Sympathetic vs Parasympathetic: What’s Happening in Your Dog’s Nervous System?
Understanding the sympathetic vs parasympathetic nervous system in dogs can help explain why your dog’s body responds so differently depending on what they’re experiencing.
Your dog hears a sudden noise outside. Their head comes up, their attention sharpens and their body becomes ready to respond.
Later that evening, the same dog is stretched out comfortably, breathing slowly and resting after dinner.
These look like behavioural changes, but there are also physiological changes happening inside the body.
A large part of that is controlled by the autonomic nervous system.
What is the autonomic nervous system?
The autonomic nervous system helps regulate many of the processes your dog doesn’t consciously control, including heart rate, breathing, blood pressure and digestion.
Two important branches are the:
Sympathetic nervous system (SNS)
and
Parasympathetic nervous system (PNS)
You may have heard these described as “fight or flight” and “rest and digest.”
Those phrases are useful shorthand, but what is actually happening is more interesting.
The sympathetic nervous system: preparing the body for action
The sympathetic nervous system helps mobilise the body when action is required.
Imagine your dog suddenly spots a cat across the road.
Their body needs to be ready.
Sympathetic activity is associated with physiological changes including an increase in heart rate, dilation of the pupils and a reduction in digestive activity as resources are directed towards responding to the situation.
You may also see a dog become more alert to their surroundings or physically prepared to move.
And importantly:
Sympathetic activity isn’t bad.
Dogs need this system.
Running, playing, exploring and responding to something unexpected all require the body to mobilise.
The problem with calling the sympathetic nervous system the “stress system” is that it can make it sound as though our goal should always be to switch it off.
It isn’t.
A healthy nervous system needs to be able to respond appropriately to what is happening.
The parasympathetic nervous system: rest, digestion and recovery
Now imagine your dog later that evening.
They’re resting somewhere comfortable. The immediate need for action has gone.
Parasympathetic activity is more strongly associated with the body’s resting functions.
Its effects include slowing the heart and supporting digestive activity. The parasympathetic nervous system is also involved in regulating many other involuntary processes throughout the body.
This is where the familiar phrase “rest and digest” comes from.
But again, it isn’t simply a switch that gets turned on when your dog lies down.
Sympathetic vs parasympathetic activity in dogs isn’t an ON/OFF switch
This is one of the most important things to understand.
The two systems aren’t simply an ON/OFF switch.
They continually contribute to the regulation of the body, with their relative influence changing according to what the dog is doing and experiencing. Veterinary literature describes the two branches as working together to maintain physiological balance.
So I don’t look at a dog and think:
“Sympathetic = bad. Parasympathetic = good.”
I’m interested in the dog’s ability to move appropriately between states.
Can they respond when they need to?
And when that need has passed, can the body settle again?
What can you actually see in your dog?
This is where things get particularly interesting for dog owners.
We can’t look at a dog and directly see their autonomic nervous system working.
What we can see are changes in the whole dog.
You may notice their breathing change.
Their posture may soften, along with their facial expression.
Attention to the environment may increase or decrease, and the body may become more or less physically settled.
Researchers studying canine welfare use physiological measurements such as heart rate and heart-rate variability (HRV) to investigate autonomic activity and stress rather than relying on a single visible behaviour.
That’s an important distinction.
A yawn, lick or sigh on its own doesn’t give us a readout saying “the parasympathetic nervous system has switched on.”
I look at the pattern of changes happening across the dog.
Why does this matter during canine massage?
Understanding the sympathetic vs parasympathetic nervous system in dogs is particularly relevant to the way I approach canine massage.
I’m working with the musculoskeletal system AND the nervous system.
I use massage and targeted deeper techniques to work directly with physical tissues.
Alongside that, I use techniques such as light-pressure touch, passive touch, sustained pressure and slower rhythmic work as part of the nervous-system side of my approach.
And throughout the session I’m watching what changes.
Breathing.
Muscle tone.
Posture.
Facial expression.
Response to touch.
Whether the dog becomes more settled or more alert.
That information influences what I do next.
The body and mind aren’t separate
This is the part of canine massage that particularly matters to the way I work.
Emotion and physiology are connected. Research into canine emotional states uses autonomic measures precisely because changes in emotional state can be accompanied by measurable physiological changes.
So I don’t believe it makes sense to think about muscular work in complete isolation from the nervous system.
Sometimes my work is deeper and very targeted.
Sometimes I’m deliberately using techniques intended to encourage a more settled state.
Often, those things exist within the same session.
The aim isn’t simply to make a dog sleepy on the massage table.
It’s to work with the physical body while also recognising that there is a nervous system attached to it — constantly receiving information and influencing what happens throughout that body.
Musculoskeletal work and nervous-system work aren’t two separate parts of my practice.
The relationship between them is the basis of how I work.