South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Grey matter is made up of neuronal cell bodies, containing the cell nucleus and associated
cells.
Afferent and efferent
Afferent pathways relay sensory information from receptors (e.g. touch or muscle stretch or
balance) back towards the spinal cord or brain.
Efferent pathways relay motor or effector information from the brain or spinal cord to muscles
or organs.
Lower motor neuron, upper motor neuron and motor reflex
Lower motor neurons are the last link in the efferent pathway that directly innervate skeletal
muscles; their cell bodies are located in the spinal cord in the ventral horn of the grey matter
and their axons course through peripheral nerves to synapse at the neuromuscular junction.
Upper motor neurons relay information to, and control the output of, lower motor neurons and
are found in the brain and spinal cord.
A reflex is the term used to describe the pathways involved where signals derived from
receptors (e.g. tendon stretch) are conveyed directly in sensory (afferent) fibres to the central
nervous system (e.g. the spinal cord) to directly generate effector signals (generally by route
of an intermediate neuron, known as the internuncial neuron). These are relayed in the lower
motor neurons to the muscles. An intact reflex requires neither conscious perception of the
stimulus nor any ascending or descending upper motor neuron or proprioceptive pathways.
Signalment and history
Consider whether the horse‟s signalment (age, sex, breed) could be of relevance to the
neurological examination (for example, a 1 year old thoroughbred colt with ataxia is more likely
to have cervical compression, than a space occupying lesion; an Arabian foal with seizures may
have idiopathic epilepsy). The history is usually especially pertinent, as perceptive owners may
have useful descriptions of the animal‟s behaviour or abnormality that can help direct the
neurological examination or may suggest possible differential diagnoses (for example, a
recumbent horse that recently fell, but has had a history of stumbling or knuckling, may have
underlying cervical vertebral malformation or stenosis; alternatively, perhaps the onset of pelvic
limb weakness may have followed a spate of respiratory disease or abortions, in an animal with
possible EHV1 myelitis).
HEAD
1. Examine the horse from a distance and assess demeanour / behaviour.
Diseases associated with altered mentation or behaviour tend to involve the forebrain.
Observe for assymetrical changes such as circling or head turning (horses usually
circle or turn towards the affected side) or excessive yawning.
Head pressing in horses is often a sign of severe obtundation caused by diffuse
cerebral disease or metabolic problems such as hepatic encephalopathy.
Levels of consciousness are determined partly by the cerebrum and partly by the
reticular activating system in the brainstem
2. Examine the cranial nerves
The cranial nerves are numbered 1-12 in order from the most rostral, to the most
caudal. A systematic examination can therefore be very helpful in accurately
identifying the site of any lesion.
Olfactory nerve (I) - rare to detect abnormalities
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