The brain stem is made up of the pons and the medulla, along with the midbrain. The brainstem takes in, sends out, and coordinates all of the brain's messages. Many of the body's automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking are also coordinated by the brainstem.
Stress may also modulate reflex circuitry in the brain stem and facilitate intestinal inflammatory responses ( Kreis, Mueller, Reber, Glatzle, Enck & Grundy, 2003).
In a very negative environment, or when experiencing something bad, very primitive regions in the brain stem are activated, causing things like elevated stress that allow us to respond to whatever is bothering us. This would in turn have an impact on our brain stem. Regions in the brainstem that control stress levels are unlikely to be able to perform the complex computations necessary to process or detect whether or not a stressor is controllable( University of Colorado at boulder, 2005).
When you experience a dire emergency, all of these systems in the brainstem are activated and function to start a fight-or-flight reaction. Stress is triggered (activated) primarily by an area in the brain stem (lowest part of brain) called the locus coeruleus.
The locus coeruleus has many connections to other parts of the brain, particularly areas that bring in and process sensory information from our environment. The locus coeruleus secretes norepinephrine and stimulates other brain centers to do the same. The locis coeruleus also controls the tempo of the brain,thus arousal and vigilance is also increased as a result. It also adjusts the action of the autonomic nervous system, which includes the SNS. The autonomic nervous system regulates blood flow, heart rate, blood pressure, and breathing. It can also temporarily shut down the gastrointestinal (GI) and sexual systems until the crisis is over. ( Itoi & Sugimoto, 2010).
