Your Body’s Response Team: Movement, Fight or Flight, Rest and Digest, and the Gut-Brain Connection
This is the second post in a 3 part series talking about the Nervous System. (Read part 1 The Body’s Communication Network here).
We categorize your nervous system into 2 main anatomical parts. The Central Nervous System which contains your brain and spinal cord and the Peripheral Nervous System which contains all the nerves that branch out from your spinal cord. When we talk about the Peripheral Nervous System we break it down into two main functional categories. The first is called the Somatic Nervous System and this sends all of your “conscious” signals. The second is the Autonomic Nervous System and this sends all of your “unconscious” signals. First, we will discuss the Somatic Nervous System (the “conscious” system) in more detail.
The Somatic Nervous System
Since the nervous system is the body’s communication network there needs to be a clear way for your body to send AND receive signals. The Somatic Nervous System controls your skeletal muscles and receives messages from your senses. When the nerves leave the spinal cord they actually leave in pairs. One part of the pair is called the motor (or efferent) pathway and one is the sensory (or afferent) pathway. The motor pathway carries a signal from the brain out to the body, for example telling your hand to reach for your coffee cup. The sensory pathway carries a signal from your body back to your brain, for example telling your brain that the coffee cup is too hot to hold right now. This motor pathway controls your skeletal muscles and tells your body how to move. The sensory pathway sends messages from your senses of taste, touch, sound and smell to your brain (your sense of sight is integrated by nerves directly into your brain due to it’s location).
The Somatic Nervous System is also responsible for what is called your “somatic reflex arc.” This is an action that occurs automatically between a motor and sensory pathway. An example of the simplest form of this is when the doctor takes a little hammer and hits just below your knee. When your patellar ligament is hit it causes your quadriceps muscle to automatically contract causing your leg to do a little jump. This type of reflex is important to prevent injury. In our example when the patellar ligament was hit the body perceives it as being “overstretched” and so at risk for injury. That is why the response is to contract the muscle (in this case the quadriceps) in order to prevent the muscle and tendon from being overstretched. The quick response of contraction is what causes your lower leg to swing out quickly. This tells your doctor that your nerves are structurally and functionally well.
The Autonomic Nervous System
The second part of the Peripheral Nervous System is the Autonomic Nervous System. This system is responsible for the “unconscious” nerve signals in your body. The nerves in this system branch out into your organs and control your involuntary body functions such as digestion, breathing, and your heart rate. We divide the Autonomic System into 3 different categories based on how the anatomy they influence and how they affect the organs that they branch into. These categories are the Sympathetic Nervous System, the Parasympathetic Nervous System and the Enteric Nervous System. Next we will look at these more in depth starting with the sympathetic and parasympathetic nervous systems. While these systems influence our body’s in opposite ways we need both of them to be able to stay safe when needed and to then be able to return to a normal state of health.
The Sympathetic Nervous System – Fight or Flight
This system branches into almost every area of your body. Have you ever heard the term “fight or flight?” This is the system that controls how your body responds to a threat or emergency, are you going to stand and fight or are you going to flee? When faced with a threat your body needs to be able to respond quickly. This means that your sympathetic nervous system is going to tell your heart to speed up so that more blood flow and oxygen is available to your muscles. It is going to tell your digestive system to stop digestion that way more blood flow can be sent to your muscles. It will tell your pupils to become larger to let in more light for better eyesight. It tells the muscles in your lungs to relax so that you can take in more oxygen with each breath. This is the system that places your body on alert so that it is ready to respond quickly to keep you safe.
The Parasympathetic Nervous System – Rest and Digest
As amazing as the body’s “fight or flight” response is, it is not a state that we can live in indefinitely. We need to have a way for our body to return to a state that we can maintain and function in. This is where the Parasympathetic Nervous System comes into play, we refer to this system as the “rest and digest” response. Compared to the “fight or flight” response system, this branches into and influences a much smaller area of your body. The Parasympathetic System tells your heart rate to return to normal, it tightens the muscles in your respiratory system so that your body doesn’t have to work as hard to breathe, it refocuses blood flow and energy to your digestive tract so that you can break down your food and absorb nutrients and it allows for sexual arousal to name a few of it’s effects on the body.
Enteric Nervous System
Your digestive system is truly amazing in how it functions and the role it plays in the body. As we discussed earlier both the Sympathetic and Parasympathetic Nervous System influence how our body digests our food. However, there is another layer of nerves that influence digestion at such an involved and independent level that we place them in their own category, the Enteric Nervous System. These nerves branch into the walls of the digestive organs and there are so many of them that it is believed there are more neurons in the digestive system then in the entire spinal cord.
Have you ever heard the term the Brain-Gut Connection? There are so many neurons within your “gut” that it almost acts as a second brain by influencing the brain in your skull. While before it was thought that problems such as anxiety and depression could cause bowel concerns like diarrhea and constipation, new research has shown that it may actually be the other way around! That people who suffer from bowel problems such as irritable bowel syndrome are actually sending messages from their enteric nervous system (gut-brain) to their central nervous system (brain) that causes an emotional response such as anxiety or depression.
