When your body prepares you for fight or flight (e.g., eyes dilating, heart pumping),which system in your body is activated?

Question

BlackTom AI · Accepted Answer

The sympathetic nervous system mediates the classic "fight or flight" responses such as pupil dilation and increased heart rate.

Relevant knowledge points:
- The autonomic nervous system (ANS) controls involuntary bodily functions and has two main branches: sympathetic (mobilizing) and parasympathetic (rest-and-digest).
- The sympathetic branch prepares the body for stress by increasing heart rate, dilating pupils (mydriasis), dilating bronchi, and releasing catecholamines (norepinephrine from sympathetic nerves and epinephrine from the adrenal medulla).
- The somatic nervous system controls voluntary skeletal muscle movement, and the central nervous system (CNS: brain and spinal cord) processes information but is not the specific effector branch producing the peripheral "fight or flight" responses.

Step-by-step reasoning:
1. A perceived threat is processed in brain regions (e.g., hypothalamus, amygdala) that activate the autonomic output.
2. The hypothalamus stimulates the sympathetic nervous system and the adrenal medulla.
3. Sympathetic neurons release norepinephrine onto target organs; the adrenal medulla secretes epinephrine into the bloodstream.
4. On the eye: sympathetic stimulation contracts radial iris muscles → pupil dilation, allowing more light.
5. On the heart: sympathetic stimulation (via β1 receptors) increases heart rate and contractility → stronger, faster pumping.
6. Additional effects (sweating, increased blood flow to muscles, decreased digestion) further support immediate action.

Why the correct answer is correct:
The described physiological changes (eyes dilating, heart pumping faster) are hallmark sympathetic effects caused by catecholamine-mediated activation of target organs.

Why other options are incorrect:
- Parasympathetic nervous system: produces opposite effects (pupil constriction, decreased heart rate).
- Somatic nervous system: controls voluntary skeletal muscles, not involuntary visceral changes.
- Central nervous system: is the processing center but not the peripheral autonomic effector causing those specific responses.

Conclusion: The correct answer is Sympathetic nervous system.

When your body prepares you for fight or flight (e.g., eyes dilating, heart pumping),which system in your body is activated?单项选择题

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