Term
| What are Nissl substances and why are they important in neuronal cell bodies? |
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Definition
Stacks of RER and clusters of ribosomes bound to mRNA to fulfill the translational requirements needed to maintain neuronal extensions.
Nissl substances extend into dendrites, where local proteins translation is carried out at the post-synpatic receptors. |
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Term
| Why is the axon hillock deficient in Nissl substance? |
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Definition
This is where the axon begins and where microtubules and neurofilaments begin to align.
Adjacent to the hillock is the "Initial segment," where most axon potentials originate (high density of voltage-gated ion channels). |
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Term
| Distinguish between the location and functions of Microfilaments (actin), intermediate filaments and microtubules in neurons. |
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Definition
Short- you need microfilaments for axons to sprout, microtubules for them to grow and intermediate filaments for them to stabalize.
1) Microfilaments are in growth cones, axon terminals, dendritic spines and cortex
cell movement
axon sprouting
receptor and ion channel localization
2) Intermediate filaments are stable and highly phosphorylated-
maintain morphology
3) Microtubules originate in MTOCs and are released to dendrites (orientation in either direction with less-normal arrangement) and axons (+ end is distal, with normal arrangement)
Intracellular transport
diameter
axon elongation. |
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Term
| How can you differentiate b/w autonomic (visceral) ganglia neurons and surrounding cells? |
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Definition
1) Large cell bodies
2) Prominent nuclei |
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Term
| Which molecular motors are critical for fast anterograde and retrograde transport, respectively and what cargos are being transported? |
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Definition
Fast anterograde- kinesin tranports newly synthesized peptides, dense core vescles, synaptic vesicles and mitochondria
Fast Retrograde- Dynein transports exogenous constituents taken up by RME, Neurotrophins in "signaling endosomes" for re-growth following injury, and viruses and toxins such as tetanus toxin. |
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Term
| Why is the rate of slow transport so critical for neuronal survival? |
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Definition
| Slow rate (due to intermittent rapid movements and pauses) transport of microtubules and neurofilaments determines the rate of axon growth during development and regeneration. |
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Term
| Where are satellite glial cells (SGCs) derived from and how to they function int the PNS? |
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Definition
1) Neural crest cells
2) These "flattened tortilla-shaped" cells surround PNS neurons providing
insulation
neurotransmitter recycling
Regulation of K ion concentration and neural excitability
Viral protection
Following injury, they divide and secrete cytokines (NGF, VEGF) and chemoattractants for inflammatory cells
Histologically, these cells cover all synapses in the DRG (continuous ring), but not in autonomic ganglia. |
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Term
Explain the basic structural elements of a peripheral nerve.
1) Connective Tissue
2) Myelination
3) Nodes of ranvier |
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Definition
1) 75% support tissue with epineurium (collagen 1 and fibroblasts), perineurium (fibroblast layer segregating axons into fascicles) and endoneurium (schwann cells, type 3 collagen and fibroblasts surrounding individual neurons).
2) Schwann cell from initial segment to terminal branches, There are cytoplasmic channels for delivery of materials
3) Nodes of Ranvier are unmyelinated sections that allow for saltatory conduction (note that basal lamina covers Nodes and Myelin) |
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Term
| What is Wallerian Degeneration |
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Definition
Cut an axon from its cell body and its distal segment will degenerate. Macrophages and Schwann cells eat myelin and axonal debris (24-48 hours).
- Ca influx initiates proteolytic processing
- Schwann cells release cytokines which recruit chemoattractant-releasing Macrophage recruitment
- Interleukins from macrophages induce neurotrophin-expression (first NGF and then BDNF retrograde transport to nucleus) in Schwann cells
- Axonal debris are phagocytosed by macrophages and Schwann cells |
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Term
| How do cell bodies respond to axon injury? |
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Definition
1) Large depolarizing voltage discharge travels back to cell body and cell spikes
2) Retrograde transport is halted
3) Nissle is dispersed and RNA and protein production is up-regulated (nucleus adopts an eccentric confirmation). |
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Term
| Following axonal injury, how to neurons regrow? |
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Definition
1) Axons sprout from nodes of Ranvier (requires microfilaments)
2) Axons grow along Schwann cell surface or inside basal lamina which contains factors that promote growth (bind through beta-1 integrins to laminin)
3) Electrical stimulation may accelerate growth
4) Schwann cells re-myelinate growing axons and a new basal lamina is produced (old is degraded). |
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