Effects of chlorobutanol on primary and secondary endings of isolated cat muscle spindles

The effects of the preservative chlorobutanol on primary and secondary endings of muscle spindles isolated from the tenuissimus muscle of the cat were investigated in this study. Chlorobutanol was applied to the bathing solution in final concentrations of between 10 and 100 microg/ml. It induced a reversible and dose dependent decrease in the discharge frequency of both types of ending without any visible length change in the sensory region of the receptor. The initial activity, the peak dynamic discharge, the maximum static discharge value and the final static discharge value were evaluated from an ending's discharge pattern obtained during ramp-and-hold stretches. These four basic discharge frequencies decreased in parallel with increasing concentrations of chlorobutanol. Their sensitivities to chlorobutanol were similar (mean values: -0.11 to -0.29 imp/s per microg/ml chlorobutanol) and were independent of the amplitude of stretch. The dynamic response and the static response of both primary and secondary endings remained unchanged, indicating that the sensitivity of the spindle to stretch was not influenced by chlorobutanol. Chlorobutanol also reduced the discharge activity of the muscle spindle afferents during sinusoidal stretches. The amplitude of the receptor potential (AC component) remained unchanged under chlorobutanol. With the available recording technique it was not possible to measure slow shifts of the membrane potential. However, a hyperpolarization of the ending's membrane might explain why the afferent discharge frequency is reduced by chlorobutanol. The calcium dynamics of the spindle do not appear to be altered by CB, as the effect exerted on the afferent discharge by a change in the extracellular calcium concentration and a blockage of calcium channels was different from the CB effect. As the inhibitory effect of CB was reduced by ouabain, it is possible that CB activates the electrogenic Na/K pump or affects a mechanism that is closely related to the activity of the pump. The properties of the axonal membrane appear not to be altered, as chlorobutanol did not change the shape of action potentials.     

Effects of slow muscle stretch on the responses of primary and secondary endings to small amplitude periodic stretches in de-efferented soleus muscle spindles

The responses of primary and secondary endings of de-efferented soleus spindles to small amplitude periodic stretches superimposed on slow ramp stretches have been studied. For primary endings, the responses become progressively larger especially during the last period of the ramp whereas for secondary endings, after an initial period of moderate growth, the amplitude of the responses display a relative reduction precisely when the responses of the primary endings are the largest. These differences can be interpreted in terms of progressive increase in stiffness of the striated polar portions of the intrafusal muscle fibers.     

Attenuated dynamic responses of primary endings of muscle spindles: a basis for depressed tendon responses in acrylamide neuropathy.

Depressed or lost tendon reflexes commonly observed in patients with peripheral neuropathies may result partly from attenuation of the dynamic discharge from the primary endings of muscle spindles. This possibility was investigated in cats with an experimental neuropathy induced with acrylamide (30 mg/kg/day intramuscularly). Achilles tendon reflexes and the dynamic discharge from primary muscle spindles were evaluated after five or ten injections of acrylamide. After five injections the animals were moderately impaired neurologically, the Achilles tendon reflex was difficult to elicit in 2 of 5 animals, and the dynamic responses of primary endings of soleus muscle spindles to stretch were depressed. Following ten injections of acrylamide the cats were severely impaired neurologically; tendon responses were either absent or difficult to elicit, and the dynamic responses of their muscle spindles to stretch were reduced by 50% (p less than 0.01). Additionally, the spindels responded to stretch with only 20 to 30% the normal number of afferent impulses. These data suggest that lost tendon responses in acrylamide neuropathy result in part from inadequate activation of motoneurons by spindle afferent discharge.     

Effects of calcium on the discharge pattern of primary and secondary endings of isolated cat muscle spindles recorded under a ramp-and-hold stretch

The impulse activity of muscle spindles isolated from the cat tenuissimus muscle was investigated under varying concentrations of external calcium (Ca(2+)). The outer capsule of the muscle spindle represents an effective diffusion barrier for Ca(2+) ions since activity changes were strong and rapid only if the capsule was partly removed from the sensory region of the receptor. The impulse activity of both primary and secondary muscle spindle endings was lowered by an increase in the external Ca(2+) concentration from 1.8 mM (normal Ringer's solution) to 2.7 mM and raised by a decrease in the Ca(2+) concentration from 1.8 to 0.9 mM. Primary endings were generally more strongly affected than secondary endings. With primary endings the firing rate changed by 23-52% when the external Ca(2+) concentration was altered by 0.9 mM. With secondary endings the discharge frequency changed by 15-24%. The afferent discharge patterns were obtained under repetitive ramp-and-hold stretches and were analyzed with regard to influences of external Ca(2+) ions on the static and dynamic components of the endings' responses. The stretch sensitivity and the adaptive response of both types of ending increased in the low Ca(2+) solution and decreased in the high Ca(2+) solution, but a specific effect on a single component of the responses to stretch was not observed. These findings indicate an overall change in excitability when the external Ca(2+) concentration was varied. The mechanical properties of the receptor were probably not affected since changes in the Ca(2+) concentration did not elicit a contraction or relaxation of the intrafusal muscle fibers. On the one hand, the observed effects can be explained according to the surface potential theory by an indirect influence of extracellular Ca(2+) ions on ion channels of the sensory nerve terminals, with Ca(2+) ions binding to negative charged sites at the endings' outer membrane. On the other hand, the results are consistent with the supposition that Ca(2+) ions act directly on ion channels of the sensory membrane of muscle spindle endings.     

Vibration sensitivity of human muscle spindles and Golgi tendon organs

The responses of the various muscle receptors to vibration are more complicated than a naïve categorization into stretch (muscle spindle primary ending), length (muscle spindle secondary endings), and tension (Golgi tendon organs) receptors. To emphasize the similarity of responses to small length changes, we recorded from 58 individual muscle afferents subserving receptors in the ankle or toe dorsiflexors of awake human subjects (32 primary endings, 20 secondary endings, and six Golgi tendon organs). Transverse sinusoidal vibration was applied to the distal tendon of the receptor‐bearing muscle, while subjects either remained completely relaxed or maintained a weak isometric contraction of the appropriate muscle. In relaxed muscle, few units responded in a 1:1 manner to vibration, and there was no evidence of a preferred frequency of activation. In active muscle the response profiles of all three receptor types overlapped, with no significant difference in threshold between receptor types. These results emphasize that when intramuscular tension increases during a voluntary contraction, Golgi tendon organs and muscle spindle secondary endings, not just muscle spindle primary endings, can effectively encode small imposed length changes. Muscle Nerve, 2007     

Ultrastructural study of motor endings on long chain intrafusal fibers in muscle spindles of the cat

Five complete poles of long nuclear chain intrafusal fibers of cat tenuissimus muscle spindles embedded in a plastic medium were cut in serial, 1 micron thick transverse sections and stained with toluidine blue. Each fiber pole displayed one plate-type motor ending positioned outside the encapsulated part of the spindle. Ultrastructurally, the endings resembled extrafusal end-plates and were more complex, in terms of prominence of sole-plate and degree of post-junctional folding, than any other motor ending present in the spindles. They were identified as the terminals of static (fast) skeletofusimotor axons, which preferentially innervate the longest nuclear chain fibers of cat spindles.     

Static and dynamic fusimotor action on the response of spindle primary endings to sinusoidal stretches in the cat

In anaesthetized cats, the discharge of single spindle primary endings of flexor and extensor muscles was studied during sinusoidal stretches of the muscle (3–4 mm peak-to-peak, 1–5 Hz). In the response to each stretch, two main components could be distinguished; they were related respectively to the speed and to the amplitude of lengthening. By analogy with the usual definitions of the ‘dynamic index’ (d) and ‘position sensitivity’ (s) during ramp stretches of the same amplitude at a velocity of 35–60 mm/sec, a ‘sinusoidal dynamic index’ (D) and a ‘sinusoidal position sensitivity’ (S) were defined. Stimulation of dynamic fusimotor fibres increased D and d, S and s, while stimulation of static fusimotor fibres decreased D and d and had a less consistent effect on S and s. The total frequency variation during a sinusoidal stretch was always increased by a dynamic fusimotor action while it could be either decreased or increased by a static fusimotor action, depending on the stretch frequency and on the rate of fusimotor stimulation. These results were obtained in various muscles, without any significant difference related to their flexor or extensor function. It is concluded that in order to identify a fusimotor effect as static or dynamic during sinusoidal muscle stretch, it is necessary to use, as here, stretch parameters which elicit a dynamic component in the primary afferent response.     

人三角肌肌梭分布的研究

目的:揭示三角肌的肌梭分布,为相关临床应用提供较详尽的形态学资料.方法:①用经甲醛固定1年以内的童尸3具(3～10a)及成人尸体2具(25a,40a),完整取下三角肌,采用Sihler's肌内神经染色法染色其肌内神经.②用经甲醛固定2年以上的童尸5具(2～11a),在三角肌前亚部、中、后亚部取材,组织学HE染色后,采用体视学方法进行肌梭密度的研究.结果:①三角肌中亚部的肌内神经分支较为丰富.②三角肌的肌梭指数为38.02个/g,肌梭联合体比例为13.31%.三角肌中亚部的肌梭密度和肌梭联合体比例与三角肌前、后亚部相比较,有统计学意义(P＜0.05).中亚部肌腹中部远端的肌梭密度与其近端相比较,无显著差异.前亚部的肌梭密度与后亚部相比较,无明显差异.结论:人三角肌三个亚部的肌梭密度不同.三角肌中亚部的肌梭密度和肌梭联合体比例大于前、后两个亚部,提示其在肩关节运动的监测和姿势调节中起着重要的作用.对该肌进行活检或病理检查取材研究时应当考虑区分亚部或深浅区.     

人三角肌肌梭分布的研究

目的 :揭示三角肌的肌梭分布 ,为相关临床应用提供较详尽的形态学资料。 方法 :①用经甲醛固定 1年以内的童尸 3具 (3～ 10a)及成人尸体 2具 (2 5a,4 0a) ,完整取下三角肌 ,采用Sihler’s肌内神经染色法染色其肌内神经。②用经甲醛固定 2年以上的童尸 5具 (2～ 11a) ,在三角肌前亚部、中、后亚部取材 ,组织学HE染色后 ,采用体视学方法进行肌梭密度的研究。 结果 :①三角肌中亚部的肌内神经分支较为丰富。②三角肌的肌梭指数为38.0 2个 / g ,肌梭联合体比例为 13.31%。三角肌中亚部的肌梭密度和肌梭联合体比例与三角肌前、后亚部相比较 ,有统计学意义 (P 0 .0 5 )。中亚部肌腹中部远端的肌梭密度与其近端相比较 ,无显著差异。前亚部的肌梭密度与后亚部相比较 ,无明显差异。结论 :人三角肌三个亚部的肌梭密度不同。三角肌中亚部的肌梭密度和肌梭联合体比例大于前、后两个亚部 ,提示其在肩关节运动的监测和姿势调节中起着重要的作用。对该肌进行活检或病理检查取材研究时应当考虑区分亚部或深浅区。     

Microvasculature of rabbit muscle spindles.

The microvasculature of the muscle spindle and its relationship to the microcirculation of teniussimus extrafusal muscle is described. Muscle spindles lie in close proximity and parallel to the central artery, vein, and nerve. The arterioles to spindle capillaries are third to fourth order branches of the central artery, whereas most arterioles to extrafusal capillaries are sixth to eighth order. Two or three capillaries enter each spindle. At least one entry consistently was encountered in the equatorial area near the sensory endings. Branches of intrafusal capillaries run longitudinally, anastomose with each other, and cradle the sensory zone in a longitudinal capillary loop. Capillaries in muscle spindles are larger than those in extrafusal muscle. These characteristic features are presumed to enhance the capability of these capillaries to provide sufficient circulation to the spindle, particularly to the region of the sensory endings.     

Comparisons in the structure of avian muscle spindles

A study of muscle spindles in several species of birds was made to determine if avian intrafusal (IF) fibes are separable into the nuclear bag and chain fiber types found in mammals, and whether prominent differences in spindle structure might exist among species. Van Gieson-stained serial sections of the sartorius, a flexor muscle, and the antigravity adductor profundus muscle were examined in the chicken, quail, pigeon and canary. Avian IF fibers did not exhibit the pronounced “bag” of nuclei characteristic of mammalian nuclear-bag fibers, although the non-striated region at mid-length was marked by a moderate excess of eccentric, vesicular nuclei. No consistent differentiation in pattern of nuclear aggregation or manner of fiber termination among fibers of a spindle was detected, nor was there unequivocal bimodality in cross-sectional areas. These characteristics in bird spindles, therefore, do not afford trustworthy criteria for separation of types of IF fibers. The number of spindles per unit volume was particularly high in the canary and lowest in the chicken muscles. Spindles in the chicken were larger and more complex than canary spindles in respect to numbers of fibes per spindle, spindle length, and cross-sectional area of intrafusal fibers at the equator. Values for the quail and pigeon ocupied an intermediate position. Relation of the differences in spindle structure to the size of the bird and to other factor is discussed, and some contrast between avian and mammalian spindles are pointed out.