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Absence of synergy for monosynaptic Group I inputs between abdominal and internal intercostal motoneurons

Ford, TW; Meehan, CF; Kirkwood, PA; (2014) Absence of synergy for monosynaptic Group I inputs between abdominal and internal intercostal motoneurons. Journal of Neurophysiology , 112 (5) pp. 1159-1168. 10.1152/jn.00245.2014. Green open access

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Abstract

Internal intercostal and abdominal motoneurons are strongly coactivated during expiration. We investigated whether that synergy was paralleled by synergistic Group I reflex excitation. Intracellular recordings were made from motoneurons of the internal intercostal nerve of T8 in anesthetized cats, and the specificity of the monosynaptic connections from afferents in each of the two main branches of this nerve was investigated. Motoneurons were shown by antidromic excitation to innervate three muscle groups: external abdominal oblique [EO; innervated by the lateral branch (Lat)], the region of the internal intercostal muscle proximal to the branch point (IIm), and muscles innervated from the distal remainder (Dist). Strong specificity was observed, only 2 of 54 motoneurons showing excitatory postsynaptic potentials (EPSPs) from both Lat and Dist. No EO motoneurons showed an EPSP from Dist, and no IIm motoneurons showed one from Lat. Expiratory Dist motoneurons fell into two groups. Those with Dist EPSPs and none from Lat (group A) were assumed to innervate distal internal intercostal muscle. Those with Lat EPSPs (group B) were assumed to innervate abdominal muscle (transversus abdominis or rectus abdominis). Inspiratory Dist motoneurons (assumed to innervate interchondral muscle) showed Dist EPSPs. Stimulation of dorsal ramus nerves gave EPSPs in 12 instances, 9 being in group B Dist motoneurons. The complete absence of heteronymous monosynaptic Group I reflex excitation between muscles that are synergistically activated in expiration leads us to conclude that such connections from muscle spindle afferents of the thoracic nerves have little role in controlling expiratory movements but, where present, support other motor acts.

Type: Article
Title: Absence of synergy for monosynaptic Group I inputs between abdominal and internal intercostal motoneurons
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1152/jn.00245.2014
Publisher version: http://dx.doi.org/10.1152/jn.00245.2014
Language: English
Additional information: Licensed under Creative Commons Attribution CC-BY 3.0: © the American Physiological Society
Keywords: Group I inputs, abdominal muscles, intercostal muscles, motoneurons, muscle synergies, posture, respiration, thoracic spinal cord, Abdominal Muscles, Animals, Cats, Excitatory Postsynaptic Potentials, Female, Intercostal Muscles, Male, Motor Neurons, Muscle Spindles, Reflex, Monosynaptic
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
URI: https://discovery.ucl.ac.uk/id/eprint/1432397
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