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This Article Full Text Full Text (PDF) All Versions of this Article: 580/3/777    most recent jphysiol.2006.126276v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Alexander, C. Articles by Harrison, P. J. Search for Related Content PubMed PubMed Citation Articles by Alexander, C. Articles by Harrison, P. J. Related Collections Neuroscience

¹ Department of Physiotherapy, Hammersmith Hospitals NHS Trust, Fulham Palace Road, London W6 8RF, UK
² Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK
³ School of Health Sciences and Social Care, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

The control of the scapulothoracic muscles trapezius (Tr) and serratus anterior (SA) has been examined in normal human subjects. Electromyographic recordings were made from the SA and Tr muscles (upper trapezius UTr, lower trapezius LTr) using surface electrodes placed bilaterally. Magnetic stimulation of the motor cortex and electrical stimulation of peripheral nerves were used to examine their descending and reflex control. The average optimal site of cortical stimulation was found to be the same for SA, UTr and LTr (an approximate centre of gravity of –0.6 cm, 3.7 cm where the centre of gravity is expressed as the mean anterio-posterior position, the mean medio-lateral position). Some asymmetry in the cortical representation of UTr was found in each individual tested. Magnetic stimulation evoked bilateral MEPs in Tr (latency contralateral (c) UTr 8.5 ± 1.6 ms, ipsilateral (i) UTr 19.0 ± 2.7 ms) but only contralateral responses were evoked in SA (11.2 ± 2.6 ms). Electrical stimulation of the long thoracic nerve at two sites was used to examine homonymous and heteronymous reflexes of SA, while electrical stimulation of cervical nerve of C3/4 was used to examine the heteronymous reflexes of Tr. Ipsilateral SA H reflexes were evoked at a latency of 9.9 ± 0.8 ms (proximal site) and 10.8 ± 1.2 ms (distal site). No group I reflexes were evoked from SA to its contralateral homologue. No group I reflexes were evoked between Tr and SA. Finally, cross-correlation of activity from the Tr muscle pairs and the SA muscle pair revealed that the motoneurones of the Tr muscles share some common presynaptic input whereas there was no detectable common presynaptic input to the SA muscle pair. This study extends and consolidates knowledge regarding the neural control of trapezius and for the first time explores the neural control of SA. The study demonstrates a contrasting bilateral control of Tr and SA. These patterns of connections are discussed in relation to the contrasting bilateral functional roles of these muscles.

(Received 12 December 2006; accepted after revision 9 January 2007; first published online 11 January 2007)
Corresponding author C. M. Alexander: Department of Physiotherapy, Hammersmith Hospital NHS Trust, Fulham Palace Rd, London W6 8RF, UK.  Email: c.alexander{at}ucl.ac.uk

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