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The seat of the mind: The brain


The brain is the most complicated organ in the human body.

This three-pound organ serves as the seat of intelligence, sense interpreter, initiator of body movement, behavior controller and the physical seat of the mind. The brain, lying in its bony shell and washed by protective fluid, is the source of all the characteristics that define our humanity.

The human brain is the crown jewel of the body.


Scientists and philosophers have been fascinated by the brain for centuries, but until recently, they thought it was nearly incomprehensible. However, the brain is starting to reveal its secrets. Because of the accelerating pace of research in neurological and behavioral science, as well as the development of new research techniques and tools, scientists have learned more about the brain in the last ten years than in all previous centuries.


This article provides an overview of the human brain in a simplistic yet profound way. It may assist you in understanding how the healthy brain functions, how to keep it healthy, and what happens when the brain is diseased or dysfunctional.



The Brain's Architecture


The brain functions as a committee of experts. All of the brain's parts work together, but each has its own unique set of characteristics. The brain is divided into three basic sections: the forebrain, midbrain, and hindbrain.


The upper part of the spinal cord, the brain stem, and a wrinkled ball of tissue called the cerebellum comprise the hindbrain. The hindbrain regulates vital body functions such as respiration and heart rate.

The cerebellum coordinates movement and is involved in rote movements that are learned. You activate the cerebellum when you play the piano or hit a tennis ball.

The midbrain is the uppermost part of the brainstem and controls some reflex actions as well as being part of the circuit that controls eye movements and other voluntary movements. The forebrain is the most developed and largest part of the human brain, consisting primarily of the cerebrum (2) and the structures hidden beneath it (see "The Inner Brai


People usually notice the cerebrum when they see pictures of the brain. The cerebrum is located at the top of the brain and is the center of intellectual activity. It stores your memories, allows you to plan ahead of time, and allows you to imagine and think. It enables you to identify friends, read books, and play games.


A deep fissure divides the cerebrum into two halves (hemispheres). Despite the split, the two cerebral hemispheres communicate with one another via a dense network of nerve fibers at the base of the fissure known as corpus callosum.

Although the two hemispheres appear to be mirror images of one another, they are not.

The ability to form words, for example, appears to be primarily in the left hemisphere, whereas the right hemisphere appears to control many abstract reasoning skills.




For some reason that is still unknown, nearly all signals from the brain to the body and vice versa cross over on their way to and from the brain. This means that the right cerebral hemisphere controls the left side of the body while the left hemisphere controls the right. When one side of the brain is damaged, it affects the opposite side of the body. A stroke in the right hemisphere of the brain, for example, can paralyze the left arm and leg.


The forebrain


The cerebrum is the largest section of the brain and a component of the forebrain. Its conspicuous outer section, the cerebral cortex, not only processes sensory and motor information, but also enables consciousness, our ability to reflect on ourselves and the external world. When most people hear the term "grey matter," this is what comes to mind. Cortex tissue is composed primarily of neuron cell bodies, and its folds and fissures (known as gyri and sulci) give the cerebrum its characteristic wrinkly appearance. The cerebral cortex is divided into two hemispheres.


Each cerebral hemisphere is divided into sections, or lobes, each of which performs a specific function. Taking a look at the cerebral hemispheres to understand each lobe and its specialty, beginning with the two frontal lobes, which are directly behind the forehead. These two lobes do the majority of the work when you plan a schedule, imagine the future, or use reasoned arguments.


The frontal lobes appear to do these things in part by acting as short-term storage sites, allowing one idea to be kept in mind while other ideas are considered. A motor area is located in the back of each frontal lobe and helps control voluntary movement. Broca's area, located nearby on the left frontal lobe, allows thoughts to be transformed into words.


Two sections behind the frontal lobes called the parietal lobes are at work when you enjoy a good meal—the taste, aroma, and texture of the food.

The primary sensory areas are located in the forward parts of these lobes, just behind the motor areas.

The rest of the body sends temperature, taste, touch, and movement information to these areas. Reading and arithmetic are also functions in each parietal lobe's repertoire.

Two areas of the brain are active when you look at the words and images on this page. These lobes, known as the occipital lobes, process images from the eyes and connect them to images stored in memory. Blindness can result from occipital lobe damage.


The temporal lobes, which are located in front of the visual areas and nest beneath the parietal and frontal lobes, are the final lobes on our tour of the cerebral hemispheres. Whether you enjoy symphonies or rock music, your brain responds by activating these lobes. An area responsible for receiving information from the ears is located at the top of each temporal lobe. The underside of each temporal lobe is important in the formation and retrieval of memories, including those associated with music. Memory and sensations of taste, sound, sight, and touch appear to be integrated in other parts of this lobe.


Cerebral Cortex


A vital layer of tissue the thickness of a stack of two or three dimes coats the surface of the cerebrum and cerebellum. The cortex is named after the Latin word for bark. The cerebral cortex is where the majority of the actual information processing in the brain takes place. When people discuss "gray matter" in the brain, they are referring to this thin rind.

The cortex is gray because the nerves in this area lack the insulation that gives the rest of the brain its white appearance. The folds in the brain increase the surface area of the brain, increasing the amount of gray matter and the amount of information that can be processed.


The Inner Mind


Structures deep within the brain, hidden from view, serve as the gatekeepers between the spinal cord and the cerebral hemispheres.

These structures not only determine our emotional state, but they also modify our perceptions and responses based on that state, allowing us to initiate movements without thinking about them. The structures described below, like the lobes in the cerebral hemispheres, come in pairs: each is duplicated in the opposite half of the brain.


The hypothalamus , which is about the size of a pearl, controls a wide range of vital functions. It wakes you up in the morning and stimulates your adrenaline during a test or job interview. The hypothalamus is also an important emotional center, as it regulates the molecules that make you feel excited, angry, or sad.

The thalamus, located near the hypothalamus, is a major clearinghouse for information traveling to and from the spinal cord and cerebrum.


From the hypothalamus and thalamus, an arching tract of nerve cells leads to the hippocampus. This tiny nub functions as a memory indexer, sending memories to the appropriate part of the cerebral hemisphere for long-term storage and retrieval when needed. The basal ganglia are nerve cell clusters that surround the thalamus. They are in charge of initiating and coordinating movements. Parkinson's disease is a disease of nerve cells that lead into the basal ganglia that causes tremors, rigidity, and a stiff, shuffling walk.


Making Connections


The brain and the rest of the nervous system are made up of many different types of cells, but the neuron is the primary functional unit.

All sensations, movements, thoughts, memories, and feelings are the result of neuronal signals. Neurons are made up of three parts. The cell body contains the nucleus, which manufactures the majority of the molecules required by the neuron to survive and function.

Dendrites are nerve cells that extend out from the cell body like tree branches and receive messages from other nerve cells. Signals then pass from the dendrites to the cell body, where they may travel down an axon to another neuron, a muscle cell, or cells in another organ.

A neuron is usually surrounded by a swarm of support cells. Some cell types form an insulating sheath around the axon. This sheath may contain a fatty molecule known as myelin, which acts as insulation for the axon and allows nerve signals to travel faster and farther.

Axons can be very short, such as those that carry signals from one cortex cell to another less than a hair's width away. Axons can also be very long, such as those that carry messages from the brain down the spinal cord.


Scientists have learned a lot about neurons by studying the synapse—the point at which a signal travels from one neuron to another. When the signal reaches the axon's end, it causes the release of tiny sacs.


Neurotransmitters


They are chemicals released by these sacs into the synapse. Neurotransmitters travel across the synapse and bind to receptors on neighboring cells. These receptors have the ability to alter the properties of the receiving cell. If the receiving cell is also a neuron, the signal can proceed to the next cell.

Some neurotransmitters stimulate (excite) cells, while others inhibit or dampen cell activity (called inhibitory).



Acetylcholine is classified as an excitatory neurotransmitter because it causes cells to become more excitable. It controls muscle contractions and secretes hormones from glands. Alzheimer's disease, which first affects memory formation, is linked to a lack of acetylcholine.


Glutamate and GABA are considered to be fundamental neurotransmitters. They exist in high concentrations within the brain, with glutamate serving as the accelerator and GABA as the brake.


Glutamate plays an essential role in learning and memory, but excessive amounts can lead to agitation, impulsive behavior, and even aggression. Excess glutamate can kill or damage neurons and has been linked to conditions such as Parkinson's disease, stroke, seizures, and increased pain sensitivity.


GABA produces the opposite result. It enhances our tranquility by inhibiting excessive nerve activity. It aids in muscle control and is an essential component of the visual system. Drugs that raise GABA levels in the brain are used to treat epileptic seizures and tremors in Huntington's disease patients.


Serotonin is a neurotransmitter that causes blood vessels to constrict and induces sleep. It also plays a role in temperature regulation. Serotonin deficiency can cause sleep problems and depression, while serotonin excess can cause seizures.


Dopamine is an inhibitory neurotransmitter that regulates mood and complex movements. Dopamine is our neurotransmitter for arousal and stimulation. We associate dopamine with rewards because it regulates our desire for sex, food, pleasure, and even creative thought.

Too little dopamine can cause depression or loss of dopamine activity in certain areas of the brain causes the muscular rigidity associated with Parkinson's disease. Many medications used to treat behavioral disorders work by altering dopamine's action in the brain. While too much can cause dependence on the stimulating agent.

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