The nervous system is one of the most complex and essential systems in the horse’s body, controlling everything from movement and reflexes to perception and behavior. It serves as the communication network, transmitting signals between the brain, spinal cord, and the rest of the body. Without it, a horse could not respond to its environment, coordinate its gaits, or even maintain basic bodily functions.
Understanding the equine nervous system is crucial for horse owners, trainers, and veterinarians, as it helps in diagnosing neurological disorders, improving training methods, and ensuring the overall well-being of the horse.
Overview of the Equine Nervous System
The nervous system in horses is divided into two main parts:
The Central Nervous System (CNS) – Composed of the brain and spinal cord, responsible for processing information and issuing commands.
The Peripheral Nervous System (PNS) – Consists of nerves that extend throughout the body, transmitting signals between the CNS and muscles, organs, and sensory receptors.
The autonomic nervous system (ANS) is a specialized part of the PNS that regulates involuntary functions, such as heart rate, digestion, and respiration.
The Central Nervous System (CNS)
The Brain
The horse’s brain is relatively small compared to its body size, weighing about 1.5 pounds (650-700 grams). However, it is highly developed in areas responsible for movement, coordination, and survival instincts.
The brain is divided into several key regions:
Cerebrum – The largest part, responsible for thought, decision-making, memory, and sensory processing.
Cerebellum – Controls balance, coordination, and fine motor skills, ensuring smooth and precise movements.
Brainstem – Connects the brain to the spinal cord and regulates automatic functions such as heartbeat, breathing, and digestion.
While horses are highly intelligent and capable of learning, their brains are wired primarily for reactive behavior rather than deep reasoning, making them reliant on instincts and conditioned responses.
The Spinal Cord
The spinal cord extends from the brainstem down the length of the spine, acting as a major highway for nerve signals. It transmits information between the brain and the rest of the body, coordinating reflexes and movement.
Cervical region – Controls the neck and forelimbs.
Thoracic and lumbar regions – Responsible for trunk and hindlimb movement.
Sacral region – Governs tail and pelvic functions.
If the spinal cord is damaged, it can result in partial or complete paralysis, depending on the severity of the injury.
The Peripheral Nervous System (PNS)
The PNS consists of cranial and spinal nerves that branch out from the CNS, carrying signals to and from different parts of the body.
Sensory and Motor Nerves
The PNS is divided into two functional components:
Sensory (Afferent) Nerves – Transmit signals from the body to the brain, allowing the horse to detect pain, pressure, heat, and movement.
Motor (Efferent) Nerves – Carry signals from the brain to the muscles, enabling movement and coordination.
A horse’s acute sensory perception allows it to respond quickly to stimuli, a survival trait developed over millions of years.
Cranial Nerves
Horses have 12 pairs of cranial nerves that emerge from the brain and control functions such as:
Sight (Optic nerve)
Hearing and balance (Vestibulocochlear nerve)
Facial movement and expression (Facial nerve)
Swallowing and digestion (Vagus nerve)
Damage to cranial nerves can result in head tilt, difficulty swallowing, or loss of coordination.
Autonomic Nervous System (ANS)
The ANS is responsible for regulating involuntary functions such as heart rate, digestion, and sweating. It is divided into:
Sympathetic Nervous System – Controls the fight-or-flight response, increasing heart rate and alertness.
Parasympathetic Nervous System – Governs the rest-and-digest state, promoting relaxation and energy conservation.
This balance between sympathetic and parasympathetic activity is critical for maintaining a horse’s overall health and ability to respond appropriately to stressors.
Neurological Reflexes and Responses in Horses
Horses have a variety of reflexes that protect them from injury and help them navigate their environment.
Key Reflexes:
Blink Reflex – Protects the eye from debris and injury.
Withdrawal Reflex – Causes the horse to pull away from painful stimuli.
Patellar Reflex – A "knee-jerk" reaction that helps assess spinal cord function.
Righting Reflex – Helps a horse regain balance when stumbling.
Trainers often work with a horse’s natural reflexes and responses to refine cues and improve training outcomes.
Common Equine Neurological Disorders
A variety of conditions can affect the horse’s nervous system, leading to loss of coordination, weakness, or behavioral changes.
1. Wobbler Syndrome (Cervical Vertebral Malformation - CVM)
A developmental disorder that causes compression of the spinal cord, leading to incoordination (ataxia) and weakness. It is most common in young, fast-growing horses.
2. Equine Protozoal Myeloencephalitis (EPM)
Caused by the protozoan Sarcocystis neurona, this disease affects the spinal cord and brain, leading to:
Muscle wasting
Weakness and incoordination
Asymmetrical nerve damage
3. Equine Herpesvirus-1 (EHV-1) Neurological Form
A viral infection that can cause spinal cord inflammation, resulting in:
Loss of coordination
Bladder dysfunction
Paralysis in severe cases
4. Stringhalt
A neuromuscular condition characterized by exaggerated hind limb movement, often caused by nerve damage.
5. Shivers
A progressive disorder that causes tremors and difficulty lifting the hind legs, commonly seen in draft breeds and Warmbloods.
The Nervous System and Training
Understanding the equine nervous system is essential for effective training and behavior modification.
1. The Startle Response
Horses have a highly developed flight instinct, meaning their sympathetic nervous system reacts instantly to perceived threats. Trainers can desensitize horses through gradual exposure to stimuli, reducing overreactions.
2. Memory and Learning
The equine brain retains information well, but horses learn best through repetition and positive reinforcement. Their strong associative memory allows them to connect experiences with outcomes, whether positive or negative.
3. Stress and Nervous System Function
Chronic stress can overactivate the sympathetic nervous system, leading to:
Increased cortisol levels
Tension and reactivity
Reduced immune function
Proper management, consistent handling, and structured training help keep the nervous system in balance, ensuring a calmer, more responsive horse.
Self Assessment Quiz
Multiple Choice Questions
What are the two main divisions of the equine nervous system?
a) Brain and spinal cord
b) Central Nervous System and Peripheral Nervous System
c) Sensory and motor nerves
d) Autonomic and somatic systems
Which part of the brain is responsible for coordination and balance?
a) Cerebrum
b) Cerebellum
c) Brainstem
d) Medulla Oblongata
The Autonomic Nervous System (ANS) controls:
a) Voluntary muscle movement
b) Reflexes only
c) Involuntary functions like heart rate and digestion
d) Conscious thought and decision-making
Which of the following diseases affects the equine nervous system?
a) Equine Protozoal Myeloencephalitis (EPM)
b) Laminitis
c) Colic
d) Cushing’s Disease
A horse’s fight-or-flight response is primarily controlled by which part of the nervous system?a) Parasympathetic Nervous System
b) Sympathetic Nervous System
c) Somatic Nervous System
d) Reflex Arc
True/False
___ The cerebrum is the largest part of the horse’s brain and is responsible for conscious thought and decision-making.
___ The spinal cord controls reflex actions without involving the brain.
___ Horses have 24 pairs of cranial nerves.
___ Damage to the cranial nerves can result in loss of coordination or difficulty swallowing.
___ The equine nervous system plays no role in training or behavior.
___ Chronic stress can negatively impact the horse’s nervous system and overall health.
Short Answer
Name two key reflexes in horses and their function.
What is the difference between the Central Nervous System (CNS) and the Peripheral Nervous System (PNS)?
How does the nervous system influence horse training and behavior?
List one neurological disorder in horses and describe its symptoms.
How does the Autonomic Nervous System (ANS) help maintain a horse’s internal balance?
