MCAT Content / Nervous System Structure And Function / Sympathetic And Parasympathetic Nervous Systems Antagonistic Control

Sympathetic and parasympathetic nervous systems: antagonistic control

Topic: Nervous System Structure And Function

Autonomic responses are mediated by the sympathetic and the parasympathetic systems, which are antagonistic to one another.

The autonomic nervous system (ANS) serves as the relay between the central nervous system (CNS) and the internal organs. It controls the lungs, the heart, smooth muscle, and exocrine and endocrine glands, mainly without conscious control. It can continuously monitor the conditions of these different systems and implement changes as needed.

There are two divisions of the autonomic nervous system that often have opposing effects: the sympathetic nervous system and the parasympathetic nervous system.

Actions of the SNS and PNS: The sympathetic and parasympathetic nervous systems often have opposing effects on target organs.

Autonomic nervous system: Autonomic responses are mediated by the sympathetic and the parasympathetic systems, which are antagonistic to one another. The sympathetic system activates the “fight or flight” response, while the parasympathetic system activates the “rest and digest” response.


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Key Points

• The autonomic nervous system controls the workings of internal organs such as the heart, lungs, digestive system, and endocrine systems; it does so without conscious effort.

• The sympathetic nervous system controls the body’s automatic response to danger, increasing the heart rate, dilating the blood vessels, slowing digestion, and moving blood flow to the heart, muscles, and brain.

• The parasympathetic nervous system works in opposition to the sympathetic; during periods of rest, it slows the heart rate, lowers the blood pressure, stimulates digestion, and moves blood flow back to the skin.

Key Terms

Sympathetic nervous system: the part of the autonomic nervous system that under stress raises blood pressure and heart rate, constricts blood vessels and dilates the pupils

Parasympathetic nervous system: one of the divisions of the autonomic nervous system, based between the brain and the spinal cord, that slows the heart and relaxes muscles

CNS: central nervous system consists of the brain and spinal cord

Conscious: to be aware of

ANS: autonomic nervous system the part of the nervous system responsible for the control of the bodily functions not consciously directed

Exocrine: glands outside of the body

Endocrine: glands inside the body

Synapse: the gap between a nerve ending and an organ receptor

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