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Monotremes are a group of egg-laying mammals, possessing a mosaic of ancestral and derived anatomical features. Despite much interest in monotremes from phylogenetic, morphological, and ecological perspectives, they have been the subject of relatively few biomechanical studies. In this study, we examined shoulder and proximal forelimb muscle anatomy and architecture in the short-beaked echidna, Tachyglossus aculeatus, through contrast-enhanced computed tomography and gross dissection. Muscle architecture is a major determinant of muscle function and can indicate specialized muscle roles, such as the capacity for generating large forces (through large physiological cross-sectional area, PCSA) or working ranges (through long fascicle lengths). We hypothesized that some muscles would exhibit architectural specializations convergent with other fossorial and/or sprawling animals, and that other muscles would reflect the echidna’s unusual anatomy and locomotor style. Instead, we found the shoulder and proximal forelimb muscles in echidna to have little variation in their architecture. The muscles generally had long fascicles and small-to-intermediate PCSAs, consistent with force production over a wide working range. Further, muscles did not show overt differences in architecture that, in therian mammals, have been linked to increased forelimb mobility and the transition from sprawling to parasagittal posture. Our measures of architectural disparity placed the echidna closer to the tegu lizard than other sprawling fossorial mammals (e.g., mole). The low architectural diversity found in the echidna’s shoulder and proximal forelimb muscles is interpreted as a lack of functional specialization into distinct roles. We hope our study will contribute to greater understanding of monotreme anatomy and biomechanical function, and to the reconstruction of musculoskeletal evolution in mammals.
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ROLE OF FORELIMB MORPHOLOGY IN MUSCLE SENSORIMOTOR FUNCTIONS DURING LOCOMOTION IN THE CAT
ABSTRACT Previous studies established strong links between morphological characteristics of mammalian hindlimb muscles and their sensorimotor functions during locomotion. Less is known about the role of forelimb morphology in motor outputs and generation of sensory signals. Here, we measured morphological characteristics of 46 forelimb muscles from 6 cats. These characteristics included muscle attachments, physiological cross-sectional area (PCSA), fascicle length, etc. We also recorded full-body mechanics and EMG activity of forelimb muscles during level overground and treadmill locomotion in 7 and 16 adult cats of either sex, respectively. We computed forelimb muscle forces along with force- and length-dependent sensory signals mapped onto corresponding cervical spinal segments. We found that patterns of computed muscle forces and afferent activities were strongly affected by the muscle’s moment arm, PCSA, and fascicle length. Morphology of the shoulder muscles suggests distinct roles of the forelimbs in lateral force production and movements. Patterns of length-dependent sensory activity of muscles with long fibers (brachioradialis, extensor carpi radialis) closely matched patterns of overall forelimb length, whereas the activity pattern of biceps brachii matched forelimb orientation. We conclude that cat forelimb muscle morphology contributes substantially to locomotor function, particularly to control lateral stability and turning, rather than propulsion.
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- Award ID(s):
- 2024414
- PAR ID:
- 10656748
- Editor(s):
- Carson, Richard; Macefield, Vaughan
- Publisher / Repository:
- John Wiley & Sons Ltd
- Date Published:
- Volume:
- 603
- Issue:
- 2
- Page Range / eLocation ID:
- 447-487
- Subject(s) / Keyword(s):
- Muscle morphology, cat forelimb, somatosensory feedback, motor function, locomotion
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.1101/2024.07.11.603106
