Robert J. MacKay, DVM, PhD, DACVIM

Mechanical injuries to peripheral nerves occur because of compression, entrapment, transection, laceration, ischemia, crushing, stretching, or chemical or burn damage. Neurapractic lesions are characterized by a failure of conduction of the action potential across the injured axonal segment.

One of the critical functions of the reticular formation of the brainstem is activation of the cerebral cortex for the awake state. This component of the formation, known as the ascending reticular activating system (ARAS), is an ill-defined meshwork of cells concentrated in the rostral brainstem that receives afferent input from all parts of the CNS and projects excitatory stimuli cortically.

The brainstem includes the diencephalon, mesencephalon (midbrain), and rhombencephalon (hindbrain). With the exception of the olfactory nerves (I), all cranial nerves are arrayed along the brainstem. The hindbrain is divided into metencephalon (cerebellum) and myelencephalon (pons and medulla oblongata).

Axons of the upper motor neuron (UMN) extrapyramidal and vestibular systems travel from cell bodies throughout the brain and pass predominantly in reticulospinal and vestibulospinal tracts to lower motor neurons (LMN) in the ventral and intermediate columns of the gray matter of the spinal cord.

The term "wobbler" or "wobbler syndrome" describes a group of developmental anomalies and degenerative conditions involving the cervical vertebrae of ataxic horses (Hahn et al. 1999; Mayhew 2009). Several more or less descriptive abbreviations are used in wobbler terminology.

Equine protozoal myeloencephalitis (EPM) is a common neurological disease of horses in the Americas. Horses with EPM most commonly have abnormalities of gait but also may present with signs of brain disease.