The composite structure of quail pectoralis muscle.

The twitch fibers of the quail pectoralis muscle were found to have one neuromuscular junction each, located in the middle third of the fiber. The length of isolated fibers varied between 8.8 and 33.2 mm, with mean and median values of 16 and 15.6 mm, respectively. The lengths of the fascicles from which the fibers were isolated varied between 30 and 51 mm. The muscle fibers taper at both ends. The neuromuscular junctions, revealed after histochemically reacting the intact muscle for acetyl cholinesterase activity, were arranged in discrete bands, separated by intervals of between 0.94 and 6.70 mm, with a mean value of 3.14 mm. The quail pectoralis muscle is thus composed of discontinuous, tapered muscle fibers, arranged in an overlapping series. It is therefore a muscle in which tension is transmitted laterally between muscle fibers.

Muscle architecture and control demands.

Muscles effect locomotion, and their gross architecture still poses analytical problems. These problems involve the arrangement of myofibers and motor units within muscles and that of muscles around joints. The arrangement of fibers may involve a range of considerations from the equivalence or nonequivalence of sarcomeres to placement, attachment, and angulation of fascicles and entire muscles; consequently, these levels and their development and coordination overlap. Many problems at the macroscopic level require clarification of how an animal uses a compartment of suite of muscles and whether morphological differences reflect functional ones. The understanding of intermediate architecture, including issues of compartmentation, pinnation, and concatenation, remains more elusive, as some morphologically distinct muscles may be functionally equivalent. As yet we have inadequate appreciation of the opportunities or limitations provided to the control system by a particular arrangement of fibers, or vice versa. Exploration of the rules that govern these conditions provides abundant opportunities for cooperation among neurobiologists, developmental biologists, physiologists and morphologists.

Muscle architecture in relation to function.

Animal muscles generate forces and induce movements at desirable rates. These roles are interactive and must be considered together. Performance of the organism and survival of the species also involve potential optimization of control and of energy consumption. Further, individual variability arising partly via ontogeny and partly from phylogenetic history often has pronounced and sometime conflicting effects on structures and their uses. Hence, animal bodies are generally adequate for their tasks rather than being elegantly matched to them. For muscle, matching to role is reflected at all levels of muscular organization, from the nature of the sarcoplasm and contractile filaments to architectural arrangements of the parts and whole of organs. Vertebrate muscles are often analyzed by mapping their placement and then "explaining" this on the basis of currently observed roles. A recent alternative asks the obverse; given a mass of tissue that may be developed and maintained at a particular cost, what predictions do physical principles permit about its placement. Three architectural patterns that deserve discussion are the classical arrangement of fibers in pinnate patterns, the more recent assumption of sarcomere equivalence, and the issue of compartmentation. All have potential functional implications. 1. The assumption of equivalence of the sarcomeres of motor units allows predictions of the fiber length between sites of origin and insertion. In musculoskeletal systems that induce rotation, the observed (but not the pinnation-associated) insertion angle will differ with the radial lines on which the fibers insert. In a dynamic contraction inducing rotation, a shift of moment arm has no effect for muscles of equal mass. 2. Classical pinnate muscles contain many relatively short fibers positioned in parallel but at an angle to the whole muscle, reducing the per fiber force contribution. However, the total physiological cross-section and total muscle force are thus increased relative to arrangements with fibers parallel to the whole muscle. Equivalent muscles may be placed in various volumetric configurations matching other demands of the organism. The loss of fiber force due to (pinnate, not equivalent) angulation is compensated for by the reduced shortening of fibers in multipinnate arrays. 3. Compartmentation, i.e., the subdivision of muscles into independently controlled, spatially discrete volumes, is likely ubiquitous. Differential activation of the columns of radial arrays may facilitate change of vector and with this of function. Compartmentation is apt to be particularly important in strap muscles with short fiber architecture; their motor units generally occupy columnar, rather than transversely stacked, subdivisions; this may affect recovery from fiber atrophy and degeneration.(ABSTRACT TRUNCATED AT 400 WORDS)

Architecture of chicken muscles: short-fibre patterns and their ontogeny.

Staining for motor endplates and chemical digestion of five major muscles of the domestic chicken shows that these confirm the short-fibre strap muscle paradigm. The individual fibres are spindle-shaped, terminating in gradually tapering ends. The motor endplates of the individual fibres align in cross-bands along the length of the fascicles. These bands are spaced much more tightly than are comparable bands in mammals; unlike the condition in mammals, many fibres are longer than twice the interband spacing. The spacings between bands differ by more than a factor of five along the length of each muscle. The proportions among bands remain relatively constant. These proportions are not affected by the degree of muscular contraction, nor do they change with ontogeny, suggesting that the arrangement is established before hatching.

The physiological basis of slow locomotion in chamaeleons.

The African chamaeleon, Chamaeleo senegalensis, will not move faster than approximately 0.1 m/second at 23 degrees C, whereas the lizard Agama agama, like most lizards its size, runs at speeds more than 10X as fast. To account for this difference, we measured various physiological parameters of the iliofibularis muscle of both lizards. The maximum speed of tetanic contraction of unloaded Chamaeleo muscle was half as fast as that of Agama muscle (2.5 vs. 5.8 resting lengths per second). Heavily loaded Chamaeleo iliofibularis contracted at nearly 1/4 the speed of Agama muscle. Time to peak isometric twitch tension and time to half relaxation were twice as long in Chamaeleo as in Agama (122 vs. 58 msec, and 168 vs. 81 msec). Much more of the Chamaeleo muscle consisted of tonic muscle fibers, and the Chamaeleo muscle, compared to Agama muscle, showed physiological evidence of having a significant amount of tonic fibers (potassium contracture and high tetanus to twitch ratios). Finally, the myofibrillar ATPase activity of the Chamaeleo muscle was 1/3 that of Agama muscle. Thus, these results show that the slow locomotion of old world chamaeleons can, in part, be explained by the physiology, biochemistry, and fiber-type distribution of their muscles.

Respiratory responses to acute heat stress in cranes (Gruidae): the effects of tracheal coiling.

Some species of cranes have extensive coiling of their trachea that substantially increases their anatomical dead space. We subjected individuals of four species of cranes (Anthropoides virgo, Balearica regulorum, Grus grus and Grus japonensis) to acute heat stress to investigate the effectiveness of this trait as a thermoregulatory adaptation. We measured cloacal temperature, respiratory flow and frequency and arterial pH during normothermic breathing and thermal panting. Extra tracheal length appears to be a helpful but nonessential adaptation to prevent cranes from becoming alkalotic while panting. Cranes in our study had relatively lower panting frequencies and greater tidal volumes than have been reported for other birds subjected to heat stress. Tracheal coiling is probably more important to vocalization than to respiration or thermoregulation.

Mechanics of the syrinx in Gallus gallus. II. Electromyographic studies of ad libitum vocalizations.

Records of electrical activity in the tracheal muscles of domestic chickens were obtained for a variety of ad libitum vocalizations. Primary attention was given to an analysis of events during the most complex call, crowing. Three pairs of muscles, Mm, tracheohyoideus, tracheolateralis, and sternotrachealis, can affect the configuration of a chicken's syrinx. The firing patterns of the three muscle pairs are related to their different abilities to affect the tension of the syringeal membranes. The influence of M. tracheohyoideus is most indirect and imprecise, and its role the least clearly defined. It appears to adjust the position of the trachea so that the syrinx is isolated from unpredictable and/or undesireable consequences of nuchal position and tracheal elasticity, and also helps draw the glottis caudad, thereby deepening the pharyngeal chamber. The other two muscles interact to control the tension of the vocal membranes. M. sternotrachealis relaxes the membranes by drawing the drum of the trachea caudad, or, via the syringeal ligament, by rotating the pessulus cranioventrad, or both. M. tracheolateralis tenses the membranes and/or prevents caudal movement of the orgin of M. sternotrachedalis, a necessity if the syringeal ligament is to rotate the pessulus. Vocalization depends on both syringeal configuration and appropriated air flow. Hence, tracheal muscles, syrinx, air sacs, and ventilatory muscles cooperate to form a vocal system. Cooperation elicits a surprising degree of redundancy. At least one call, a high pitched wail, may be produced by two very different techniques.