What is grey matter?
Grey matter is a type of tissue in your brain and spinal cord (central nervous system) that plays a crucial role in allowing you to function normally from day to day. It consists of high concentrations of neuronal bodies, axon terminals (endings) and dendrites.
A nerve cell (neuron) consists of:
- A large cell body (neuronal body), which contains a nucleus. The nucleus controls the cell’s activities and contains the cell’s genetic material.
- One elongated extension (axon) for sending electrical signals.
- Many branches (dendrites) for receiving signals from other cells.
Grey matter forms early in fetal development. Once a baby is born, the volume of grey matter increases until around the age of 8. After this, the density of grey matter increases until about the age of 20. This increase in density allows for high processing and further mental development. Neurons don’t renew or regenerate, however. So, if a neuron is damaged or dies, it doesn’t get replaced.
The nervous systems of all mammals (rats, dolphins, humans, etc.) are similar. However, the human brain has many structural differences. Human brains have many convolutions on the surface. The “grooves” are called sulci, and the “bumps” are called gyri. This thin sheet of sulci and gyri contains neurons that lie on the surface of your brain. This is called grey matter.
The sulci and gyri that form grey matter allow tremendous expansion of the surface area of your brain during development when your brain must fold and “wrinkle” on itself to fit within your skull. This allows humans to have significantly more grey matter than other mammals. For example, a human brain has approximately 1,000 times more grey matter on the surface than a mouse.
What’s the difference between grey matter and white matter?
White matter and grey matter are both essential parts of your brain and spinal cord. Approximately 40% of your brain consists of grey matter and 60% is made of white matter.
Grey matter consists of neuronal cell bodies and their dendrites. The dendrites are short protrusions (like little fingers) that communicate with neurons close by. In contrast, your white matter consists of the long axons of neurons that transmit impulses to more distant regions of your brain and spinal cord.
Because grey matter has a large number of neuronal bodies (which contain the nucleus of the cell), this is where information processing happens. The grey matter is the seat of a human’s unique ability to think and reason. The grey matter is the place where the processing of sensation, perception, voluntary movement, learning, speech and cognition takes place.
White matter’s role is to provide communication between different grey matter areas and between grey matter and the rest of your body.
Grey matter gets its color from a high concentration of cell bodies of neurons. White matter gets its color from a protective covering over the axons called the myelin sheath.
