Experimental Study for the Central Reflex Arc of the Flexion Reflex.

Han, Yong Pyo

Original Article

Journal of Korean Neurosurgical Society 1980;9(2): 335-344.

Department of Neurosurgery, Wonju Christian Hospital, Wonju, Korea.

ABSTRACT

The flexion reflex is generally known as a withdrawal reflex in response to a painful stimulus. Since Sherrington's first detail report in 1910, it has been established that the flexion reflex is a central reflex evoked by a painful stimulus applied to the skin or afferent nerves. Recent studies indicate that the reflex is not a single component but has two components, the early and the late. Although many aspects of the reflex is known, it is still obscure as to the pathways for the low components of the reflex. The central reflex are of the each component has not been localized systematically. Furthermore, there are considerable discrepancies in literatures regarding to the type of afferent nerve fiber responsible for the flexion reflex. The present study was, therefore, conducted to find out the pathways for the flexion reflex including the location of the central reflex are and the afferent nerve fiber types in an experimental animal. Sixteen healthy adult cats(2-3.5kg) were preanesthetized with ketamine hydrochloride(20 mg/kg, im.) and decerebrated anemically by ligating the basilar artery and the bilateral common carotid arteries. Animals were paralyzed with gallamine triethiodide and kept under artificial respiration. The flexion reflex was elicited by stimulating the sural nerve and recorded as a form of compound action potential from the nerve supplying to the semitendinous muscle. The central reflex are of the flexion reflex was localized by comparing the reflex components of decerebrate cats with those of decerebrated and spinalized cats. The type of afferent nerve fiber responsible for each component of the flexion reflex was identified by recording afferent volleys from the sural nerve at 40-50 mm proximal to the stimulating site. The results are summarized as follows: 1) The flexion reflex is composed of two components, the early and the late. The early and the late components have a latency of 7.8 and 173.8 msec, and a duration of 7.3 and 906.3 msec, respectively. 2) The central reflex are of the early component and most of the late component is in the spinal cord while some of the late component is mediated by either rostral part of the spinal cord or the brain stem, most likely medulla oblongata. 3) The afferent nerve fibers responsible for the early component are A and A fibers and that of the late component is C fibers. In general, temporal summation from C fibers is necessary to elicit the late component. These results indicate that the two componts of the flexion reflex have different pathways. This may imply that the two components have different functional role.