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Parallel reflex pathways from flexor muscle afferents evoking resetting and flexion enhancement during fictive locomotion and scratch in the cat
Author(s) -
Stecina Katinka,
Quevedo Jorge,
McCrea David A.
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.095505
Subject(s) - stimulation , reflex , anatomy , withdrawal reflex , neuroscience , hindlimb , stimulus (psychology) , medicine , central pattern generator , psychology , rhythm , psychotherapist
Reflex actions of muscle afferents in hindlimb flexor nerves were examined on ipsilateral motoneurone activity recorded in peripheral nerves during midbrain stimulation‐evoked fictive locomotion and during fictive scratch in decerebrate cats. Trains of stimuli (15–30 shocks at 200 Hz) were delivered during the flexion phase at intensities sufficient to activate both group I and II afferents (5 times threshold, T ). In many preparations tibialis anterior (TA) nerve stimulation terminated ongoing flexion and reset the locomotor cycle to extension (19/31 experiments) while extensor digitorum longus (EDL) stimulation increased and prolonged the ongoing flexor phase activity (20/33 preparations). The effects of sartorius, iliopsoas and peroneus longus muscle afferent stimulation were qualitatively similar to those of EDL nerve. Resetting to extension was seen only with higher intensity stimulation (5 T ) while ongoing flexor activity was often enhanced at group I intensity (2 T ) stimulation. The effects of flexor nerve stimulation were qualitatively similar during fictive scratch. Reflex reversals were consistently observed in some fictive locomotor preparations. In those cases, EDL stimulation produced a resetting to extension and TA stimulation prolonged the ongoing flexion phase. Occasionally reflex reversals occurred spontaneously during only one of several stimulus presentations. The variable and opposite actions of flexor afferents on the locomotor step cycle indicate the existence of parallel spinal reflex pathways. A hypothetical organization of reflex pathways from flexor muscle afferents to the spinal pattern generator networks with competing actions of group I and group II afferents on the flexor and extensor portions of this central circuitry is proposed.