Gray matter (Lat. substantia grisea) is the outer layer of the two brain hemispheres, i.e the cerebrum. The gray matter serves as a center of several specialized regions of the brain which regulate and control memory, attention, thought, language, consciousness, perception, etc.
Hence, it’s labeled as the center of all intellectual abilities in the human brain.
Where Is The Gray Matter Located?
The cerebral cortex is covered by an outer layer of gray matter, which is also present in the brain, brainstem, and cerebellum, as well as throughout the spinal cord and the medulla oblongata.
This gray layer covers the layer made of proteins and phospholipids, called the white matter of the brain.
The gray matter follows the furrows (sulci) and the ridges (gyri) of the cerebrum, in order to cover its entire surface. Deeper in the cerebrum, there are small areas of gray matter called basal ganglia, which are composed of nerve cell bodies and dendrites of neurons.
The Function of Gray Matter
The gray matter of the cerebral cortex includes brain regions involved in the control of muscles and sensory perceptions, such as:
- memory,
- emotions,
- speech,
- self-control,
- decision making,
- seeing,
- hearing, etc.
With the help of the nerve cell bodies and dendrites of neurons, the gray matter processes information from the sensory organs toward its centers for regulation and control of our intellectual processes and skills.
Anatomy and Structure of Gray Matter
The gray matter of the human brain consists of:
-
- Neuronal cell bodies
- Dendrites of neurons
-
- Axons
- Glial cells (astrocytes and oligodendrocytes)
- Synapses
- Capillaries
- Basal ganglia (or basal nuclei)
Neuronal Cell Bodies (Soma)
The neuronal cell bodies (Gr. soma – body) are spherical constructional parts of the neuron that create the central nervous system. Their primary role is to send and receive signals, i.e. information which they gain from the exterior sensory stimuli via electrical impulses to the particular centers of the brain.
Dendrites of Neurons
Dendrites of neurons are extensions of a nerve cell that receive the signal from the other neurons via chemical signals and electric impulses obtained by the sensory organs. Then, they transmit this information to the soma, i.e. the body of the neuronal cell.
Axons
The impulses from the sensory organs are conducted from the cell body to the other cells via axons.
The axons are long, single-nerve cells that transmit impulses away from the cell body. Neurons always have only one axon.
Glial Cells (Astrocytes and Oligodendrocytes)
Glial cells are non-neuronal cells of the nervous system that create a physical support system for the neurons, which is vital for the proper functioning of both the nervous tissue and the central nervous system of the human brain.
Their function is to protect the neurons from outside influences and regulate the internal environment of the brain.
There are two subtypes of glial cells:
- Astrocytes
-
Oligodendrocytes
Astrocytes are star-shaped connective tissue cells of the central nervous system. Their function is to link the nerve cells to blood vessels and form the blood-brain barrier by wrapping the brain capillaries.
Furthermore, they regulate the levels of extracellular neurotransmitters, and participate in the body’s immune response.
Oligodendrocytes are cells with several branches stemming from them. They provide support and insulation to the axons by producing myelin. This process is very important for increasing the speed of nerve conduction.
Synapses
The specialized links between the neurons which aid their functional communication are called synapses.
The synapses are small gaps at the end of a neuron which serve as a passage for the signal. Through the synapses, the information from the sensory organs is transferred from one neuron to another.
These small neuron connectors play a vital role in the proper function of the brain, especially in the processes regarding memory.
Capillaries
These small blood-carrying vessels create a structure that forms the blood-brain barrier. They are involved in numerous metabolic and transport processes that are of vital importance for the proper functioning of the brain.
The capillaries play a role in the physical transport mechanisms of the central nervous system by allowing only the most important nutrients to pass through them, thus protecting the brain.
Basal ganglia (Basal Nuclei)
Basal ganglia (or basal nuclei) of the cerebrum are large portions of gray matter located deep within the central core of the white matter in both cerebral hemispheres.
They are made of large groups of brain nuclei and are a complex interface between sensory inputs and motor skills, especially for semi-automatic movements, such as walking.
The basal ganglia of the gray matter include the following structures:
- Caudate nucleus – This structure has a great role in the process of learning, storing, and processing information. It uses previous experiences as feedback in order to design our future actions and reactions in the brain.
- Lentiform nucleus – a large, lens-shaped layer of gray matter which consists of a collection of brain nuclei.
- Amygdaloid nuclear complex (or Amygdala) – a walnut-shaped group of more than 10 nuclei located in the temporal lobe, responsible for the regulation and control of our emotions, survival instincts, and memory.
- Claustrum – a thin layer of gray matter deep inside the insula which coordinates and synchronizes different functions of the brain. In fact, the sensory information from almost all parts of the brain arrives at the claustrum, giving it the function of a ‘command center’ of the brain.
- Substantia nigra – a basal ganglia structure within the midbrain. It’s further divided into a reticulata (a network-like construction) and a compacta (a close-together construction) part based on the position of neurons within each part.
The substantia nigra plays a great role in the regulation of movements and production of dopamine (a neurotransmitter which improves the blood-pumping of the heart, as well as the blood flow to the kidneys).
- Subthalamic nucleus – a small, lens-shaped nucleus in the brain, that accounts for a major part of the subthalamus, and performs motor control and action selection in the brain.
The basal ganglia of the brain control and regulate various functions of the brain, such as voluntary motor movements, emotion, cognition, movement of eyes, learning of habits, etc.
During the performance of these processes, they are interconnected with the cerebral cortex, thalamus, brainstem, as well as other centers of the brain.
What Is the Difference Between the Gray Matter and the White Matter of the Human Brain?
The most distinguished difference between the gray matter and the white matter is their distinct color. While the neuronal cell bodies and the capillaries nested in the gray matter give it a gray-pinkish color, the white matter gets its color from the whiteness of myelin.
Myelin is a protein and phospholipid (fatty) sheet that wraps the nerve fibers in the brain, protecting them and speeding up the electrical impulses carried to the brain centers by the neurons.
At the same time, myelin insulates the axons (nerve fibers) of the white matter, thus protecting them from the electrically charged atoms and molecules.
To continue with, gray matter consists of whole neuronal cells, while white matter contains neuronal connections. Also, gray matter contains the centers where the information from the sensory organs are processed and transported via neurons, while white matter contains the neuronal connections.
What Happens if the Gray Matter of the Human Brain Is Dysfunctional?
Any damage to any part of the brain is usually irreversible and can result in the loss of function of the respective area.
For instance, damage to the caudate nucleus of the basal ganglia can result in obsessive-compulsive behavior, loss of drive, and hyperactivity.
Also, an injury to the subthalamic nucleus of the gray matter can result in movement disorders. The subthalamic nucleus is also a target site for neurosurgical treatment in Parkinsonian patients.
Individuals with fewer nerve cells in the subthalamic nucleus suffer from Huntington’s disease – a condition that leads to progressive degeneration of the brain cells.
The patients affected with this disease note difficulty in concentration, clumsiness, memory lapses, as well as difficulty with swallowing, moving, speaking, and breathing.
A broken vessel of the brain can lead to headaches, blurred vision, dizziness, difficulty in speaking, etc.
To Sum Up
The gray matter of the human brain consists of approximately 50 billion neurons and perhaps 10 times more supporting cells.
It covers both brain hemispheres – the left and the right side of the brain, and gets its distinct gray color from the neural cell bodies it contains. In contrast, the white matter of the brain gets its color from the myelinated nerve fibers which are white due to their protein construction.
The main functions of the gray matter include all of the intellectual processes, our ability to sense, and some of our behavior patterns. In this regard, it transfers the stimuli received by the sensory organs via neurons to the respective centers of the brain where they are further processed, regulated, and controlled.
In case the gray matter (or any part of the brain in this regard) becomes dysfunctional, it may put some of the most vital functions of the body at risk, the functions controlled by the centers located in the gray matter of the cerebral cortex.
Fun Facts
Did you know?
- The human brain is the busiest organ of the human body. The gray matter aids your process of thinking, learning, and reasoning – without you even thinking of those processes.
- Even though it’s symmetrically divided into two hemispheres, our brain isn’t symmetrical when it comes to the distribution of the neurotransmitters located in the gray matter. Namely, the left hemisphere of the brain contains more neurons than the right hemisphere of the brain. This, in part, explains the fact that the majority of people are right-handed since the left brain hemisphere controls the right side of our body.
- The human brain is one of the major consumers of oxygen in the human body. The gray and white matter of the brain share the needed portion of oxygen in uneven parts. The gray matter consumes 94% of the total oxygen supply needed by the brain, while the white matter consumes only the remaining 6%.
- Any type of physical activity, even yoga, can help us increase the volume of the gray matter of our brain. A healthy breakfast or learning something new also helps in this regard.
- The human brain is so complex, that even the highly-developed modern science and technology cannot find answers for some of its super-functions or a cure for the numerous nervous system diseases.
- The gray matter of the human brain holds the key to our intelligence, to academic success, as well as to life-skills in general.
- The human brain has a jelly-like structure because of the high water concentration in its structure. Namely, 77% to 80% of its entire mass is actually water. The greater part of this water concentration reaches the brain through our blood, i.e. the capillaries.
This makes our daily hydration, i.e., intake of water, very important for our brain’s wellbeing and proper functioning.
- It’s important to note that smoking leads to a decrease in volume of the gray matter of the brain. Namely, smokers lose the volume of gray matter at a faster rate than non-smokers.
A few more examples of bad habits which lead to a decrease in volume of the gray matter include: simultaneous use of media (watching TV while checking your phone and printing some material, for instance), stressful situations and stress in general, excessive screen-time (addiction to playing computer games), etc.
- The electrical connections between the neurons in the brain depend on how much we use our ability to learn. The more we learn, the more those connections are generated and upgraded.
- Our memory is stronger when the electrical connections between the neurons in the brain which transfer information from the sensory organs to the corresponding centers are more frequent.