Peripheral Nervous Tissue I & II (Peripheral nerve injury and repair…
Peripheral Nervous Tissue I & II
Histological Features of Neuronal Cell Body
Similar Characterisitics can be used to peripheral ganglia neuronal cell bodies
Histological Features of PNS Ganglion
Aggregates of nerve cell bodies
Arrangement of satelitte cells provides a way to distinguish sensory ganglia from autonomic ganglia
Satellite cells = provide support for ganglionic neurons.
Dorsal Root Ganglia: satelittle cells envelop each neuronal cell body Have centrally located nuclei
Sympathatic Gangllia: satellite cell ring is less complete, numerous incoming pregnaglionic fibers that synapse on sympathetic postganglionic neurons. Eccentrically located nuclei.
Parasympathetic Ganglia: Can ONLY be distinguished from sympathetic ganglia if found embedded in walls of terminal organs.
Enteric Ganglia: Interconnected plexues=submucosal and myentric plexus. Distinguished by postion on smooth muscle layer on the gut wall. Found between circular and longitudina smooth muscle.
Peripheral nerve/axon cross setions
Epineurium: Tough extenal layer surround large collection of nerve fibers. Loos connective tissue between bundles of axons and blood vessel. Type 1 collage and fibroblasts.
Perineurium: Layer of fibroblasts surrounding individual nerve fascicles. Fibroblast joined by tight junction are associated with basal lamina.
Endoneurium: Fine meshwork surrounding individual axons, Schwann cells, capillaries, and fibroblasts. Meshwork composition = Type 3 collagen.
H&E Features: Individual axons = dark dots, myelin sheath= clear space, Unmyleinated axons are difficult to discern.
EM Features: Myleinated nerve fibers = Concentric wrappings, Nodes of Ranvier = space between adjacent schwann cell, numerous junctions, basal lamina cover this region.
Most . common type of inherited neurological condition
Mutations in over 40 genes
Lose ability to use their hands, feet, lower legs, and arms as peripheral nerves to the extremities degenerate. Muscle become weak. Symptoms appear during the first and second decade of life. Contracted plantar fascia, weak tibialis anterior, leads to numbness
CMT1 Subtypes primary demyleinating neuropathies. Abnormal myleination.
CMT2 subtypes are primary axonal neuropathies. Effects the Axonal Cytoskeleton; can affect axonal transport. Associated with NEFL mutation = affects nuerofilament assembly forms aggregates that bloock transport of mitrochoncria and other cargoes.
Microfilaments: Most abundanctin growth cones, terminals, dentric spines, and outer portions of a neuron.
Axonal actin= latice like rings that wrap around the axon beneath the plasma membrane. Function in cell mmovement, axon sprouting, positioning of receptors and ion channels at specific sites on neuronal surfaces
Intermediates filaments aka neurofilaments= highly phosphorylated side arms, limit packing density. Stabilizers of neuronal morphology and cross sectional diameter, mechanical shock absorber.
Microtubules: scaffolds for axon transports, most stable in neurons. they are nucleated at MOC.
Microtubules act as tracks for motors that drive the transport of materials in axons.
Kinesin are motors for movement of cargo away from the cell body
aka anterograde transport
Dynein is motor responsible for moving cargo towards the cell body aka retrograde transports
Dynenin-Dynactin Complex: Dynactin is a activor of dynenin. Associated with both kinesin and dynein.
Varicella-Zoster Vrius - Herpes Virsus, starts during childhood. Linked to chicken pox. Affects retrograde axonal transport. Reactive by secondary infection aka shingles. Reactivation involves antereograde axonal transport.
Rabies Virus - Neurotropic virus, travels via motor nerves/sensory nerves and ganglia into the spinal cord to the brain via retrograde axonal transport. Replicates in teh CNS, spreads to the salviary glands and antrerograde axonal transport. Lack of treatment leads to encelphatophy.
Peripheral nerve injury and repair
Associated with a strong calcium influx and interruption of signals normally transported to cell body.
neurofilament proteolysis and destabilization of microtubules.
Cytokines recruit and active macrophages; remove Myelin debris.
Wallerian degeneration- Distal segment of nerve degenerates and is cleared away.
Upregulations of RAG, apopotosis is triggered
Chromoatolsysis = histological term, changes in cells visible during damage.
Local translation of transcription factors and importin proteins.
Axons grow along the inner surface of the basal lamina and surface of the Schwann cells
Old basal lamina is degraded and new basal lamina is produced.