So the final lecture on this section is going to look at damage and repair of nervous tissue. So the nervous system exhibits what's known as plasticity. Plasticity is the ability of neural connections to change.
So where a neuron may terminate on one neuron, it terminates on another or adds new ones in. Plasticity is very similar to learning. That's really what learning and memory are, are creating new connections between neurons. And that's what we call plasticity. So in order for you to learn this material, you're going to have to repeat it multiple times.
You're going to hear me say it. You're going to answer questions in your playposits about it. You're going to do a assignment on Blackboard that's going to review this material.
You're hopefully writing it down and taking notes. You're hopefully looking at your textbook and reading the textbook. Maybe making some flashcards, reviewing those flashcards. But the more you look at the material, the more you interact with it, the more new connections you're creating in your brain. You're increasing the plasticity of your brain, which is creating memory for you to remember this when you take your quiz and your exam eventually on unit three.
Now, studies have shown that in order for you to learn or create these new pathways, every single new piece of material that you encounter, you have to encounter it 21 times on average to create a new memory or a plasticity, which is why many of these assignments that I'm giving you are repetitive. You're looking at the same thing multiple times because I'm hoping by looking at it multiple times, plus you're studying. That will get you to 21 times interacting with the material.
So if you're not doing well on the exam, look back and see, have I interacted with all of this material 21 times over the previous three or four weeks? If the answer to that is no, then you haven't created the plasticity in your brain and you're not going to remember or recall it. Now, the more different ways you interact with the material, the better.
So just listening to it said 21 times is not as good as you reading it, listening to it, looking at the PowerPoint, writing down notes. Actually, the very best way to create plasticity and to lower that 21 times is to actually write it, not type it, write it, form the actual words is the best way to create memory or plasticity. All right. So plasticity is based on experience. Now, regeneration.
is the ability of nervous tissue to replicate or repair. Now, nervous tissue exhibits lots of plasticity, not so much ability to repair or replicate. So in the central nervous system, there's very little or no repair.
In other words, once you get hit in the head with a baseball, that's going to create a contusion on the brain or a motor vehicle accident. or whatever it happens to be. And those contusions are going to kill some of the neurons in your brain.
Well, once they're dead, they're dead forever. You're not going to make new ones. So once you're born, in fact, way before you're born, you're pretty much done with creating nervous tissue. Now you can create plasticity or connections between your neurons, but you can't make new neurons. So once the neurons are dead, they're dead.
So in the central nervous system, that's pretty much it. This is because the neuroglial cells inhibit a formation of new neurons, particularly the oligodendrocytes that create the myelin sheath. You also are missing growth stimulating cues, hormonal factors that are present during fetal development.
Those are gone after birth. So you don't have those stimulatory factors, so you can't create new neurons. Also in the nervous system, there's very rapid formation of scar tissue. Once that scar tissue forms and fills in, you can't put new neurons there. So all of those factors combined together to mean that in the central nervous system, you're not really going to regenerate neurons.
That's why if you get a spinal cord injury, if it actually kills the spinal cord cells, like you get a severing of the spinal cord somewhere, that loss of function is going to be permanent. because you can't regenerate. Now in the peripheral nervous system, sometimes you can repair damage to neurons.
Not always, but sometimes. In the peripheral nervous system, you can. First of all, if the cell body of the neuron is intact. If you've damaged the cell body, you're not going to repair it. If you just damage the axon, it's possible you could repair it.
Also, the Schwann cells need to be functional to create a myelin sheath and what's known as a regeneration tube. If the Schwann cells have been destroyed, you're not going to be able to repair. Also, it has to occur so that scar tissue is not formed too rapidly. If scar tissue comes in and replaces it before you can make a regeneration tube, then you're not going to be able to repair those neurons.
Now, even when you repair them, it takes a long time. If you've ever had surgery and they cut through the skin, you'll feel numbness on the skin for many months, sometimes years after, and sometimes you never get all the feeling back because of the damage to those sensory neurons. Now, the steps in the repair process, if it does occur, and remember, this is only in the peripheral nervous system, the steps are chromatolysis, valerian degeneration, and the formation of a regeneration tube.
So in chromatolysis... you're going to get redistribution of what are known as nissil substances or nissil bodies. These nissil substances here in the soma, so your soma, your cell body, has got to be intact.
If your cell body is not intact, then these nissil substances aren't going to be able to do their job. So these nissil substances meet the need for increased protein synthesis. Then you get what's known as Willerian degeneration. These are biochemical and morphological structural.
changes that occur to allow for axonal regeneration. Then the Schwann cells will form a regeneration tube where you get a solid myelin sheath around the damaged neuron. So these Schwann cells come in, regenerate around it, and create this regeneration tube to allow that axon to heal. So that's why you need your cell body has to be intact.
and your Schwann cells have to be intact. Now, if scar tissue comes in and forms before this regeneration tube can form, then you're not able to form it and you're not able to repair that neural.