Divisions of the nervous system

Revised 2025-10-16 10:53:20 AM EDT

Though the nervous system is in many ways a single continuous system, for teaching and research purposes, we often refer to “divisions” of the nervous system in order to talk about tissue that has specific functions or specific anatomy. Knowing a little about the seven divisions of the nervous system described below will help you on the MBLEx as well as create a foundation for learning more about the nervous system and communicating with other healthcare providers.

Central nervous system (CNS)

The most obvious way to divide up the nervous system is to separate the brain and spinal cord from all of the other nervous tissue outside of the brain and spinal cord. We use the term central nervous system (CNS) to refer to brain plus spinal cord. It is where information is gathered, compared, weighed against memory and context, and turned into plans. The cortex at the surface of the brain supports attention and decision‑making; deeper structures pattern emotion, memory, and autonomic tone; the spinal cord coordinates reflexes and passes messages to and from the body.

Sidenote

Massage connection

For massage therapists, it’s important to appreciate that sensation does not equal perception. Sensory receptors in the skin and fascia generate nerve signals, but the CNS decides what those signals mean. A slow, predictable stroke is more likely to be categorized as “safe and helpful,” while abrupt, unfamiliar input is more likely to be flagged for caution. Over time, the CNS can even re‑learn what to expect from a previously guarded area, which is one reason regular, skillful touch can change a client’s baseline comfort.

Peripheral nervous system (PNS)

The peripheral nervous system (PNS) is everything neural outside of the brain and spinal cord (cranial nerves and spinal nerves, and all their branches, and more). The PNS carries two streams of traffic:

Definitions

Afferent (sensory)

Information headed toward the CNS from receptors in the skin, muscles, joints, and organs.

Efferent (motor and autonomic)

Commands headed away from the CNS to effectors (skeletal muscle, smooth muscle, cardiac muscle, glands).

Because the PNS travels through a number of narrow and sensitive passageways (paraspinal tissues, thoracic outlets, and limb tunnels, and more), it is sensitive to posture and local tissue tone. A tight scalene or pectoralis minor can irritate the brachial plexus; a crowded carpal tunnel can compress the median nerve. Skilled positioning and gradual soft‑tissue work can ease mechanical stress on these pathways.

Below you will see how the peripheral nervous system can be further divided into divisions that have specific function: the somatic nervous system, the sympathetic nervous system, the enteric nervous system, and a grouping of them called the autonomic nervous system.

Somatic nervous system

Within the peripheral nervous system is the somatic nervous system, which carries conscious sensation from skin, muscles, and joints, and provides voluntary control of skeletal muscle. When you decide to flex your wrist, somatic motor neurons fire. When you feel a slow, broad forearm stroke on the erectors, somatic sensory fibers carry the message to the cord and brain, where it becomes touch, pressure, and movement awareness.

Somatic pathways are the main conversation partners during bodywork. They are fast, specific, and highly trainable. Clients who practice mindful attention to bodily sensations often report more benefit from massage because somatic input has become easier for the CNS to interpret and integrate.

Sympathetic nervous system

The sympathetic nervous system prepares the body to mobilize – the classic “fight or flight” response, though in daily life it more often means “focus and get things done.” Typical effects include increased heart rate and contractility, dilation of airways, metabolic fuel release, and reduced digestive activity. Blood is shunted toward skeletal muscle; sweat glands activate for cooling.

Sympathetic tone is not “bad”; we need it to stand, think, and move. Problems arise when sympathetic dominance becomes the baseline – clients may report shallow breathing, jaw clenching, headaches, or difficulty falling asleep. Fast, choppy, or overwhelming sensory input can reinforce this state.

Parasympathetic nervous system

The parasympathetic nervous system promotes rest, digest, and repair. Heart rate slows, blood flow returns to the viscera, and the gut produces enzymes and motility patterns for absorption. Many parasympathetic fibers travel with the vagus nerve, which influences the heart, lungs, and most abdominal organs.

Parasympathetic tone supports long‑term health: nutrient absorption, immune readiness, and restorative sleep. Clients often describe a pleasant heaviness in the limbs, spontaneous deeper breathing, or a warm abdomen – all markers of a parasympathetic shift.

Sidenote

Massage connection

Techniques that emphasize exhalation, gentle abdominal work, and comfortable neck positioning (reducing mechanical stress around vagal pathways) tend to cultivate parasympathetic dominance. Give clients time to re‑orient before standing so the baroreflex can catch up.

Enteric nervous system

The enteric nervous system is the “second brain” of the gut – a vast network of neurons embedded in the walls of the esophagus, stomach, and intestines. It can coordinate motility, secretion, and local blood flow, even when separated from CNS input. The enteric system constantly converses with both sympathetic and parasympathetic branches: sympathetic input generally slows digestion, while parasympathetic input (especially via the vagus) speeds and enriches it.

Nutrition, stress, sleep, and medication shape enteric behavior. Many clients notice that after a calming session, their digestion feels smoother or they become aware of gurgling (a sign that peristalsis has resumed).

Sidenote

Massage connection

Slow, clockwise abdominal strokes over the colon, combined with breath coaching, can encourage enteric rhythms – particularly helpful for clients with stress‑related bowel irregularity (within scope and with appropriate medical screening).

Autonomic nervous system (ANS)

The autonomic nervous system is an umbrella term for the combination of nervous system divisions that run on automatic, without our direct moment-to-moment conscious control: sympathetic, parasympathetic, and enteric nervous systems. These divisions keep you alive while your attention is elsewhere. They connect to the smooth muscle of blood vessels and viscera, to the heart, and to glands. The ANS does not turn sensation into conscious “feelings” as directly as the somatic system does; instead, it quietly adjusts heart rate, blood pressure, breathing depth, gut motility, pupil size, and more.

The ANS is best understood as a dynamic balance between its sympathetic and parasympathetic divisions, while the enteric nervous system handles much of the gut’s moment‑to‑moment control. Stress, pain, and novelty tilt the system toward mobilization; safety, familiarity, and satiation tilt it toward restoration.

Sidenote

Massage connection

Predictable rhythm, warm contact, and diaphragmatic breathing cues invite parasympathetic settling. You can feel this as softened abdominal tone, slower respiration, and a client who spontaneously sighs.