Reflex Arcs Are Widespread in the Nervous System, and Reflexes Underlie a Major Portion of the Neurological Examination
Reflex arcs are ubiquitous in the nervous system and are the basis of much of an animal’s subconscious, involuntary response to its environment. Much of a veterinarian’s clinical examination of the nervous system involves evoking reflex responses, such as the pupillary light reflex, muscle stretch (knee jerk) reflex, and flexor reflex.
If any of the five components of the reflex arc malfunctions, the expected reflex response is altered or does not occur. It is important to know the general anatomy, physiology, and expected normal clinical response of the common reflexes in order to perform a neurological examination so that lesions can be localized. For example, loss of pupillary constriction to light in conjunction with normal responses to other visual stimuli, such as avoiding a rapidly oncoming object, suggests that the problem is probably not with the sensory receptor or sensory neuron components of the reflex arc. Several such reflexes are discussed in detail in subsequent chapters.