Peripheral Nervous Tissue Flashcards
Spinal Cord Anatomy (matters, horns, roots)
- Gray matter - butterfly center portion w/ 2 ventral and 2 dorsal horns
- At center of gray matter is the central canal
- Ventral horn contains cell bodies of efferent/motor neurons
- Dorsal horn contains cell bodies that the afferent/sensory neurons synapse on
- White matter- outer surrounding; made of mostly myelinated nerve fibers (myelin gives white color)
- Dorsal Root (incoming sensory fibers) + Ventral Root (outgoing motor fibers) join to form a spinal nerve
Nissl + Location
Nissl - stacks of rough ER; in cell body and dendrites; stain dark
Nissl substance/bodies extend into dendrites but NOT axon/axon hillock
3 Filaments in Neuronal Cells
- Actin - mainly on outer surface of the cell bodies and dendrites; function = cell movement, axon sprouting, positioning receptors and ion channels on surfaces
- Intermediate Filaments - (“neurofilaments”) stable and located in axon
- Microtubules - nucleated at MTOC then released into dendrites or axons; function= intracellular transport and axon elongation
- In axons they are highly organized with + end distal
- In dendrites thy are less organized w/ multiple orientations
3 Types of Axon Transport
- 1- Fast Anterograde
- 2- Fast Retrograde
- 3- Slow Anterograde
Which motors are used for each type of axon transport?
- Kinesin= toward + end = anterograde
- Dynein = toward - end = retrograde
- **one cargo can have multiple motors
Neurotrophin
Factors that affect changes in gene expression
Promote growth and survival of neurons early in dev; modulate synaptic transmission and response to stress/injury in adults
Similar to cytokines
Signals
Ex) nerve growth factor, brain-derived neurotropic factor, etc
Schwann Cells in Myelinated v Un-myelinated Axons
Myelinated…Schwann cell cytoplasm on both sides of wrapping; Schwann cell nucleus on outside; Nodes of Ranvier b/n adjacent Schwann cells
Un-myelinated…cytoplasm of 1 Schwann cell will surround must axons; axons embedded in invaginations of Schwann cytoplasm
3 Connective Tissue Sheaths Around Nerve
- Epineurium - surrounds collection of nerve fibers - type I collagen
- Perineurium - surrounds individual nerve fasicles - contains fibroblasts, tight junction (gives them prominent appearance on images) and basal lamina
- Endoneurium - surrounds individual axons, Scwann cells, capillaries and fibroblasts - fine mesh network of collagen III
Satelitte Cells
- Envelope neuronal cell bodies
- Look like flat tortillas
- Functions:
- Normally insulate, control neuronal microenvironment, recycle neurotransmitters, regular ion conc/excitability
- Divide in injury/nerve cell damage/viral infection; release cytokines and chemoattractants for inflammatory cells like macrophages
Histological Diff B/n DRGs and ANS Ganglia
DRGs - unipolar (2 axonal processes); clear central nucleus w/ prominent nucleolus; surrounded completely by dark, flattened satellite cells; no synapses
ANS Ganglia- multipolar (mult dendrites + 1 axon); nuclei often not centered; ring of satellite cells present but not as complete as sensory b/c need space for synapsing
Shingles Process
- infected w/ chicken pox virus —> primary skin infection but also viral particles use retrograde transport system (dynein) —> travel back to DRG where it stays dormant for years; then later people develop shingles when viral particles use anterograde transport to travel from DRG —> dermatome (kinesin)
Rabies Process
- viral particles in saliva multiply in infected muscle; then travel —> SC via retrograde transport through motor neuron; travel trans-synaptically to brain (CNS effects) and parasympathetic pre-gang —> post-gang —> salivary glands (specifically facial nerve)
- Retrograde transport uses endosome complex - include both receptor and ligand inside the endosome
Charcot-Marie-Tooth Disease
- Genetic, progressive disease that affects about 1/25,000
- Usually affects long axons 1st (motor and sensory) SO symptoms are difficulty w/ motor control and numbness in the 20s
- Eventually have arched foot or digits b/c denervation of muscles that normally oppose
- 40+ genes; examples…
- PMP22/MP2- myelin problem; trouble compacting and trouble w/ signaling —> dec in nerve conduction velocity —> symptoms
- MFN2- prob w/ axon; disruption of mitochondria transport
- Connexin 32- in gap junctions of Schwann cell S-L clefts
7 Steps of Peripheral Nerve Repair
- 1- All axon and myelin distal to injury dies (Wallerian Degeneration)
- 2- Schwann cells proliferate - prod less myelin and more adhesion molecule, cytokines and growth factors; phagocytose debris
- 3- Macrophages are recruited and remove debris and stir Schwann cells to make NGF
- 4- Injury signals —> cell body via dyne complex; Schwanns also make neurotrophins —> cell body
- 5- Upreg of genes involved in growth and apoptosis
- 6- Motor neurons upreg integrins
- 7- Regrowth (Schwann cell continue to proliferate and form conduits or growth promoting channels, axon sprout from nearest (proximal) Node of Ranvier, The basal lamina contains molecules promoting axon growth like laminin., basal lamina and Schwann cells shield axons from endoneurial components that can inhibit growth, Schwann cells remyelinate axons and form a new basal lamina )
