Sympathetic and Parasympathetic Responses

Sympathetic vs. Parasympathetic Responses

Sympathetic Response (Fight, Flight, Freeze, Fawn)

  • The sympathetic response, often termed "fight or flight," prepares the body for perceived threats.
  • More recently, the "freeze" and "fawn" responses have been added to describe different reactions to threat.
  • The sympathetic response is associated with arousal and excitement.
Examples of Sympathetic Activation:
  • Facing a dangerous animal (e.g., saber-toothed tiger).
  • Sitting for an exam.
  • Receiving communication from someone you like.
  • Job interview.
Physiological Changes During Sympathetic Activity:
  • Mental Alertness: Increases to optimize cognitive function in the face of a threat or challenge.
  • Metabolic Rate: Increases as cells consume more oxygen and glucose for energy.
  • Digestion and Urination: Processes slow down or halt to conserve energy.
  • Energy Reserves: Activated to provide fuel for increased metabolic demands.
  • Respiratory Rate: Increases to supply more oxygen to muscles and tissues.
  • Heart Rate and Blood Pressure: Increase to facilitate rapid oxygen and nutrient delivery.
  • Sweat Glands: Activated to dissipate heat as body temperature rises.

Parasympathetic Response (Rest and Digest)

  • The parasympathetic response is characterized by relaxation and recovery, often referred to as "rest and digest."
  • It counteracts the effects of the sympathetic nervous system, promoting energy conservation and replenishment.
Physiological Changes During Parasympathetic Activity:
  • Metabolic Rate: Decreases as the body conserves energy.
  • Heart Rate and Blood Pressure: Decrease to promote relaxation.
  • Secretion of Salivary and Digestive Glands: Increases to facilitate digestion.
  • Urination and Defecation: Processes become active to eliminate waste.
  • SLUD Acronym: Salivation, lacrimation, urination, defecation.

Sympathetic and Parasympathetic Balance

  • The sympathetic and parasympathetic systems work in tandem to maintain homeostasis.
  • They innervate the same organs but produce opposite effects.
Examples of Opposing Actions:
  • Pupils: Parasympathetic stimulation constricts pupils, while sympathetic stimulation dilates them.
  • Heart: Parasympathetic nerves slow heart rate, while sympathetic nerves increase heart rate and contractility.
Importance of Balance:
  • Maintaining balance between sympathetic and parasympathetic activity is crucial for overall health and well-being.
  • Chronic activation of the sympathetic nervous system can lead to burnout and health problems.
  • Homeostasis is achieved when the parasympathetic system provides adequate recovery from sympathetic activation.

Role of PNS

  • PNS divides into Somatic and Autonomic.
  • Autonomic further divides into Sympathetic and Parasympathetic divisions.