0:00 In this video, we're going to talk about nerve injuries and the different types 0:13 . 0:13 But before we start, we should recap what a nerve is, as well as where it can 0:18 be found. 0:20 So here we have the brain and the spinal cord. 0:23 The brain and the spinal cord make up the central nervous system, or CNS. 0:28 If we zoom into the section of the spinal cord, let's look at some familiar 0:33 structures. 0:33 We have the dorsal side of the spinal cord or the back, and then we have the 0:38 ventral 0:38 side of the spinal cord or the front. 0:42 We have a dorsal root and ventral roots, which are basically clusters of 0:46 neurons that connect 0:48 essentially to form a spinal nerve. 0:52 And so this is a nerve. 0:54 A nerve is not one neuron, but it's many neurons, all packaged up into this 1:01 structure. 1:03 Now whereas the brain and the spinal cord is part of the central nervous system 1:07 , the 1:08 spinal nerves is part of the peripheral nervous system, or PNS. 1:16 In the spinal nerve, if we look at a cross-section of it, we can find blood 1:21 vessels, 1:22 you know, veins and arteries. 1:25 Surrounding the nerve, in this case a spinal nerve, we have a sheath called the 1:31 epineurium. 1:32 Now within the spinal nerve, we have clusters of bundles of neurons making up a 1:38 fascicle. 1:40 If we were to pull out one of these fascicles, it is surrounded by another she 1:45 ath called 1:45 the perineurium. 1:49 And remember, all these sheaths are essentially like protective. 1:53 And within each fascicle, we find neurons. 1:57 Neurons here can be either un-mylinated or myelinated with Schwann cells. 2:04 And surrounding these neurons, we have another sheath called the endonurium. 2:10 So again, starting from the very top, we have epineurium surrounding the spinal 2:15 nerve. 2:15 We have a perineurium surrounding the fascicle, and we have an endonurium 2:19 surrounding a, 2:20 in this case, myelinated neuron. 2:23 So now let's briefly recap what a neuron is and its structure, because it's 2:28 quite relevant 2:28 to understanding the types of nerve injuries. 2:32 So here we have a typical motor neuron. 2:34 We have the dendrites, which receive signal, the soma, the body. 2:37 We have axons, and this is a myelinated neuron because it has Schwann cells. 2:41 And then we have the terminals with a terminal bulb, where neurotransmitters 2:45 are released 2:46 and initiate a sort of response. 2:52 Okay, now let's talk about nerve injuries or neuron injuries. 2:57 Let's start off by looking at the central nervous system, CNS. 3:01 So now most CNS fibers, the neurons, they do not regenerate, and there's three 3:06 reasons 3:06 why. 3:07 Firstly, cleanup is slow. 3:09 Secondly, oligodendrocytes, which are a type of glile cell inhibit regeneration 3:16 . 3:16 And thirdly, the environment is not very optimal. 3:20 However, neurons in the peripheral nervous system, or PNS, can regenerate. 3:26 And this is because cleanup is a lot faster in the peripheral nervous system by 3:30 macrophages, 3:31 allowing for parts of the neuron that are able to regenerate, to regenerate. 3:36 Secondly, Schwann cells actually assist in the regeneration process. 3:40 And thirdly, time is of the essence. 3:43 So if we can clean up parts that cannot regenerate, et cetera, et cetera, 3:47 regeneration can occur. 3:50 But however, time is of the essence. 3:55 Another fundamental thing to understand is that if the cell's body, the soma is 4:01 damaged, 4:02 at least the cell the neuron cannot regenerate. 4:06 However, if the axon is damaged or the terminal, well, neurons can then 4:12 regenerate. 4:13 It will just grow the axon back as well as the terminal. 4:18 And the speed of the growth is about 1 millimeters per day. 4:24 Now on to looking at the classifications of nerve injuries, will you have three 4:29 main types? 4:33 Before looking at the three main types of nerve injuries, we should, again, 4:36 just recap 4:37 a normal neuron here. 4:39 So remember, it has an axon and it has an endonurium sheath-type thing 4:43 surrounding it. 4:45 So this is normal. 4:47 Now the first type of nerve injury, or the least severe, is called neuropraxia, 4:53 where 4:53 it is essentially demyelination. 4:56 And this is essentially a reversible conduction block. 5:00 So again, if I were to draw the neuron here and the endonurium surrounding it, 5:08 neuropraxia 5:09 is essentially when you have compression here. 5:13 And so the axon and endonurium is still intact, however, the myelin sheath is 5:19 sort of compressed. 5:21 And an example of this is when one experiences radial nerve compression, a 5:28 wrist drop. 5:29 So if you wake up, maybe in the middle of the night and you've compressed your 5:36 nerve, 5:37 you have this sort of sensation. 5:42 The second type of neuron nerve injury is called axonotemesis, which is 5:47 essentially where 5:48 you have demyelination plus axon loss. 5:52 Now if I were to draw a diagram, here we have the neuron, and here as you can 5:57 see, we have 5:58 a segment lost, however, the endonurium is still intact. 6:03 And so this actually allows, this means that the neuron can regrow, can grow 6:12 back. 6:13 And so because it also has the body, the body is still there, the body can, you 6:17 know, grow 6:19 the axon back as well as the terminal. 6:21 However, the terminal in this case will die off. 6:28 So the distal end will undergo what's known as wallerian degeneration. 6:37 The second type of nerve injury is commonly seen in crash injuries and 6:44 displaced basically 6:46 bone when you're fractured. 6:52 The third type of nerve injury, which is the most severe, is called neurotem 6:56 esis, which 6:56 is essentially when you have demyelination plus axon loss, as well as one of 7:05 the following. 7:07 You can have either damage of the endonurium, which I have just drawn here. 7:12 And this means that you can have a fair growth, but not as well as if you would 7:19 still have 7:20 the endonurium intact. 7:23 As you can think of the endonurium as sort of like a pathway telling where the 7:29 neuron 7:29 should grow back. 7:32 And then, or you can have involvement of the perineurium, and if you remember 7:35 the perineurium 7:36 is the sheath surrounding a fascicle. 7:40 And if this was damaged, you would have poor growth. 7:45 And finally, if you have epineurium involvement, so remember the epineurium is 7:48 the one surrounding 7:49 the whole nerve, you will have no growth. 7:53 And like always, the distal ends of the neuron that is basically slouched off 7:58 will undergo 7:59 degeneration no matter what. 8:02 Okay, so I hope that made sense. 8:09 So remember the three types of nerve injury. 8:11 You have neuropraxia, axonotemesis, and neurotemesis. 8:16 Thank you for watching.
