Name the two divisions of the autonomic nervous system.
Understand the different roles of each division of the autonomic nervous system in helping the body react to stressful events.
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1. Emotions such as fear or anger can produce physical arousal. You become aware of this arousal as your muscles tighten, your heart races, your mouth goes dry, and your stomach flutters. This is called the fight or flight response.
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2. When you perceive an external threat—such as a snake within striking distance—your autonomic nervous system prepares your body for a vigorous muscular response by activating one of its two divisions.
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3. The sympathetic division of the autonomic nervous system triggers the adrenal glands to release stress hormones that increase your heart rate, blood pressure, and blood sugar levels—making you alert and ready for action, with lots of energy for muscular exertion.
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4. The sympathetic division also triggers dilated pupils that let more light into your eyes, increases respiration that supplies needed oxygen, and diverts blood to the large muscles to facilitate running away or fighting.
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5. When the stress passes, the parasympathetic division of the autonomic nervous system becomes active and produces the opposite effect, calming you and conserving your energy.
Practice: The Autonomic Nervous System
Roll over each structure on both sides of the figure to see a brief description of its role in the autonomic nervous system.
dilates pupil
speeds heartbeat
inhibits digestion
increases glucose release
releases stress hormones; slows kidney function
relaxes bladder
stimulates orgasm
contracts pupil
slows heartbeat
stimulates digestion
increases bile release
contracts bladder
increases blood flow
Quiz
For each row, select each physical response and drag it into the appropriate column. When all the physical responses have been placed, select the CHECK ANSWER button.
| Sympathetic Division | Parasympathetic Division | |
| EYES | ||
| SALIVATION | ||
| SKIN | ||
| RESPIRATION | ||
| HEART | ||
| DIGESTION | ||
| ADRENAL GLAND |