The vagus nerve, the longest nerve in the body, originates in the brainstem and extends down into the abdomen. It monitors and receives information about the functioning of the heart, lungs, and other internal organs so that you can focus attention on other matters.
What Is the Vagus Nerve?
Vagus means wandering , and the vagus nerve, after it leaves the base of the brain, sends branches to the ears, the throat, the heart, the lungs, and the digestive tract, with stops along the way at the vocal cords and the diaphragm, before descending into the abdomen. The branches of the vagus nerve enable the organs to adjust instantly to the demands of a person’s internal and external environment.
The vagus nerve is why your heart races and stomach curdles when you sense a threat and why your breathing slows and your body relaxes when friends welcome you to their house. The vagus nerve is the key player in the autonomic nervous system controlling your internal organs.
The vagus nerve is a major pathway of the parasympathetic nervous system, which, along with the sympathetic nervous system, constitutes the autonomic nervous system. Normally, sympathetic and parasympathetic nerves act synergistically and together create the state of equilibrium known as homeostasis. Disruption of the balance of sympathetic and parasympathetic activity is characteristic of a number of physical disorders with a strong psychological component—irritable bowel syndrome, for example—and some therapies target stimulation of the vagus nerve as a way to restore physiologic, and psychologic, balance.
Containing both sensory and motor fibers, the vagus nerve is in charge of both sensations and movement. Through its many branches, it controls swallowing and speech. It carries the sense of taste and sensations felt by the ears. It is responsible for involuntary muscle and gland control of the viscera, encompassing the heart, the lungs, the esophagus, and the rest of the digestive tract. It controls breathing and heart function, including heart rate. It relays sensations originating in the cervix and other organs of the abdomen.
Why Is the Vagus Nerve Important?
Because information flows both to and from the brain via vagal pathways, the vagus nerve can be thought of as a major mind-body highway. The many branches of the vagus nerve are increasingly seen as pathways for promoting or restoring health and ameliorating the physiologic unease that gives rise to anxiety and other negative mental states.
States of visceral calm get relayed up to the brainstem, which then transmits the information to more highly evolved brain structures, allowing full access to the brain’s means of expression and enabling social interaction—which has the effect of perpetuating the state of neural calm. But in potential danger states, such as completely novel environments, those higher systems turn off and we become defensive and on high alert: The vagal circuitry narrows our focus and prepares us to fight or flee—the so-called stress response.
If the danger is so overwhelming that there’s no escape or there’s a feeling of being trapped, a third circuit of vagal operations engineers a shutdown. In this out-of-focus, numb state, social contact becomes aversive. Such bodily responses are not voluntary, and often people are not aware of what triggered them, although they are likely aware that their heart is pounding or their body is trembling.
Because the vagus nerve operates bidirectionally, states of homeostasis and calm, which are necessary for restoration and growth, can be induced from the bottom up or the top down. That is, the brain can deploy cognitive and other strategies to dissipate states of bodily unease (top down), or it can activate the vagus nerve at a number of points in its path to create psychological comfort and a sense of safety (bottom up).
What Does the Vagus Nerve Do?
Defense is a major obligation of every living system, and humans are no different. It is the job of the autonomic nervous system to detect danger and keep us safe. Before we are even consciously aware of it, the autonomic nervous system detects threats and responds, enacting a defense strategy to help us survive. Activation of the stress response, setting off a cascade of physiologic changes to prepare the body for fast action if needed, is a hallmark of the strategy. So is an outpouring of signaling chemicals and pro-inflammatory compounds that circulate through the body, including the brain. Anxiety is the name we give to the visceral unease we feel under such conditions.
Many of the chemical changes stirred by the detection of threat act directly on the brain, jolting it into alertness, sharpening senses, prompting a search for something amiss—even setting off a sense of doom—and shutting down such higher brain functions such as decision-making and creativity . Heart rate, breathing, blood pressure, all go into high gear, readying the body for movement. The shifts in physiologic state in response to threat are kicked off by the sympathetic branch of the autonomic nervous system.
By contrast, the vagus nerve, the main component of the parasympathetic branch of the nervous system, is the architect of safety. It acts to down-regulates the response to threat, to restore visceral order and psychological calm. Its action is needed to enable renewal and growth. And in shutting down defenses, it sets the psychological stage for social interaction.
The vagus nerve connects the brain with the major organ systems of the body. It links mental and physical processes. It is the means by which the mind and body are physiologically inseparable; signals that affect one directly affect the other, although they find expression in different ways.
The Mind-Body Highway
As a large neural pathway between much of the body and the brain, the vagus nerve operates automatically to control many functions. It is also susceptible to influence in multiple ways.
Breathing. Heart rate. Blood pressure. Digestive functions including movement of food through the gut. All are controlled by the vagus nerve.
Vagal tone is a term often used to indicate the balance between sympathetic and parasympathetic (vagal) activity in relation to the heart, and it is assessed by measuring the heart’s ability to respond appropriately to situations that demand an increase or decrease in cardiac output and thus a faster or slower heart rate (heart rate variability). Good vagal tone allows the system to ramp up quickly as conditions demand (say, a sudden need to flee a dangerous situation) and to settle down after an experience of stress. Low vagal tone is a feature of inflammatory bowel disease, irritable bowel syndrome, and other disorders of the gastrointestinal tract.
As the autobahn of mind-body interaction, the vagus nerve is a powerful modulator of mood, a major pathway of the stress response, and a participant in conditions as diverse as heart disease and vocal paralysis. The feeling of anxiety— the mental state of modern times— is a reflection of the agitated physiologic state created by threat and relayed to the brainstem via the autonomic nervous system. As it is interpreted by higher brain structures, the physiologic turmoil turns on a suite of negative emotions. Through the use of higher brain structures—memory, previous learning, networks of associations—people create narratives of worry to explain the visceral unease. Thoughts focus on problems and other bad things. People create catastrophic “what if…” scenarios having a whole range of negative outcomes. There may be a feeling of impending doom.
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