The brain parenchyma includes all of the functional tissue in the brain. It is made up of neurons and glial cells and is divided into white matter and grey matter, which is further divided into lobes and regions.
In animals, parenchyma comprises all of the functional tissue of an organ, but not the structural tissue. In the heart, the parenchyma is made up of myocytes; in the kidney, it is comprised of nephrons; and in the brain, it is comprised of glial cells and neurons. Glial cells are the non-neuronal cells of the brain, producing myelin, protecting the nerves, and maintaining homeostasis in the brain. Neurons conduct all of the nerve activity from the brain to every other part of the body.
White matter and grey matter in the brain are differentiated by density during a CT scan. White matter is mostly composed of myelinated axons, while grey matter is seen as more dense because it has fewer axons but is composed mostly of cell bodies. The brain parenchyma is also divided into six lobes, the left and right frontal, temporal and occipital lobes. On CT images, there are no distinctive borders between the different lobes, so medical professionals often refer to regions of the brain instead.