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What Are the Functional Differences Between the Sympathetic and Parasympathetic Nervous System?

The sympathetic nervous system is involved in preparing the body for stress-related activities while the parasympathetic nervous system is associated with returning the body to routine, day-to-day operations. The two systems have complementary functions, operating in tandem to maintain the body’s homeostasis. Homeostasis is a state of equilibrium, in which biological conditions are maintained at optimal levels (Lumen). A general description of the autonomic nervous system can be found here: What are the functions controlled by the autonomic nervous system unconsciously?

The following lists include not only the functions of the sympathetic and parasympathetic, but also the effects on the body that I have noticed happen when either system gets activated:


  • dilated pupils

  • nightmares

  • physical tension

  • decreasing motility of the large intestine

  • itchiness, pruritus

  • widening bronchial passages, dilates bronchioles (breaths easily)

  • inhibition of the lacrimal gland and salivation

  • poor engagement

  • heart racing

  • paling or flushing, or alternating between both

  • over-arousal, energized, speeded up, hyperactivity

  • muscle tension (jaw/neck/shoulders)

  • perspiration

  • tense jaw/lips, muscle spams

  • anxiety, rumination

  • tachycardia, agitation, emotional reactivity

  • constipation, digestion slows down or stops

  • difficulty falling asleep

  • irritable, aggressive

  • eye strain

  • increase peristalsis in the esophagus

  • piloerection (goosebumps)

  • Inhibition of erection

  • loss of hearing

  • loss of peripheral vision

  • relaxation of the bladder

  • shaking

  • social withdrawal

  • dry mouth

  • dizziness

  • lightheadedness

  • no urination

  • increases orgasmic response

  • constriction of most blood vessels

  • increases metabolic rate

  • burning stomach

  • burning in chest

  • slows down digestion

  • disinhibition of spinal reflexes

  • dilate in skeletal muscle

  • increase in blood pressure

  • inhibits tumescence

  • promotes emission prior to ejaculation


  • cold hands or feet

  • constricted pupils

  • constricts the bronchiolar diameter

  • crying

  • defecation

  • diarrhea

  • difficulty breathing

  • difficulty walking

  • dilates blood vessels

  • disinhibited

  • dizziness, nausea

  • ear ringing

  • emotional sensitivity

  • increased mucous production

  • releases epinephrine

  • heart-pounding

  • heaviness

  • immature, silliness

  • low blood sugar symptoms

  • poor engagement

  • sadness

  • stimulates salivation

  • tightness in the chest/throat/neck

  • urination

  • vasodilation (red face)

  • slowed heart rate

  • flatulence

  • cramping, uneasy stomach

  • glassy eyes

  • runny nose

  • short breath

  • secrete mucus

  • immobility

  • lack of deep sleep

  • increases blood flow

  • decreases blood pressure

  • gastric juice secreted

  • increases digestion

  • sphincter relaxed

  • bladder wall contracted

  • increases glycogen to glucose conversion

  • belching

  • increases stomach motility

  • engorges the male and female genitals

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