Relationship of the Mechanical Properties of the Cat Inferior Oblique Muscle to the Anatomy of Its Motoneurons and Nerve Branches

Shall, Mary S.; Sorg, P.J.; McClung, J. Ross; Gilliam, Edwin E.; Goldberg, Stephen J.

doi:10.1159/000313649

Cited by 13 publications

(11 citation statements)

References 5 publications

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“…A similar anatomical uniformity has also been reported for rhesus monkey lateral rectus muscle motoneurons [Langer et al, 1986]. This primate motoneuron size homogeneity may indicate that cell size does not play a major role in motor unit recruitment [Goldberg, 1990;Shall et al, 1995;Dean, 1996Dean, , 1997 during various eye movements.…”

Section: Discussionsupporting

confidence: 68%

Motoneurons of the Lateral and Medial Rectus Extraocular Muscles in Squirrel Monkey and Cat

McClung

Shall²,

Goldberg³

2001

Cells Tissues Organs

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The goal of this study was to examine and compare the number and size of motoneurons in the cat and squirrel monkey abducens nucleus. We also examined medial rectus muscle motoneuron compartmentalization in the squirrel monkey oculomotor nucleus and compared those cells to abducens nucleus motoneurons. Retrograde labeling of the motoneurons, using cholera toxin conjugate of horseradish peroxidase (CTHRP) injected into cat and monkey lateral or medial rectus muscles, was observed after 24 h. The CTHRP was histochemically localized with tetramethylbenzidine. The slide-mounted sections were analyzed using a computerized imaging system. Cat abducens nucleus motoneurons showed a wide range of cell sizes (26.0–66.0 µm, mean = 37.2 ± 6.2 µm), four or more dendrites per cell and an average of 1,418 cells within a relatively loosely packed nucleus. Squirrel monkey abducens nucleus motoneurons were significantly smaller than those in the cat with a narrower range of cell sizes (20.0–44.0 µm, mean = 31.7 ± 3.8 µm), four or more dendrites per cell and an average of 2,473 cells densely packed within the nucleus. Squirrel monkey medial rectus muscle motoneurons were organized into MRa, MRb and MRc subgroups. MRa motoneurons comprise the primary innervation for the medial rectus muscle and were similar in size to abducens nucleus motoneurons while the MRc subgroup cells were significantly smaller in size. Similar relationships among medial rectus motoneurons have been seen in rhesus monkeys. The relationship of these anatomical findings to previous physiological results regarding the generation of extraocular muscle force in the squirrel monkey is discussed.

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Section: Discussionsupporting

confidence: 68%

Motoneurons of the Lateral and Medial Rectus Extraocular Muscles in Squirrel Monkey and Cat

McClung

Shall²,

Goldberg³

2001

Cells Tissues Organs

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“…In addition, the role of MIF muscle fibers in eye movements is also not understood. No recordings have been knowingly made from the motoneurons supplying MIFs in awake mammals; neither is the location of motoneurons innervating MIF muscle fibers known, although they are assumed to be in the nIII, nIV, and nVI motor nuclei (Shall et al, 1995). In this study, we have attempted to locate the motoneurons of MIFs in monkeys.…”

mentioning

confidence: 99%

Motoneurons of twitch and nontwitch extraocular muscle fibers in the abducens, trochlear, and oculomotor nuclei of monkeys

Büttner‐Ennever

Horn

Scherberger

et al. 2001

J of Comparative Neurology

145

193

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Eye muscle fibers can be divided into two categories: nontwitch, multiply innervated muscle fibers (MIFs), and twitch, singly innervated muscle fibers (SIFs). We investigated the location of motoneurons supplying SIFs and MIFs in the six extraocular muscles of monkeys. Injections of retrograde tracers into eye muscles were placed either centrally, within the central SIF endplate zone; in an intermediate zone, outside the SIF endplate zone, targeting MIF endplates along the length of muscle fiber; or distally, into the myotendinous junction containing palisade endings. Central injections labeled large motoneurons within the abducens, trochlear or oculomotor nucleus, and smaller motoneurons lying mainly around the periphery of the motor nuclei. Intermediate injections labeled some large motoneurons within the motor nuclei but also labeled many peripheral motoneurons. Distal injections labeled small and medium-large peripheral neurons strongly and almost exclusively. The peripheral neurons labeled from the lateral rectus muscle surround the medial half of the abducens nucleus: from superior oblique, they form a cap over the dorsal trochlear nucleus; from inferior oblique and superior rectus, they are scattered bilaterally around the midline, between the oculomotor nucleus; from both medial and inferior rectus, they lie mainly in the C-group, on the dorsomedial border of oculomotor nucleus. In the medial rectus distal injections, a "C-group extension" extended up to the Edinger-Westphal nucleus and labeled dendrites within the supraoculomotor area. We conclude that large motoneurons within the motor nuclei innervate twitch fibers, whereas smaller motoneurons around the periphery innervate nontwitch, MIF fibers. The peripheral subgroups also contain medium-large neurons which may be associated with the palisade endings of global MIFs. The role of MIFs in eye movements is unclear, but the concept of a final common pathway must now be reconsidered.

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“…11 The feline inferior oblique is innervated by distinct medial and lateral branches that generate different contractile responses. 20 In human and monkey, the inferior oblique is also innervated in compartmental fashion by two separate motor nerve trunks. 21 Possible compartmentalization is less clear for the inferior rectus, which has a selective lateral trunk that overlaps diffuse arborization of another trunk throughout the entire EOM.…”

Section: Anatomic Evidence For Eom Compartmentalizationmentioning

confidence: 99%

Compartmentalization of extraocular muscle function

Demer

2014

Eye

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Ocular motor diversity exceeds capabilities of only six extraocular muscles (EOMs), but this deficiency is overcome by the plethora of fibers within individual EOMs surpassing requirements of homogeneous actuators. This paper reviews emerging evidence that regions of individual EOMs can be differentially innervated to exert independent oculorotary torques, broadening the oculomotor repertoire, and potentially explaining diverse strabismus pathophysiology. Parallel structure characterizes EOM and tendon fibers, with little transverse coupling of experimentally imposed or actively generated tension. This arrangement enables arbitrary groupings of tendon and muscle fibers to act relatively independently. Coordinated force generation among EOM fibers occurs only upon potentially mutable coordination of innervational commands, whose central basis is suggested by preliminary findings of apparent compartmental segregation of abducens motor neuron pools. Humans, monkeys, and other mammals demonstrate separate, nonoverlapping intramuscular nerve arborizations in the superior vs inferior compartments of the medial rectus (MR) and lateral rectus (LR) EOMs that could apply force at the superior vs inferior portions of scleral insertions, and in the medial vs lateral compartments of the superior oblique that act at the equatorial vs posterior scleral insertions that might preferentially implement incycloduction vs infraduction. Magnetic resonance imaging of the MR during several physiological ocular motor behaviors indicates differential compartmental function. Differential compartmental pathology can influence clinical strabismus. Partial abducens palsy commonly affects the superior LR compartment more than the inferior, inducing vertical strabismus that might erroneously be attributed to cyclovertical EOM pathology. Surgery may selectively manipulate EOM compartments.

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Relationship of the Mechanical Properties of the Cat Inferior Oblique Muscle to the Anatomy of Its Motoneurons and Nerve Branches

Cited by 13 publications

References 5 publications

Motoneurons of the Lateral and Medial Rectus Extraocular Muscles in Squirrel Monkey and Cat

Motoneurons of the Lateral and Medial Rectus Extraocular Muscles in Squirrel Monkey and Cat

Motoneurons of twitch and nontwitch extraocular muscle fibers in the abducens, trochlear, and oculomotor nuclei of monkeys

Compartmentalization of extraocular muscle function

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