If the Parasympathetic Nervous System can be thought of as a brake...
....the Sympathetic Nervous System can be thought of as an Accelerator.
Sympathetic Nervous System has three main functions:
*Regulating the cardiovascular system
*Regulating body temperature
*Implementing the "Fight-or-Fight" reaction
The sympathetic nervous system exerts multiple influences on the heart and blood vessels.
*Release of epinephrine from the adrenal medulla results in vasoconstriction in most vascular beds....
*Stimulation to arterioles and veins causes vasoconstriction diverting blood flow away from the GI tract, peripheral extremities, & skin which contributes to increased blood pressure.
....& vasodilation in others:
*Provides vasodilation for the coronary vessels of the heart
*INCREASES cardiac output via increase of heart rate & contractility of cardiac cells providing a mechanism for enhanced blood flow to skeletal muscles
By influencing the heart and blood vessels, the sympathetic nervous system can achieve three homeostatic objectives:
*Maintenance of blood flow to the brain
*Redistribution of blood flow during exercise
*Compensation for loss of blood, primarily by causing vasoconstriction
The sympathetic nervous system helps regulate body temperature in three ways:
*By regulating blood flow to the skin, sympathetic nerves can increase or decrease heat loss. By dilating surface vessels, sympathetic nerves increase blood flow to the skin and therby accelerate heat loss. Conversely, constricting cutaneous vessels conserves heat.
*Sympathetic nerves to sweat glands promote secretion of sweat, thereby helping the body cool.
*By inducing piloerection (erection of hair), sympathetic nerves can promote heat conservation.
When we are faced with adversity, the sympathetic nervous system orchestrates the "Fight-or-Flight" response which consists of:
*Increasing heart rate and blood pressure
*Shunting blood away from the skin & viscera & into skeletal muscles
*Dilating the bronchi to improve oxygenation
*Dilating the pupils (perhaps to enhance visual acuity)
*Mobilizing stored energy, thereby providing glucose for the brain and fatty acids for muscles
The sensation of being "cold with fear" is brought on by...
...the shunting of blood away from the skin.
The phrase "wide-eyed with fear" may be based on pupillary dilation.
Sympathetic agents that alter cardiovascular function are used to treat:
Sympathetic Nervous System is associated with the "Fight-or-Flight" response which corresponds with arousal & energy generation & inhibition of digestion.
*Diverting blood flow away from the GI tract & skin via vasoconstriction....
*....Enhancing blood flow to skeletal muscles & the lungs by as much as 1200% (Skeletal muscles only)
*Constricts all the intestinal sphincters and the urinary sphincter.
*Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye for far vision.
*Dilate bronchioles which allows for greater alveolar oxygen exchange
*Provides vasodilation for the coronary vessels of the heart.
*Increases heart rate & contractility cardiac cells, thereby providing a mechanism for enhanced blood flow to skeletal muscles