The effects of double activations of single motor units on discharge patterns of primary muscle spindle endings in the cat

1982 ◽  
Vol 28 (3) ◽  
pp. 303-307 ◽  
Author(s):  
U. Windhorst ◽  
R. Schwestka ◽  
W. Koehler
Keyword(s):  
Muscle Spindle ◽  
Motor Units ◽  
Single Motor ◽  
Single Motor Units ◽  
Primary Muscle Spindle Endings ◽  
Discharge Patterns ◽  
Muscle Spindle Endings

Muscle Spindle Afferent Input to Motoneurons in Human Masseter

1999 ◽  
Vol 82 (1) ◽  
pp. 505-507 ◽  
Author(s):  
Sheila D. Scutter ◽  
Kemal S. Türker
Keyword(s):  
Muscle Spindle ◽  
Motor Units ◽  
Afferent Input ◽  
H Reflex ◽  
Skewed Distribution ◽  
Reflex Response ◽  
Muscle Spindle Afferents ◽  
Single Motor ◽  
Single Motor Units ◽  
Inhibitory Mechanisms

The H-reflex response in large and small single motor units in human deep anterior masseter was studied to investigate the distribution of muscle spindle afferents onto masseter motoneurons. We found that only the larger units displayed H-reflex responses. This indicates preferential distribution of muscle spindle input onto large motoneurons or a skewed distribution of tonic presynaptic inhibitory mechanisms.

Recruitment and Discharge Patterns of Single Motor Units During Speech Production

1977 ◽  
Vol 20 (4) ◽  
pp. 613-630 ◽  
Author(s):  
Harvey M. Sussman ◽  
Peter F. MacNeilage ◽  
Randall K. Powers
Keyword(s):  
Dynamic Range ◽  
Isometric Force ◽  
Discharge Rate ◽  
Motor Units ◽  
Size Principle ◽  
Single Motor ◽  
Single Motor Units ◽  
Movement Dynamics ◽  
Discharge Patterns ◽  
Anterior Belly

Recruitment and discharge patterns of single motor units (MUs) in the anterior belly of digastric were studied during speech in three subjects, using electrodes facilitating selective recording at high force levels. Fixed recruitment order was observed in over 99% of all comparisons. Later recruited units invariably possessed muscle action potentials of higher amplitude, suggesting that units were activated in accordance with the “size principle.” Additional evidence for this was that later recruited units, of a set of three studied during speech, motor unit training, and isometric force ramps, showed greater sensitivity to input, and greater dynamic range than earlier recruited units. Units in this set were much more sensitive to rapid changes in input associated with speech gestures than to static activation even at high force levels. Several significant relations between discharge characteristics and aspects of movement dynamics were observed, including relations between (1) recruitment interval (MU1 to MU3) and latency of mandibular lowering, (2) onset of initial discharge of MU1 and relative mechanical advantage of the mandible, (3) number of MUs active and velocity and displacement of the mandible, and (4) discharge rate of MU3 and velocity and displacement of the mandible.

Reflex changes in muscle spindle discharge during a voluntary contraction

1988 ◽  
Vol 59 (3) ◽  
pp. 908-921 ◽  
Author(s):  
A. M. Aniss ◽  
S. C. Gandevia ◽  
D. Burke
Keyword(s):  
Muscle Spindle ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Triceps Surae ◽  
Sensory Threshold ◽  
Single Motor ◽  
Posterior Tibial ◽  
Single Motor Units ◽  
Flexor Muscles ◽  
Electrical Stimuli

1. This study was undertaken to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the foot reflexly affect fusimotor neurons innervating the plantar and dorsiflexors of the ankle during voluntary contractions. 2. Recordings were made from 29 identified muscle spindle afferents innervating triceps surae and the pretibial flexors. Trains of electrical stimuli (5 stimuli, 300 impulses per second) were delivered to the sural nerve at the ankle (intensity: 2-4 times sensory threshold) and to the posterior tibial nerve at the ankle (intensity: 1.5-3 times motor threshold for the small muscles of the foot). The stimuli were delivered while the subject maintained an isometric voluntary contraction of the receptor-bearing muscle, sufficient to accelerate the discharge of each spindle ending. This ensured that the fusimotor neurons directed to the ending were active and influencing the spindle discharge. The effects of these stimuli on muscle spindle discharge were assessed using raster displays, frequencygrams, poststimulus time histograms (PSTHs) and cumulative sums ("CUSUMs") of the PSTHs. Reflex effects onto alpha-motoneurons were determined from poststimulus changes in the averaged rectified electromyogram (EMG). Reflex effects of these stimuli onto single-motor units were assessed in separate experiments using PSTHs and CUSUMs. 3. Electrical stimulation of the sural or posterior tibial nerves at nonnoxious levels had no significant effect on the discharge of the 14 spindle endings in the pretibial flexor muscles. The electrical stimuli also produced no significant change in discharge of 11 of 15 spindle endings in triceps surae. With the remaining four endings in triceps surae, the overall change in discharge appeared to be an increase for two endings (at latencies of 60 and 68 ms) and a decrease for two endings (at latencies of 110 and 150 ms). The difference in the incidence of the responses of spindle endings in tibialis anterior and in triceps surae was significant (P less than 0.05, chi 2 test). 4. For both triceps surae and pretibial flexor muscles the electrical stimuli to sural or posterior tibial nerves had clear effects on the alpha-motoneuron pool, whether assessed using surface EMG or the discharge of single-motor units. Based on EMG recordings using intramuscular wire electrodes, the reflex effects differed for the gastrocnemii and soleus. 5. In this study, reflex changes in the discharge of human spindle endings were more difficult to demonstrate than comparable changes in the discharge of alpha-motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscle spindle discharge in response to contraction of single motor units

1983 ◽  
Vol 49 (2) ◽  
pp. 291-302 ◽  
Author(s):  
B. McKeon ◽  
D. Burke
Keyword(s):  
Muscle Spindle ◽  
Discharge Rate ◽  
Human Subjects ◽  
Motor Units ◽  
Muscle Spindles ◽  
Single Motor Unit ◽  
Single Motor ◽  
Twitch Contraction ◽  
Single Motor Units ◽  
Tendon Organ

1. In human subjects, microelectrode recordings were made from 25 muscle spindle afferents and two tendon organ afferents coming from muscles innervated by the peroneal nerve. 2. Stimulation at low intensity through the recording microelectrode activated efferent axons innervating motor units in close proximity to the muscle spindle or tendon organ. There was a clear alteration in the discharge of 17 afferents (15 muscle spindle, 2 tendon organ) in response to twitch contractions that involved only one, two, or three motor units. With three other afferents there was a less overt but statistically significant alteration in discharge rate by the twitch contraction of a single motor unit. 3. The sensitivity of 21 receptors (20 spindles, 1 tendon organ) to twitch contractions of anatomically close motor units was contrasted with their sensitivity to twitches of more remote motor units in the muscle. In no instance was the sensitivity to the contraction of remote motor units greater than that to the contraction of local motor units stimulated through the microelectrode; with remote stimulation many units usually had to be activated before the resulting twitch contraction altered the discharge of an afferent. 4. It is concluded that muscle spindles as well as tendon organs can play a role in monitoring the activity of motor units anatomically close to the receptor.

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