The Three Nervous System Stress Response Pathways
Introduction: When an event is perceived as stressful or threatening, there are two ways (nerves and hormones) that the brain sends messages to the body to get ready to fight or flee or freeze. The three nerve systems send messages quickly so the body can act immediately.
1- Neuromuscular nervous system: The nerves sending messages to skeletal muscle can keep skeletal muscles tightening indefinitely (for hours and days).
Benefits: Muscles are instantly tightening and ready to move to fight and/or run.
Liabilities: If the neuromuscular nervous system is activated too frequently or continuously it can lead to neuromuscular dysfunctions (e.g. sore muscles, TMJ or jaw pain, headache, back ache, etc.) as well as increasing emotional arousal and anxiety.
2- Sympathetic nervous system: The nerve messages to other body organs will immediately result in opening airways, increasing respiration, increasing oxygen consumption, increasing heart rate, increasing volume of blood pumped by the heart, increasing blood pressure, sending blood away from the extremities and moving it toward the working muscles/heart/brain, decreasing digestion, increasing sweat, and stimulating the adrenal glands to release adrenaline and noradrenaline.
Benefits: The body is instantly ready to support the skeletal muscles in fight/flight by providing more blood and oxygen to them and shutting down body functions unnecessary for immediate survival.
Liabilities: Unlike the nerves to skeletal muscles, the sympathetic nervous system’s nerves to major body organs will begin to fatigue under chronically high stimulation and will only be able to release neurotransmitter signals to the organs for about 5 to 10 minutes. If the stressful situation lasts longer than this, it is important to continue the actions of these organs for survival. The body’s backup plan to deal with this is to also use hormones messengers since they can keep the effects going for longer periods of time.
3- Parasympathetic nervous system: Although the majority of nerve messages sent in stressful situations are through the neuromuscular and sympathetic nervous systems, messages are also sent to the body by the parasympathetic nerves.
Benefits: It has been proposed that the freeze response is a unique bypass mechanism to prevent the continual release of too much cortisol and thyroxine in the face of extreme or long lived stressors.
Liabilities: Since this system promotes slowing and restorative functions (the opposite effect of the two systems described above) it can result in “freezing” in the midst of the stressful situation (being immobilized, unresponsive, or perhaps even feeling weak and faint). This lack of action may mean failure to fight or escape in threatening situations, or immobilization when giving a speech, etc.
Kathy Somers, University of Guelph, Stress Management and High Performance Clinic
Adapted by, G Ross Clark