A brainstem is a small, hidden piece of brain that does not get as much love as it should. Even with the recent explosion in brain research, other parts of the brain get more attention and therefore are better understood. But the fact is, neither the rest of the brain nor any part of the body could continue to function without the brainstem working at peak condition.
The brainstem is at the base of the brain, slightly in front of the cerebrum. You can think of it as the place where the spinal cord plugs into the brain, in the center of the brain between the two hemispheres. It provides a connecting bridge between the cerebrum, the lobe at the lower back of the brain, and the cerebellum, the larger upper lobe in each hemisphere.
The brainstem divides into three important parts, the midbrain, medulla, and pons. The midbrain is responsible for regulating functions contributing to sensory perception, motor control, sleep cycles, and body temperature. The pons regulates many of the body's autonomic functions, such as breathing, urination, some sensory perceptions, swallowing, balance, and cranial nerve functions. Finally, the medulla regulates other autonomic systems not controlled by the pons, including respiration, heartbeat, and blood pressure.
More than any other section of the brain, a functioning brainstem is absolutely necessary for humans to live. This essential part regulates heart rate, breathing, and major organ function--the elements of being alive that we never think about. All bodily systems are in some way dependent on the brainstem. When it stops functioning, a person is "brain dead." No other essential functions continue when the brainstem ceases to work.
Many of the systems that run the human body begin in the brainstem. From there they either extend upward into the cerebrum or cerebellum or down the spinal column and into the rest of the body. Experts often refer to these systems as "rhythm generators" because they regulate rhythmic movements like chewing, blinking, eye focus, respiration, swallowing, and heartbeat. Other systems originating in the brainstem control pain, consciousness, hunger, and sensory perception.
Most people know the brain sends signals down the spinal cord, and from there they go out to the rest of the body through the network of nerves. But not everyone is aware that the brainstem is the gatekeeper in this system of communication. No information gets to or from the rest of the brain or the rest of the body without going through the brainstem. This is how the body knows to increase heart rate and breathing when someone is scared or to send pain signals following an injury. Even if other areas of the brain must respond to a situation, they can only do so after the stem transmits and reacts to the message.
The neural network that regulates pain is in the brainstem. A concentrated pathway in the midbrain is a major center of all kinds of information delivered by the senses from all over the body. Once the midbrain receives that information, this busy nerve highway sends messages back to the rest of the body to stop activating nerve cells that could result in too much pain. At the same time, the body begins to manufacture its own internal opioid pain relievers the brainstem will send to the affected site.
The cranial nerves control almost every function of the face, head, neck, and shoulders, and they are all operated by the brainstem. These major nerves control the senses of smell, taste, sight, hearing, and touch on the skin of the face, ears, head, and neck. They also regulate eye and jaw movement, salivation, tear ducts, balance, voice, and neck and shoulder movements.
The brain is, of course, housed within the bony structure of the skull designed to protect it from any external assaults. But even within that protective structure, the brainstem has a lot of defense. Like all parts of the brain, three layers of membranes -- meninges -- cover it, along with cerebrospinal fluid cushioning. But the brainstem is positioned so deep in the interior of the brain that it is also surrounded by spongy brain tissue and muscle.
Unfortunately, even though the brainstem is well-protected, damage can still occur. Strokes, Parkinson's, lesions, multiple sclerosis, seizures, meningitis, brain tumors, or even a simple infection can attack it from the inside. From the outside, the brainstem can undergo trauma resulting in a concussion or brain damage. Any of these assaults to the brainstem can result in far-reaching effects in the brain and body.
A person who has a stroke, seizures, lesions, or head trauma can face problems with major systems including the heart, respiration, and difficulties with movement or balance. There can be problems with smaller functions as well, such as chewing, reading and writing, hand-eye coordination, and speech. Arms, legs, hands, and other body parts can become paralyzed, and muscle control may be limited.
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