The vasomotor center is a group of sympathetic nerve cells contained within the medulla oblongata, a structure of the brainstem. Regulated involuntarily without conscious effort by the autonomic nervous system (ANS), the vasomotor center is responsible for vital vegetative functioning of the human body, namely the blood pressure, breathing, and heart rate. Primarily the duty of the peripheral nervous system, ANS function allows for control of tasks happening elsewhere in the body other than the brain and spinal cord. Vasomotor imbalances can cause shock, ANS failure, and even death.
Situated just beneath limbic system structures, the brainstem is the lowermost portion that connects the brain to the cervical region of the spinal cord. Located in the middle of the brainstem, the medulla functions primarily as an internal switchboard, relaying information to and from the brain. Communication occurs through a network of neurons collectively described as the reticular formation, also known as the reticular activating system (RAS), when discussing arousal and sleep patterns.
Consisting of parasympathetic and sympathetic divisions working in opposition to one another, the ANS provides the body with a mechanism for controlling the activity of organs, such as the heart, lungs, and blood vessels. While the parasympathetic component actually regulates vital operations for survival, sympathetic activities employ those for adapting to stress. If fear is experienced, for example, certain physiological demands will necessitate a "flight or fight" response, initiating a counteracting action from the parasympathetic nervous system.
Mechanisms for blood pressure and heart rate control are possible due to baroreceptors, nerve fibers within blood vessels sensitive to sympathetic nervous system activity. An increase in blood pressure triggers baroreceptors to send information to the vasomotor center, which, in turn, lowers pressure to maintain homeostasis. Vessels constrict during periods of increased sympathetic functioning and dilate when decreased, any of which has a direct effect on heart rate, lowering it when the vasomotor center is inhibited and increasing rhythm upon stimulation.
Certain people experience vasomotor center disorders causing hypotension, loss of vasomotor tone, and general autonomic imbalance or failure. Indicated by a reading of 90 millimeters of mercury (mmHg) over 60 mm Hg or less, hypotension is the condition of having low blood pressure which is manifest by fainting, dizziness, nausea, and fatigue. When blood pressure is too low, circulation is inefficient, a result of decreased vasomotor tone. Dysautonomia pertains to ANS failure or imbalance caused by damage or certain disease conditions including diabetes and epilepsy. Parkinson's, postural tachycardia syndrome (POTS), mitral valve prolapse, and multiple systems atrophy (MSA) are primary ANS disorders affecting many people in the United States as of 2011.