Chapter

Late Responses

Jay A. Liveson and Dong M. Ma

in Laboratory Reference for Clinical Neurophysiology

Published in print May 1999 | ISBN: 9780195129243
Published online March 2012 | e-ISBN: 9780199847792 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780195129243.003.0009
Late Responses

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The H reflex is a monosynaptic segmental reflex. Although it is present in many nerves in children, the response disappears by adulthood. In the adult, the reflex is usually studied in the tibial nerve, although it has also been reported in the forearm. It is felt by some to reflect the state of the S1 root. It is the analog of (although not completely equivalent to) the ankle jerk. The afferent arc consists of 1a fibers. There is a single synapse in the cord followed by an efferent discharge of the S1 (and possibly L5) anterior horn cells, whose fibers travel through the sciatic nerve to the gastrocnemius, soleus, and other tibial-innervated muscles. This is a late-latency response that must be distinguished from the F wave. It is evoked at low stimulus intensity; its amplitude exceeds that of the direct (M wave) muscular response when maximal.

Keywords: H reflex; tibial nerve; afferent arc; late-latency response; F wave; ankle jerk; anterior horn cells; sciatic nerve

Chapter.  3610 words.  Illustrated.

Subjects: Neuroscience

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