Muscle spindle is the key proprioceptor in skeletal muscles and plays important roles in many physiological activities, such as maintaining posture, regulating movement and controlling speed variation. It has significant clinical relevance and is emerging as a promising therapeutic target for the treatment of motor functional impairment and metabolic diseases. In this review, we summarized muscle spindle distribution and the mechanism of mechanical signal transmission, and reviewed the research progress on morphological and structural characteristics of muscle spindles.
Muscle Spindles/physiology* ; Muscle, Skeletal/physiology* ; Clinical Relevance

OBJECTIVETo investigate the characteristics in the topographic distribution of the muscle spindles in human masticatory muscles.

METHODSThe muscle spindles of the masticatory muscles on both sides of 3 human corpses fixed in formalin for more than 1 year were observed histologically and analyzed quantitatively using an image analysis system.

RESULTSThe mean muscle spindle density was 32.11/g in the masseter, significantly higher in the deep muscular fibers (70.76/g) with high proportion of spindle complexes than in the superficial layers of the muscle belly (P<0.05). The mean spindle density in the temporalis was 5.44/g, higher in the anterior portion (7.44/g) than in the posterior portion (3.78/g, P<0.01). The medial pterygoid had a mean spindle density of 4.43/g.

CONCLUSIONThese results indicate a heterogeneous distribution of muscle spindles in the masticatory muscles with different morphologies or in different portions of the same muscle, depending on muscle fiber type and muscular architecture.

Humans ; Masticatory Muscles ; innervation ; physiology ; Muscle Spindles ; anatomy & histology ; physiology

Capsule restricts the further study on muscle spindle function and the involved mechanism. The aim of this study was to establish the isolation method of intrafusal fibres from the isolated rat muscle spindle. Intrafusal fibres were harvested from muscle spindle of soleus muscle in rats using neutrase-collagenase digestion. A variety of incubation mediums have been tested to find out an appropriate medium of intrafusal fibers in vitro. Trypan blue staining was used to detect cell death, and patch clamp was used to record resting potential. The results showed that the intrafusal fibres incubated with amine acid-saline solution were almost all dead. DMEM could maintain good condition of the fibres, but excess CO2 ventilation would induce cellular swelling or even death. While Leiboviz's 15 (L-15) medium can guarantee 1-2 h of physiological condition of the intrafusal fibres. Coverslips treated with gelatin, polylysine and serum was the better interfaces for the intrafusal fibres to adhere easily, compared with regularly treated coverslip. The resting potential of intrafusal fibres was (-45.3 ± 5.1) mV, consistent with others obtained from in vivo muscle spindle from cats and frogs. These results suggest that the isolation method of the intrafusal fibres has been successfully established in the present study, providing a new approach in better understanding of muscle spindle activities and the involved mechanism.
Animals ; Cell Culture Techniques ; methods ; Muscle Spindles ; physiology ; Muscle, Skeletal ; physiology ; Rats

OBJECTIVETo investigate the effects of 100 Hz sinusoidal vibration on H reflex and M wave in rat soleus muscle following immobilization.

METHODSThe immobilization of rat soleus muscle was induced as a disuse muscle model, and 100 Hz sinusoidal vibration was generated by a vibrator and applied to the immobilized soleus muscle, then the changes of H reflex and M wave in muscle were observed after 14 d.

RESULTSCompared to control, after 14 d of immobilization M(max) in soleus muscle decreased (P<0.01), stimulus threshold and S(max) increased (P<0.01); Hmax and H(max)/M(max) decreased (P<0.05, S(max) increased (P<0.05). Compared to immobilized soleus muscle, after 14 d of immobilization with 100 Hz sinusoidal vibration, the M(max) increased(P<0.01), stimulus threshold and S(Mmax) decreased (P<0.05), H(max) (P<0.01) increased and H(max)/M(max) increased (P<0.05).

CONCLUSION100 Hz sinusoidal vibration plays a significant antagonist role against the changes in H reflex and M wave in rat soleus muscle following immobilization.

Animals ; Electromyography ; Female ; H-Reflex ; physiology ; Hindlimb Suspension ; Muscle Contraction ; physiology ; Muscle Spindles ; physiology ; Muscle, Skeletal ; physiology ; Rats ; Rats, Sprague-Dawley ; Vibration

The aim of this study was to observe the electrophysiological characteristics of the isolated rat muscle spindle. The muscle spindle was isolated from rat soleus and the afferent discharge of the isolated muscle spindle was recorded by air-gap technique. In the basic physiological salt solution, the spontaneous impulses of muscle spindle were at a lower level with irregular intervals. The mean frequency of afferents was (51.78 ± 25.63) impulses/1 000 s (n = 13). The muscle spindle afferents were significantly increased and maintained over time by the addition of certain amino acids during the observation. The number of the action potential recorded per 1 000 s was 200-1 000 [mean: (687.62 ± 312.56) impulses/1 000 s, n = 17]. In addition to the typical propagated action potential, a large number of abortive spikes were observed. The results indicate that the activities of isolated muscle spindles in rats can be well maintained by the addition of certain amino acids. The results initially establish and provide the possibility for further research conducted in isolated rat muscle spindles.
Action Potentials ; physiology ; Amino Acids ; pharmacology ; Animals ; Electrophysiological Phenomena ; Female ; In Vitro Techniques ; Muscle Spindles ; physiology ; Muscle, Skeletal ; physiology ; Rats ; Rats, Sprague-Dawley ; Sodium Chloride ; pharmacology