Parasympathetic stimulation causes
**Core Concept**
Parasympathetic stimulation is mediated by the parasympathetic nervous system (PNS), a branch of the autonomic nervous system (ANS) that promotes relaxation, reduces stress, and conserves energy. The PNS is responsible for the "rest and digest" response, which contrasts with the sympathetic nervous system's "fight or flight" response.
**Why the Correct Answer is Right**
Parasympathetic stimulation causes the release of acetylcholine (ACh) from parasympathetic nerve terminals, which binds to muscarinic receptors on target organs. This leads to the activation of various physiological responses, including decreased heart rate, decreased blood pressure, and increased salivation. The parasympathetic system also stimulates the contraction of smooth muscle in the digestive tract, promoting peristalsis and the movement of food through the digestive system.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because parasympathetic stimulation does not typically cause an increase in blood pressure.
* **Option B:** This option is incorrect because parasympathetic stimulation does not typically cause an increase in heart rate; instead, it decreases heart rate.
* **Option D:** This option is incorrect because parasympathetic stimulation does not typically cause an increase in respiratory rate.
**Clinical Pearl / High-Yield Fact**
The parasympathetic nervous system is often referred to as the "rest and digest" system, and its stimulation can help to counteract the effects of stress and anxiety on the body. This is why parasympathetic stimulation is often used in clinical settings to treat conditions such as hypertension and anxiety disorders.
**Correct Answer:** C. Increased salivation.