Final answer:
The parasympathetic nervous system is activated during non-stressful situations to calm the body, lowering the heart rate, reducing blood pressure, and promoting digestion. It counteracts the sympathetic nervous system's 'fight or flight' response by restoring the body to a state of rest and conserving energy.
Step-by-step explanation:
Parasympathetic Nerves Activation
The parasympathetic nervous system is strongly influenced and activated during non-stressful situations, enabling the body to engage in "rest and digest" activities. Unlike the sympathetic nervous system, which prepares the body for stressful and emergency situations, the parasympathetic nervous system calms the body down and conserves energy. It lowers the heart rate, reduces blood pressure, and stimulates digestion, among other functions. This relaxation response is often associated with peaceful scenarios, for example, like those during a picnic, where both 'picnic' and 'parasympathetic' start with the letter 'p'.
This system's preganglionic neurons have cell bodies in the brainstem and sacral spinal cord, and they release acetylcholine onto postganglionic neurons located near target organs. The postganglionic neurons then release acetylcholine, or sometimes nitric oxide, onto target organs to induce the rest-and-digest response. After the sympathetic nervous system is activated by a stressor, the parasympathetic nervous system resets organ function.
For example, after an individual experiences a situation that required a 'fight or flight' response, like a hunter in the wild, the threat resolution sees the parasympathetic nervous system returning bodily functions to a relaxed state. This system is also responsible for restorative processes like constricting pupils, restoring bladder control, and regulating glucose storage in the liver.