Nervous System II Flashcards
What is the rate of axon growth?
2 mm/day
What are the spinal levels associated with preganglionic sympathetic neurons of the
autonomic system? What about preganglionic parasympathetic?
Preganglionic symp: T1-12, L1-3 (thoracolumbar). Preganglionic ParaSymp: CN III,
VII, IX, X, S2-4 (craniosacral)
How does sympathetic innervation work?
From spinal cord, medulla, hypothalamus, there is a neuron that will synapse in the
sympathetic ganglion via white ramums communicans. From here, that neuron will travel
via gray ramus communicans to the target.
How does parasympathetic innervation work?
The presynaptic nerve will reach ganglion that are at the end organ, where there is a
synapse to a short postganglionic neuron that will act on the end organ.
What are neural tube derivatives of the nervous system?
Motor neurons, pre-ganglion autonomic cells, Glia (O, A, E) GFAP
What are the neural crest derivatives we have learned thus far?
Sensory neurons (neurofilament), post-ganglion autonomic cells (unmyelinated), Schwann cells, Satellite Cells (DRG, Autonomic G, Pacinian, Meissner’s), Melanocytes, Pia, Arachnoid, Odontoblasts
Q: Describe the Schwann cell
PNS: Schwann cell: mitotic, electrical insulation: myelin. 1 Schwann cell: one axon: one
internode. Basal lamina. Non-myelinated axons still have Schwann cell wrap
Explain the 4 steps in myelination of large-diameter PNS axons.
(1) Neurolemmocyte starts to wrap around a portion of an axon. (2) Neurolemmocyte
cytoplasm and plasma membrane begin to form consecutive layers around axon. (3) The overlapping inner layers of the neurolemmocyte plasma membrane form the myelin sheath.
(4) Eventually, the neurolemmocyte cytoplasm and nucleus are pushed to the periphery of
the cell as the myelin sheath is formed.
What proteins are involved in a clinical correlate of Schwann Cell myelination?
Lipid proliferation – PMP-22 + P0 (Autoimmune destruction = demyelination) –
autoimmune neuritis
Describe the Schwann Cell myelination?
E to E fusion, squeeze out cyto –> P to P fusion. 20-30 rotations. Cyto percolates in
Clefts Schmidt-Lanterman. Covers nodes of Ranvier. Basal lamina continuous.
What are the Schmidt-Lantermen clefts?
The clefts of Schmidt-Lanterman are areas in which small amounts of Schwann cell
cytoplasm are not displaced to the periphery during Schwann cell formation of the myelin.
They subdivide the myelinated axon into irregular portions
Discuss CNS myelination.
One oligodendrocyte – multiple neurons. Same process as in Schwann cells. MBP + PLP
(autoimmune destruction = MS). Fewer clefts of Schmidt-Latermann. No Basal lamina or
coverage of nodes – CNS has BBB. Channels concentrated at nodes of Ranviet.
Unmyelinated axons fully nude
Why is nerve regeneration poor in the CNS?
No basal lamina, astrocyte stacking
Discuss nerve generation in PNS
Initial distal Wallerian axonal degeneration, then reorganization of proximal segment.
Macrophages clean up, stim –> Schwann cells. Schwann cells proliferate –> neurotropins.
Schwann cells + basal lamina guide neurons
What is it called when there are lost axons?
Neuroma
