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.

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.

Active force and sensory response of single isolated cat muscle spindles in vitro

1984 ◽  
Vol 52 (6) ◽  
pp. 1131-1139 ◽  
Author(s):  
Y. Fukami
Keyword(s):  
Discharge Rate ◽  
Muscle Spindles ◽  
Sensory Response ◽  
Cross Sectional ◽  
Tetanic Force ◽  
Intrafusal Fibers ◽  
Nuclear Chain ◽  
Tetanic Tension ◽  
Sensory Endings

Active tetanic tension developed by stimulation of a nerve innervating single isolated muscle spindles of the cat was measured. The maximum tetanic force varied among spindles, ranging from 2.3 to 8.5 mg. For four spindles, the maximum tetanic force was converted into the force per unit cross-sectional area of nuclear chain and nuclear bag fibers. The results are discussed in terms of structural and functional complexities of the intrafusal fibers. The length-tension diagram of single isolated spindles showed maximum tetanic tension occurring at a spindle length longer than 1o, which was defined as the length beyond which passive tension starts to develop. This result, which appears to be different from the corresponding diagram for extrafusal muscle, is discussed in relation to the existing reports on the mechanical properties of intrafusal fibers. Spindle sensory response vs. tetanic tension was analyzed for single isolated spindles with two independent nerve supplies, one containing sensory and the other containing fusimotor axons. The results suggest that the static discharge rate of sensory endings may be linearly related, within the range examined, to the tetanic plateau tension of intrafusal fibers.

The role of muscle spindles in constraining motor control

2002 ◽  
Vol 44-46 ◽  
pp. 943-949 ◽  
Author(s):  
Bjørn Gilbert Nielsen
Keyword(s):  
Motor Control ◽  
Muscle Spindles

scholarly journals Role of muscle spindle feedback in regulating muscle activity strength during walking at different speed in mice

2018 ◽  
Vol 120 (5) ◽  
pp. 2484-2497 ◽  
Author(s):  
William P. Mayer ◽  
Andrew J. Murray ◽  
Susan Brenner-Morton ◽  
Thomas M. Jessell ◽  
Warren G. Tourtellotte ◽  
...  
Keyword(s):  
Muscle Spindle ◽  
Amplitude Modulation ◽  
Muscle Activity ◽  
Sensory Feedback ◽  
Walking Speed ◽  
Muscle Spindles ◽  
Afferent Feedback ◽  
Triceps Surae ◽  
Extensor Muscles

Terrestrial animals increase their walking speed by increasing the activity of the extensor muscles. However, the mechanism underlying how this speed-dependent amplitude modulation is achieved remains obscure. Previous studies have shown that group Ib afferent feedback from Golgi tendon organs that signal force is one of the major regulators of the strength of muscle activity during walking in cats and humans. In contrast, the contribution of group Ia/II afferent feedback from muscle spindle stretch receptors that signal angular displacement of leg joints is unclear. Some studies indicate that group II afferent feedback may be important for amplitude regulation in humans, but the role of muscle spindle feedback in regulation of muscle activity strength in quadrupedal animals is very poorly understood. To examine the role of feedback from muscle spindles, we combined in vivo electrophysiology and motion analysis with mouse genetics and gene delivery with adeno-associated virus. We provide evidence that proprioceptive sensory feedback from muscle spindles is important for the regulation of the muscle activity strength and speed-dependent amplitude modulation. Furthermore, our data suggest that feedback from the muscle spindles of the ankle extensor muscles, the triceps surae, is the main source for this mechanism. In contrast, muscle spindle feedback from the knee extensor muscles, the quadriceps femoris, has no influence on speed-dependent amplitude modulation. We provide evidence that proprioceptive feedback from ankle extensor muscles is critical for regulating muscle activity strength as gait speed increases. NEW & NOTEWORTHY Animals upregulate the activity of extensor muscles to increase their walking speed, but the mechanism behind this is not known. We show that this speed-dependent amplitude modulation requires proprioceptive sensory feedback from muscle spindles of ankle extensor muscle. In the absence of muscle spindle feedback, animals cannot walk at higher speeds as they can when muscle spindle feedback is present.

scholarly journals A HISTOCHEMICAL INVESTIGATION OF INTRAFUSAL FIBERS IN TORTOISE MUSCLE SPINDLES

1972 ◽  
Vol 20 (3) ◽  
pp. 200-204 ◽  
Author(s):  
ALAN CROWE ◽  
ABDUL H.M.F. RAGAB
Keyword(s):  
Propylene Glycol ◽  
Muscle Spindle ◽  
Succinic Dehydrogenase ◽  
Muscle Spindles ◽  
Histochemical Investigation ◽  
Intrafusal Muscle ◽  
Intrafusal Fibers ◽  
Intrafusal Muscle Fibers ◽  
Extensor Digitorum Brevis ◽  
Intrafusal Muscle Fiber

Histochemical investigations upon intrafusal muscle fibers of spindles in the extensor digitorum brevis 1 muscle of the tortoise have been carried out. The localization of phosphorylase, succinic dehydrogenase and adenosine activities together with the demonstration of lipids by the propylene glycol-Sudan method all failed to produce results which could be used to categorize the intrafusal fibers into more than one type. From these results and from previous histologic investigations it is suggested that the tortoise muscle spindle contains just one kind of intrafusal muscle fiber.

scholarly journals The role of muscle spindles in the development of the monosynaptic stretch reflex

2012 ◽  
Vol 108 (1) ◽  
pp. 83-90 ◽  
Author(s):  
Zhi Wang ◽  
LingYing Li ◽  
Eric Frank
Keyword(s):  
Muscle Fibers ◽  
Muscle Spindles ◽  
Synaptic Connections ◽  
Intrafusal Muscle ◽  
Intrafusal Fibers ◽  
Sensory Axons ◽  
Neurotrophin 3 ◽  
Erbb2 Receptor ◽  
Intrafusal Muscle Fibers

Muscle sensory axons induce the development of specialized intrafusal muscle fibers in muscle spindles during development, but the role that the intrafusal fibers may play in the development of the central projections of these Ia sensory axons is unclear. In the present study, we assessed the influence of intrafusal fibers in muscle spindles on the formation of monosynaptic connections between Ia (muscle spindle) sensory axons and motoneurons (MNs) using two transgenic strains of mice. Deletion of the ErbB2 receptor from developing myotubes disrupts the formation of intrafusal muscle fibers and causes a nearly complete absence of functional synaptic connections between Ia axons and MNs. Monosynaptic connectivity can be fully restored by postnatal administration of neurotrophin-3 (NT-3), and the synaptic connections in NT-3-treated mice are as specific as in wild-type mice. Deletion of the Egr3 transcription factor also impairs the development of intrafusal muscle fibers and disrupts synaptic connectivity between Ia axons and MNs. Postnatal injections of NT-3 restore the normal strengths and specificity of Ia–motoneuronal connections in these mice as well. Severe deficits in intrafusal fiber development, therefore, do not disrupt the establishment of normal, selective patterns of connections between Ia axons and MNs, although these connections require the presence of NT-3, normally supplied by intrafusal fibers, to be functional.

Impulse initiation in the mammalian muscle spindle during combined fusimotor stimulation and succinyl choline infusion

1996 ◽  
Vol 75 (4) ◽  
pp. 1703-1713 ◽  
Author(s):  
R. W. Carr ◽  
D. L. Morgan ◽  
U. Proske
Keyword(s):  
Muscle Spindles ◽  
Functional Independence ◽  
Steady Increase ◽  
Succinyl Choline ◽  
Intrafusal Fiber ◽  
Mammalian Muscle ◽  
Intrafusal Fibers ◽  
Gamma S ◽  
Root Stimulation ◽  
Stimulation Of

1. This is a report of observations on the responses of the primary and secondary endings of soleus muscle spindles of the anesthetized cat to the combined effects of the depolarizing neuromuscular blocker succinyl choline (SCh), given intravenously, and fusimotor stimulation. The findings were interpreted in terms of a dual pacemaker model for activity generated in the bag1 intrafusal fiber interacting with activity coming from bag2 and chain fibers. 2. In preliminary experiments it was found, using whole ventral root stimulation at fusimotor strength, that spindle responses to fusimotor stimulation were not blocked by SCh, whereas extrafusal junctions blocked rapidly. In the presence of SCh, fusimotor responses of spindle secondary endings were, on average, slightly larger than their control values before SCh was given, whereas fusimotor responses of primary endings were slightly smaller. 3. A study of the responses of spindle primary endings to stimulation of single dynamic (gamma D) and static (gamma S) axons in the presence of SCh revealed a fundamental difference in behavior. None of the responses to stimulation of gamma D axons (9 gamma D axons with 8 primary endings) showed significant summation with the responses to SCh. By contrast, the 20 gamma S axons studied showed varying degrees of summation with the responses to SCh. The responses of secondary endings to gamma S stimulation in the presence of SCh resembled those of primary endings and gamma S stimulation. 4. To explain these differences it is proposed that the primary ending has two separate sites of impulse initiation, one close to terminals on the bag1 intrafusal fiber (innervated by gamma D axons) and a second close to terminals on the bag2 and chain fibers (innervated by gamma S axons). It is proposed that the maintained increase in spindle firing observed during SCh infusion is the result of a bag2 contracture. The response to gamma S stimulation, contracting bag2 and chain fibers, adds to the SCh response. The degree of summation varies depending on whether the gamma S activates bag2 fibers, chain fibers, or both. The bag1 contracture, together with the effects of gamma D stimulation, acts through a separate pacemaker and therefore does not sum with the steady increase in spindle firing in the presence of SCh. There may be pacemaker switching between the bag1 generator and the bag2 and chain generator. 5. If the model is representative of most spindles containing the three kinds of intrafusal fibers, and the contractions of bag2 and chain fibers generate activity through a common impulse generator, then this bears on the question of the functional independence of the bag2 and chain fiber systems.

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.

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