Mammalian muscle spindle: peripheral mechanisms

1990 ◽  
Vol 70 (3) ◽  
pp. 643-663 ◽  
Author(s):  
C. C. Hunt
Keyword(s):  
Muscle Spindle ◽  
Muscle Length ◽  
Quantitative Information ◽  
Gain Compression ◽  
Mammalian Muscle ◽  
Intrafusal Fibers ◽  
Transduction Mechanisms ◽  
Contractile Activation ◽  
Dependent Processes ◽  
Sensory Endings

The responses of sensory endings of the muscle spindle to stretch are produced by transduction in the sensory terminals and by impulse initiation in the sensory axon, both of which appear to be largely linear and non-time-dependent processes. The marked nonlinearity of spindle responses to length, the processes of gain compression, and the aftereffects of fusimotor activity and of stretch appear to reside mainly in the mechanical properties of the intrafusal fibers. Although the basis of the dynamic sensitivity of the primary ending in the passive spindle is still not well understood, dynamic fusimotor effects have been shown to depend on activation of the bag 1 fiber. Static fusimotor actions result from contraction in the bag 2 and/or chain fibers. Certainly, a great deal is known about the muscle spindle at the level of changes in sensory discharge to variations in muscle length and to fusimotor stimulation, although new insights continue to arise from experiments of this type. However, there is a need for further quantitative information that will lead to greater understanding of transduction mechanisms, impulse initiation, and intrafusal fiber contractile activation.

The Mammalian Muscle Spindle

Physiology ◽  
1997 ◽  
Vol 12 (1) ◽  
pp. 37-42 ◽  
Author(s):  
U Proske
Keyword(s):  
Motor Control ◽  
Muscle Spindle ◽  
Muscle Spindles ◽  
Mammalian Muscle ◽  
Intrafusal Fibers ◽  
Sensory Endings

A brief, summarizing description is given of the structure and physiology of the mammalian muscle spindle. The question is addressed, What might be the roles of the three different kinds of intrafusal fibers on which the sensory endings lie? The role of muscle spindles in proprioception and in motor control is discussed.

Two kinds of resting discharge in cat muscle spindles

1991 ◽  
Vol 66 (2) ◽  
pp. 602-612 ◽  
Author(s):  
J. E. Gregory ◽  
D. L. Morgan ◽  
U. Proske
Keyword(s):  
Muscle Length ◽  
Silent Period ◽  
Muscle Spindles ◽  
The Other ◽  
Passive Tension ◽  
Intrafusal Fibers ◽  
Isometric Muscle Contraction ◽  
Discharge Behavior ◽  
Isometric Muscle ◽  
Sensory Endings

1. The behavior of primary endings of cat soleus muscle spindles was studied during shortening steps carried out at different muscle lengths. 2. Spindles were of two kinds: one, silent spindles, whose afferents fell silent after the shortening, at least over part of the range of lengths tested. The second, spontaneous spindles, resumed firing at all lengths. 3. For silent spindles, the duration of the silent period, measured at lengths where they did recover a resting rate, depended directly on muscle length and became shorter at longer lengths. This is what would be expected if the slack introduced in the spindle by the shortening step was removed more rapidly at longer lengths by the higher passive tension. For spontaneous spindles, on the other hand, the duration of the silent period after the shortening was largely independent of muscle length and depended on the spindle's rate of firing immediately before the shortening. 4. At intermediate lengths the discharge of slack spontaneous spindles remained unaffected by an isometric muscle contraction. It was therefore not possible to produce a pause in the discharge, behavior normally taken as typical of spindles. The discharge could be interrupted by the contraction if this was combined with a large shortening movement. 5. It is proposed that when intrafusal fibers are slackened by a shortening step, the resting discharge in spontaneous spindles is generated by a maintained depolarization of the annulospiral ending resulting from extension of the terminal coils by forces from within the receptor. A shortening contraction compresses the spirals to interrupt the discharge. The sensory endings of silent spindles remain below threshold until the spirals have been opened out sufficiently by external stretch.

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.

scholarly journals Electrical and mechanical factors in the adaptation of a mammalian muscle spindle

1960 ◽  
Vol 153 (2) ◽  
pp. 209-217 ◽  
Author(s):  
O. C. J. Lippold ◽  
J. G. Nicholls ◽  
J. W. T. Redfearn
Keyword(s):  
Muscle Spindle ◽  
Mammalian Muscle ◽  
Mechanical Factors

The isolated mammalian muscle spindle

1980 ◽  
Vol 3 (11) ◽  
pp. 258-265 ◽  
Author(s):  
I.A. Boyd
Keyword(s):  
Muscle Spindle ◽  
Mammalian Muscle

scholarly journals Spike Sorting of Muscle Spindle Afferent Nerve Activity Recorded with Thin-Film Intrafascicular Electrodes

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Milan Djilas ◽  
Christine Azevedo-Coste ◽  
David Guiraud ◽  
Ken Yoshida
Keyword(s):  
Thin Film ◽  
Muscle Spindle ◽  
Signal To Noise Ratio ◽  
Muscle Length ◽  
Detection Scheme ◽  
Threshold Detection ◽  
Complex Wavelets ◽  
Intrafascicular Electrodes ◽  
Stimulation System

Afferent muscle spindle activity in response to passive muscle stretch was recorded in vivo using thin-film longitudinal intrafascicular electrodes. A neural spike detection and classification scheme was developed for the purpose of separating activity of primary and secondary muscle spindle afferents. The algorithm is based on the multiscale continuous wavelet transform using complex wavelets. The detection scheme outperforms the commonly used threshold detection, especially with recordings having low signal-to-noise ratio. Results of classification of units indicate that the developed classifier is able to isolate activity having linear relationship with muscle length, which is a step towards online model-based estimation of muscle length that can be used in a closed-loop functional electrical stimulation system with natural sensory feedback.

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