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What is Grey Matter?

Our brain is deemed as one of the most complex and intriguing structures. But anatomically it can be divided into a few discrete parts which are: the right and left hemispheres, frontal lobes, occipital, temporal, and parietal lobe. Another common divider for the brain is grey matter and white matter.

Grey and white matter tissues are present in our central nervous system. Grey matter forms the outermost layer of our brain and has a pinkish-grey tone (that’s where the name comes from). The grey matter has an essential role in enabling human beings to function normally on a daily basis. Grey matter and white matters are both vital sections of the brain and spinal cord.

We will learn a great deal about the grey matter in the brain in this article. We will be covering functions of grey matter, the difference between grey and white matter, and also learning how to increase grey matter through certain activities.

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Grey Matter Contents

The material between our ears is present in two shades; white and grey. The difference between these two matters is in the amount of fat content. The grey matter contains:

  • High concentration of neuronal cell bodies (which is responsible for its grey tone).

  • Unmyelinated Axons - Axons are elongated portions of the neuron which is placed at the center of the cell in between axon and soma. These axons are unmyelinated which means they do not have a covering of fatty protein which is whitish in color.

  • Non-neuron Brain Cells Which are also Called Glial Cells - These cells provide energy and nutrients to the neurons. They also help in transporting glucose to the brain, clean excess chemicals out of the brain, and may also affect the intensity of how neurons communicate.

Grey matter forms from ectoderm (the outermost layer of skin) in early development years and continues to form till we attain 8 years of age. After this point, the grey matter starts decreasing in brain areas but the matter density increases. This higher density allows further mental development and higher processing powers of our brains.

Grey Matter in Brain 

Grey matter in the brain is found in abundance in the cerebellum, brain stem, cerebrum, and spinal cord. 

  • The cerebrum has a sheet of grey matter of thickness of 2 to 5 mm.

  • Grey matter in the brain is highly concentrated in the Cerebellum, which is just 10% of the total brain volume. The cerebellum contains more neural cell bodies than all the other parts of the brain combined.

Grey Matter Composition and Placement

The grey matter has somas which are neuronal cell bodies. These structures are circular in shape and contain the nucleus of the cells. Our cerebellum has 10 to over 50 billion cells.

  • White matter is a layer of nerve fibers lying below the grey matter surface. White matter connects neurons in the grey matter to other parts of the brain.

  • Grey matter is present throughout the inside of the spinal cord in a horn-like structure and white matter fills up the surrounding sections of the spinal cord.

  • Grey matter around the cerebrum is referred to as the cortex of the brain. We have two major cortexes in our brains: cerebellar and cerebral cortexes.

  • The cortex has a wrinkled appearance due to the presence of ridges (called gyri) and grooves (called sulci).

  • Gyri and sulci increase the surface area of the brain which allows more neurons to be present (which is not possible on a smooth surface). This is crucial for the effective working of the brain.

  • Grey matter also contains glial cells which are supportive to the neurons. Glial cells, specifically oligodendrocytes (they produce myelin) and astrocytes are present in numbers that are 10 times more than neurons.

  • Grey matter also has capillary blood vessels and neuropil which is a mix of glia, dendrites, and unmyelinated axons.

Grey Matter Function

Grey matter performs many functions in our bodies that are basic for living. It enables us to control our movements, regulate emotions, retain memories, and controls many other aspects of human life that depend on grey matter in brain. 

  • Grey matter processes information in the brain. Grey matter receives signals from our sensory organs or other areas within the grey matter. There are structures in grey matter that process these signals. These sensory stimuli are then directed to the neurons present in our central nervous system where synapses produce a response to the stimuli.

  • Grey matter in the cerebellum affects human personalities and plays a role in:

    • Motor functioning and automatic movements

    • Intelligence

    • Organization

    • Planning 

    • Processing sensory information

    • Language processing

  • The grey matter of the spinal cord has its own functions. The anterior column of grey matter connects to the brain via a pathway known as the pyramidal tract (originating in the cerebral cortex) and is essential for motor movements

  • The posterior grey matter in the spinal cord helps in receiving sensory signals and enables our body’s constant interaction with the environment.

  • The lateral grey matter in the spinal cord is present in the middle and regulates the autonomic nervous system by activating the sympathetic nervous system. Our bodies’ response to stressful situations is stimulated by the sympathetic nervous system. For example, when our heartbeat accelerates, the nervous system sends extra blood to muscles.

How to Increase Grey Matter

There are a few ways of boosting your mood and reducing stress which also leads to an increase in the grey matter in the brain.

  • Meditation - As per a study from Harvard University, long-term meditation has been shown to increase the amount of grey matter in the brain within the sensory and insula region and sensory and auditory cortex. Meditation alters brain wave patterns and helps you sleep better. 

  • Physical Activities - Apart from the health benefits of physical activities, science has proven that working out increases grey matter in the brain. Cardiovascular exercises enhance the central nervous system and increase both grey matter and white matter in our brains.

  • Playing Video Games - Many people feel that playing video games is bad for your brain. But according to a study done by the Macquarie University of Sydney and the University of Electronic Science and Technology of China, video games change the brain structure. They heighten the connection between a few insular cortex subregions and result in a larger surface area and greater volume of grey matter 

FAQs (Frequently Asked Questions)

1. What is the difference between white matter and grey matter in the brain?

Ans: The difference between white and grey matter is highlighted below:

  • Grey matter mostly consists of soma which are neuronal cell bodies that are spherical bodies containing the neuron’s nucleus. White matter area of brain mostly contains myelinated axons (long relays extending out of soma)

  • White matter has a high content of lipid fat which grey matter does not have.

  • Grey matter is fully developed by the time a person is in his or her 20s while white matter develops all through the 20s and peaks in middle age.

  • Grey matter conducts, processes, and sends information to various parts of our bodies while white matter interprets sensory information form different body parts.

2. Explain the different layers of the grey matter of spinal cord.

Ans: Our spinal cord is a vital hub in our body that processes and relays information and connects our brain to the rest of the body. Grey matter in the spinal cord, based on its function, can be classified in three different ways:

1. Four Main Columns

a. Dorsal horn (posterior horn) - These have neurons that receive somatosensory signals of the body and then send them to the brain through an ascending pathway.

b. Ventral horn (anterior horn) - This has mainly motor neurons.

c. Intermediate column - These along with lateral horn supply neurons to pelvic and visceral organs.

d. Lateral horn - This column works similar to the intermediate column.

2. Six different Nuclei

a. Marginal zone - This is situated at the tip of the dorsal horn and relays temperature and pain stimuli to the brain.

b. Susbtantia gelatinosa - This is present at the top of the dorsal horn and relays pain, temperature, and light touch sensation to the brain.

c. Nucleus proprius - Situated at the neck of the dorsal horn, nucleus proprius relays temperature and mechanical sensations to the brain.

d. Dorsal nucleus of Clarke - DNC is responsible for relaying unconscious proprioceptive sensation to the brain. These are found only in two spinal segments which are L3 and C8.

e. Intermediolateral nucleus (IMN) - It is present in the lateral horn as well as the intermedial column. Sensory information from the viscera is conveyed to the brain through IMN.

f. Medial and lateral motor neurons (MNs) - They are inside the ventral horn and are made up of motor neurons. They innervate skeletal and visceral muscles.

3. Ten Rexed Laminae 

These are layers inside the spinal cord which have cells grouped as per their structure and function and not just based on location.

a. Lamina I - They correspond to the marginal zone and cells in this lamina respond to thermal or noxious stimuli.

b. Lamina II - They correspond to the substantia gelatinosa and cells in this lamina respond to noxious or non-noxious stimuli. They modulate sensory input and help the brain in interpreting whether incoming signals are painful or not.

c. Lamina III - They partially correspond to the nuclear proprius and are involved in the sensation of light touch and proprioception.

d. Lamina IV - These cells connect with the cells in lamina II and partially correspond to the nuclear proprius. They relay and process non-anxious sensory information.

e. Lamina V - It receives the descending information from the brain and relays sensory information including potentially painful ones (nociceptive) to the brain.

f. Lamina VI - It has many tiny interneurons that are involved in spinal reflexes. 

g. Lamina VII - This is a large zone that receives information from lamina II to lamina VI. Its job is to relay information to the viscera. DNC is part of Lamina VII. It also produces cells that are involved in the autonomic system.

h. Lamina VIII - Cells in this layer modulate motor output to skeletal muscle.

i. Lamina IX - It is a distinct group of motor neurons that provide neurons to skeletal muscle.

j. Lamina X - This layer crosses over from one side of the spinal cord to another.