Most of the space in the brain is taken up by axons, which are often bundled together in what are called nerve fiber tracts. A myelinated axon is wrapped in a fatty insulating sheath of myelin, which serves to greatly increase the speed of signal propagation. (There are also unmyelinated axons). Myelin is white, making parts of the brain filled exclusively with nerve fibers appear as light-colored white matter, in contrast to the darker-colored grey matter that marks areas with high densities of neuron cell bodies. COUNT 5
QSN1 Axons grouped together are known as what? ANS1 nerve fiber tracts QSN2 An axon that can greatly increase speed of signals is wrapped in what? ANS2 sheath of myelin QSN3 Myelin is what color in the brain? ANS3 white QSN4 Most of the space in the brain is made up of what structures? ANS4 axons QSN5 Grey matter of the brain consist of lots of what? ANS5 neuron cell bodies