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 the spinal cord.
The peripheral nervous system (PNS) includes everything outside the CNS — that is, the nerves branching out from the spinal cord to muscles and organs, as well as the nerve pathways returning sensory information from receptors in 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, vision, hearing, touch, and balance.
Voluntary vs. Autonomic Nervous System
The nervous system can also be divided into a voluntary and an autonomic system.
The voluntary nervous system is what we use when performing conscious actions — for example, sitting down, lifting an object, or walking.
The autonomic nervous system (ANS), on the other hand, functions independently of conscious control. It is divided into the parasympathetic and the sympathetic nervous systems.
Parasympathetic and Sympathetic Functions
The parasympathetic nervous system ensures that vital processes continue automatically — the heart keeps beating, the intestines work, and we keep breathing, even while we sleep.
The sympathetic nervous system triggers the well-known fight-or-flight response, which activates when we are startled, stressed, or afraid. The heart rate increases, muscles tense, sweating begins, and the pupils dilate dramatically.
The autonomic nervous system connects the brain to all organs in the body — and therefore can influence organ-related disorders. It also connects the brain to all muscles in the body.
The parasympathetic system causes blood vessels to dilate, allowing blood to reach the extremities, while the sympathetic system constricts blood vessels, directing blood flow to the heart and brain. This balance maintains blood pressure and ensures a continuous supply of oxygen throughout the body.
When the System Becomes Imbalanced
During periods of increased sympathetic activation, the body releases adrenaline and noradrenaline, preparing the muscles for action. However, if this state becomes chronic, muscle fatigue develops: the elastic muscle proteins decrease, and the muscles remain tight, stiff, and sore. This is far from ideal for a horse expected to perform as an athlete.
At this point, the body enters a negative feedback loop. Such muscles lose strength, flexibility, and proper communication with the brain.
This condition is known as functional dysautonomia — meaning the autonomic nervous system is out of balance.
Horses in this state are neither physically nor mentally well-functioning, and they will not recover unless this underlying dysfunction is acknowledged and treated.