An Introduction to the Human Brain: Facts, Anatomy, and Functions
The Human Brain
The human brain is an awesome and fascinating organ that is slowly yielding its secrets to researchers. More than any other part of our body, the brain seems to be "us". It's the place where we think, make decisions, solve problems, analyze situations, recall memories, and plan our creations. It receives information from sense organs and sensory receptors, creates images, sounds, sensations and feelings in our mind, and controls, coordinates, and monitors body activities.
The brain has intrigued scientists and the general public for a long time. Understanding its anatomy and physiology may enable researchers to discover cures for specific diseases.
The structure and activity of the brain are complex and can be studied at different layers of detail. The description below is suitable for senior high school students and for other people who are interested in this amazing component of the human body.
Interesting Brain Facts
- An adult human's brain weighs about 3 pounds, or around 1.4 kilograms.
- The brain is responsible for about 2% of an adult's weight but contains about 20% of the body's blood supply due to its high oxygen requirement.
- At normal temperatures, brain cells can begin to die in as little as three or four minutes without oxygen.
- There are about 100 billion neurons in the brain (cells that conduct nerve impulses) and at least as many glial cells. Glial cells don't get as much publicity as neurons. They are actually a very important component of the brain because they are the support cells for the neurons. Without glial cells, the neurons would be unable to work properly.
- The brain contains no pain receptors and so cannot feel pain. The meninges, blood vessels, and other structures that cover or surround the brain do contain pain receptors, however.
- The brain receives nerve impulses from pain receptors throughout the body, causing us to feel pain in those areas.
- The surface of a living brain is a pink-grey color while the underneath is lighter.
- The surface of the brain is filled with "grey matter" that contains the cell bodies of the neurons in the brain. The cell body of a neuron contains its nucleus.
- The paler "white matter" is where the axons of the neurons are located. These extensions from the cell body are covered in a fatty material called myelin. Myelin is beneficial because it speeds up the conduction of nerve impulses
- In the central nervous system (brain and spinal cord), myelin is made by cells called oligodendrocytes. In the peripheral nervous system, it's made by Schwann cells.
- The largest part of the brain is the cerebrum. The surface of the cerebrum is known as the cerebral cortex and consists of ridges and fissures. The technical name for a ridge is a gyrus (plural = gyri) and the technical name for a fissure is a sulcus (plural = sulci).
- A deep groove in the middle of the cerebrum separates it into the right and left cerebral hemispheres.
- The cerebral hemispheres are connected by a band of tissue within the brain called the corpus callosum.
- Underneath the cerebrum, at the base and back of the brain, is the cerebellum. Like the cerebrum, the cerebellum exists as two hemispheres.
- In front of the cerebellum is the brain stem. This connects the brain to the spinal cord. From top to bottom the brainstem consists of the midbrain, the pons, and the medulla oblongata (or medulla).
- Deep inside the brain, above the brainstem and surrounded by the cerebrum, is the diencephalon. The diencephalon contains the thalamus, which has two lobes beside each other, and the hypothalamus, which is located below and in front of the thalamus.
- Twelve pairs of cranial nerves branch from the brain and connect it to other areas of the body. The first two pairs are connected to the cerebrum. The other ten are connected to the brainstem. Fibers in these nerves take information to or from the brain.
Functions of the Cerebrum
The cerebrum is the site of our higher mental functions such as reasoning and learning. It stores memories, receives information from sense organs and sensory receptors, controls the movement of the skeletal muscles, and is responsible for speech and understanding language.
Interestingly, the right side of the brain controls the muscles and movements of the left side of the body, and vice versa. This is why someone who suffers brain damage from a stroke on the right side of the brain may have trouble moving their limbs on the left of their body. In addition, information from sensory receptors on the right side of the body is sent to the left side of the brain, and vice versa.
Both hemispheres of the cerebrum are equally important and have very similar functions. It's often said that the left side is more involved in reasoning and understanding while the right side is more active in spatial analysis and in artistic and musical activities. Scientists have some doubt about this claim, however. Information is sent between the hemispheres through the corpus callosum.
The Lobes of the Cerebrum
Each cerebral hemisphere is divided into lobes. These seem to have specific responsibilities, although there is an overlap in some areas, such as in storing memories. It's important to realize that our knowledge of the brain is still incomplete.
The following are important jobs of each lobe. Additional areas of the brain are required to perform some of the designated tasks.
- The frontal lobe (blue on the upper diagram): problem solving, planning, cognition, body movement, and speech production
- The area that controls speech production—Broca's area—is usually located in the left frontal lobe, but not always. It seems to be on the left side in all right handed people and in most left handed people. In some left handed people, speech is controlled by an area in the right frontal lobe or is partially controlled by each hemisphere.
- The parietal lobe (yellow): receives information from sensory receptors; responsible for sense of touch, pressure, pain, and temperature; gives us spatial abilities, such as the ability to judge size and distance.
- The temporal lobe (green): hearing and smell. Wernicke's area is responsible for understanding language. It's located in the left temporal lobe and extends up into the lower part of the parietal lobe.
- The occipital lobe (pink): receives information from the eye and is responsible for vision
Association areas in the lobes are responsible for recognition of sensory stimuli and for higher mental functions such as planning and decision making.
Functions of the Cerebellum, Thalamus, and Hypothalamus
- The cerebellum coordinates the movements triggered by the cerebrum and maintains posture and balance.
- The thalamus acts like a relay station. It monitors nerve impulses arriving in the brain and sends them to the correct area of the cerebrum.
- The hypothalamus has many very important functions. It regulates body temperature and blood pressure and controls our sense of hunger and thirst. It also controls the pituitary gland, which is connected to the hypothalamus by a stalk-like structure. The pituitary gland is often referred to as the "master gland" in the body because it releases hormones that control other glands in the body.
Functions of the Midbrain, Pons, and Medulla Oblongata
- The midbrain is also called the mesencephalon. It has a variety of functions. For example, it stimulates the muscles that cause eye movement, change lens shape, and control the size of the pupil. In addition, it contains an area called the substantia nigra, which has dark patches that are rich in melanin, the pigment in our hair and skin. Many of the neurons in the substantia nigra produce dopamine as part of their normal function. In Parkinson's disease, these neurons degenerate and the dopamine is no longer made.
- The pons is a relay center for nerve impulses and is involved in sleep and arousal.
- The medulla oblongata controls breathing and heart rate as well as digestion, swallowing, sneezing, and vomiting. It contains the reticular activating system, which controls sleep, wakefulness, arousal, and attention. This system extends into the pons and midbrain.
The Limbic System
There are many small and specialized structures, areas, and networks in the brain in addition to the large and obvious parts. Like other brain parts, these don't work in isolation. They receive and send nerve impulses from and to other regions of the brain.
The limbic system is one example of a network in the brain. It consists of brain structures and nerves that are important in emotions, behavior, and long-term memory creation. (Other parts of the brain are also involved in these processes.) Two especially significant structures in the limbic system are the amygdala and the hippocampus.
The amygdala, or amygdaloid body, is the limbic system structure that seems to be most concerned with emotions. The amygdala is an almond shaped area in each temporal lobe. It's important in coordinating the body's response to environmental stimuli that cause emotion and plays a major role in pleasure, fear, anger, aggression, and sadness.
The hippocampus is also located in the temporal lobe. There are two hippocampi, one in each temporal lobe, just as there are two amygdalas (or amygdalae). The shape of the hippocampus resembles that of a seahorse. Seahorses belong to the genus Hippocampus. The hippocampus in the brain is especially important in forming memories.
The Meninges and Meningitis
The meninges are three tissue layers that cover the central nervous system. The outer layer is thick, tough, and inflexible and is known as the dura mater. It helps to stop the brain from moving around. The middle layer is called the arachnoid and the inner layer is known as the pia mater. There is a space between the arachnoid and the pia mater, called the subarachnoid space, which is filled with cerebrospinal fluid.
Meningitis is inflammation of the meninges, which is potentially very dangerous. Inflammation involves swelling of tissues. Swelling of the meninges can put pressure on the brain and damage it. Meningitis can be caused by a virus or a bacterium. Viral meningitis is much less serious than bacterial meningitis. In fact, the body may deal with the disorder itself and the illness may not require any treatment. (A doctor must be consulted, however.) Bacterial meningitis is sometimes a very serious condition and requires treatment.
Ventricles and Cerebrospinal Fluid
Cerebrospinal fluid is a clear and colorless liquid that is made in the brain, chiefly by a structure called the choroid plexus. A choroid plexus is located in each of the four ventricles, or cavities, of the brain. The fluid circulates through the ventricles, the canal in the spinal cord, and the subarachnoid space. It eventually enters a vein.
Cerebospinal fluid, or CSF, acts as a cushion for the brain, helping to protect it from damage when the head is hit. It gives buoyancy to the brain to help support it and prevent the brain's weight from damaging its own neurons and blood vessels. It also carries waste substances away from the brain.
The Importance of Brain Studies
There is still a great deal that needs to be learned about the operation of the brain. The hope is that as we learn more about the organ we will be able to create better treatments for brain problems. In addition, discovering how the brain works is a fascinating endeavor in its own right.
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© 2012 Linda Crampton