Fight or flight response

Fight or Flight Response

The fight or flight response is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first described by Walter Bradford Cannon in the early 20th century. This response is a critical component of the autonomic nervous system and is essential for survival.

Physiology

The fight or flight response is initiated by the sympathetic nervous system, which is part of the autonomic nervous system. When a threat is perceived, the hypothalamus activates the sympathetic nervous system by sending signals through the autonomic nerves to the adrenal glands. These glands respond by releasing adrenaline (also known as epinephrine) and noradrenaline (norepinephrine) into the bloodstream.

Effects on the Body

The release of adrenaline and noradrenaline leads to several physiological changes:

• **Increased Heart Rate**: The heart beats faster to pump more blood to the muscles and vital organs.
• **Dilated Pupils**: The pupils dilate to allow more light to enter the eyes, improving vision.
• **Increased Breathing Rate**: Breathing becomes faster and deeper to increase oxygen intake.
• **Redirected Blood Flow**: Blood is redirected away from the digestive system and towards the muscles and brain.
• **Increased Blood Sugar Levels**: The liver releases glucose to provide energy to the muscles.

These changes prepare the body to either fight the threat or flee from it, hence the term "fight or flight."

Historical Background

The concept of the fight or flight response was first introduced by Walter Bradford Cannon, an American physiologist, in his book "The Wisdom of the Body" published in 1932. Cannon's work built upon earlier research by Claude Bernard on the stability of the internal environment, or homeostasis.

Modern Understanding

Today, the fight or flight response is understood as part of the broader stress response system. It is closely related to the hypothalamic-pituitary-adrenal axis (HPA axis), which regulates the release of cortisol, another hormone involved in the stress response.

Clinical Implications

While the fight or flight response is essential for survival, chronic activation of this response can lead to health problems. Conditions such as anxiety disorders, post-traumatic stress disorder (PTSD), and chronic stress are associated with prolonged activation of the fight or flight response.

See Also

• Sympathetic nervous system
• Parasympathetic nervous system
• Stress (biology)
• Adrenaline
• Cortisol

References

• Cannon, W. B. (1932). The Wisdom of the Body. New York: W.W. Norton & Company.
• Selye, H. (1956). The Stress of Life. New York: McGraw-Hill.