Dimensional analysis and dynamic response characterization of mammalian peripheral vestibular structures

Extensive morphometric measurements were made on the vestibular system of the rabbit (Oryctulagus cuniculus), the gerbil (Meriones unguiculatus), the chinchilla (Chinchilla laniger), and the squirrel monkey (Saimiri sciureus) from serial sections of temporal bones. Additionally, a more limited set of measurements were also completed on the owl monkey (Aotus trivirgatus), the Capuchin monkey (Cebus sp.), the harp seal (Pagophilus groenlandicus Erxleben, 1777), and the two-toed sloth (Choloepus sp.). The following measurements were made: (1) radius of curvature (R) of each membranous semicircular canal (herein called semicircular duct—see nomenclature in Nomina Anatomica (1968)) (2) cross-sectional diameter of the ducts and the osseous semicircular canals, and (3) some pertinent morphometrics of the cristae ampullares and the utricle. In all species studied (1) the radii of curvature of the three semicircular ducts are dissimilar, with that of the lateral duct being as small as, or smaller than, those of the anterior and posterior ducts; (2) R for the anterior duct is largest in the harp seal and the rabbit; (3) the canal and duct dimensions are largest in the Capuchin and squirrel monkeys, the two-toed sloth, and the harp seal, and smallest in the gerbil; (4) the proportion of otic fluid “space” that is occupied by endolymph shows a ranking of gerbil > rabbit > two-toed sloth > chinchilla = owl monkey > squirrel monkey > Capuchin monkey > harp seal; and (5) the gross ampullary and utricular dimensions are largest in the harp seal and smallest in the gerbil. These measurements were used for determining the time constants describing semicircular-canal dynamics in the Steinhausen (1931, 1933) and Oman-Marcus (1980) equations.     

The quadriceps gastrocnemius muscle

The gastrocnemius muscle forms the belly of calf muscles in the posterior compartment of the leg. This paper reports a four-headed gastrocnemius (named quadriceps gastrocnemius) muscle as a new variant and when present can alter the anatomy and/or the boundaries of the popliteal fossa. The four heads are named as medial, intermedio-medial, intermedio-lateral and medial. The newly identified heads, intermedio-medial and intermedio-lateral heads form the inferior boundaries of the popliteal fossa. Clinical conditions like popliteal entrapment syndrome may arise because of distal fossa congestion created by the intermedio-medial and intermedio-lateral heads. This supernumerary heads may also be useful for grafting and they also provide bulkier mass for gastrocnemius proximal attachment. The knowledge of anatomical variants presented is useful to surgeons, prosectors and radiologists.     

Development of a mammalian fast muscle: dynamic and biochemical properties correlated

1. The isometric properties and related biochemical properties of a developing rat fast muscle (extensor digitorum longus, EDL) have been determined during the 21 days after birth.

2. At birth the maximum rate of rise of tension in a tetanus, a measure of speed of contraction, is slow; it begins to increase only after the 5th day and reaches adult values by 21 days.

3. The increase in actomyosin ATPase activity of the rat EDL correlates closely (P 0·001) with the changes in the maximum rate of rise during the same period of development.

4. The relaxation phase of a tetanic response begins to increase in speed promptly after birth, and reaches adult values by the 21st day. The rate of calcium accumulation by the isolated sarcoplasmic reticulum (SR) increases with a similar time course.

5. The separate contributions of contraction and relaxation mechanisms to the changes in the more conventional isometric properties of maturing muscles have been analysed.

     

Regeneration of the rat gastrocnemius muscle from sibling and non-sibling muscle fragments

Regeneration of the gastrocnemius muscle from minced transplanted muscle fragments was studied in 46 rats. The jumping complex of muscles (gastrocnemius, soleus and plantaris) was removed from the donor and minced into 1 mm³ fragments. In one experimental series minced muscle was orthotopically implanted into sibling animals, and in the other series minced muscle was implanted into non-sibling animals of the same strain. During the first week after implantation, regenerative activity in the homotransplanted muscle fragments was intense and did not differ histologically from that occurring in autotransplanted muscle. Staritng in the second week, areas of regenerating homotransplanted muscle fibers became infiltrated with small lymphocytes. Despite relatively massive cellular rejection in the regenerates, individual skeletal muscle fibers regenerated to maturity. Regenerates from homotransplanted muscles often attained the same gross from as regenerates from auto-transplanted material, but in no case was the amount of muscle fibers in homografted regenerates greater than 50% of that seen in regenerates arising from autografted muscle fragments. About half of the advanced regenerates were reduced to broad bands of connective tissue containing no muscle fibers.     

Compartmentalization of single muscle units in cat lateral gastrocnemius

Summary The distribution of muscle fibers in single muscle units in cat lateral gastrocnemius (LG) muscle was analyzed using the method of glycogen depletion. Single, type FF motor units in LG were identified by stimulation of dissected ventral rootlets and then activated to produce depletion of glycogen in their innervated muscle fibers. Serial histological sections were made of the entire triceps surae muscles and then reacted for the demonstration of glycogen. Projected tracings of the sections were used to compare the distribution of glycogen depleted muscle fibers to the heads of the LG muscle. Results of analysis of single muscle units indicate that the muscle fibers innervated by single cat LG type FF motor units are distributed to the same regions of muscle which are innervated by primary branches of the nerve to the LG muscle. The single units are thus compartmentalized. These results support the hypothesis that each of the neuromuscular compartments of LG contains a unique population of motor units. It is suggested that compartmentalization of muscles about primary branches of their muscle nerves may from a major organizational principle in the design of skeletal muscles.     

Force-length characteristics of the in vivo human gastrocnemius muscle

In this study, the force-length characteristics of the in vivo medial (GM) and lateral (GL) heads of the human gastrocnemius muscle were estimated from measurements in eight healthy male subjects. This involved: 1) dynamometry-based measurements of the moment generated during maximal isometric plantar flexion; 2) ultrasound-based measurements of fascicular length and pennation angle; and 3) ultrasound-based calculations of moment arm lengths. All measurements were taken over the ankle angle range from 20 degrees of dorsiflexion to 30 degrees of plantar flexion. Tendon forces were calculated by dividing the moments recorded by the muscle moment arm lengths, and fascicular forces were calculated by dividing the tendon forces estimated by the cosine of pennation angle. In the transition from 30 degrees of plantar flexion to 20 degrees of dorsiflexion, the GM muscle fascicular length and force increased linearly from 24 to 39 mm and from 222 to 931 N, respectively. Over the same ankle angle range, the GL muscle fascicular length and force increased linearly from 30 to 47 mm and from 139 to 393 N, respectively. Estimates of the sarcomeric lengths corresponding to the fascicular lengths measured indicated that the two muscles operated in the range 1.4-2.2 microm, below the optimal length region for force generation according to the cross-bridge mechanism of contraction. These results indicate that the force-length relation of the in vivo human gastrocnemius muscle is limited to the ascending limb of the bell-shaped force-length curve obtained from experiments on isolated material.     

Growth of medial gastrocnemius muscle and Achilles tendon in Wistar rats

Dimensions, architecture, material properties and functional characteristics of medial gastrocnemius muscles and Achilles tendons of young and old Wistar rats were compared. Dimensions associated with length of the leg segment grow isometric with it. Muscle belly transsectional dimensions, volume of muscle tissue and associated functional indices increase out of proportion either with the dimensions of the limb segment or the weight of the animal. As the properties of the contractile tissue remain the same and relative proportions of tissue components alter, changes in architecture result. These are not reflected in transsection of the tendon. Functional characteristics of the muscle tendon complex can be explained by architectural or dimensional-peculiarities emerging in the complex by growth processes of which the main is that the muscle belly of this pennated muscle grows in length mainly by increments in girth of the muscle fibers proper.     

兔腓肠肌表面肌电信号与肌肉收缩及运动中枢的关系

背景：以往的验证实验均采用电刺激方法诱发肌肉收缩,施加电流的影响使接收到的表面肌电信号混有外来电流成分,无法有效分析其与肌肉收缩,特别是与高位运动中枢的关系。 目的：观察新西兰兔腓肠肌表面肌电信号与肌肉收缩及高位、低位运动中枢的关系。 方法：在新西兰兔清醒状态下通过针刺右侧跟腱诱发腓肠肌收缩,局麻清醒状态下离断右侧坐骨神经,分别在针刺跟腱、钳夹离断的坐骨神经远侧断端、针刺腓肠肌和被动活动腓肠肌时,检测腓肠肌表面肌电信号的强弱及类型。局麻下于L3平面横断脊髓,针刺左侧跟腱诱发腓肠肌收缩,检测腓肠肌表面肌电信号的强弱和类型。 结果与结论：正常状态下经针刺跟腱诱发腓肠肌随意收缩时,可接收到400 μV、持续4 s的宽底随意波;横断脊髓后针刺跟腱诱发的反射性腓肠肌收缩接收到的信号小于100 μV、持续时间小于1 s;离断坐骨神经后刺激跟腱、神经和肌肉时,均未引起肌肉收缩,但可接收到强度小于10 μV、持续时间小于0.5 s的干扰波;被动活动关节牵拉腓肠肌时未检测到肌电信号活动。说明兔腓肠肌表面肌电信号产生于肌肉收缩之前,是以高位运动中枢为主、低位运动中枢为辅发放到肌肉的驱动电信号的综合,而非肌肉收缩本身产生。     

Enhancement of muscle regeneration in the rat gastrocnemius muscle by low energy laser irradiation

Summary The effect of low-energy laser (He-Ne) irradiation on the rate of skeletal muscle regeneration after partial excision of the rat gastrocnemius muscle was studied using quantitative histological morphometric methods. The injured zones of the experimental rats were subjected to direct He-Ne laser (632.8 nm wavelength) irradiation (6.0 mW for 2.3 min) immediately following injury and once daily thereafter for 5 days. Muscles that were injured as above and subjected to red or room light irradiation served as a control group. The volume fraction (percent of total volume of injured zone) of the mononucleated cells in the injured zone decreased gradually with time after injury, but more rapidly in the laser irradiated muscles than in the control. At 3 days post-injury the myotubes in the laser-irradiated muscles populated a significantly higher percentage (13.9 ± 1.1%) of the injured area than in the control muscles (7.8 ± 1.0%). The volume fraction of the young myofibers in the laser irradiated muscles exceeded 30.6 ± 2.2% and 49.6 ± 5.6% at 8 and 11 days post-injury, respectively, while in control muscles these structures comprised only 9.6 ± 1.0% and 27.2 ± 3.8% of the injured zone at 8 and 11 days after injury, respectively. It is concluded that He-Ne laser irradiation during the regeneration process promotes muscle maturation in the injured zone following partial excision of the rat gastro-cnemius muscle.     

Sonographic studies of human soleus and gastrocnemius muscle architecture: gender variability

The purpose of this study was to establish if there are gender differences in muscle architecture in relaxed human soleus and gastrocnemius muscles of normal, live subjects. Ultrasonography was used to measure fiber bundle length, muscle thickness, and angles of pennation in a total of ten predetermined sites in the medial and lateral heads of gastrocnemius and the anterior and posterior soleus in 19 males and 16 females. Percentage differences between males and females for each parameter were recorded. Gender differences were statistically analyzed using multivariate analysis of variance. In the gastrocnemius and soleus muscles of males and females the differences between the overall fiber bundle length, angle of pennation and muscle thickness were statistically significant (P < 0.05). Overall, females were found to have longer average muscle fiber bundle length and males thicker muscles and larger angles of pennation. The greatest percentage differences of the architectural parameters between males and females were in the posterior soleus: 13% difference in fiber length and 26% difference in angle of pennation in the midline of posterior soleus and 26% difference in muscle thickness of the lateral part of posterior soleus. No correlation was found between leg length and fiber length, angle of pennation or muscle thickness. Fiber length (decreased), angle of pennation (greater) and muscle thickness (greater) of most parts of the gastrocnemius and soleus muscles were significantly different in males and females. Leg length of males and females did not correlate to these architectural parameters. Accepted: 18 February 2000