12/03/2020
🍁 Gray Matter and White Matter
The Central Nervous System has two kinds of tissue namely grey matter and white matter. Grey matter, which has a pinkish-grey color in the living brain, contains the cell bodies, dendrites and axon terminals of neurons, so it is where all synapses are.
White matter is made of axons connecting different parts of grey matter to each other.
The grey matter serves to process information in the brain. Structures within the grey matter process signals generated in the sensory organs or other areas of the grey matter. This tissue directs sensory (motor) stimuli to nerve cells in the central nervous system where synapses induce a response to the stimuli.
White matter is found in the deeper tissues of the brain (subcortical). It contains nerve fibers (axons), which are extensions of nerve cells (neurons). Many of these nerve fibers are surrounded by a type of sheath or covering called myelin. Myelin gives the white matter its color.
White matter is composed of bundles, which connect various gray matter areas (the locations of nerve cell bodies) of the brain to each other, and carry nerve impulses between neurons.
While 20 percent of all the oxygen we breathe goes directly to the brain, an overwhelming majority of that (95 percent) suffuses into the gray matter. Overall, gray matter occupies 40 percent of the cerebrum, while white matter fills the remaining 60 percent.
⚜ Functions :
♦ Grey matter contains most of the brain's neuronal cell bodies. The grey matter includes regions of the brain involved in muscle control, and sensory perception such as seeing and hearing, memory, emotions, speech, decision making, and self-control. The anterior grey column contains motor neurons.
♦ The type of fat in myelin makes it look white, so myelin-dense white matter takes on a white hue as well.
⚜ Glial Cells :
In contrast, gray matter is mostly neuron cell bodies and non-neuron brain cells called glial cells. These glial cells provide nutrients and energy to neurons.
⚜ Loss of Gray Matter :
Once damage has occurred, the cell cannot support its axons or dendrites and the entire cell dies. This is especially true in neurons that have large cell bodies and long axons. In contrast, after a white matter injury, a healthy cell body may be able to repair the damaged axon.
White matter sits underneath the brain's cortex, or grey matter. In general, White Matter Damage (WMD) is caused by a lack of oxygen to that part of the brain. Periventricular leucomalacia (PVL) is a condition in which decreased blood flow to brain tissue causes it to soften up and eventually die.
In addition to the well-recognized sensorimotor deficits that can accompany white matter involvement such as visual loss, paresis, spasticity, ataxia, gait disorder, and incontinence, a wide variety of neurobehavioral dysfunction can occur, including focal disconnection syndromes, neuropsychiatric disorders.
