The Autonomic Nervous System
The nervous system can be divided into the central and peripheral nervous systems.
The central nervous system (CNS) consists of the brain and spinal cord.
The peripheral nervous system (PNS) includes everything outside the CNS — the nerves that branch from the spinal cord and travel to the muscles and organs, as well as the nerves that carry information from receptors in those muscles and organs back to the spinal cord.
In the head, there are 12 cranial nerves, which are also part of the peripheral nervous system. These cranial nerves transmit sensory information to the brain — such as smell, sight, hearing, touch, and balance.
Voluntary and Autonomic Systems
The nervous system can further be divided into the voluntary and autonomic systems.
The voluntary nervous system is what we use when performing conscious actions, such as sitting down or lifting an object.
The autonomic nervous system (ANS), by contrast, operates independently of conscious control. It is divided into the parasympathetic and sympathetic systems.
Parasympathetic and Sympathetic Function
The parasympathetic nervous system ensures that vital functions continue even when we are resting — for example, while sleeping, the heart continues to beat, the intestines keep working, and we keep breathing — all without any conscious effort.
The sympathetic nervous system, on the other hand, is responsible for the body’s “fight-or-flight” response, which activates when we are startled, stressed, or frightened.
In this state, the heart rate increases, muscles tense, sweating begins, and the pupils dilate.
The autonomic nervous system connects the brain to all organs in the body and therefore influences organ function. It also connects the brain to all muscles, regulating both internal and external activity.
The parasympathetic system causes blood vessels to dilate, allowing blood to flow to the extremities, while the sympathetic system causes them to contract, directing blood flow to the heart and brain.
This balance maintains blood pressure and ensures a constant supply of oxygen throughout the body.
When the System Falls Out of Balance
During prolonged sympathetic activation, adrenaline and noradrenaline are released, preparing the muscles for action.
If this state becomes chronic, the muscles begin to fatigue — their elastic proteins break down, and they remain tense, stiff, and sore.
This is far from ideal for a working dog expected to perform at a high level.
At this point, the body enters a negative cycle: such muscles lose strength, elasticity, and communication with the brain.
This condition is known as functional dysautonomia, meaning the autonomic nervous system is out of balance.
Dogs in this state are neither physically nor mentally well-functioning, and they will not recover unless this underlying dysfunction is acknowledged and treated.