The Mind-Body Cure. Bal Pawa
(Figure 2.1). The nerves are bundles of fibers and receptors that sense changes within our body (for example, a feeling of hunger) and our external environment (for example, the sound of screeching tires). The nerves send these messages to the CNS to be interpreted. Nerves outside our brain and spinal cord make up the peripheral nervous system, a complex information highway that comprises the somatic nervous system and the autonomic nervous system (ANS).
The central nervous system, which in humans includes the brain and spinal cord, coordinates the body's activities and stores memories and emotions through 3 levels of increasingly specific nerve systems. This central system first connects with the peripheral nervous system, which includes nerves from the brain and spine that relay messages from all parts of the body to the nervous system and back. These peripheral nerves connect with the somatic and autonomic nervous systems, which send and receive messages about the body's voluntary and involuntary movements respectively. Finally, the autonomic nerves coordinate messages to and from the parasympathetic and sympathetic nervous systems, which activate our calming rest-and-digest or defensive fight-or-flight responses.
Our Voluntary and Involuntary Brain: The Somatic and Autonomic Nervous Systems
The somatic nervous system sends messages from our central nervous system to our organs, muscles, and skin when we decide to do something. It controls our voluntary movement. For example, we use it every time we take a big bite out of a juicy hamburger. Our somatic nervous system sends the message from our brain to our body to pick up and bite into that burger. The somatic nervous system directs the nerves that coordinate this action. These are all choices we make; they are voluntary responses rather than automatic reactions.
But what starts our mouth watering when the food arrives? What stimulated our hunger in the first place? What gets our heart pumping when we jog? These functions are under the control of the ANS, which controls our involuntary, or automatic, reactions. We don’t always choose these actions. The ANS has two arms to regulate the involuntary functions in the body—the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS)—and their interaction forms the basis of the mind-brain-body connection.
Communication between the brain and the body occurs through nerve pathways, and an autonomic nerve pathway connects two nerve cells (neurons) (Figure 2.2). One cell is located in the brainstem or spinal cord and it is connected by nerve fibers to the second cell, which is located in a cluster of nerve cells called an autonomic ganglion (more than one are called ganglia). These ganglia are connected to a specific organ, gland, or muscle by a further set of nerve fibers. Signals travel from one cell to another along the nerve fibers, often down from the brain to the body and back up from the body to the brain.
The central nervous system communicates with the autonomic nervous system through the vagus nerve and autonomic ganglia, which run from the brainstem (pons and medulla oblongata) to organs such as the lungs, heart, and gut. The parasympathetic system uses both pathways for rest-and-digest responses, whereas the sympathetic system engages autonomic ganglia near the spine to manage fight-or-flight situations.
One of the main nerve pathways that connects the ANS to the body is the vagus nerve, which is also known as the “wandering nerve” because this long nerve has the widest distribution in the body. It travels from the brain into organs in the neck, chest, and abdomen. The tenth of twelve cranial nerves (meaning they originate in the brainstem), the vagus nerves come in a pair but we refer to them in the singular form.
Most of the time, the ANS works automatically, without conscious thought. It determines how fast our heart beats, how vigorously our stomach contracts, and how much air gets into our lungs. It also responds automatically to our subconscious thoughts, which communicate with the ANS at every instant, and determines whether our stress hormones are turned on or off. Although the ANS is an automatic system for the most part, our mind has dominance over the brain and can regulate the ANS to a great degree.
➤ Homeostasis: Balancing the Gas with the Brakes
I often like to compare the autonomic nervous system with a car engine. The sympathetic nervous system functions to stimulate—or rev up—the body, so I refer to it in this book as “the gas.” Also known as the fight-or-flight reaction, it is one of our most primitive systems, designed to prepare the body for stressful or emergency situations. The SNS allowed us to run away from predators, and these lightning-speed stress reflexes still keep us out of harm’s way—such as swerving to avoid an oncoming car—on a daily basis. Our body is designed to handle this shortterm stress reaction and then return to a normal, resting state called homeostasis.
When the body senses danger, the SNS is activated and the brain sends a signal to the adrenal glands to release the stress hormones adrenaline and cortisol. Activating the SNS increases heart rate, makes the heart contract with more force, and widens the airways to make breathing easier. It releases stored energy to increase muscle strength and blood sugar, and it causes the pupils to dilate. At the same time, it slows down body processes such as digestion and urination that are less important in dealing with an imminent threat.
The human body is not designed to remain revved up for long periods of time. In fact, all living things tend toward homeostasis, or equilibrium, and our bodies are no different. When our systems remain within certain pre-set limits—a body temperature of 98.6°F or a heart rate of 60 to 100 beats per minute, for example—they are better able to function optimally, which means better health. Our ancestors may have triggered their SNS regularly, but these episodes of cortisol and adrenaline surging through their bodies were mostly short-lived. Once our ancestors got away from danger, their brains deemed the external environment safe again and their heart rate slowed, their breathing eased, and their stress levels dropped. In other words, our ancestors found time to recover and soothe themselves by eating and sleeping. Most animals still do this: ducks ruffle their feathers and cats lick themselves to return to balance.
In humans, the parasympathetic nervous system (PNS) functions to inhibit—or slow down—the body and bring about this equilibrium, which is why I refer to it in this book as “the brakes.” Also known as the rest-and-digest response, it releases hormones and chemicals that relax the body and allow it to recover its normal functioning. When the body is no longer under threat, the PNS is activated and the brain signals the body to release dehydroepiandrosterone (DHEA), a hormone associated with longevity and health; our happy hormone, serotonin; and our natural painkillers, the endorphins. Activating the PNS enhances blood flow to the gut, increases contractions of the gut and release of gastric juices, and turns on secretions that aid the digestion process. At the same time, it slows our heart rate to a resting state and reduces our blood pressure by allowing our blood vessels to return to their usual diameter. In essence, almost every one of our body systems returns to a resting state. It’s like putting up our feet and sipping lemonade on our porch swing.
This intricate system of gas (SNS) and brakes (PNS) operates as a series of checks and balances, ensuring that neither system dominates and that our body returns to homeostasis. In some people, this system becomes overactive (the gas is on all the time). In many of us, the ANS becomes dysfunctional and goes into alarm phase even when there’s only minimal stress. Too much gas for too long will create discomfort and disease. So to address the root cause of stress-induced discomfort and disease, we must look at how our mind interacts with the ANS at every instant—how it hits the gas or pumps the brakes, depending on our internal thoughts—and learn to regulate it with conscious effort.