Acute Stress Response

Click here to view a video on stress and the stress response.

1.  A message from one of the senses (sight, sound, smell, touch or taste) stimulates the brain’s reticular activating system (RAS), which filters information to decide whether the stimulus is important. For example, if we are confronted with some life-threatening situation such as a car out of control hurtling towards us or someone about to attack us. This person’s RAS would filter (at great speed) this sensory information as a dangerous stressor.

2.  The RAS sends the message to the hypothalamus, instructing it to be on the alert for possible action. The message is also sent to the cortex, informing it of a threatening stimulus.

3.  The cortex interprets the message from the RAS and provides cognitive interpretation about whether the stimulus is a threat or not.

4.  The cortex sends the message back to the hypothalamus, which integrates this cognitive message with emotional content from the limbic system to begin activation of the stress response. The neurological connection between the cortex, the limbic system and the hypothalamus provides the mechanism for how thoughts and emotions play a role in the stress response.

5.  If safety is perceived, the stress response is turned off. The body turns to its normal state.

6.  If a threat is perceived, the hypothalamus stimulates activation of the adrenal glands.

7.  The adrenal glands are made up of two components; the adrenal medulla and the adrenal cortex. The hypothalamus stimulates the adrenal medulla via electrochemical impulses and stimulates the adrenal cortex via the pituitary, which releases the hormone ACTH into the bloodstream.

8.  Once stimulated, the adrenal medulla releases adrenaline and other hormones that affect the cardiovascular system increasing heart rate and metabolism and constricting blood vessels.

9.  When the adrenal cortex is stimulated, it discharges cortisol, which increases energy in the body by releasing glucose, fatty acids and amino acids (protein) from cells and organs into the bloodstream. Aldosterone (a hormone produced by the adrenal cortex with action in the renal tubule to regulate sodium and potassium balance in the blood) also is discharged, which increases energy by retaining sodium (salt), which in turn increases blood pressure, blood volume and the amount of blood being pumped through the heart.

10.  If the stress response results in physical action (fight or flight), the body can expend the energy created by the stress response and then return to homeostasis or balance.