Autonomic nervous system blood pressure control

The autonomic nervous system is divided into the sympathetic and parasympathetic components, which typically exert opposing effects. The sympathetic system is involved in the fight or flight reaction (increased blood pressure and heart rate, and accommodation for increased vision, for example) that prepares the organism for stressful situations. The parasympathetic system conversely establishes a more relaxed situation, for instance, the rest period after a meal. The autonomic nervous system that is responsible for the independent control of the mechanical and secretory functions of the gastrointestinal tract is sometimes called the enteric system. 

Autonomic and hormonal control of cardiovascular function. Note that two feedback loops are present the autonomic nervous system loop and the hormonal loop. The sympathetic nervous system directly influences four major variables peripheral vascular resistance, heart rate, force, and venous tone. It also directly modulates renin production (not shown). The parasympathetic nervous system directly influences heart rate. In addition to its role in stimulating aldosterone secretion, angiotensin II directly increases peripheral vascular resistance and facilitates sympathetic effects (not shown). The net feedback effect of each loop is to compensate for changes in arterial blood pressure. Thus, decreased blood pressure due to blood loss would evoke increased sympathetic outflow and renin release. Conversely, elevated pressure due to the administration of a vasoconstrictor drug would cause reduced sympathetic outflow, reduced renin release, and increased parasympathetic (vagal) outflow. 

The human nervous system can be divided into two major functional areas the somatic nervous system and the autonomic nervous system (ANS). The somatic division is concerned primarily with voluntary function—that is, control of the skeletal musculature. The ANS is responsible for controlling bodily functions that are largely involuntary, or automatic, in nature. For instance, the control of blood pressure (BP) and other aspects of cardiovascular function is under the influence of the ANS. Other involuntary, or vegetative, functions such as digestion, elimination, and thermoregulation are also controlled by this system. 

Methaqualone also affects involuntary body functions that are controlled by the autonomic nervous system, lowering blood pressure, breathing rate, and pulse and bringing about a state of deep relaxation. Though thought to be an aphrodisiac because it lowers inhibitions, methaqualone, as a CNS depressant, usually impairs sexual performance, inhibiting arousal and climax. 

The afferent neurons of the autonomic nervous system are important in the reflex regulation, for example, by sensing pressure in the carotid sinus and aortic arch and signaling the CNS to influence the efferent branch of the system to respond. Conditions such as trauma, fear, hypoglycemia, cold, or exercise activate the sympathetic neurons. Both sympathetic and parasympathetic neurons emerge from the brain stem or spinal cord. Blood pressure is regulated largely by sympathetic control of vascular tone. 

Norepinephrine Mostly excitatory, but inhibitory in some areas. Secreted by neurons in the locus ceruleus (subcortical area) to widespread areas of the brain, controlling wakefulness, overall activity, and mood. Also diffusely secreted in the sympathetic nervous system. Diffuse and widespread symptoms, including depression, changes in blood pressure, heart rate, and diffuse physiological responses, among many others. An important transmitter in the sympathetic branch of the autonomic nervous system. Diffusely affected by many medications. Several antidepressants work specifically on this neurotransmitter and its receptor sites. Many medications for general medical conditions affect this neurotransmitter as well. 

Because capillary walls are thin (to permit diffusion) the blood that is delivered to them must be delivered under reduced pressure. This is accomplished by the arterioles, which combine relatively muscular walls with a narrow lumen. The arterial blood pressure is a function of cardiac output and the total peripheral vascular resistance, which is primarily a function of the degree of normal tension (tonus) of the smooth muscle cells in the walls of the arterioles. If this tonus increases above the normal range for extended periods of time, hypertension (high blood pressure) will result. This tonus is under the control of the autonomic nervous system and of adrenergic hormones (catecholamines). 

In the peripheral nervous system, norepinephrine is an important neurotransmitter in the sympathetic branch of the autonomic system. Sympathetic nerve transmission operates below the level of consciousness in controlling physiological function of many organs and tissues of the body. The sympathetic system plays a particularly important role in regulating cardiovascular function in response to postural, exertional, thermal, and mental stress. With sympathetic activation, the heart rate is increased, peripheral arterioles are constricted, skeletal arterioles are dilated, and the blood pressure is elevated. In addition, sympathetic nerve stimulation dilates pupils inhibits smooth muscles of the intestines, bronchi, and bladder and closes the sphincters. Sympathetic signals work in balance with the parasympathetic portion of the autonomic nervous system to maintain a stable internal environment. 

Dysautonomias also range from mechanistically straightforward disorders in which altered autonomic function plays a primary pathophysiological role (e.g., pure autonomic failure), to conditions in which altered autonomic fimction worsens an independent pathophysiological state (e.g., cardiac failure), and to more mysterious disorders in which the involvement of the autonomic nervous system is less clear (e.g., chronic fatigue syndrome). Abnormalities of blood pressure control represent the common presenting cfinical features of the dysautonomias. In those involving... 

The ANS is the major involuntary portion of the nervous system and is responsible for automatic, unconscious bodily functions, such as control of heart rate and blood pressure and both gastrointestinal and genitourinary functions. The ANS is divided into two major subcategories the parasympathetic autonomic nervous system (PANS) and the sympathetic autonomic nervous system (SANS). 

A) The patient had a concurrent familial condition that limited autonomic nervous system control of the blood pressure... 

Shepherd REJ, Shepherd JT Control of the blood pressure and the circulation in man. In Autonomic EaUure A Textbook of Clinical Disorders of the Autonomic Nervous System, 4th Edition. Mathias CJ, Bannister R (Eds.), Oxford University Press, Oxford, England, 72-75 (1999). 

Blood pressure is under the control of the autonomic (sometimes called the involuntary or reflex) nervous system. 

---