Nerve Injury Flashcards
The peripheral nervous system is a bit (more/less) prone to injury because of its exposure to our environmental circumstances.
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If it’s encased in bone, it’s (central/peripheral) nervous system and if it’s not encased in bone, it’s the (central/peripheral) nervous system. So for the cerebrum, cerebellum, and brain stem, it sits in the skull vault, so that will be (central/peripheral) nervous system. That’s a perfectly fine distinction to make until we get the cranial nerves. And then same thing for the spinal cord. If it sits within the spinal column, sitting in between the vertebral bodies and the lateral recess - apophyseal joints and the lamina, that is the (central/peripheral) nervous system. Anything that exits is (central/peripheral) nervous system.
central; peripheral; central; central; peripheral
So if we consider what are the components of a peripheral nerve, we know that if we take the dorsal root that’s coming out of the posterior aspect of the spinal cord and the ventral root that’s coming out of the anterior aspect of the spinal cord, the area that they meet together and come out is what we call a (sensory/peripheral) nerve.
peripheral
Peripheral nerves are going (away from/into) the limbs.
into
Because that axon exits the spinal cord and comes out of the entire lower motor neuron. The axon that comes out is technically considered part of the (central/peripheral) nervous system. Same thing with the dorsal root. It comes in and the sensory fibers that are coming in.. Even though the dendrites are coming in and synapsing onto different regions within the dorsal gray, the dendrites along with the dorsal root are considered part of the (central/peripheral) nervous system.
peripheral; peripheral
So the central nervous system has liquid and the oligodendrocytes that are responsible for myelination of the axons that are in the (central/peripheral) nervous system. In the P N S, peripheral nervous system, (oligodendrocytes/schwann cells) are responsible for myelination of the axons. What’s important? Within the central nervous system, the oligodendrocytes have tentacles, if you will, that come off the central nucleus and surround and wrap multiple axons together and keep them clustered together. So you’ll have one, a liquid and the oligodendrocyte that is responsible for the myelination and wrangling in of several axonal structures. Once we go into the peripheral nervous system, things become a little bit different. We don’t have the oligodendrocytes, we have Schwann cells. And one Schwann cell is responsible for one segment of myelination around the peripheral nerve. So instead of having one oligodendrocyte responsible for the myelination of several axons, what we actually have here is one axon that’s myelinated by several different Schwann cells. So we lose some of the wrangling properties of keeping similar functioning cells together that we have from the oligodendrocytes. We don’t have that with respect to the Schwann cells.
central; schwann cells;
The lower motor neuron has a cell body that sits somewhere in the (dorsal/ventral) gray, and the axon starts to exit out. Depending on the length of the nerve, some of these lower motor neurons can run axons that are 36 inches long depending on where they’re ending up. So it’s got what, maybe 23 percent of its cell mass sitting in the ventral gray and then the rest of it sitting out in the periphery. What’s going on there? So what actually happens is there is a barrier that lives within the cord. And what it does is it prevents (oligodendrocyte/schwann cell) migration from the spinal cord to the outside peripheral bodies. And so what happens is, the part of the cell that lives within the ventral gray, so the cell body and a few millimeters of axon that lives within the cord are going to be myelinated by (oligodendrocytes/schwann cells) and they’re going to be wrangling the cells in. And then once that lower motor neuron axon exits the ventral gray and leaves the periphery, it’s going to be myelinated by (oligodendrocytes/Schwann cells). That’s going to be the same thing for the dorsal root. All of the sensory fibers that are coming in, when they sit in the periphery, they are going to be myelinated via (oligodendrocytes/Schwann cells). And then as that axon continues in to synapse with different areas within the dorsal gray, that axon and the part of the axon that is residing within the dorsal gray are going to be myelinated by (oligodendrocytes/schwann cells). That is an important academic bit of minutiae.
ventral; oligodendrocyte; oligodendrocytes; Schwann cells; Schwann cells; oligodendrocytes
But in general, injuries that happen peripherally and outside of the central nervous system appear to be (less/more) apt to be repaired than injuries that happen within the central nervous system. In the CNS there are chemical components, genetic, that inhibit the repair and growth of axonal injuries and neuron injuries that happen within the central nervous system. So there is, we think at least for now, some reason for differentiating what part of the cell body and neuron sits within the central nervous system versus the peripheral nervous system because the overall potential to injury maybe dictated by where the injury happens and what part of that cell body is damaged, slash injured, and where it sets.
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The cell body of a neuron contains the Golgi apparatus, mitochondria, and structures known as Nissl bodies. Now the mighty ______ and Golgi _____ are all responsible for maintaining cell metabolism. _____ bodies are endoplasmic reticulum and ribosomes that are found within the cell body and are responsible for (cell/protein) synthesis. So if you don’t have these structures, you have no protein synthesis. If you have no protein synthesis and you do not have energy being supplied along the length of this entire cell. You do not have a viable cell.
mitochondria; apparatus; Nissl; protein;
There’s a transportation system that has been created between the cell body and the axon down to the dendrite to maintain (protein/metabolic) processes throughout the cell body and the axon and the dendrites
metabolic
Axonal transport or acts of plasmic flow is critical to the function of the cell. And without that, the cell will degenerate and die. There are two types of acts of plasma flow. And the first one is referred to as (anterograde or ortho grade/retrograde) which is transportation happening from the cell body, coming down to the axon towards the terminal boutons. There will be carrying of nutrients from the cell body down to the terminal end, taking neurotransmitters that have been put into synaptic vesicles from the cell body and relaying it back down to the terminal button. There is a (anterograde/retrograde) transportation that is happening from the terminal end through the axon back to the cell body. Furthermore there will be metabolic waste and neurotransmitters that need to be repackaged via the neuron organelles to be repackaged into neurotransmitter packages that are going to be released by the synaptic buttons.
anterograde or ortho grade; retrograde
There is a fast and a slow component too for axonal transportation. Fast axonal transportation or plasma flow happens at a rate of about (100-200/400) millimeters per day and it’s related to signal components. Slow plasmic flow is where axonal transportation happens at a rate of about a (100-200/400) millimeters per day.
400; 100-200
Interruption of that flow is going to result in signaling delays which will result in death of the axon and the terminal button. And if there’s death of the axon and the terminal button, there is eventually going to be death of the cell ____. So interruption of that area can result in eventual neuronal death, it certainly is going to impact neurological signaling.
body
Fast axonal transport happens in (only anterograde/both anterograde and retrograde) transportation.
both anterograde and retrograde
A nerve is a collection of _____ that are gathered together in fascicles based on their collective function and their end target destination. _____ tissue surrounds the nerve.
axons; connective
From a histological perspective, there are essentially four layers of nerve connective tissue. So we’re going to work from innermost layer to the outermost layer. The innermost layer is a (neurolemma or basal lamina sheath/epineurium), which covers the outermost layer of the ______ cell that is going to be myelinating the axon if there is myelination across the nerve. So if we’re dealing with heavily myelinated fiber or a moderately myelinated b fiber that’s going to be there. If we’re dealing with C-fibers, there aren’t going to be _____ cells that are associated with that C-fiber.
neurolemma or basal lamina; Schwann; Schwann
Next up then we have the connective tissue that are associated with the nerve. So the first layer is referred to as the (epineurium/endoneurium). And we have that endoneurium sheath sitting right here. We would consider that to be an extension of the (dura/pia) mater from the meninges. And that endoneurium keeps a light level of fluid interspersed between the actual axons and maintains a positive pressure containing all the axonal fibers together. Because remember, in the central nervous system, we’ve got the oligodendrocytes wrapping things together, but we don’t have that within the Schwann cells. So the endoneurium is going to provide that function along with a little bit of fluid to help with axonal nutrition to some degree, as well as cushioning to some degree within that endoneurium sheath.
endoneurium; pia;
The next layer that we then have is what we refer to as the (endoneurium/perineurium). And the (endoneurium/perineurium) wraps and keeps all of the different fascicles together. The perineurium are born from the (arachnoid/pia) mater. The main function of the perineurium is to act as a diffusion barrier. There are vessels and veins embedded within the perineurium. And the diffusion barrier is there, much like the blood-brain barrier that we have in the central nervous system. And that perineurium functions as a nerve blood barrier.
perineurium; perineurium; arachnoid;
Lastly, we have the epineurium, which is the most (internal/external) layer. And it is similar to the (dura/pia) mater in form. It is the most external layer. It’s there to protect the nerve from compression. It is associated with adipose within connective tissue.
external; dura;
