The brain is a complex organism controlling thought, memory, emotion, touch, motor skills and so much more. In fact, the brain is behind every process regulating the human body. Therefore, it’s extremely important. The brain and the spinal cord make up the central nervous system (CNS).
What is the brain made of?
Weighing in at about 3 pounds in an average human adult, the brain is about 60% fat. The remaining 40% is a combination of proteins, water, carbohydrates and salts. The brain itself is not a muscle. However, it does contain blood vessels and nerves, including neurons and glial cells.
What are gray matter and white matter?
Gray matter and white matter are two different regions of the central nervous system. In the brain, the grey matter refers to the darker, outer portion of the organ. White matter, conversely, describes the lighter, inner section underneath. In the spinal cord, white matter and gray matter are in reverse.
Gray matter is primarily composed of neuron somas. Neuron somas are round central cell bodies. White matter, therefore, is mostly made of axons. Axons are long stems connecting neurons together wrapped in myelin, a form of protective coating. The different composition of neuron parts is why the two appear as separate shades on certain scans.
Gray matter is mostly responsible for processing and interpreting information while white matter takes that information and transmits it to other parts of the nervous system.
How does the brain work?
The brain sends and receives both chemical and electrical signals throughout your body. These different signals control different processes. Your brain interprets each of them. Some of these processes make you feel tired, others cause you pain and so on and so forth. Some of these messages are kept inside the brain whereas others are relayed through the spine and across the body’s vast network of nerves.
The Main Parts of the Brain and Their Functions
The brain can be divided at its highest level into three parts:
- The cerebrum,
- The brain stem,
- And cerebellum.
Cerebrum
The cerebrum is the front of the brain. It is comprised of gray matter in the cerebral cortex and white matter in the center. This is the largest part of the brain. It initiates and coordinates movement and regulates our body temperature. The cerebrum is also responsible for regulating speech, judgement, thinking and reasoning, problem-solving, emotional responses and learning. Other functions of the cerebrum relate to vision, hearing, touch and the other senses.
Cerebral Cortex
The cerebral cortex describes the outer gray matter covering the cerebrum. It has a large surface area due to its folds and comprises about half of the brain’s weight. Divided into two halves or hemispheres, the cerebral cortex is covered with ridges (gyr) and folds (sulci). The two halves join together at a large, deep sulcus known as the interhemispheric fissure. This runs from the front of the head to the back. The right hemisphere controls the left side of the body and the left controls the right side. The two hemispheres communicate with one another through a large, c-shaped structure of white matter and nerve pathways referred to as the corpus callosum, which is in the center of the cerebrum.
Brainstem
This is the middle of the brain. The brainstem connects the spinal cord with the cerebrum. The different parts of the brain stem are:
- The midbrain,
- The pons,
- And the medulla.
The Midbrain, aka mesencephalon, is a complex structure with a range of different neuron clusters known as nuclei and colliculi, neural pathways and other structures. The midbrain facilitates various functions including hearing and movement, calculation of responses and environmental changes. Inside the midbrain is the substantia nigra, an area that is rich in dopamine neurons and part of the basal ganglia, enabling movement and coordination. The substantia nigra is most notably affected in Parkinson’s disease.
The pons is the origin for four of the 12 cranial nerves. It enables a wide variety of processes including tear production, chewing, blinking, focusing vision, balance, hearing and facial expressions. Pons is Latin for the word “bridge” and it is accurate because the pons bridges the midbrain and the medulla.
At the bottom of the brainstem, the medulla is where the brain meets the spinal cord. Essential to survival, the medulla regulates heart rhythm, breathing as well as oxygen and carbon dioxide levels. Reflexive activities such as swallowing, vomiting, coughing and sneezing originate in the medulla. The spinal cord extends from the bottom of the medulla and through a large opening in the bottom of the skull. It is supported by vertebrae and carries messages from the brain to and from the rest of the body.
Cerebellum
Also known as the “little brain”, the cerebellum is about the size of a fist. It’s located in the back of the head, below the temporal and occipital lobes. It resides above the brainstem. Just as the cerebral cortex has two hemispheres so does the cerebellum. Its function is to coordinate voluntary muscle movements and to maintain posture, balance and equilibrium. Studies are being conducted to see what role the cerebellum plays in thoughts, emotions and social behavior as well as its possible involvement in addictions and psychological disorders like schizophrenia.
Meninges
The brain has three protective coverings referred to as meninges. The outermost layer is referred to as the dura. This layer is thick and tough. Within this layer are two deeper layers – the periosteal layer (cranium) and the meningeal layer which is below the periosteal layer. Any spaces between the layers allow for the passages of veins and arteries which supply blood flow to the brain. The arachnoid mater is weblike as its name suggests (arachnid being the Latinate term for spider). This web connects tissue without nerves or blood cells. The cerebrospinal fluid (CSF) lies below the arachnoid mater and it cushions the entire central nervous system. CSF circulates around these structures to remove impurities. Finally, the pia mater is a thin layer of membrane which cradles the surface of the brain. It also follows its contours. This part of the brain is full of veins and arteries just like the dura.
In the next article, we’ll talk about the lobes, what they control, deeper structures of the brain and nerves.
Deanna Goodson 