The heteronymous monosynaptic actions of triceps surae group Ia afferents on hip and knee extensor motoneurones in the cat

1986 ◽  
Vol 61 (2) ◽  
Author(s):  
S. Edgley ◽  
E. Jankowska ◽  
D. McCrea
Keyword(s):  
Knee Extensor ◽  
Triceps Surae ◽  
Ia Afferents ◽  
Extensor Motoneurones

Reduction of Ib autogenetic inhibition in motoneurons during contractions of an ankle extensor muscle in the cat

1990 ◽  
Vol 64 (5) ◽  
pp. 1380-1389 ◽  
Author(s):  
D. Zytnicki ◽  
J. Lafleur ◽  
G. Horcholle-Bossavit ◽  
F. Lamy ◽  
L. Jami
Keyword(s):  
Triceps Surae ◽  
Rapid Reduction ◽  
Excitatory Connection ◽  
Golgi Tendon Organs ◽  
Ia Afferents ◽  
Group I ◽  
Spinal Mechanism ◽  
Autogenetic Inhibition ◽  
Tendon Organs ◽  
Afferent Volleys

1. Triceps surae and plantaris (Pl) motoneurons were recorded intracellularly in chloralose or pentobarbital sodium (Nembutal)-anesthetized cats during unfused tetanic contractions of gastrocnemius medialis muscle (GM) produced by stimulating either a cut branch of the GM nerve or the muscle directly. 2. In alpha-motoneurons, during a series of GM twitches at 10/s, contraction-induced inhibitory potentials, probably the result of input from Golgi tendon organs (autogenetic inhibition), rapidly subsided before the end of the series. In contrast, excitatory potentials, probably the result of the activation of spindle primary endings during relaxation from contraction, persisted. 3. In gastrocnemius lateralis-soleus (GL-S) and Pl motoneurons lacking an excitatory connection with Ia afferents from GM, the sustained contraction of this muscle also elicited a declining inhibition. Rapid reduction of contraction-induced autogenetic inhibition was also observed in homonymous gamma-motoneurons. During unfused tetanic contractions lasting 0.5-4s, inhibitory potentials quickly subsided, but an abrupt increase in contractile force elicited a new series of decreasing inhibitory potentials. 4. The assumption that the inhibition induced by GM unfused tetanic contractions was due to activation of homonymous Ib afferents was supported by observations of the effects of electrical stimulation of the GM nerve. In Pl motoneurons lacking an excitatory connection with Ia afferents from GM, repetitive trains applied to the GM nerve, at a strength just above threshold for group I fibers, elicited rapidly declining inhibitory potentials similar to those produced by GM contraction. It was verified that during such stimulation, the amplitude of the group I afferent volleys did not decrease. 5. Reduction of contraction-induced Ib inhibition during sustained GM contraction was still present after a low spinalization of the preparation. As GM tendon organ discharges were verified to persist throughout prolonged contractions, the observed decline of autogenetic inhibition is likely to depend on a spinal mechanism, possibly involving presynaptic inhibition of Ib afferents and/or mutual inhibition of Ib-inhibitory interneurons.

Functional Coupling of Motor Units Is Modulated During Walking in Human Subjects

2003 ◽  
Vol 89 (2) ◽  
pp. 960-968 ◽  
Author(s):  
D. M. Halliday ◽  
B. A. Conway ◽  
L.O.D. Christensen ◽  
N. L. Hansen ◽  
N. P. Petersen ◽  
...  
Keyword(s):  
Motor Unit ◽  
Human Subjects ◽  
Knee Extensor ◽  
Motor Units ◽  
Central Peak ◽  
Triceps Surae ◽  
Human Gait ◽  
Functional Coupling ◽  
Flexor Muscle ◽  
Healthy Human

Time- and frequency-domain analysis of the coupling between pairs of electromyograms (EMG) recorded from leg muscles was investigated during walking in healthy human subjects. For two independent surface EMG signals from the tibialis anterior (TA) muscle, coupling estimated from coherence measurements was observed at frequencies ≤50 Hz, with identifiable peaks occurring in two frequency bands ranging approximately from 8 to 15 and 15 to 20 Hz. The coherence between TA recordings was greatest toward the end of swing, reduced in early swing, and largely absent in midswing. In time-domain estimates constructed from paired TA EMG recordings, a short-lasting central peak indicative of motor-unit synchronization was observed. This feature of motor-unit coupling was also reduced in mid swing. In paired recordings made among triceps surae, quadriceps, and hamstring muscles, a similar pattern of correlation to that for paired TA recordings was observed. However, no significant coupling was observed in recordings for which one EMG recording was made from an ankle flexor/extensor muscle and the other from a knee extensor/flexor muscle. These results demonstrate that for TA a modulation exists in the functional coupling of motor units recruited during swing. The data also indicate that human motoneurons belonging to different muscles are only weakly coupled during walking. This absence of widespread short-term synchronization between the activities of muscles of the leg may provide a basis for the highly adaptive nature of human gait patterns.

Influence of vibration resistance training on knee extensor and plantar flexor size, strength, and contractile speed characteristics after 60 days of bed rest

2009 ◽  
Vol 107 (6) ◽  
pp. 1789-1798 ◽  
Author(s):  
Edwin R. Mulder ◽  
Astrid M. Horstman ◽  
Dick F. Stegeman ◽  
Arnold de Haan ◽  
Daniel L. Belavý ◽  
...  
Keyword(s):  
Resistance Training ◽  
Knee Extensor ◽  
Bed Rest ◽  
Voluntary Contraction ◽  
Triceps Surae ◽  
Neural Activation ◽  
Cross Sectional ◽  
Rate Of Torque Development ◽  
Exercise Regimen ◽  
Torque Development

Spaceflight and bed rest (BR) result in loss of muscle mass and strength. This study evaluated the effectiveness of resistance training and vibration-augmented resistance training to preserve thigh (quadriceps femoris) and calf (triceps surae) muscle cross-sectional area (CSA), isometric maximal voluntary contraction (MVC), isometric contractile speed, and neural activation (electromyogram) during 60 days of BR. Male subjects participating in the second Berlin Bed Rest Study underwent BR only [control (CTR), n = 9], BR with resistance training (RE; n = 7), or BR with vibration-augmented resistance training (RVE; n = 7). Training was performed three times per week. Thigh CSA and MVC torque decreased by 13.5 and 21.3%, respectively, for CTR (both P < 0.001), but were preserved for RE and RVE. Calf CSA declined for all groups, but more so ( P < 0.001) for CTR (23.8%) than for RE (10.7%) and RVE (11.0%). Loss in calf MVC torque was greater ( P < 0.05) for CTR (24.9%) than for RVE (12.3%), but not different from RE (14.8%). Neural activation at MVC remained unchanged in all groups. For indexes related to rate of torque development, countermeasure subjects were pooled into one resistance training group (RT, n = 14). Thigh maximal rate of torque development (MRTD) and contractile impulse remained unaltered for CTR, but MRTD decreased 16% for RT. Calf MRTD remained unaltered for both groups, whereas contractile impulse increased across groups (28.8%), despite suppression in peak electromyogram (12.1%). In conclusion, vibration exposure did not enhance the efficacy of resistance training to preserve thigh and calf neuromuscular function during BR, although sample size issues may have played a role. The exercise regimen maintained thigh size and MVC strength, but promoted a loss in contractile speed. Whereas contractile speed improved for the calf, the exercise regimen only partially preserved calf size and MVC strength. Modification of the exercise regimen seems warranted.

Analysis of muscle receptor connections by spike-triggered averaging. 2. Spindle group II afferents

1976 ◽  
Vol 39 (6) ◽  
pp. 1393-1402 ◽  
Author(s):  
E. K. Stauffer ◽  
D. G. Watt ◽  
A. Taylor ◽  
R. M. Reinking ◽  
D. G. Stuart
Keyword(s):  
Rise Time ◽  
Mean Amplitude ◽  
Triceps Surae ◽  
Medial Gastrocnemius ◽  
Synaptic Delay ◽  
Conduction Time ◽  
Ia Afferents ◽  
Spike Triggered Averaging ◽  
Group Ii ◽  
Group Ii Afferents

1. The spike-triggered averaging (STA) method has been used to study synaptic connections of nine spindle group II afferents from medial gastrocnemius to 151 motoneurons of leg muscles in the cat. 2. EPSPs were found in 40 cells, predominantly of triceps surae with latency from cord entry ranging from 0.3 to 4.2 ms. Those with latency less than or equal to 1.4 ms were deduced to be monosynaptic in confirmation of Kirkwood and Sears (13). Mean amplitude for MG-LGS cells was 30.1 muV and mean rise time 1.0 ms (compared with 65.4 muV and 1.0 ms for monosynaptic Ia EPSPs from the preceding report (26)). It is argued that monosynaptic latency for spindle group II afferents could be as large as 1.65 ms. 3. The occurrence of a presynaptic spike permitted the division of EPSP latencies into central conduction time and synaptic delay components. Sindle group II central conduction times were significantly longer than those of Ia afferents, while there were no differences in the synaptic delays associated with the two afferent types. 4. EPSPs of longer latency were judged to be di- or trisynaptic. They were smaller and had longer rise times than the monosynaptic effects. Evidence is presented to show that short rise time of an individual PSP does not guarantee that it is monosynaptic. Rise times are different only on a population basis. 5. Inhibitory responses were found with latencies and mean rise times appropriate for di- and trisynaptic connections. Their mean amplitude was 4.6 muV. 6. The distribution of EPSPs and IPSPs was generally consistent with their exerting stretch reflex effects similar to that of Ia afferents and inconsistent with the inclusion of them in the grouping known as “flexor reflex afferents.”

Influence of synaptic identity on single-Ia-afferent connectivity and EPSP amplitude in the adult cat: homonymous versus heteronymous connections

1992 ◽  
Vol 68 (4) ◽  
pp. 1046-1052 ◽  
Author(s):  
C. B. Webb ◽  
T. C. Cope
Keyword(s):  
Spinal Cord ◽  
Conduction Velocity ◽  
Triceps Surae ◽  
Medial Gastrocnemius ◽  
Separate Experiment ◽  
Excitatory Postsynaptic Potential ◽  
Epsp Amplitude ◽  
Ia Afferent ◽  
Ia Afferents ◽  
Entry Points

1. This study makes use of the pattern of synaptic connections between motoneurons and Ia afferents of triceps surae muscles in the cat to test the relative importance of synaptic identity, neuronal size, and neuronal topography as determinants of Ia-afferent connectivity and excitatory postsynaptic potential (EPSP) amplitude. 2. The synaptic actions of single-Ia medial gastrocnemius (MG) afferents were measured by intracellular recording in MG and lateral gastrocnemius (LG) motoneurons. The spike-triggered averaging technique was used to measure EPSPs generated by homonymous or heteronymous Ia afferents and motoneurons, i.e., neurons supplying the same or different muscles, respectively. In agreement with earlier studies, the pooled sample showed that the number of functional connections and the size of EPSPs were both significantly greater for homonymous than for heteronymous neurons. 3. Afferent conduction velocity, motoneuron conduction velocity, rheobase current, and position of the motoneuron relative to the spinal cord afferent entry were all correlated with EPSP amplitude, but the amplitude difference between homonymous and heteronymous connections remained significant after the statistical removal analysis of covariance (ANCOVA) of the contribution of these variables. Stepwise multiple-regression analysis showed that synaptic identity explained the greatest fraction of the variance in EPSP amplitude (9%), with significant but smaller fractions accounted for by rheobase current or motoneuron conduction velocity. 4. In a separate experiment, the monosynaptic affects from both homonymous and heteronymous single-Ia afferents were examined in each of 88 MG or LG motoneurons. The single-Ia afferents used in this portion of the study were sampled from both MG and LG muscles and selected for similar conduction velocities and spinal cord entry points.(ABSTRACT TRUNCATED AT 250 WORDS)

Spinal Interneurons That Receive Input From Muscle Afferents Are Differentially Modulated by Dorsolateral Descending Systems

2001 ◽  
Vol 85 (2) ◽  
pp. 1005-1008 ◽  
Author(s):  
Daofen Chen ◽  
Renee D. Theiss ◽  
Koji Ebersole ◽  
John F. Miller ◽  
W. Zev Rymer ◽  
...  
Keyword(s):  
Muscle Afferents ◽  
Triceps Surae ◽  
Evoked Responses ◽  
Primary Input ◽  
Spinal Interneurons ◽  
Ia Afferents ◽  
Anomalous Muscle ◽  
Group I ◽  
Cord Injury ◽  
Descending Systems

The possibility that descending systems have differential actions on the spinal interneurons that receive input from muscle afferents was investigated. Prolonged, physiological inputs were generated by stretch of the triceps surae muscles. The resulting firing patterns of 25 lumbosacral interneurons were recorded before and during a reversible cold block of the dorsolateral white matter at the thoracic level in nonparalyzed, decerebrate preparations. The strength of group I muscle afferent input was assessed from the response to sinusoidal tendon vibration, which activated muscle spindle Ia afferents directly and tendon organ Ib afferents via the resulting reflex force. The stretch-evoked responses of interneurons with strong responses to vibration were markedly suppressed by dorsal cold block, whereas the stretch-evoked responses of interneurons with weak vibration input were enhanced. The cells most strongly activated by vibration received their primary input from Ia afferents and all of these cells were inhibited by the cold block. These results suggest that a disruption of the descending system, such as occurs in spinal cord injury, will lead to a suppression of the interneuronal pathways with group Ia input while enhancing excitability within interneuronal pathways transmitting actions from higher threshold afferents. One possible consequence of this suppression would be a decreased activity among the Ia inhibitory interneurons that mediate reciprocal inhibition, resulting in abnormal reciprocal relations between antagonists and promoting anomalous muscle cocontraction.

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