Some things here that I did not know. Cells in the brain that transmit nerve impulses are mostly white-colored, because their constituents are mainly lipids or fatty acid chains that form the insulating myelin. The parts of the brain that process information are grey-colored cells. They contain more proteins than the white cells.
From the MRI scans, my brain has an abnormally high amount of white matter present. Nobody offered to explain why -- but everyone who made an attempt to analyze the pictures made this observation.
So what? I don´t know. Still learning...
| Schwannoma Classification and external resources | |
That is what was growing on my spinal cord.
Named after the German physiologist Theodor Schwann, Schwann cells (also referred to as neurolemnocytes) are a variety of glial cell that keep peripheral nerve fibres (both myelinated and unmyelinated) alive. In myelinated axons, Schwann cells form the myelin sheath (see below). The sheath is not continuous. Individual myelinating Schwann cells cover about 100 micrometre of an axon. The end result is a string of Schwann cells along the length of the axon, much like a string of sausages. The gaps between adjacent Schwann cells are called the nodes of Ranvier. The vertebrate nervous system relies on the myelin sheath for insulation and as a method of decreasing membrane capacitance in the axon. The action potential jumps from node to node, in a process called saltatory conduction, which can increase conduction velocity up to X10, without an increase in axonal diameter. In this sense, Schwann cells are the peripheral nervous system's analogues of the central nervous system oligodendrocytes. However, unlike oligodendrocytes, each myelinating Schwann cell provides insulation to only one axon (see image). This arrangement permits saltatory conduction of action potentials with repropagation at the Nodes of Ranvier, the gaps between myelinated segments. In this way, myelination greatly increases speed of conduction and saves energy .
Schwannomas are very homogeneous tumors, consisting only of Schwann cells. The tumor cells always stay on the outside of the nerve, but the tumor itself may either push the nerve aside and/or up against a bony structure, thereby causing damage.
