Impulse rates and sensitivity to stretch of soleus muscle spindle afferent fibers during locomotion in premammillary cats

1985 ◽  
Vol 53 (2) ◽  
pp. 341-360 ◽  
Author(s):  
J. Taylor ◽  
R. B. Stein ◽  
P. R. Murphy
Keyword(s):  
Muscle Spindle ◽  
Soleus Muscle ◽  
Muscle Afferents ◽  
Emg Activity ◽  
Step Cycle ◽  
Muscle Spindle Afferents ◽  
Large Length ◽  
Length Changes ◽  
Stretch Sensitivity ◽  
Stimulation Of

Impulse from soleus muscle afferents were recorded in premammillary cats that were walking on a treadmill. In normal walking the effects of gamma-motoneurons on impulse rates of muscle spindle afferents are confounded by the effects of the large length changes that occur. To isolate the effects of gamma-motoneurons the leg was fixed in place for recording and denervated except for soleus muscle. Because gamma-motoneurons produce marked effects on the stretch sensitivity of muscle afferents, soleus muscle was oscillated about a present length so the stretch sensitivity of its afferents could be determined. The impulse rate of secondary muscle spindle afferents in soleus muscle was generally increased at all phases of the step cycle. The mean rate approximately doubled during walking (82 imp/s), compared with nonwalking (rest) periods (44 imp/s). The sensitivity to sinusoidal length changes was generally reduced throughout the step cycle (mean reduction = 33%). Primary muscle spindle afferents also showed an increased mean rate during walking (47 imp/s) compared with rest (24 imp/s). The impulse rate peaked after the muscle reached its maximum force and often showed a second peak before the maximum electromyogram (EMG) activity. The sensitivity to sinusoidal stretches varied cyclically during locomotion. During the extension phase it sometimes exceeded the resting value, but was greatly reduced during the flexion phase (mean reduction = 49% over whole cycle). Control experiments were carried out in which static and dynamic gamma-motoneurons were stimulated and activity from muscle spindle afferents was recorded in anesthetized cats. With the amplitude and frequency of stretch applied, stimulation of dynamic gamma-motoneurons usually increased and stimulation of static gamma-motoneurons usually decreased the sensitivity of primary muscle spindle afferents to sinusoidal stretch. The patterns observed in muscle spindle afferents suggest a strong, maintained activation of static gamma-motoneurons throughout the step cycle and a phasic activation of dynamic gamma-motoneurons, which is consistent with previous direct recordings from gamma-motoneurons. With this pattern of activating gamma-motoneurons, the secondary muscle spindle afferents will provide a good feedback signal of the large length changes that normally occur in the muscle during locomotion. The changes in sensitivity of primary muscle spindle afferents will complement central changes so the gain of the stretch reflex from extensors is high during extension (when required to help support the weight of the body) and low during flexion (when a high gain would be counterproductive).

Activity patterns in individual hindlimb primary and secondary muscle spindle afferents during normal movements in unrestrained cats

1979 ◽  
Vol 42 (2) ◽  
pp. 420-440 ◽  
Author(s):  
G. E. Loeb ◽  
J. Duysens
Keyword(s):  
Muscle Spindle ◽  
Activity Patterns ◽  
Muscle Length ◽  
Muscle Spindle Afferents ◽  
General Observation ◽  
Postural Changes ◽  
Motor Activities ◽  
Specific Muscle ◽  
Length Changes ◽  
Rapid Modulation

1. Chronically implanted microelectrode wires in the L7 and S1 dorsal root ganglia were used to record unit activity from cat hindlimb primary and secondary muscle spindle afferents. Units could be reliably recorded for several days, permitting comparison of their activity with homonymous muscle EMG and length during a variety of normal, unrestrained movements. 2. The general observation was that among both primary and secondary endings there was a broad range of different patterns of activity depending on the type of muscle involved and the type of movement performed. 3. During walking, the activity of a given spindle primary was usually consistent among similar step cycles. However, the activity was usually poorly correlated with absolute muscle length, apparently unrealted to velocity of muscle stretch, and could change markedly for similar movements performed under different conditions. 4. Spindle activity modulation not apparently related to muscle length changes was assumed to be influenced by fusimotor activity. In certain muscles, this presumption leads to the conclusion that gamma-motoneurons may be activated out of phase with homonymous alpha-motoneurons as well as by more conventional alpha-gamma-motoneuron coactivation. 5. Simultaneous recordings of two spindle primary afferents from extensor digitorum longus indicated that spindles within the same muscle may differ considerably with respect to this presumed gamma-motoneuron drive. 6. Spindle secondary endings appeared to be predominantly passive indicators of muscle length during walking, but could demonstrate apparently strong fusimotor modulation during other motor activities such as postural changes and paw shaking. 7. Both primary and secondary endings were observed to undergo very rapid modulation of firing rates in response to presumed reflexly induced intrafusal contractions. 8. It is suggested that the pattern of fusimotor control of spindles may be tailored to the specific muscle and task being performed, rather than necessarily dominated by rigid alpha-gamma coactivation.

Responses of cat peroneus brevis muscle spindle afferents during recovery from nerve-crush injury

1983 ◽  
Vol 50 (2) ◽  
pp. 344-357 ◽  
Author(s):  
D. Hyde ◽  
J. J. Scott
Keyword(s):  
Muscle Spindle ◽  
Common Peroneal Nerve ◽  
Firing Frequency ◽  
Muscle Spindle Afferents ◽  
Nerve Crush ◽  
Firing Rates ◽  
The Common ◽  
Peroneus Brevis ◽  
Nerve Crush Injury ◽  
Stimulation Of

The responses of regenerated muscle spindle afferents to ramp-and-hold stretch of the peroneus brevis muscle in the cat were recorded at periods from 26 to 140 days after crushing the common peroneal nerve. During the early stages of recovery a number of abnormally responding afferents were observed. The most marked abnormality was the absence or rapid failure of firing during the held phase of the stretch. The proportion of abnormal afferents became less as recovery progressed. Electrical stimulation of isolated static and dynamic gamma-axons increased the firing rates of the afferents during the ramp-and-hold stretch such that a gamma static axon would restore the response of an abnormal afferent to the held phase of the stretch. The regenerated afferents have been classified according to the degree of abnormality displayed. These abnormalities can be accounted for by assuming a subtractive reduction in the firing frequency of the regenerated afferents. This is attributed to an increase in the pacemaker threshold.

Coordinated Interlimb Compensatory Responses to Electrical Stimulation of Cutaneous Nerves in the Hand and Foot During Walking

2003 ◽  
Vol 90 (5) ◽  
pp. 2850-2861 ◽  
Author(s):  
Carlos Haridas ◽  
E. Paul Zehr
Keyword(s):  
Electrical Stimulation ◽  
Motor Coordination ◽  
The Body ◽  
Emg Activity ◽  
Motor Tasks ◽  
Step Cycle ◽  
Reflex Responses ◽  
Cutaneous Reflex ◽  
Reflex Pathways ◽  
Stimulation Of

It has been shown that stimulation of cutaneous nerves innervating the hand (superficial radial, SR) and foot (superficial peroneal, SP) elicit widespread reflex responses in many muscles across the body. These interlimb reflex responses were suggested to be functionally relevant to assist in motor coordination between the arms and legs during motor tasks such as walking. The experiments described in this paper were conducted to test the hypothesis that interlimb reflexes were phase-dependently modulated and produced functional kinematic changes during locomotion. Subjects walked on a treadmill while electromyographic (EMG) activity was collected continuously from all four limbs, and kinematic recordings were made of angular changes across the ankle, knee, elbow, and shoulder joints. Cutaneous reflexes were evoked by delivering trains of electrical stimulation pseudorandomly to the SP nerve or SR nerves in separate trials. Reflexes were phase-averaged according to the time of occurrence in the step cycle, and phasic amplitudes and latencies were calculated. For both nerves, significant phase-dependent modulation (including reflex reversals) of interlimb cutaneous reflex responses was seen in most muscles studied. Both SR and SP nerve stimulation resulted in significant alteration in ankle joint kinematics. The results suggest coordinated and functionally relevant reflex pathways from the SP and SR nerves onto motoneurons innervating muscles in nonstimulated limbs during walking, thus extending observations from the cat to that of the bipedal human.

Dynamic response of human muscle spindle afferents to stretch

1990 ◽  
Vol 63 (6) ◽  
pp. 1297-1306 ◽  
Author(s):  
B. B. Edin ◽  
A. B. Vallbo
Keyword(s):  
Dynamic Response ◽  
Muscle Spindle ◽  
Human Subjects ◽  
Muscle Afferents ◽  
Human Muscle ◽  
Golgi Tendon Organ ◽  
Muscle Spindle Afferents ◽  
Partial Data ◽  
Extensor Muscles ◽  
Tendon Organ

1. One hundred and twenty-four muscle afferents from the finger extensor muscles were recorded from the radial nerve in human subjects. 2. The afferents were provisionally classified as muscle spindle primary (78/124) and secondary afferents (25/124), and Golgi tendon organ afferents (21/124), on the basis of their response to 1) maximal twitch contractions, 2) 20- and 50-Hz sinusoids superimposed on ramp-and-hold stretches, 3) stretch sensitization, and 4) isometric contractions and sudden relaxations. 3. Ramp-and-hold stretches at two velocities, 10 and 50 degrees/s, were applied to the appropriate metacarpophalangeal (MCP) joint while the parent muscle remained relaxed. For each unit three discrete parameters were assessed: the presence or absence of 1) an initial burst at the commencement of the ramp stretch, 2) a deceleration response at the beginning of the hold phase, and 3) a prompt silencing at muscle shortening. In addition, two kinds of dynamic indexes were calculated for 79 of the muscle spindle afferents. 4. Most spindle afferents responded readily to stretch, whereas the Golgi tendon organ afferents produced very poor stretch responses. All of them lacked a static response, whereas the dynamic response, when present at all, consisted of only a few impulses. 5. The dynamic index was higher for spindle primaries than for secondaries, and this difference was statistically significant although the distribution was unimodal for spindle afferents as a group. Hence, this parameter was a poor discriminator. 6. Initial bursts, deceleration responses, and silences during imposed shortening were more common in spindle primaries than in secondaries. The differences were significant in all these respects. 7. The three discrete parameters were statistically pairwise independent for the spindle afferents, justifying the combination of the three into a useful battery for discrimination between primary and secondary spindle afferents and the use of this battery as a partial data base for a probability approach towards a solid classification of human muscle afferents.

Synaptic transmission from muscle afferents during fictive locomotion in the mesencephalic cat

1984 ◽  
Vol 51 (5) ◽  
pp. 986-997 ◽  
Author(s):  
S. J. Shefchyk ◽  
R. B. Stein ◽  
L. M. Jordan
Keyword(s):  
Muscle Afferents ◽  
Monosynaptic Reflex ◽  
Fictive Locomotion ◽  
Step Cycle ◽  
Postsynaptic Potentials ◽  
Inhibitory Postsynaptic Potentials ◽  
Ankle Muscles ◽  
Low Threshold ◽  
Second Peak ◽  
Stimulation Of

Modulation of synaptic potentials produced by electrical stimulation of low-threshold muscle afferents in lumbar alpha-motoneurons innervating knee and ankle muscles was studied by intracellular recording during "fictive locomotion" induced by stimulating the mesencephalic locomotor region (MLR) in paralyzed, mesencephalic cats. Averaging postsynaptic potentials in different phases of the fictive step cycle indicated that relatively little amplitude modulation occurred. In nearly half of the 38 motoneurons analyzed, there was a statistically significant tendency for excitatory postsynaptic potentials (EPSPs) to increase in amplitude during the depolarized phase of the oscillation in the membrane potential produced during fictive locomotion (locomotor-drive potential). In 8% the EPSPs decreased under the same conditions, while the rest displayed a constant amplitude during all phases of the fictive step cycle. Only three cells showed a distinct second peak in the EPSP at a latency consistent with transmission in a di- or trisynaptic pathway. Late inhibitory postsynaptic potentials (IPSPs) were also rarely observed. Thus oligosynaptic pathways from muscle afferents to the motoneuron groups studied are not prominent during the locomotor cycle in this preparation. We suggest that the marked modulation of monosynaptic reflex amplitude observed in mesencephalic cats (1) arises mainly from the effects of the locomotor-drive potential in bringing the cells closer to threshold during some phases of locomotion. Specific modulation during fictive locomotion of transmission in pathways from muscle afferents, which has been demonstrated for cutaneous pathways (28), was not observed. The implications of these results for the control of locomotion are discussed briefly.

Modulation of ipsi- and contralateral reflex responses in unrestrained walking cats

1980 ◽  
Vol 44 (5) ◽  
pp. 1024-1037 ◽  
Author(s):  
J. Duysens ◽  
G. E. Loeb
Keyword(s):  
Emg Activity ◽  
Strict Sense ◽  
Skin Area ◽  
Step Cycle ◽  
Reflex Responses ◽  
Plantar Surface ◽  
Electrical Shocks ◽  
Excitatory Responses ◽  
Flexor Digitorum ◽  
Stimulation Of

1. The modulation of reflex responses in up to 10 simultaneously recorded hindlimb muscles was studied in unrestrained cats walking on a treadmill. Single electrical shocks of various strengths were applied to different skin areas of teh hindlimb at different times of the step cycle while the resulting EMG responses were sampled and analyzed. 2. Two excitatory response peaks (P1 and P2) at a latency of about 10 and 25 ms, respectively, were seen in all flexors examined (sartorius, semitendinosus, tibialis anterior, extensor digitorum longus). Stimulation of most skin areas was effective but responses were most easily obtained from stimuli applied to the foot or ankle. During the step cycle there was a marked modulation of the amplitudes of the responses, especially the P2 responses, which grew larger toward the end of stance when a maximum was reached, followed by a steady decline throughout swing. This pattern was very similar for various flexors, although these muscles differed considerably in their normal EMG activity pattern during walking. 3. Flexor responses were absent when the same stimuli were applied during the early stance phase. Instead, inhibition of the ongoing EMG activity was seen at a latency of 10 ms or less in all extensors examined (semimembranosus, quadriceps, soleus, gastrocnemius medialis, flexor digitorum longus). The inhibition was followed by a late excitatory peak (P3) at about 35-ms latency in all extensors except soleus. 4. Certain stimulation sites yielded exceptions to the above patterns. Stimulation of the skin area innervated by the sural nerve yielded larger and earlier MG excitatory responses as compared to stimulation of other skin areas. Activation of the plantar surface of the foot often failed to elicit P2 responses in the hip flexor sartorius, which showed inhibition instead. 5. In the hindlimb contralateral to the stimulus, excitatory responses occurred both in flexors and extensors at a latency of 20-25 ms. The pattern of modulation of these responses was similar to the ipsilateral modulation of P2 flexor and P3 extensor responses. Soleus failed to show a crossed response. 6. The data indicate that flexor and extensor responses differ both with respect to their latency and to their correlation with the ongoing EMG reactivity. It is concluded that these stimuli do not demonstrate reflex reversal in the strict sense in the normal walking cat but that there is modulation of transmission in a flexor excitatory and extensor inhibitory pathway, possibly by the flexor part of the spinal locomotor oscillator. In addition, there are some specialized flexor inhibitory and extensor excitatory pathways. The slow soleus muscle does not seem to be excited through these pathways.

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