Neuroglia
These were originally described as supporting cells (glia means 'glue'), but they have a multitude of other functions, such as
Found in CNS and PNS
CNS
Oligodendroglia
Myelinate CNS axons
Myelin is an insulating sheath around axons; consists of multiple layers of neuroglial membrane; significantly increases the impulse propagation rate along axons
Myelin is mostly phospolipids - gives white appearance
White matter - myelinated axons in the CNS, these axons are bundle together and form tracts in the CNS
Ex) Corticospinal tract - from motor cortex in the cerebrum, synapes with neurons that exit the spinal cord as spinal nerves
Ex) Reticulospinal tract - from a structure in the brain called the reticular formation, synapse with neurons that exit the spinal cord
This is contrasted with Gray matter - mostly cell bodies (also neroglia and unmyelinated axons) in the CNS
Cell bodies (and therefore Gray Matter) are organized in bundles within the CNS referred to as nuclei - these act as stations that send out or receive information in the CNS
These nuclei do not initiate movements, but once movements are underway, they provide the general pattern and rhythm for movement (walking, ex)
Information arrives in the basal nuclei from sensory, motor and integrative areas of the cerebral cortex
Usually, tracts leaving the basal nuclei have an inhibitory effect on motor neurons. This is established by the release of the neurotransmitter dopamine in the nearby nuclei called the substantia nigra