they gave me the whole story it told me these are generally input these are generally output and they were actually accurate this would be plus one pause the video and try to come up with your own lists the differentiated dendrite from an axial okay if you pause the video and you came up with a laundry list I want to go through some that I've seen from students in the past okay this idea of generally the input and generally the output may have been one of the first definitions for axons and dendrites until it was shown to be wrong a later one was that dendrites signal toward the soma and that axons signal away from the soma and people thought this was a really great definition and everything was settled we knew the difference between an axon and a dendrite until people started thinking about sensory neurons when you prick your finger so if I can prick this person's finger with a needle and they bleed they're going to take this sensory information from this neuron and it's going to go in through the dorsal root pass by the soma the dorsal root ganglia and go into the dorsal Horn through the dorsal root and synapse on the gray matter of the dorsal horn this is an axon and you can see here it's actually traveling towards the soma not away from the soma this definition fell apart but we could say generally signal toward the soma when these dendrites hear a signal which they usually do they're going to send what's called a graded potential through the soma and it will reach the axon hillock and potentially cause an action potential so we can say generally here because then that action potential signals away from the summer but not always not always and we need to be accurate here this is why it's important that students not leave the second half off don't leave me to assume that because dendrite signal toward the soma that axons away from the samba that's not always the case you need to articulate it okay well this is a great one dendrites do graded potentials they cause graded potentials and you'll learn more about these but that's these ripples through this pond of a soma that accumulate at the trigger zone or the axon hillock whereas notice that I'm doing the comparison axons use action potentials okay and we'll come back to this one at the very end the definition of a dendrite versus an axon is a little hard to make sense of from textbooks they seem like they're going back and forth and there's no real clear definition but there is and we'll come back to that let's think about the anatomy a little bit well one of the things about dendrites is they tend to branch at acute angles the signal for the sign for angles an acute angle a cute little angle is a very there is a angle smaller than ninety degrees whereas axons branch axons can send off collaterals add ninety degree angles at ninety degree angles so when axons are coming on down they tend to branch at 90-degree angles they can send off collaterals the pretend rights now the axon terminals are a little bit different they'll start to go like so but the dendrites these are all acute angles we don't see any obtuse angles here okay also we learned in a prior video that dendrites contain all organelles all types that's if we don't include the nucleus as an organelle whereas axons do not have rough ER or Golgi apparatus now we could if we did a comparison I go through all semester asking students for differences and then on the final I hit them with how are these things the same my students I've heard them sitting there and they get to this question and I hear them say crap out loud everybody looks over and they realize that they just got to the same question they arrived at you also should be thinking about similarities have no nucleus let's do the other what some people consider an organelle these also have no nucleus these signal these can also signal okay these are part of a neuron those are part of the neuron okay students have given me upwards of 26 similarities or differences I mean that's really the most that I got out of hundreds of students you know I think a really strong answer is over 15 I think over 10 is a very solid answer worthy of 5 out of 5 here so part gotten maybe 1 2 3 4 I'm probably approaching full credit if this was a 5 point question ok I'm hitting on all the key things just accumulating points here and being accurate in the process we saw that axons have a lot of microtubules one way that you that doesn't mean that dendrites do not have microtubules it means that they have less microtubules or tubulin and this helps you understand their structure and function one of the ways you can identify axons and who's talking to who in general not for sure but in general is by staining the excellence and you can stain that tubulin protein and see where things are going in some neural tissue and you can look for those 90-degree collaterals to be sure that you're dealing with an axon and maybe not someone who's listening like a dendrite you don't know for sure but it's likely okay you can start tracing some networks and then test them in other ways okay let's do some more or less term these tend to signal long distances these tend to signal locally or short distances another term for this graded potential is a local potential local distances or short distances okay now your textbook likely says that dendrites are unmyelinated and if you leave this empty I'm going to give you no credit because you're not telling me what axons are and I know that most students believe that axons are myelinated but we just learned they are not always myelinated that would not be accurate and it turns out that they aren't usually myelinated generally myelinated and that dendrites are generally unmyelinated but I learned more from my students than they learned from me and I had this question true false dendrites are always on myelinated and I had a student marked false and I always allow my students to contest a question and I show them where it says it in the textbook and they say well I think the textbook is wrong and I say go find me a review article that reviews the topic show me original research that shows otherwise show me that that review article accurately represented the original research and show me that that original research was duplicated that's a scientific process right there and if it has been replicated then maybe it needs to be adopted by our textbooks and they have found me cases where dendrites are myelinated I talk more about them in the reproductive chapters in physiology so I'm telling you now you're gonna be expected to know that these are inputs and these are outputs confirm with your professor what they want but these are unmyelinated and these are myelinated but hopefully you go investigate your for yourself some exceptions to those rules to have a more complete understanding so how in the world do we really discern a dendrite from an axon we could come up with many more of these I've heard some great ones from students in the past and hopefully you came up with some of your own okay but here's the official definition an axon can generate an action potential an AP I dendrite cannot and this action potential this action potential that's why I kind of wanted to come back to this concept this is what always held true for scientists in defining excellence they can generate an action potential and they do that from this area called the trigger zone this area of the soma that's collected all the graded potentials from these dendrites obvious input and ideas from the dendrites it sums it up and if it reaches a certain threshold it's going to fire an action potential then we'll talk to other cells those are some of the differences between a dendrite and an axon and a little bit more about their anatomy