With big words like autonomic, sympathetic and parasympathetic, it’s no wonder why most people shut down, run away or go blank when their doctor begins talking about the nervous system. Perhaps we just need a language shift.
Broadly speaking, the nervous system is our communication system. It provides the brain with information about what is happening in the world around itself and the world within itself.
Imagine a tree. The top of the tree is the brain. The roots of the tree are like the nerves that communicate touch, sight, sound, taste and smell. The top of the tree relies on the sensing of the roots below to inform it on the state of its environment.
When the brain receives this information, it then has to make sense of its meaning and decide what action to take. The brain then communicates this action plan back down the nerves to the muscles to move the organism based on the information it has received.
In other words, the brain takes in information through its five senses, and decides how to move the organism based on the meaning of information it receives.
Senses (environmental input) -- > Brain (interpret meaning) --> Action (movement)
So how does the brain decide the appropriate action to take? Although the human nervous system has developed an increasing complexity over time, our human behavior is still informed by our animalistic past. If we go back to how our organism developed over time we see two priorities of any animal – survival and reproduction. Living long enough to get your genes into the next generation was the unconscious priority of any animal. So when the brain received information about its environment, action was also oriented around these two priorities.
Are you with me so far?
In the next post we will talk about how the sympathetic and parasympathetic nervous system developed around the priorities of survival and reproduction.
How do the sympathetic and parasympathetic nervous system relate to the two highest priorities of any animal - survival and reproduction? If you think of which of the above two is the most important it becomes clear that if you don’t survive you cannot reproduce. So on some level, the nervous system evolved to value survival over reproduction.
So what threatens survival? If we look evolutionarily, threats included a deficiency of inputs like lack of food and essential nutrients, lack of warmth, lack of water, etc. – Or the threat was an attack from high levels predators or a neighboring group member.
What is the response of most animals to threat? The survival instinct historically was to move away from or attack the environment that was threatening survival. Move away from the predator, move away from the food desert, move away from the dry-waterless environment, move away from the darkness. Or attack the high-level predator or neighboring group member. The system that responds to threat is the sympathetic nervous system. It evolved to move the organism away from danger or attack the immediate threat to maintain survival.
You have felt the sympathetic nervous system when you are about to speak in front of a group and your palms begin sweating, your heart starts beating faster, your breathing speeds up and you notice tension in your body.
So how did we historically turn off the sympathetic nervous system? We found safety. In the form of a new food source, a new water source, sunlight, or we won the fight/outran the predator.
We could finally stop moving and relax when our life was no longer in danger. The side of the nervous system that activates with safety is called the parasympathetic nervous system. It turns on when our organism is digesting, resting, or relaxing. It is the state where the organisms feels safe and has its needs met.
You have felt the parasympathetic nervous system when you feel a sense of calm, peace or deep relaxation.
Because these movements were so important to survival of the organism and the promulgation of the species, the sympathetic and parasympathetic nervous system do not require conscious thought or action. They happen quickly and automatically - like a reflex – which is why together they are known as the autonomic (automatic) nervous system.
Are you with me still? Do we have any questions?