Neurological Examination of Horses Overview

Aims of Neurological Examination

• There are two main aims of neurological examination:
  1. To aid determination of the presence or absence of neurological disease.
  2. To localise the lesion(s) when neurological disease is suspected.

Indications for Neurological Examination

• Neurological testing may be indicated by:
  1. History
     • For example, the owner reports a seizure-like episode.
  2. Clinical examination
     • For example, an unexplained area of muscle atrophy or patchy sweating.
  3. Information from other tests
     • Particularly negative, confusing or corroborating evidence from these.
     • For example:
       • A horse evaluated for pelvic limb lameness that may in fact have a neurological problem.
       • A horse with altered mentation or depression that has already been found to have abnormal hepatic function.

Approaches to Neurological Examination

• A methodical approach is necessary, whatever the background, to ensure no aspect of examination is omitted.
• Two different approaches may be taken:
  1. Systems based
     • The different neurological modalities of the systems are examined in turn.
  2. Anatomic
     • Tests are performed in turn working from head to tail.
• A combination of the two approaches tends to be used in practice.

Neuroanatomy

• Certain basic facts must be understood before a decent neurological examination may be performed.

White and Grey Matter

• White matter consists of myelinated axons of nerve cells.
• Grey matter is made up of neuronal cell bodies, containing the nucleus.

Afferent and Efferent

• Afferent pathways relay sensory information from receptors towards the spinal cord or brain.
  • For example:
    • Touch
    • Muscle stretch
    • Vision
    • Balance
• Efferent pathways relay motor or effector information from the brain or spinal cord to muscles or organs.

Motor Neurons and Motor Reflexes

• Lower motor neurons are the last link in the efferent pathway.
  • Directly innervate skeletal muscles.
  • Cell bodies are located in the ventral horn of the grey matter of the spinal cord.
  • Their axons run in peripheral nerves and synapse at the neuromuscular junction.
• Upper motor neurons communicate with lower motor neurons.
  • They:
    • Relay information to lower motor neurons
    • Control the output of lower motor neurons.
  • Upper motor neurons are found in the brain and spinal cord.
• The term reflex describes a certain sort of nervous pathway.
  • The sequence of events in a reflex is as follows:
    1. Signals are derived from receptors.
       • For example, tendon stretch.
    2. Signals are conveyed directly in sensory (afferent) fibres.
    3. Afferent signals reach the central nervous system.
    4. Effector signals are generated in the CNS.
       • This generally occues via an intermediate neuron, known as the internuncial neuron.
    5. Effector signals are relayed in the lower motor neurons to the muscles.
  • A reflex does NOT require:
    • Conscious perception of the stimulus
    • Ascending or descending upper motor neuron pathways
    • Ascending or descending proprioceptive pathways