What is the part of the brain that controls the basic and vital functions of the body such as heartbeat and blood circulation?

The medulla oblongata, often simply called the medulla, is an elongated section of neural tissue that makes up part of the brainstem. The medulla is anterior to the cerebellum and is the part of the brainstem that connects to the spinal cord. It is continuous with the spinal cord, meaning there is not a clear delineation between the spinal cord and medulla but rather the spinal cord gradually transitions into the medulla.

What is the medulla oblongata and what does it do?

For most of the 18th century, the medulla oblongata was thought to simply be an extension of the spinal cord without any distinct functions of its own. This changed in 1806, when Julien-Jean-Cesar Legallois found that he could remove the cortex and cerebellum of rabbits and they would continue to breathe. When he removed a specific section of the medulla, however, respiration stopped immediately. Legallois had found what he believed to be a "respiratory center" in the medulla, and soon after the medulla was considered to be a center of vital functions (i.e. functions necessary for survival).

Over time, exactly which "vital functions" were linked to the medulla would become more clear, and the medulla would come to be recognized as a crucial area for the control of both cardiovascular and respiratory functions. The role of the medulla in cardiovascular function involves the regulation of heart rate and blood pressure to ensure that an adequate blood supply continues to circulate throughout the body at all times. To accomplish this, a nucleus in the medulla called the nucleus of the solitary tract receives information from stretch receptors in blood vessels. These receptors---called baroreceptors---can detect when the walls of blood vessels expand and contract, and thus can detect changes in blood pressure.

Watch this 2-Minute Neuroscience video to learn more about the medulla oblongata.

When baroreceptors send signals indicating that blood pressure is deviating from a desired range, then reflexive mechanisms are enacted to return it to equilibrium. For example, when a fall in blood pressure is detected by baroreceptors, they send information regarding such a change to the nucleus of the solitary tract. The nucleus of the solitary tract then activates neurons in the ventrolateral medulla that control sympathetic nervous system innervation of neurons that increase heart rate and blood pressure. At the same time, inhibition of parasympathetic activity ensures there will not be a conflicting drive to lower heart rate and/or blood pressure. Overall, these reflexive actions ensure that critical organs like the brain will not be affected by transient fluctuations in blood pressure.

There are also neurons in the medulla that receive information from receptors called chemoreceptors, which are found within blood vessels and can detect changes in the chemical composition of the blood. These chemoreceptors can recognize changes in oxygen and carbon dioxide levels, and medullary neurons use this information to respond to oxygen need by increasing respiration. These neurons are found in and around the nucleus of the solitary tract and another nucleus in the medulla called the nucleus ambiguus. The medulla isn't only involved in adjusting respiration in response to need, however; the medulla also generates normal breathing movements by stimulating the nerve that supplies the diaphragm. This stimulation begins at around 11 to 13 weeks of gestation in humans and continues until death.

While these cardiovascular and respiratory centers are clearly what led 19th century neuroscientists to consider the medulla the center of vital functions, the full range of activities of the medulla is considerably more diverse. In addition to the reflexive cardiovascular and respiratory actions mentioned above, neuronal groups in the medulla are also responsible for other reflexive actions like swallowing, coughing, sneezing, and vomiting. Vomiting is controlled by an area of the medulla called the area postrema, which is not protected by the blood-brain barrier. This lack of blood-brain barrier protection allows neurons in the area postrema to come into contact with the blood. By doing so, area postrema neurons can detect potentially toxic substances in the blood and trigger vomiting if present.

There are a number of other important nuclei in the medulla. Several cranial nerve nuclei are found there, as well as the inferior olivary nuclei, which are densely interconnected with the cerebellum and thought to play a role in motor control. The nucleus gracilis and nucleus cuneatus are both found in the medulla; they are important nuclei along a pathway called the dorsal columns-medial lemniscus, which carries sensory information to the brain.

The medulla's position as the lowest part of the brainstem also causes it to also be a conduit for a number of tracts that pass from the spinal cord into the brainstem and from the brainstem into the spinal cord. For example, the corticospinal tract---a major descending tract for voluntary movement---passes from the medulla into the spinal cord. The corticospinal tract and another tract called the corticobulbar tract, which is involved with movement of the head and neck, form triangular bundles of fibers in the medulla that create ridges on the outside of the brainstem. The bundles and associated ridges have been termed the medullary pyramids, and the corticospinal and corticobulbar tracts are often referred to as the pyramidal tracts because of their association with the pyramids. At the junction of the medulla and spinal cord, the corticospinal tract decussates, or crosses over to the other side of the body, before continuing down into the spinal cord. The location of this decussation is referred to as the pyramidal decussation.

Thus, the medulla oblongata's functions are extraordinarily diverse and include those that are essential to life as well as to other important activities like movement. Due to its role in regulating vital functions, however, you could make the argument that the medulla is perhaps the most important area of the brain.

Reference:

Nolte J. The Human Brain: An Introduction to its Functional Anatomy. 6th ed. Philadelphia, PA. Elsevier; 2009.

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Introduction
The Architecture of the Brain
The Geography of Thought
The Cerebral Cortex
The Inner Brain
Making Connections
Some Key Neurotransmitters at Work
Neurological Disorders
The National Institute of Neurological Disorders and Stroke

Introduction

The brain is the most complex part of the human body. This three-pound organ is the seat of intelligence, interpreter of the senses, initiator of body movement, and controller of behavior. Lying in its bony shell and washed by protective fluid, the brain is the source of all the qualities that define our humanity. The brain is the crown jewel of the human body.

For centuries, scientists and philosophers have been fascinated by the brain, but until recently they viewed the brain as nearly incomprehensible. Now, however, the brain is beginning to relinquish its secrets. Scientists have learned more about the brain in the last 10 years than in all previous centuries because of the accelerating pace of research in neurological and behavioral science and the development of new research techniques. As a result, Congress named the 1990s the Decade of the Brain. At the forefront of research on the brain and other elements of the nervous system is the National Institute of Neurological Disorders and Stroke (NINDS), which conducts and supports scientific studies in the United States and around the world.

This fact sheet is a basic introduction to the human brain. It may help you understand how the healthy brain works, how to keep it healthy, and what happens when the brain is diseased or dysfunctional.

Image 1
 

The Architecture of the Brain

The brain is like a committee of experts. All the parts of the brain work together, but each part has its own special properties. The brain can be divided into three basic units: the forebrain, the midbrain, and the hindbrain.

The hindbrain includes the upper part of the spinal cord, the brain stem, and a wrinkled ball of tissue called the cerebellum (1). The hindbrain controls the body’s vital functions such as respiration and heart rate. The cerebellum coordinates movement and is involved in learned rote movements. When you play the piano or hit a tennis ball you are activating the cerebellum. The uppermost part of the brainstem is the midbrain, which controls some reflex actions and is part of the circuit involved in the control of eye movements and other voluntary movements. The forebrain is the largest and most highly developed part of the human brain: it consists primarily of the cerebrum (2) and the structures hidden beneath it (see "The Inner Brain").

When people see pictures of the brain it is usually the cerebrum that they notice. The cerebrum sits at the topmost part of the brain and is the source of intellectual activities. It holds your memories, allows you to plan, enables you to imagine and think. It allows you to recognize friends, read books, and play games.

The cerebrum is split into two halves (hemispheres) by a deep fissure. Despite the split, the two cerebral hemispheres communicate with each other through a thick tract of nerve fibers that lies at the base of this fissure. Although the two hemispheres seem to be mirror images of each other, they are different. For instance, the ability to form words seems to lie primarily in the left hemisphere, while the right hemisphere seems to control many abstract reasoning skills.

For some as-yet-unknown reason, nearly all of the 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 primarily controls the left side of the body and the left hemisphere primarily controls the right side. When one side of the brain is damaged, the opposite side of the body is affected. For example, a stroke in the right hemisphere of the brain can leave the left arm and leg paralyzed.

            The Forebrain                              The Midbrain                             The Hindbrain

The Geography of Thought

Each cerebral hemisphere can be divided into sections, or lobes, each of which specializes in different functions. To understand each lobe and its specialty we will take a tour of the cerebral hemispheres, starting with the two frontal lobes (3), which lie directly behind the forehead. When you plan a schedule, imagine the future, or use reasoned arguments, these two lobes do much of the work. One of the ways the frontal lobes seem to do these things is by acting as short-term storage sites, allowing one idea to be kept in mind while other ideas are considered. In the rearmost portion of each frontal lobe is a motor area (4), which helps control voluntary movement. A nearby place on the left frontal lobe called Broca’s area (5) allows thoughts to be transformed into words.

When you enjoy a good meal—the taste, aroma, and texture of the food—two sections behind the frontal lobes called the parietal lobes (6) are at work. The forward parts of these lobes, just behind the motor areas, are the primary sensory areas (7). These areas receive information about temperature, taste, touch, and movement from the rest of the body. Reading and arithmetic are also functions in the repertoire of each parietal lobe.

As you look at the words and pictures on this page, two areas at the back of the brain are at work. These lobes, called the occipital lobes (8), process images from the eyes and link that information with images stored in memory. Damage to the occipital lobes can cause blindness.

The last lobes on our tour of the cerebral hemispheres are the temporal lobes (9), which lie in front of the visual areas and nest under the parietal and frontal lobes. Whether you appreciate symphonies or rock music, your brain responds through the activity of these lobes. At the top of each temporal lobe is an area responsible for receiving information from the ears. The underside of each temporal lobe plays a crucial role in forming and retrieving memories, including those associated with music. Other parts of this lobe seem to integrate memories and sensations of taste, sound, sight, and touch.

The Cerebral Cortex

Coating the surface of the cerebrum and the cerebellum is a vital layer of tissue the thickness of a stack of two or three dimes. It is called the cortex, from the Latin word for bark. Most of the actual information processing in the brain takes place in the cerebral cortex. When people talk about "gray matter" in the brain they are talking about this thin rind. The cortex is gray because nerves in this area lack the insulation that makes most other parts of the brain appear to be white. The folds in the brain add to its surface area and therefore increase the amount of gray matter and the quantity of information that can be processed.

The Inner Brain

Deep within the brain, hidden from view, lie structures that are the gatekeepers between the spinal cord and the cerebral hemispheres. These structures not only determine our emotional state, they also modify our perceptions and responses depending on that state, and allow us to initiate movements that you make without thinking about them. Like the lobes in the cerebral hemispheres, the structures described below come in pairs: each is duplicated in the opposite half of the brain.

The hypothalamus (10), about the size of a pearl, directs a multitude of important functions. It wakes you up in the morning, and gets the adrenaline flowing during a test or job interview. The hypothalamus is also an important emotional center, controlling the molecules that make you feel exhilarated, angry, or unhappy. Near the hypothalamus lies the thalamus (11), a major clearinghouse for information going to and from the spinal cord and the cerebrum.

An arching tract of nerve cells leads from the hypothalamus and the thalamus to the hippocampus (12). This tiny nub acts as a memory indexer—sending memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary. The basal ganglia (not shown) are clusters of nerve cells surrounding the thalamus. They are responsible for initiating and integrating movements. Parkinson’s disease, which results in tremors, rigidity, and a stiff, shuffling walk, is a disease of nerve cells that lead into the basal ganglia.

Image 5

Making Connections

The brain and the rest of the nervous system are composed of many different types of cells, but the primary functional unit is a cell called the neuron. All sensations, movements, thoughts, memories, and feelings are the result of signals that pass through neurons. Neurons consist of three parts. The cell body (13) contains the nucleus, where most of the molecules that the neuron needs to survive and function are manufactured. Dendrites (14) extend out from the cell body like the branches of a tree and receive messages from other nerve cells. Signals then pass from the dendrites through the cell body and may travel away from the cell body down an axon (15) to another neuron, a muscle cell, or cells in some other organ. The neuron is usually surrounded by many support cells. Some types of cells wrap around the axon to form an insulating sheath (16). This sheath can include a fatty molecule called myelin, which provides insulation for the axon and helps nerve signals travel faster and farther. Axons may be very short, such as those that carry signals from one cell in the cortex to another cell less than a hair’s width away. Or axons may be very long, such as those that carry messages from the brain all the way down the spinal cord.

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Scientists have learned a great deal about neurons by studying the synapse—the place where a signal passes from the neuron to another cell. When the signal reaches the end of the axon it stimulates the release of tiny sacs (17). These sacs release chemicals known as neurotransmitters (18) into the synapse (19). The neurotransmitters cross the synapse and attach to receptors (20) on the neighboring cell. These receptors can change the properties of the receiving cell. If the receiving cell is also a neuron, the signal can continue the transmission to the next cell.

Image 7

Some Key Neurotransmitters at Work

Neurotransmitters are chemicals that brain cells use to talk to each other. Some neurotransmitters make cells more active (called excitatory) while others block or dampen a cell's activity (called inhibitory).

Acetylcholine is an excitatory neurotransmitter because it generally makes cells more excitable. It governs muscle contractions and causes glands to secrete hormones. Alzheimer’s disease, which initially affects memory formation, is associated with a shortage of acetylcholine.

Glutamate is a major excitatory neurotransmitter. Too much glutamate can kill or damage neurons and has been linked to disorders including Parkinson's disease, stroke, seizures, and increased sensitivity to pain.

GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter that helps control muscle activity and is an important part of the visual system. Drugs that increase GABA levels in the brain are used to treat epileptic seizures and tremors in patients with Huntington’s disease.

Serotonin is a neurotransmitter that constricts blood vessels and brings on sleep. It is also involved in temperature regulation. Low levels of serotonin may cause sleep problems and depression, while too much serotonin can lead to seizures.

Dopamine is an inhibitory neurotransmitter involved in mood and the control of complex movements. The loss of dopamine activity in some portions of the brain leads to the muscular rigidity of Parkinson’s disease. Many medications used to treat behavioral disorders work by modifying the action of dopamine in the brain.

Neurological Disorders

The brain is one of the hardest working organs in the body. When the brain is healthy it functions quickly and automatically. But when problems occur, the results can be devastating. Some 100 million Americans suffer from devastating brain disorders at some point in their lives. The NINDS supports research on more than 600 neurological diseases. Some of the major types of disorders include: neurogenetic diseases (such as Huntington’s disease and muscular dystrophy), developmental disorders (such as cerebral palsy), degenerative diseases of adult life (such as Parkinson’s disease and Alzheimer’s disease), metabolic diseases (such as Gaucher’s disease), cerebrovascular diseases (such as stroke and vascular dementia), trauma (such as spinal cord and head injury), convulsive disorders (such as epilepsy), infectious diseases (such as AIDS dementia), and brain tumors. Knowing more about the brain can lead to the development of new treatments for diseases and disorders of the nervous system and improve many areas of human health.

The National Institute of Neurological Disorders and Stroke

Since its creation by Congress in 1950, the NINDS has grown to become the leading supporter of neurological research in the United States. Most research funded by the NINDS is conducted by scientists in public and private institutions such as universities, medical schools, and hospitals. Government scientists also conduct a wide array of neurological research in the more than 20 laboratories and branches of the NINDS itself. This research ranges from studies on the structure and function of single brain cells to tests of new diagnostic tools and treatments for those with neurological disorders.

For information on other neurological disorders or research programs funded by the National Institute of Neurological Disorders and Stroke, contact the Institute's Brain Resources and Information Network (BRAIN) at:

BRAIN P.O. Box 5801 Bethesda, MD 20824 (800) 352-9424

www.ninds.nih.gov