Myelination of neurons in a developing nervous system occurs when Schwann cells or oligodendrocytes grow around an axon so their plasma membranes form concentric layers. Provides electrical insulation since membranes are mostly lipid which is a poor current conductor. Insulating myelin sheath increases the speed of nerve impulse propagation. In multiple sclerosis, myelin sheaths deteriorate causing a disruption of nerve impulse transmission and consequent loss of coordination. Impulses are action potentials, electrical signals propagated along neuronal membranes Signal transmission along the length of a neuron depends on voltages created by ionic fluxes across neuron plasma membranes.
All cells have an electrical membrane potential or voltage across their plasma membranes.
The charge outside the cell is designated as zero, so the minus sign indicates that the cytoplasm inside is negatively charged compared to the extracellular fluid. Is about -70mV in a resting neuron. Differences in the ionic composition of the intracellular and extracellular fluids.