What is the Autonomic Nervous System?
The autonomic nervous system controls the automatic functions of the body. These are the functions that you do not consciously think about (breathing, heart beating, digestion). The autonomic nervous system lies within the brain and spinal cord and is composed of two divisions: sympathetic and parasympathetic.
Sympathetic Nervous System
The sympathetic nervous system controls the “fight or flight” response. When faced with stressful or dangerous situations, this system causes certain changes in the body to ensure survival. The main goal of this response is to divert energy towards vital bodily functions (brain, heart) and away from less vital functions (digestion). There are several changes that occur to accomplish this goal.
Parasympathetic Nervous System
The parasympathetic nervous system controls the “rest and digest” response. When in relaxing and safe situations, this system diverts energy to everyday, life-sustaining functions. This includes increasing digestion to promote the creation and storage of energy, as well as promoting urination to rid the body of waste. Additionally, the parasympathetic system relaxes the body by decreasing breathing as well as heart rate and blood pressure.
The sympathetic nervous system controls the “fight or flight” response, activated in times of stress and danger. The parasympathetic nervous system controls the “rest and digest” response, the opposite of the sympathetic nervous system. Together, these two system regulate important bodily systems to ensure that we stay alive.
Some of these changes include relaxing airways (increase breathing), increasing heart rate and blood pressure, and decreasing digestion. When breathing, heart rate and blood pressure are increased, more oxygen is flowing through the body, which allows for more energy to be delivered to important systems. Additionally, by decreasing less vital functions like digestion and urination, that energy can be used elsewhere to ensure survival.
How does the sympathetic nervous system do all of this at once? In response to a stressful or dangerous situation, the sympathetic nervous system releases specific neurotransmitters that activate these responses across the body. These neurotransmitter are called norepinephrine, also known as adrenaline, and epinephrine.
The main neurotransmitter of the parasympathetic nervous system is acetylcholine. When released within the body during the “rest and digest” response, it causes the above responses throughout the body.