The Equine Nervous System: Part 2 - Diving Deeper

Diving Deeper into the Horse’s Neuroanatomy and Behavior

In Part 1 of our nervous system overview, we explored how the brain, spinal cord, and peripheral nerves work together to help horses sense, move, and survive. In this second installment, we take that understanding further by examining the complex inner workings of the equine nervous system. You'll discover how this system influences movement, emotion, coordination, and neurological disorders—and how to recognize when something goes wrong.

Make sure you have read our article "The Equine Nervous System"

The Central Nervous System: More Than Just the Brain

The Cerebrum – Horse Instinct Headquarters

Unlike humans, horses rely far more on instinct than critical thinking. The cerebrum, or largest part of the brain, is smoother in horses, reflecting this difference. (Read our article "Horse Brain vs. Human Brain") to learn more. Its primary roles are controlling voluntary movement, interpreting sensory input, and supporting behaviors linked to survival.

For example, when your horse spooks at a fluttering bag, it's the sensory centers in the cerebrum that trigger the reaction. But instead of “thinking it through,” the cerebrum routes that sensory input straight to a fast motor response—run first, question later.

The Cerebellum – The Master of Balance

Nestled at the back of the brain, the cerebellum manages muscle coordination, balance, and posture. When your horse navigates uneven terrain or performs a dressage maneuver, the cerebellum is working behind the scenes to fine-tune every stride.

Some breeds, like Arabians, can suffer from cerebellar abiotrophy, a hereditary condition where cells in this region degenerate. Foals with this disorder may appear clumsy or uncoordinated from an early age (MSD Vet Manual).

The Spinal Cord – Superhighway of Signals

The spinal cord is the horse’s information superhighway. It’s divided into sections—cervical, thoracic, lumbar, sacral, and caudal—and sends motor commands to muscles while relaying sensory information back to the brain.

When a hoof brushes something unexpected, like a prickly plant, the spinal cord helps process that input quickly, sometimes without even involving the brain—this is the magic of reflexes.

Peripheral Nervous System: The Body’s Messenger Network

Spinal Nerves – Coordinated Powerhouses

Each segment of the spine sends out paired spinal nerves that control specific areas of the body. The brachial plexus, for instance, powers the front limbs, while the lumbosacral plexus energizes the hindquarters. These nerve networks allow a horse to synchronize its limbs in a gallop or rear on cue.

Cranial Nerves – The Sensory Specialists

Twelve cranial nerves branch directly from the brain and manage everything from smell (CN I) and vision (CN II) to jaw movement (CN V – the trigeminal nerve). One key nerve is the facial nerve (CN VII), responsible for ear and lip movement, essential for expressing emotion and communication.

Damage to cranial nerves can cause visible symptoms like facial asymmetry or eye droop, often seen in head trauma or neurological illness.

Autonomic Nervous System: Balancing Survival and Serenity

Sympathetic System – The “Spook Mode”

This is the horse's fight-or-flight switch. When a horse senses danger, the sympathetic nervous system spikes heart rate, redirects blood to muscles, and boosts alertness. It's the reason your horse can bolt at the rustle of a bush.

This reaction is deeply rooted in equine evolution and controlled by a cascade of nerve signals and adrenaline.

Parasympathetic System – Calm and Connected

The parasympathetic system, in contrast, promotes rest, digestion, and relaxation. When a horse is dozing in the sun or calmly chewing hay, it’s the parasympathetic system at work, conserving energy and supporting health.

The balance between these systems is delicate—and when it's disrupted (e.g., due to chronic stress or poor training practices), a horse’s health and behavior can suffer.

Common Neurological Disorders in Horses

1. Equine Protozoal Myeloencephalitis (EPM)

   
   

EPM is a neurological disease caused primarily by the protozoan Sarcocystis neurona. Horses become infected by ingesting feed or water contaminated with opossum feces containing the parasite's sporocysts. While exposure is common, only a small percentage of horses develop clinical signs, which may include asymmetric incoordination, muscle atrophy, and cranial nerve deficits. The Spruce PetsMerck Veterinary Manual+2ceh.vetmed.ucdavis.edu+2tvmdl.tamu.edu+2

Diagnosis involves neurological examinations and testing of blood or cerebrospinal fluid for antibodies. Treatment typically includes antiprotozoal medications and supportive therapies. Early intervention is key to improving outcomes. University of Minnesota Extension

2. Cervical Vertebral Stenotic Myelopathy (CVSM)

   
   

Also known as "wobbler syndrome," CVSM is characterized by compression of the spinal cord due to malformations or instability in the cervical vertebrae. This condition leads to symmetrical ataxia, weakness, and a "wobbly" gait. It commonly affects young, rapidly growing horses, particularly Thoroughbreds. WikiVet+1Veterian Key+1Veterian Key

Diagnosis is achieved through imaging techniques like radiography and myelography. Treatment options range from surgical intervention to conservative management, depending on the severity and progression of the disease .

3. Equine Degenerative Myeloencephalopathy (EDM)

   
   

EDM is a neurodegenerative disorder affecting the spinal cord and brainstem, leading to symmetric ataxia and proprioceptive deficits. It is believed to result from a combination of genetic predisposition and vitamin E deficiency during the developmental stages of young horses. HorsesDaily+3Mad Barn USA+3ceh.vetmed.ucdavis.edu+3

Clinical signs often emerge within the first year of life. Diagnosis is challenging and typically involves ruling out other conditions. While there is no definitive cure, ensuring adequate vitamin E intake may help prevent or slow the progression of the disease. CDFA+2WikiVet+2HorseDVM+2

4. Equine Herpesvirus Myeloencephalopathy (EHM)

   
   

EHM is the neurological manifestation of Equine Herpesvirus-1 (EHV-1) infection. The virus can cause inflammation of the blood vessels in the brain and spinal cord, leading to neurological deficits such as hind limb weakness, incoordination, and urinary incontinence. EHM is highly contagious and has been associated with outbreaks in equine facilities. MDPI+6vetequine.theclinics.com+6APHIS+6

Diagnosis involves PCR testing of nasal swabs and blood samples. Management includes isolation of affected horses, supportive care, and antiviral medications. Vaccination against EHV-1 may reduce the severity of the disease but does not guarantee complete protection against the neurological form. CDFA+4University of Minnesota Extension+4Colorado Department of Agriculture+4

Self Assessment Quiz:

Multiple Choice

1. What is the primary function of the cerebellum in horses?

a. Sensory interpretation

b. Memory formation

c. Balance and coordination

d. Emotional regulation

2. Which condition results from hereditary degeneration of Purkinje cells in the cerebellum?

a. EPM

b. Trigeminal-mediated headshaking

c. Cerebellar abiotrophy

d. EDM

3. Which plexus is responsible for innervating the horse’s hindlimbs?

a. Cervical plexus

b. Thoracic plexus

c. Brachial plexus

d. Lumbosacral plexus

4. Which cranial nerve is involved in trigeminal-mediated headshaking?

a. CN II (Optic)

b. CN V (Trigeminal)

c. CN VII (Facial)

d. CN IX (Glossopharyngeal)

5. What is the role of the sympathetic nervous system in horses?

a. Regulate digestion

b. Promote muscle recovery

c. Manage "rest and digest" functions

d. Activate "fight or flight" responses

6. Which neurological disorder is caused by a protozoal infection, typically from contaminated opossum feces?

a. CVSM

b. EHM

c. EPM

d. EDM

7. Which of the following symptoms is most characteristic of CVSM ("Wobbler Syndrome")?

a. Asymmetrical muscle wasting

b. Head pressing

c. Involuntary headshaking

d. Symmetrical ataxia and hind limb weakness

8. What deficiency is thought to contribute to the development of Equine Degenerative Myeloencephalopathy (EDM)?

a. Calcium

b. Magnesium

c. Vitamin E

d. Iron

9. What is a key diagnostic method for Equine Herpesvirus Myeloencephalopathy (EHM)?

a. Ultrasound

b. PCR testing of nasal swabs

c. Endoscopy

d. Liver enzyme test

10. Which part of the nervous system is most involved in involuntary body functions like heart rate and digestion?

a. Peripheral nervous system

b. Somatic nervous system

c. Autonomic nervous system

d. Central nervous system

Short Answer

1. Describe the difference between a spinal nerve and a cranial nerve in terms of origin and general function.

2. Name two clinical signs of Equine Protozoal Myeloencephalitis (EPM).

3. What are two management strategies for horses diagnosed with trigeminal-mediated headshaking?

4. Briefly explain why the parasympathetic nervous system is important for recovery and digestion.

5. List two imaging methods used to diagnose Cervical Vertebral Stenotic Myelopathy (CVSM).

Answer Key (For Reference)

Multiple Choice:

1. C

2. C

3. D

4. B

5. D

6. C

7. D

8. C

9. B

10. C

    
    

Short Answer:

1. Spinal nerves originate from the spinal cord and manage motor/sensory input to/from the body. Cranial nerves originate from the brain and manage head/neck functions including sensory input (e.g., smell, vision) and motor control (e.g., chewing, facial expression).

2. Ataxia, muscle atrophy, weakness, cranial nerve signs.

3. Use of nose nets, medications (e.g., anticonvulsants), or environmental modifications

4. It conserves energy by slowing heart rate, enhancing gastrointestinal activity, and supporting rest and recovery after stress.

5. Radiography (X-rays) and myelography.