Parasympathetic Nervous System
Now that we’ve explored the stress and survival-oriented fight-or-flight side of the autonomic nervous system, it’s time to meet its opposite number: the parasympathetic nervous system—our rest and digest system that helps the body relax, recover, and conserve energy.
WHERE IS THE PARASYMPATHETIC SYSTEM?
The parasympathetic (PNS) is like a sandwich, located above and below the sympathetic system. While the sympathetic system is in the middle spine, the parasympathetic system resides in two main regions:
Brainstem: The “transition zone” between the brain and spinal cord, where several cranial nerves (more on those soon) originate:
Cranial Nerve III (Oculomotor Nerve): Controls pupil constriction.
Cranial Nerve VII (Facial Nerve): Stimulates saliva and tear production.
Cranial Nerve IX (Glossopharyngeal Nerve): Affects saliva production and swallowing.
Cranial Nerve X (Vagus Nerve): The most important nerve of the parasympathetic system, influencing the heart, lungs, digestive organs, and more.
Sacral Spinal Cord (S2-S4): Near the base of the spine, or tailbone. Often called the sacral outflow, it controls functions in the pelvic organs, including the bladder, rectum, and reproductive organs.
A HANDY MNEMONIC FOR THE PNS
A great way to remember the key functions of the parasympathetic nervous system is with the mnemonic: lachrymation, salivation, defecation, and urination. These reflect the PNS’s role in tear production, saliva, healthy digestion, and bladder function.
Think about a baby—they’re almost entirely in a parasympathetic state, focused on rest, digestion, and bodily functions, until they gradually learn how to activate their sympathetic system to interact with the world. This highlights the foundational role of the PNS in creating calm and supporting survival.
HOW THE PNS WORKS: KEY PLAYERS AND THEIR ROLES
The Vagus Nerve (Cranial Nerve X)
You may have already heard about the vagus nerve—it’s become almost synonymous with the parasympathetic system. While it is the most important nerve in the PNS, it’s not the only one. The vagus nerve is like a superhighway running from the brainstem down through the neck, face, ears, thorax, and abdomen, connecting the brain to many key organs, including the heart, lungs, and digestive tract.
Nerves like the vagus transmit signals, but they don’t work alone—neurotransmitters like acetylcholine carry these signals to target organs. This team effort allows the vagus nerve to regulate critical body functions.
Functions of the Vagus Nerve:
Heart: Slows heart rate by toggling down the activity of the heart’s natural pacemaker (the SA node).
Lungs: Constricts airways to regulate breathing when at rest (remember, the SNS dilates the airways to increase oxygen perfusion throughout the body when we need to escape).
Digestive System: Stimulates the release of digestive enzymes, promotes gut motility (movement of food through the intestines), and increases blood flow to the stomach and intestines.
Immune System: Plays a role in reducing inflammation by signaling the release of anti-inflammatory molecules.
Curious Facts: It’s sometimes called the "wandering nerve" due to its extensive pathway throughout the body. Also, there are actually two vagus nerves, one on each side of the body—but we often talk about them as “the” (singular) vagus nerve for simplicity because they work together seamlessly to perform the same functions. But cha got two!
Acetylcholine (ACh):
Acetylcholine is the main neurotransmitter of the PNS—the chemical messenger that carries signals from the vagus nerve and other parasympathetic nerves to receptors on target organs.
Muscarinic Receptors (M-receptors): Found on organs like the heart, lungs, and intestines. These mediate the slowing of the heart, stimulation of digestion, and other calming effects.
Nicotinic Receptors (N-receptors): Found at neuromuscular (nerve-muscle) junctions and some parts of the nervous system but are less involved in the parasympathetic system.
Other neurotransmitters also play supporting roles:
Nitric Oxide (NO): Promotes vasodilation (widening of blood vessels), improving blood flow to organs during rest.
Vasoactive Intestinal Peptide (VIP): Encourages smooth muscle relaxation and digestive fluid secretion.
edited from image. No affiliation nor product recommendation.
HOW SIGNALS ARE CARRIED IN THE PNS
Activation Begins: Signals start in the brainstem (specifically in the medulla) or the sacral spinal cord.
Vagus Nerve Carries Signals: The vagus nerve (or other parasympathetic nerves) carries the signal to target organs.
Acetylcholine is Released: Once the nerve reaches its target (e.g., the heart, lungs, or digestive tract), it releases acetylcholine.
Receptors Activate: Acetylcholine binds to cholinergic receptors, triggering specific responses like slowing the heart, stimulating digestion, or relaxing muscles.
WHY THE PNS IS IMPORTANT
Neither system is more important than the other. We need ‘em both. Think of them like a scale, always trying to find balance. However, in our modern world, I’d say we need to work on activating our PNS more!
Stress recovery: Calms the body after stress, reducing adrenaline and cortisol levels.
Remember, our SNS releases adrenaline and cortisol, which can make us amped and irritable. Our PNS helps us relax by reducing the SNS’s release of these stress signals.
Digestive health: Promotes digestion by increasing blood flow to the stomach and intestines.
The SNS constricts blood flow to our digestion (because let’s face it, we don’t care if we’re digesting that meal if we’re running from a monster). The PNS promotes digestion, especially our bowel movements. This is why chronic stress can lead to IBS or other digestive issues.
Immune function: Rest promotes health.
As you may recall, cortisol suppresses our immune systems and can be pro-inflammatory. When we’re under chronic stress, we tend to catch more colds or get more injuries. This is why we’re always taught to rest when we’re sick, we’re essentially trying to activate our PNS so we can heal.
Sleep quality: Calm promotes sleep.
The SNS, cortisol especially, can make us tired and wired, making sleep feel like a mirage in the desert. Calming the nervous system, shifting into the PNS, promotes restorative sleep.
HOW TO GIVE YOUR PNS SOME TLC
Anything that activates the vagus nerve will help calm the nervous system.
Actionable Tips:
Cold exposure: Splash cold water on your face or take a cold shower.
Humming, Gargling, Horse Lips: The vagus nerves and its branches play a key role in controlling the vocal cords and the larynx. Vibrations from the vocal cords stimulate (massage) the vagus nerve, turning on the PNS.
Diaphragmatic Breathing: Slow, deep breaths from your belly also activate the vagus nerve.
Mindfulness or Meditation: Calm thoughts help calm emotions. Remember, it’s usually a thought that creates an emotion (e.g. “I’m stupid” promotes shame or hopelessness). So, if we can calm our thoughts, we can calm our emotions and reduce internal stress.
Gentle movement: Yoga or stretching encourage relaxation. Because they usually calm the mind, encourage you to connect to your breath, and invite your body to also release tension.
Connection: Laughing, singing, or spending time with loved ones to activate social aspects of the parasympathetic system. When we feel connected, we feel safe, which is the opposite of stressed.
Craniosacral Therapy (CST): This gentle, hands-on therapy directly works with the craniosacral system, helping to balance and support the PNS. CST encourages deep relaxation by relieving tension in the fascia and improving the flow of cerebrospinal fluid, promoting a calm and balanced state. It’s especially effective for those dealing with chronic stress, anxiety, or nervous system dysregulation. This is something I specializes in, if you’d like to make an appointment click here. If you’re looking for a practitioner in your area you might start with Upledger’s find a practitioner page.
We need both systems working in harmony and moderation. Try one or two of the tips above and see how they feel. Next, we’ll dive into the final branch of the autonomic nervous system: the enteric nervous system, your gut’s “second brain”!
What's coming:
The Autonomic Nervous System - The Intro
The Sympathetic Nervous System - "Fight or Flight"
The Parasympathetic System and the Vagus Nerve - "Rest & Digest"
The Enteric Nervous System - The Gut-Brain Connection
The Somatic Nervous System - Move & Sense
The Cranial Nerves - Pathways of Sensory and Motor Control
Brain Regions and Their Roles in Thought, Mood, and Movement
How the Nervous System Impacts Mental Health & Trauma Recovery
Craniosacral Therapy - Enhancing Nervous System Balance
Are there specific areas of the nervous system you're curious about? Drop a comment below, and I'll be sure to cover them as we journey through this incredible body-wide network!
