Age effects on force produced by intrinsic and extrinsic hand muscles and finger interaction during MVC tasks.

Finger-pressing forces are produced by activation of the intrinsic hand muscles, which are finger specific, and the extrinsic muscles that connect to multiple fingers. We tested a hypothesis of greater weakening of intrinsic hand muscles with age and quantified associated indexes of finger interaction such as enslaving (force production by unintended fingers) and force deficit (loss of finger force in multifinger tasks compared with single-finger tasks). Twelve young (23-35 yr old) and 12 elderly (70-95 yr old) men and women performed single-finger and four-finger maximal pressing tasks, in which force was applied at the proximal phalanges (PP, the intrinsic muscles are major focal force generators) and at the distal phalanges (DP, the extrinsic muscles are focal force generators). The decline in the peak force with age was greater at PP (30%) than at DP (19%). Larger indexes of finger interaction were observed at PP (enslaving = 17.2 +/- 9.4%, force deficit = 36.1 +/- 11.1%) than at DP (enslaving = 14.9 +/- 8.8%, force deficit = 27.7 +/- 10.8%) across ages and genders. We conclude that intrinsic hand muscles show disproportionate weakening with age. The greater indexes of finger interaction in PP tests with greater involvement of intrinsic hand muscles suggest that the finger interactions are predominantly of a central origin across ages and genders.     

Electromyographic activity of intrinsic and extrinsic muscles of the human tongue.

In healthy human subjects, electromyographic activities (EMG) were obtained from various tongue muscles. Main actions such as protrusion, retraction, and changing of the shape of the tongue can be correlated with the EMG activity of the respective muscles. Amongst all tongue muscles the paired genioglossus (protruder) is of greatest importance since it prevents a relapse of the tongue with occlusion of the airways and the attendant risk of suffocation. To counteract the relapse of the tongue, the tonic activity of the genioglossus is markedly increased in the supine position; this activity is further increased with cervical flexion. In addition, the genioglossi are activated during respiration, particularly during the inspiratory phase. These activity patterns reflect the important role the genioglossus plays in the mechanics of maintaining an open air passage to the lungs.     

Pennation angles of the intrinsic muscles of the foot

As mathematical models of the musculoskeletal system become increasingly detailed and precise, they require more accurate information about the architectural parameters of the individual muscles. These muscles are typically represented as Hill-type models, which require data on fiber length, physiological cross-sectional area (PCSA) and pennation angle. Most of this information for lower limb muscles has been published, except for data on the pennation angle of the intrinsic muscles of the foot. Each (n=20) intrinsic muscle of three human feet was dissected free. The dorsal and plantar surfaces were photographed and a digitized color image was imported into Abobe Photoshop. The muscles were divided into "anatomical units". For each anatomical unit (n=26), a line was drawn along the tendon axis and a number of other lines were drawn along individual muscle fibers. The angle between the tendon line and each fiber line was defined as the pennation angle of that fiber. By visual inspection, an effort was made to take measurements such that they represented the distribution of fibers in various parts of the muscle. Although some individual muscles had higher or lower pennation angles, when averaged for all specimens, the second dorsal interosseous had the smallest pennation angle (6.7+/-6.81 degrees) while the abductor digiti minimi had the largest (19.1+/-11.19 degrees). Since the cosines of the angles range from 0.9932 to 0.9449, the effect of the pennation angle on the force generated by the muscle was not great.     

Anatomy of the squirrel wrist: bones, ligaments, and muscles

Anatomical differences among squirrels are usually most evident in the comparison of flying squirrels and nongliding squirrels. This is true of wrist anatomy, probably reflecting the specializations of flying squirrels for the extension of the wing tip and control of it during gliding. In the proximal row of carpals of most squirrels, the pisiform articulates only with the triquetrum, but in flying squirrels there is also a prominent articulation between the pisiform and the scapholunate, providing a more stable base for the styliform cartilage, which supports the wing tip. In the proximal wrist joint, between these carpals and the radius and ulna, differences in curvature of articular surfaces and in the location of ligaments also correlate with differences in degree and kind of movement occurring at this joint, principally reflecting the extreme dorsal flexion and radial deviation of the wrist in flying squirrels when gliding. The distal wrist joint, between the proximal and distal rows of carpals, also shows most variation among flying squirrels, principally in the articulations of the centrale with the other carpal bones, probably causing the distal row of carpal bones to function more like a single unit in some animals. There is little variation in wrist musculature, suggesting only minor evolutionary modification since the tribal radiation of squirrels, probably in the early Oligocene. Variation in the carpal bones, particularly the articulation of the pisiform with the triquetrum and the scapholunate, suggests a different suprageneric grouping of flying squirrels than previously proposed by McKenna (1962) and Mein (1970). J. Morphol. 246:85-102, 2000. Published 2000 Wiley-Liss, Inc.     

Capillaries of the intrinsic nerves of human skeletal muscles

Development of blood capillaries in the human intraorganic nerves has been studied. The intramuscular nerves of fetuses, newborns, children and mature persons (88 cases in all) make the object of the investigation. Combination of light optic methods and electron microscopy is used. The development of blood capillaries of the human intraorganic nerves is a complex process, indissolubly connected with development of myelin and amyelin conductors. The capillaries in the nerves appear on the 3d month of the intrauterine development and their structure is the most favourable for intensively proceeding, at this time, the myelinization process. With progress of nervous fibers and stromal elements, differentiation of the blood capillaries takes place. By the 6th month of the interuterine life, the capillaries of the intramuscular nerves are mainly formed. The structural unit in interrelation of the capillaries and nerve elements is the complex: capillary-lemmocyte-nervous fiber. Further changes are of slower character.     

Significance of the pattern of motor innervation of the intrinsic laryngeal muscles of cat.

Simple and compound forms of motor endings, showing a particular distribution, were found in the intrinsic laryngeal muscles of the cat. The muscles carrying compound and multiple endings were stained densely black with Sudan black B; while the muscles with simple and single endings showed black and pale fibres. A probable relationship is suggested between the contraction properties and the pattern of motor innervation of intrinsic laryngeal muscles of the cat.     

Capping revisited: II. Low sensitivity to sulfydryl reagents

While thiols had been shown to either delay capping of lymphocyte membrane components or to leave it unaffected, sulfydryl reagents can block the process. However, capping is not completely blocked by doses of SH reagents below 10^?3M and thus, appears to be particularly resistant to SH poisoning. The extent of inhibition is concentration dependent, and in the lower dose range, some facilitation of capping can even be obtained. The effects of the drugs on the capping process actually depend on their reaction with SH radicals as shown by competition with free thiols. Some of the SH reagents used here are known inhibitors of lymphocyte triggering. There is no direct correlation, however, namely, there is in general rather little inhibition of capping at doses of SH reagents sufficient to completely abolish triggering.