Difference Between White Matter and Grey Matter

Main Difference – White Matter vs Grey Matter

White matter and grey matter are two components in the brain and the spinal cord. The brain and the spinal cord consist of nerves that belong to the central nervous system. The major function of the central nervous system is to coordinate the functions of the body based on the information carried by the peripheral nervous system. White matter occurs in both brain and the spinal cord. But, grey matter is the major component of the brain. The main difference between white matter and grey matter is that white matter mainly consists of myelinated axons whereas grey matter mainly consists of cell bodies, axon terminals, and dendrites. The white colour occurs due to the lipid components of the myelin.

Key Areas Covered

1. What is White Matter
      – Definition, Characteristics, Function
2. What is Grey Matter
      – Definition, Characteristics, Function
3. What are the Similarities Between White Matter and Grey Matter
      – Outline of Common Features
4. What is the Difference Between White Matter and Grey Matter
      – Comparison of Key Differences

Key Terms: Axons, Brain, Cell Bodies, Grey Matter, Myelin, Nerve Cells, Neuroglia, Spinal Cord, White Matter

What is White Matter

The white matter is the pale coloured parts of the brain and the spinal cord. It occupies 60% of the brain. The white matter occurs in the subcortical regions of the brain. It is mainly composed of myelinated axons of the nerve cells. The lipid components of the myelin give the colour to the white matter. Myelin is secreted by oligodendrocytes, which insulate the axons of the nerve cells in the brain. Myelin has two functions in the nerve cells. By insulating the axons, it increases the speed of transmission of the nerve impulses. Typically, most of the longer axons are myelinated. Myelin protects the nerve fibres from injury as well. The white and grey matter of the brain is shown in figure 1.

Main Difference - White Matter vs Grey Matter

Figure 1: White and Grey Matter of the Brain

Since the white matter comprises of nerve axons, it is mainly involved in the transmission of nerve impulses. The myelin sheath of the white matter can be destroyed during multiple sclerosis.

What is Grey Matter

The grey matter is the dark coloured parts of the brain and the spinal cord. The grey matter occupies 40% of the brain. In the brain, the grey matter occurs on the surface of the cortical regions. The grey matter contains the cell bodies of the nerve cells of the central nervous system, neuroglia, axon terminals, and capillaries. These components collectively give a pinkish-grey colour to the grey matter. It also contains unmyelinated axons. Since grey matter contains the cell bodies of the nerve cells, it is the information processing part of the brain. It retrieves information from the sensory organs through the white matter. The instructions are also sent through the white matter to the effector organs.

Difference Between White Matter and Grey Matter

Figure 2: White and Grey Matter of the Spinal Cord

The exact locations of the grey matter are;

Cerebral cortex
Cerebellar cortex
Deep within the hypothalamus, thalamus, subthalamus, and basal ganglia
Deep within the dentate nucleus, emboliform nucleus, fastigial nucleus, and globose nucleus
In the brain stem, red nucleus, olivary nucleus, substantia nigra, and cranial nerve nuclei
In the spinal cord, anterior horn, lateral horn, and posterior horn

Similarities Between White Matter and Grey Matter

White matter and grey matter are two components of the brain and the spinal cord.
Both white matter and grey matter is composed of the components of the nerve cells.
Both white matter and grey matter together form the spinal tracts to send signals from the central nervous system to the rest of the body.

Definition

White Matter: White matter is the paler tissue of the brain and the spinal cord, which mainly consists of nerve fibres with their myelin sheaths.

Grey Matter: Grey matter is the darker tissue of the brain and the spinal cord, which mainly consists of nerve cell bodies and branching dendrites.

Composition

White Matter: White matter is composed of myelinated axons of the nerve cells.

Grey Matter: Grey matter composed of cell bodies, axon terminals, and dendrites.

Myelinated Axons

White Matter: White matter has a large number of myelinated axons.

Grey Matter: Grey matter has fewer myelinated axons.

Colour

White Matter: White matter gets its light colour due to the lipid components of the myelin.

Grey Matter: Grey matter gets its pinkish-grey colour due to the neuronal cell bodies and the capillary blood vessels.

Axons

White Matter: The nerve cells in the white matter contain long axons.

Grey Matter: The nerve cells in the grey matter contain short axons.

In the Brain

White Matter: In the brain, white matter occurs in the cortex.

Grey Matter: In the brain, grey matter occurs on the surface areas.

In the Spinal Cord

White Matter: White matter occurs on the surface of the spinal cord.

Grey Matter: Grey matter occurs inside the spinal cord.

Proportions in the Brain

White Matter: White matter occupies 60% of the brain.

Grey Matter: Grey matter occupies 40% of the brain.

Development

White Matter: The highest development of the white matter is identified at the twenties.

Grey Matter: The highest development of the grey matter is identified at the middle age of life.

Role

White Matter: White matter transmits both sensory and motor impulses between the peripheral nervous system and the grey matter.

Grey Matter: Grey matter processes the retrieved information from the white matter and sends the instructions back to the effector organs through the white matter.

Function

White Matter: White matter controls the involuntary functions of the body such as blood pressure, heart rate, and body temperature.

Grey Matter: Grey matter controls the senses of the body such as hearing, feeling, seeing, speech, and memory.

Conclusion

White and grey matter are the two components of the brain and the spinal cord. The brain and the spinal cord collectively make up the central nervous system of vertebrates, coordinating the functions of the body. White matter is mainly composed of myelinated axons. Myelin gives the white colour to the white matter. The grey matter contains cell bodies, neuroglia, and axon terminals. Since white matter contains nerve axons, it transmits the nerve impulses in and out of the central nervous system. The grey matter processes the information from the peripheral nervous system by the cell bodies of the nerve cells. The main difference between white matter and grey matter is their components and functions.

Reference:

1. “White matter of the brain.” MedlinePlus Medical Encyclopedia, Available here. Accessed 11 Sept. 2017.
2. Robertson, BSc Sally. “What is Grey Matter?” News-Medical.net, 5 Nov. 2014, Available here. Accessed 11 Sept. 2017.

Image Courtesy:

1.”1202 White and Gray Matter” By OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “1313 Spinal Cord Cross Section” By OpenStax – (CC BY 4.0) via Commons Wikimedia