Autonomic Nervous System: Sympathetic vs Parasympathetic - Anatomy and Physiology

1. Which neurotransmitter and receptor type do parasympathetic postganglionic neurons use at target organs?

   Acetylcholine acting on muscarinic receptors.

2. What effect does sympathetic activation have on bronchiolar diameter?

   Bronchodilation, mediated mainly by beta-2 receptors responding to circulating epinephrine.

3. Which autonomic division increases gastrointestinal motility and secretion?

   The parasympathetic division (rest and digest).

4. What effect does each autonomic division have on the pupil?

   Sympathetic activity dilates the pupil (radial muscle); parasympathetic activity constricts it (sphincter pupillae).

5. Where do parasympathetic preganglionic neurons arise?

   In the brainstem (cranial nerves III, VII, IX, and X) and sacral segments S2 to S4 (craniosacral outflow).

6. How do sympathetic and parasympathetic ganglia differ in location?

   Sympathetic ganglia lie near the spinal cord (short preganglionic fibers); parasympathetic ganglia lie in or near target organs (long preganglionic fibers).

7. Which neurotransmitter do most sympathetic postganglionic neurons release?

   Norepinephrine. A key exception is sweat glands, whose sympathetic fibers release acetylcholine.

8. A patient receives atropine, a muscarinic receptor blocker. What happens to resting heart rate?

   It increases. Blocking muscarinic receptors removes the vagal tone that normally slows the SA node.

9. From which spinal cord segments do sympathetic preganglionic neurons arise?

   T1 to L2 (thoracolumbar outflow), from the lateral horn of the gray matter.

10. Which neurotransmitter and receptor are used at all autonomic ganglia?

    Acetylcholine acting on nicotinic receptors, in both sympathetic and parasympathetic ganglia.

11. Why is the adrenal medulla considered part of the sympathetic division?

    It acts as a modified postganglionic ganglion: preganglionic fibers stimulate it to release epinephrine and norepinephrine into the blood.

12. The vagus nerve is stimulated. What happens to heart rate?

    Heart rate decreases. Vagal (parasympathetic) acetylcholine slows the SA node.

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