The vagus nerve, cranial nerve X, is the longest cranial nerve in the body, containing both motor and sensory functions. Of note, the sciatic nerve is the largest and longest peripheral nerve in your body and is also a mixed nerve, also containing both motor and sensory functions. The vagus nerve originates in the brainstem and innervates the muscles of the throat, circulation, respiration, digestion, and elimination. It represents the main component of the parasympathetic nervous system; 80 percent of its nerve fibers are sensory, which means the feedback is critical for homeostasis.

First, our “fight and flight” response is our survival strategy, a response from the sympathetic nervous system. If you were going to run from tiger, for example, you want this response to save your life. When we have a fight response, we can have anger, rage, irritation, and frustration. If we are having a flight response, we can have anxiety, worry, fear, and panic. Physiologically, our blood pressure, heart rate, and adrenaline increase and it decreases digestion, pain threshold, and immune responses.
Second, we have a “freeze” state, our dorsal vagal state, which is our most primitive pattern, and this is also referred to as our emergency state. This means that we are completely shut down, we can feel hopeless and feel like there’s no way out. We tend to feel depressed, conserve energy, dissociate, feel overwhelmed, and feel like we can’t move forward. Physiologically, our fuel storage and insulin activity increases and our pain thresholds increase.
Lastly, our “rest and digest” is a response of the parasympathetic system, also known as a ventral vagal state. It is our state of safety and homeostasis. If we are in our ventral vagal state, we are grounded, mindful, joyful, curious, empathetic, and compassionate. This is the state of social engagement, where we are connected to ourselves and the world. Physiologically, digestion, resistance to infection, circulation, immune responses, and our ability to connect is improved.

Research

The polyvagal theory: New insights into adaptive reactions of the autonomic nervous system | S. Porges (2009)

Learn More

Neuroanatomy, Cranial Nerve 10 (Vagus Nerve) Continuing Education Activity | National Library Of Medicine
Vagus Nerve: What To Know | Web MD
What Is The Vagus Nerve? | Cleveland Clinic
What Is The Vagus Nerve? | Healthline