Summation of extraocular motor unit tensions in the lateral rectus muscle of the cat

Goldberg, Stephen J.; Wilson, Kristi; Shall, PT Mary S.

doi:10.1002/(sici)1097-4598(199710)20:10<1229::aid-mus4>3.0.co;2-e

Cited by 54 publications

(39 citation statements)

References 28 publications

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“…Berthier and Blaineau, 1997;Patel and Lieber, 1997). Many studies indicated that these tissues are capable of transmitting force (Goldberg et al, 1997;Huijing, 1999a;Monti et al, 2001;Street and Ramsey, 1965;Street, 1983). Therefore, changes in the position of the extramuscular connective tissue relative to the muscle may also result in changes within intramuscular connective tissue and muscle fibres (i.e.…”

Section: Extramuscular Connective Tissuesupporting

confidence: 83%

Extramuscular myofascial force transmission forin siturat medial gastrocnemius and plantaris muscles in progressive stages of dissection

Rijkelijkhuizen

Baan

Haan

et al. 2005

Journal of Experimental Biology

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SUMMARY The aim of this study was to establish the extent of extramuscular myofascial force transmission for dissected rat medial gastrocnemius (GM) and plantaris (PL) muscles. Initially, this was done with GM still connected to extramuscular connective tissue (general fascia, neuro-vascular tract and compartmental fascia). Neighbouring muscles were also connected to these tissues. In a later stage, it was dissected progressively until finally a fully dissected in situ GM was obtained, for which the neuro-vascular tract (i.e. the nerves, bloodvessels and the surrounding connective tissue)was the only extramuscular tissue left intact. Force of GM was measured not only at its distal tendon in progressive stages of dissection, but also at its dissected proximal tendon. In the stage where GM was still connected to extramuscular tissues, the experiments showed that up to 40.5±5.9%(mean ± s.e.m.) of the force exerted by the neighbouring PL muscle was transmitted onto the calcaneal bone, even when the PL tendon was not connected to this bone. After distal PL-tenotomy, a difference between proximally and distally measured forces of GM constituted evidence for myofascial force transmission. In the fully dissected in situ GM muscle, no relevant myofascial force transmission occurred in the reference position (the position of the GM origin corresponding to a knee angle of 120°). However, some myofascial force transmission occurred when the relative position of the origin of the fully dissected GM muscle was changed with respect to the neuro-vascular tract.

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Section: Extramuscular Connective Tissuesupporting

confidence: 83%

Extramuscular myofascial force transmission forin siturat medial gastrocnemius and plantaris muscles in progressive stages of dissection

Rijkelijkhuizen

Baan

Haan

et al. 2005

Journal of Experimental Biology

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“…Series and parallel couplings of fibers would imply that transmission of the contractile force of any one fiber to aggregate EOM force would depend on the contractile state of other fibers (Miller et al 2002). This is consistent with the observation in cat LR that simultaneous stimulation of multiple motor units in about 25% of cases generates less total tension than the sum of the tensions of each motor unit stimulated separately, a form of nonlinear summation (Goldberg et al 1997). It seems doubtful that any single currently available technique, neither GL tension measurement at the insertional tendon nor MRI of EOM cross sections, could fully characterize the complex EOM contractile behavior in a manner that would correlate closely with motor neuron firing.…”

Section: Co-contraction In Convergence?mentioning

confidence: 99%

Magnetic Resonance Imaging of Human Extraocular Muscles in Convergence

Demer

Kono

Wright

2003

Journal of Neurophysiology

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ular muscle (EOM) paths during asymmetrical convergence were evaluated by tri-planar, contrast-enhanced magnetic resonance imaging of the orbits of eight young adults during binocular fixation of a target aligned to one eye at 800 and 15 cm distance. Cross sections and paths of EOMs were determined from area centroids. In convergence, the aligned eye rotated and translated negligibly, while its inferior oblique (IO) muscle exhibited significant contractile thickening. There were no significant contractile changes in the cross sections of aligned eye rectus or superior oblique (SO) muscles in convergence. The converging eye rotated nasally 22.4°but translated negligibly. The converging eye medial (MR) and lateral rectus (LR) muscles exhibited large contractile cross-section changes, and the IO showed significant contractile thickening, while the vertical rectus muscles and the SO did not. Anterior paths of three aligned eye rectus EOMs could be determined in convergence and shifted consistent with a 1.9°extorsion of the rectus pulley array. Such extorsional reconfiguration of the rectus pulleys would move the pulleys in coordination with globe extorsion and avoid imparting torsional action to these EOMs. Extorsional rectus pulley shift in convergence is inconsistent with the reconfiguration predicted to explain the temporal tilting of Listing's planes, instead suggesting that this temporal tilting is due to variations in oblique EOM innervation. Absence of globe translation in convergence argues against overall EOM co-contraction. The reconfiguration of EOM geometry in convergence has important implications for single-unit studies of neural control.

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“…Finally, the summation of motor unit tensions was examined when approximately five motor units were simultaneously activated (Goldberg et al, 1997b). It was found that there were force decrements of Ӎ50% in ϳ25% of the motor units studied (i.e., some units did not summate linearly).…”

Section: Abstract: Extraocular; Eye Movement; Abducens; Motoneuron; mentioning

confidence: 99%

“…We have previously shown in the cat (2.5 to 3.5 kg animals) lateral rectus muscle that the twitch and tetanic contractile forces elicited in response to stimulation of the whole abducens nerve are below what would be expected if one multiplied the average force of the motor units (i.e., twitch tension Ӎ29.0 mg and maximum tetanic tension Ӎ194.0 mg) by the known number of lateral rectus motoneurons (n Ӎ 1,100) in the cat abducens nucleus (Shall and Goldberg, 1992;Goldberg et al, 1997b;Goldberg and Shall, 1997). In summary, ϳ15.0 gm of twitch force (Barmack et al, 1971;Goldberg et al, 1997b) and ϳ110.0 gm of tetanic force (Cooper and Eccles, 1930;Barmack et al, 1971;Goldberg and Shall, 1997) have been observed when, instead, one would "expect" ϳ29.0 gm of twitch force (Goldberg et al, 1997b) and 237.0 gm of tetanic force (Goldberg and Shall, 1997).…”

Section: Motor Units and The Whole Musclementioning

confidence: 99%

Extraocular Motor Unit and Whole-Muscle Responses in the Lateral Rectus Muscle of the Squirrel Monkey

Goldberg¹,

Meredith²,

Shall

1998

J. Neurosci.

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Because primate studies provide data for the current experimental models of the human oculomotor system, we investigated the relationship of lateral rectus muscle motoneuron firing to muscle unit contractile characteristics in the squirrel monkey. Also examined was the correlation of whole-muscle contractile force with the degree of evoked eye displacement. A force transducer was used to record lateral rectus whole-muscle or muscle unit contraction in response to abducens whole-nerve stimulation or stimulation of single abducens motoneurons or axons. Horizontal eye displacement was recorded using a magnetic search coil.(1) Motor units could be categorized based on contraction speed (fusion frequency) and fatigue. (2) The kt value (change in motoneuronal firing necessary to increase motor unit force by 1.0 mg) of the units correlated with maximum tetanic tension. (3) There was some tendency for maximum tetanic tension of this unit population to separate into three groups. (4) At a constant frequency of 100 Hz, 95% of the motor units demonstrated significantly different force levels dependent on immediately previous stimulation history (hysteresis). (5) A mean force change of 0.32 gm/° and a mean frequency change of 4.7 Hz/° of eye displacement were observed in response to whole-nerve stimulation.These quantitative data provide the first contractile measures of primate extraocular motor units. Models of eye movement dynamics may need to consider the nonlinear transformations observed between stimulation rate and muscle tension as well as the probability that as few as two to three motor units can deviate the eye 1°.

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Summation of extraocular motor unit tensions in the lateral rectus muscle of the cat

Cited by 54 publications

References 28 publications

Extramuscular myofascial force transmission forin siturat medial gastrocnemius and plantaris muscles in progressive stages of dissection

Extramuscular myofascial force transmission forin siturat medial gastrocnemius and plantaris muscles in progressive stages of dissection

Magnetic Resonance Imaging of Human Extraocular Muscles in Convergence

Extraocular Motor Unit and Whole-Muscle Responses in the Lateral Rectus Muscle of the Squirrel Monkey

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