brainstem

[breyn-stem]
noun
the portion of the brain that is continuous with the spinal cord and comprises the medulla oblongata, pons, midbrain, and parts of the hypothalamus, functioning in the control of reflexes and such essential internal mechanisms as respiration and heartbeat.
Also, brain stem.


Origin:
1875–80; brain + stem1

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Collins
World English Dictionary
brainstem (ˈbreɪnˌstɛm)
 
n
the stalklike part of the brain consisting of the medulla oblongata, the midbrain, and the pons Varolii

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

brain stem or brainstem
n.
The portion of the brain, consisting of the medulla oblongata, pons Varolii, and mesencephalon, that connects the spinal cord to the forebrain and cerebrum.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
brainstem   (brān'stěm')  Pronunciation Key 
The part of the vertebrate brain located at the base of the brain and made up of the medulla oblongata, pons, and midbrain. The brainstem controls and regulates vital body functions, including respiration, heart rate, and blood pressure. See also reticular formation.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

brain stem

area at the base of the brain that lies between the deep structures of the cerebral hemispheres and the cervical spinal cord. It is divided into three sections: midbrain (mesencephalon), pons (metencephalon), and medulla oblongata (myelencephalon). The brainstem houses many of the control centres for vital body functions, such as swallowing, breathing, and vasomotor control. All of the cranial nerve nuclei, except those associated with olfaction and vision, are located in the brainstem, providing motor and sensory function to structures of the cranium, including the facial muscles, tongue, pharynx, and larynx, as well as supplying the senses of taste, equilibrium, and hearing. The brainstem also has nuclei important for sympathetic and parasympathetic autonomic functions. All efferent and afferent pathways between the cerebrum and cerebellum course through the brainstem, and many of them decussate, or cross, within this structure. Because of the important neural structures concentrated in this small portion of the nervous system, even very small lesions of the brainstem may have profound effects. Disorders involving the brainstem include trauma, tumours, strokes, infections, and demyelination (multiple sclerosis). Complete loss of brainstem function is regarded by some experts as equivalent to brain death.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The brains of reptiles correspond more or less to the structures known in
  mammals as the brain stem and the cerebellum.
Basic life functions such as breathing, blood flow and heartbeat are controlled
  by the brain stem, located at the brain's base.
His brain swelled, squeezed the brain stem, and stopped his heart.
The brain stem for the chicken would be kept intact so that the homeostatic
  functions continue to operate, allowing it to grow.
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