Muscle fiber and motor unit behavior in the longest human skeletal muscle

Harris, AJ, Duxson, MJ, Butler, JE, Hodges, PW, Taylor, JL and Gandevia, SC (2005) Muscle fiber and motor unit behavior in the longest human skeletal muscle. Journal of Neuroscience, 25 37: 8528-8533. doi:10.1523/JNEUROSCI.0923-05.2005

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Author Harris, AJ
Duxson, MJ
Butler, JE
Hodges, PW
Taylor, JL
Gandevia, SC
Title Muscle fiber and motor unit behavior in the longest human skeletal muscle
Journal name Journal of Neuroscience   Check publisher's open access policy
ISSN 0270-6474
Publication date 2005
Sub-type Article (original research)
DOI 10.1523/JNEUROSCI.0923-05.2005
Open Access Status File (Publisher version)
Volume 25
Issue 37
Start page 8528
End page 8533
Total pages 6
Place of publication Washington, DC
Publisher Soc Neuroscience
Collection year 2005
Language eng
Subject C1
321024 Rehabilitation and Therapy - Occupational and Physical
730303 Occupational, speech and physiotherapy
Abstract The sartorius muscle is the longest muscle in the human body. It is strap-like, up to 600 mm in length, and contains five to seven neurovascular compartments, each with a neuromuscular endplate zone. Some of its fibers terminate intrafascicularly, whereas others may run the full length of the muscle. To assess the location and timing of activation within motor units of this long muscle, we recorded electromyographic potentials from multiple intramuscular electrodes along sartorius muscle during steady voluntary contraction and analyzed their activity with spike-triggered averaging from a needle electrode inserted near the proximal end of the muscle. Approximately 30% of sartorius motor units included muscle fibers that ran the full length of the muscle, conducting action potentials at 3.9 +/- 0.1 m/s. Most motor units were innervated within a single muscle endplate zone that was not necessarily near the midpoint of the fiber. As a consequence, action potentials reached the distal end of a unit as late as 100 ms after initiation at an endplate zone. Thus, contractile activity is not synchronized along the length of single sartorius fibers. We postulate that lateral transmission of force from fiber to endomysium and a wide distribution of motor unit endplates along the muscle are critical for the efficient transmission of force from sarcomere to tendon and for the prevention of muscle injury caused by overextension of inactive regions of muscle fibers.
Keyword Neurosciences
Human Muscle
Motor Unit
Sartorius Muscle
Muscle Fiber
Conduction Velocity
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 06:41:22 EST