The muscle spindle has both sensory and motor components. Muscle spindles are encapsulated by connective tissue, and are aligned parallel to extrafusal muscle fibers, unlike Golgi tendon organs, which are oriented in series. Axons of motoneurons also terminate in muscle spindles they make synapses at either or both of the ends of the intrafusal muscle fibers and regulate spindle sensitivity. They are composed of 3-10 intrafusal muscle fibers, of which there are three types, dynamic nuclear bag fibers (bag 1 fibres), static nuclear bag fibers (bag 2 fibres) and nuclear chain fibers and the axons of sensory neurons. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.Muscle spindles are found within the fleshy portions of muscles, embedded in so-called extrafusal muscle fibers. The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. This is particularly important when the recommended agent is a new and/or infrequently employed drug.ĭisclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.ĭrug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. Reinnervation by gamma motor neurons is either incomplete or significantly delayed.Ĭopyright: All rights reserved. Phenol block thus results in a complete denervation of muscle spindles, followed by a fairly rapid sensory reinnervation. A much smaller number (38%) received gamma innervation. After 6 weeks, spindles were readily identified and nearly all (>90%) received recognizable afferent innervation. None received efferent (gamma) innervation. The remainder of which were innervated by afferents only.
In those spindles studied, most (>80%) were completely denervated. Four weeks after phenol block, muscle spindles were difficult to find, as their immunoreactivity to antibody ALD 19 was reduced. The integrity of the sensory and motor reinnervation of spindles was evaluated using a monoclonal antibody specific for a high molecular weight neurofilament protein. Spindles were identified by the immunoreactivity of nuclear bag 1 fibers to slow tonic myosin (antibody ALD 19).
We studied the innervation of muscle spindles in the plantar lumbrical muscles of untreated rats and in rats 4 and 6 weeks after a single phenol block. We simulated the clinical procedure by bathing the lateral plantar nerve of rats in 7% phenol solution for 20 min. It produces relief of symptoms by chemical denervation. Infusion of phenol into peripheral nerves is used clinically to manage spasticity.
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