Symposium Changing perspectives on the functional organization of the segmental motor system

1986 ◽  
Vol 64 (4) ◽  
pp. 495-498 ◽  
Author(s):  
Marc D. Binder
Keyword(s):  
Skeletal Muscles ◽  
Motor System ◽  
Functional Organization ◽  
Motor Units ◽  
Muscle Spindles ◽  
Spinal Reflex ◽  
Reflex Pathways ◽  
Afferent Fibers ◽  
Neuromuscular Compartments ◽  
Tendon Organs

Results from a wide variety of recent studies on the architecture and innervation of skeletal muscles, the neuromechanical characteristics of motor units, and the properties and spinal reflex actions of muscle proprioceptors present a number of challenges to conventional views of the functional organization of the segmental motor system. To illustrate the nature of these challenges, studies directed toward several specific issues are reviewed. These include the functional subdivision of single muscles into two or more neuromuscular compartments; the patterns of synaptic input from peripheral afferent fibers to motoneurons innervating muscle units of different "type;" and the convergence in the segmental reflex pathways from muscle spindles and tendon organs to motoneurons.

Ensemble discharge from Golgi tendon organs of cat peroneus tertius muscle

1990 ◽  
Vol 64 (3) ◽  
pp. 813-821 ◽  
Author(s):  
G. Horcholle-Bossavit ◽  
L. Jami ◽  
J. Petit ◽  
R. Vejsada ◽  
D. Zytnicki
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Good Correspondence ◽  
Golgi Tendon Organs ◽  
Afferent Fibers ◽  
Slow Type ◽  
Tendon Organs ◽  
Fast Twitch ◽  
Force Profiles ◽  
Tendon Organ

1. The responses of individual tendon organs of the cat peroneus tertius muscle to motor-unit contractions were recorded in anesthetized cats during experiments in which all the Ib-afferent fibers from the muscle had been prepared for recording in dorsal root filaments. This was possible because the cat peroneus tertius only contains a relatively small complement of approximately 10 tendon organs. 2. Motor units of different physiological types were tested for their effects on the whole population of tendon organs in the muscle. Effects of unfused tetanic contractions were tested under both isometric and anisometric conditions. Each motor unit activated at least one tendon organ, and each tendon organ was activated by at least one motor unit. Individual slow-type units were found to act on a single or two receptors, whereas a fast-type unit could activate up to six tendon organs. 3. In one experiment, the effects of 8 motor units on 10 tendon organs were examined. One fast-twitch, fatigue resistant (FR)-type unit acted on six tendon organs, of which four were also activated by another FR unit. The contraction of each unit, on its own, elicited a range of individual responses, from weak to strong. The discharge frequencies of individual responses displayed no clear relation with the strength of contraction, nor did they accurately represent the shape of force profiles. But when all the discharges were pooled, a fairly good correspondence appeared between variations of contractile force and variations of averaged discharge frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor Mechanisms Underlying Heterogenic Reflexes Among the Triceps Surae Muscles of the Cat

1999 ◽  
Vol 81 (2) ◽  
pp. 467-478 ◽  
Author(s):  
T. Richard Nichols
Keyword(s):  
Triceps Surae ◽  
Spinal Reflex ◽  
Medial Gastrocnemius ◽  
Entire Group ◽  
Passive Components ◽  
Mechanical Coupling ◽  
Golgi Tendon Organs ◽  
Reflex Pathways ◽  
Tendon Organs ◽  
Triceps Surae Muscles

Receptor mechanisms underlying heterogenic reflexes among the triceps surae muscles of the cat. The soleus (S), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles of the cat are interlinked by rapid spinal reflex pathways. In the decerebrate state, these heterogenic reflexes are either excitatory and length dependent or inhibitory and force dependent. Mechanographic analysis was used to obtain additional evidence that the muscle spindle primary ending and the Golgi tendon organ provide the major contributions to these reflexes, respectively. The tendons of the triceps surae muscles were separated and connected to independent force transducers and servo-controlled torque motors in unanesthetized, decerebrate cats. The muscles were activated as a group using crossed-extension reflexes. Electrical stimulation of the caudal cutaneous sural nerve was used to provide a particularly strong activation of MG and decouple the forces of the triceps surae muscles. During either form of activation, the muscles were stretched either individually or in various combinations to determine the strength and characteristics of autogenic and heterogenic feedback. The corresponding force responses, including both active and passive components, were measured during the changing background tension. During activation of the entire group, the excitatory, heterogenic feedback linking the three muscles was found to be strongest onto LG and weakest onto MG, in agreement with previous results concerning the strengths of heteronymous Ia excitatory postsynaptic potentials among the triceps surae muscles. The inhibition, which is known to affect only the soleus muscle, was dependent on active contractile force and was detected essentially as rapidly as length dependent excitation. The inhibition outlasted the excitation and was blocked by intravenous strychnine. These results indicate that the excitatory and inhibitory effects are dominated by feedback from primary spindle receptors and Golgi tendon organs. The interactions between these two feedback pathways potentially can influence both the mechanical coupling between ankle and knee.

Propriospinal control of interneurons in spinal reflex pathways from tendon organs in the cat

1983 ◽  
Vol 261 (2) ◽  
pp. 317-320 ◽  
Author(s):  
E. Jankowska ◽  
A. Lundberg ◽  
D. Stuart
Keyword(s):  
Spinal Reflex ◽  
Reflex Pathways ◽  
Tendon Organs

Vesicoanal, urethroanal, and urethrovesical reflexes initiated by lower urinary tract irritation in the rat

1999 ◽  
Vol 277 (4) ◽  
pp. R1002-R1012 ◽  
Author(s):  
Karl B. Thor ◽  
Mark A. Muhlhauser
Keyword(s):  
Spinal Cord ◽  
Acetic Acid ◽  
Urinary Bladder ◽  
Anal Sphincter ◽  
Striated Muscle ◽  
Spinal Reflex ◽  
Intraluminal Pressure ◽  
Reflex Pathways ◽  
Afferent Fibers ◽  
Primary Afferent Fibers

Irritation of the urinary bladder causes activation of normally “silent” nociceptive primary afferent fibers. In the present study, it is reported that irritation of the urinary bladder or urethra with infusion of 0.5% acetic acid robustly activates motoneurons that innervate the striated muscle of the external anal sphincter via spinal reflex mechanisms. The activation of anal motoneurons following irritation of the bladder and urethra are termed vesicoanal and urethroanal reflexes, respectively. The reflexes can be mimicked by acute application of capsaicin to the bladder and urethra, and they show desensitization following prolonged topical application of capsaicin or following chronic systemic pretreatment with capsaicin. The reflexes can be demonstrated in chronic spinal cord-transected animals, indicating that the reflex pathways are organized within the spinal cord. The urethroanal reflex is also physiologically activated by urethral distension and/or increases in intraluminal pressure. In addition to activation of anal sphincter activity, slight distension, pressure increases, or instillation of 0.5% acetic acid into the urethra inhibited bladder contractions through activation of an inhibitory urethrovesical reflex. These reflexes are discussed in terms of clinical characteristics of urethritis and prostatitis. Anecdotally, it was discovered that the bladder can buffer acetic acid.

scholarly journals RELATION OF FUNCTION TO DIAMETER IN AFFERENT FIBERS OF MUSCLE NERVES

1954 ◽  
Vol 38 (1) ◽  
pp. 117-131 ◽  
Author(s):  
Carlton C. Hunt
Keyword(s):  
Fiber Diameter ◽  
Afferent Fiber ◽  
Muscle Spindles ◽  
Medial Gastrocnemius ◽  
Diameter Distribution ◽  
Afferent Fibers ◽  
Significant Difference ◽  
Stretch Receptors ◽  
Group Ii ◽  
Tendon Organs

1. A method of isolation of individual afferent fibers from muscle has yielded a representative sample of the fibers which comprise groups 1 (12 to 20 µ) and II (4 to 12 µ) of the afferent fiber diameter distribution of muscle nerves in cat. 2. Afferent fibers from muscle stretch receptors account for groups I and II of the afferent diameter spectrum of muscle nerves to soleus and medial gastrocnemius. Fibers from tendon organs are largely confined to the diameter range above 12 µ. This fiber group, which has a simple one-peak diameter distribution, is termed group IB. Fibers from muscle spindles show a bimodal diameter distribution and account for the remainder of fibers in the 12 to 20 µ group (termed IA) and substantially all of group II (4 to 12 µ). 3. No significant difference has been found in the receptor characteristics of the large (group IA) and intermediate sized (group II) spindle afferent fibers other than a slightly higher threshold of the latter to steady external stretch.

Functional organization of the spinal reflex pathways from forelimb afferents to hindlimb motoneurones in the cat

1978 ◽  
Vol 139 (1) ◽  
pp. 21-33 ◽  
Author(s):  
E.D. Schomburg ◽  
H.-M. Meinck ◽  
J. Haustein ◽  
J. Roesler
Keyword(s):  
Functional Organization ◽  
Spinal Reflex ◽  
Reflex Pathways ◽  
Forelimb Afferents

Reduced motor unit activation of muscle spindles and tendon organs in the immobilized cat hindlimb

1995 ◽  
Vol 78 (3) ◽  
pp. 901-913 ◽  
Author(s):  
M. A. Nordstrom ◽  
R. M. Enoka ◽  
R. M. Reinking ◽  
R. C. Callister ◽  
D. G. Stuart
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Muscle Spindles ◽  
Tibialis Posterior ◽  
Fiber Types ◽  
Single Motor Unit ◽  
Tetanic Force ◽  
Single Motor ◽  
Single Motor Units ◽  
Tendon Organs

Six weeks of limb immobilization of a healthy muscle (cat tibialis posterior) at a short length resulted in a significant reduction of mean fiber area for all fiber types (I, 71% of control; IIa, 77% of control; IIb, 79% of control), whereas fiber type proportions were unchanged. For motor units, there was a reduction in peak tetanic force (type slow > fast fatigue resistant > fast fatigable); an increase in the twitch-to-tetanus ratio for fast fatigue-resistant and slow units; and no effect on the twitch force, twitch time course, or fatigability. The reduction in peak force was greater than expected because of fiber atrophy in slow units. Immobilization had a minimal effect on muscle spindle afferent (Ia and spindle group II) responses to a ramp-and-hold stretch of the passive muscle. Tendon organ (Ib) afferents had an increased responsiveness to stretch after immobilization but only when the muscle was stretched from a short resting length. However, immobilization reduced the modulation of muscle afferent discharge in response to tetanic contractions of single motor units. The decline in responsiveness of spindles was a result of the reduced tetanic force of motor units. In contrast, tendon organs in immobilized muscle were twice as likely to convey no information on the contraction of a single motor unit and were more likely to be unloaded, suggesting that immobilization caused the functional denervation of some muscle fibers. Thus the responses of muscle spindles and tendon organs in immobilized muscle reflected atrophic changes in extrafusal fibers but did not provide evidence for substantial disturbance of receptor function.

A New Procedure for Assessment of Proprioception

1992 ◽  
Vol 74 (1) ◽  
pp. 91-98 ◽  
Author(s):  
Bernd Leplow ◽  
Volkert Schlüter ◽  
Roman Ferstl
Keyword(s):  
Information Processing ◽  
Muscle Contraction ◽  
Healthy Subjects ◽  
Masseter Muscle ◽  
Muscle Activation ◽  
Muscle Spindles ◽  
Afferent Fibers ◽  
Afferent Information ◽  
Voluntary Muscle Contraction ◽  
Tendon Organs

A new method for the assessment of proprioception was developed and tested with 40 healthy subjects on two facial muscles (i.e., masseter and zygomatic muscles). The experiment was repeated after 3 1/2 months. In our study, proprioception was studied with respect to sensations arising from the muscle spindles and tendon organs. Therefore, myesthesia was investigated, which was assessed by the correspondence between a voluntary muscle contraction and its immediate replication. Good perception was defined by a small integral of differences, standardized by duration and intensity of the contraction, and its replication. Results show that this measure is independent of the characteristics of muscle activation. In concordance with our hypothesis, myesthesia was superior in a muscle richly supplied with muscle spindles and afferent fibers (i.e., masseter muscle), to that for a muscle less prepared for afferent information processing (i.e., zygomatus major).

scholarly journals Motor Unit Recruitment and Proprioceptive Feedback Decrease the Common Drive

2009 ◽  
Vol 101 (3) ◽  
pp. 1620-1628 ◽  
Author(s):  
Carlo J. De Luca ◽  
Jose A. Gonzalez-Cueto ◽  
Paolo Bonato ◽  
Alexander Adam
Keyword(s):  
Time Lag ◽  
Motor Units ◽  
Muscle Spindles ◽  
Proprioceptive Feedback ◽  
Inhibitory Influence ◽  
Firing Rates ◽  
Golgi Tendon Organs ◽  
Common Drive ◽  
The Common ◽  
Tendon Organs

It has been documented that concurrently active motor units fire under the control of a common drive. That is, the firing rates show high correlation with near-zero time lag. This degree of correlation has been found to vary among muscles and among contractions performed at different force levels in the same muscle. This study provides an explanation indicating that motor units recruited during a contraction cause an increase in the variation (SD) and a decrease in the degree (amplitude) of the correlation of the firing rates. The degree of correlation is lower in muscles having greater spindle density. This effect appears to be mediated by the proprioceptive feedback from the spindles and possibly the Golgi tendon organs. Muscle spindles in particular respond to the mechanical excitation of the nonfused muscle fibers and provide a discordant excitation to the homonymous motoneurons, resulting in a decrease in the correlation of the firing rates of motor units. The implication of this work is that the decreased correlation of the firing rates in some muscles is not necessarily an indication of a decreased common drive from the CNS, but rather an inhibitory influence of the proprioceptive feedback from the peripheral nervous system. This explanation is useful for understanding various manifestations of the common drive reported in the literature.

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