Cotten Pamela B, Piscitelli Marina A, McLellan William A, Rommel Sentiel A, Dearolf Jennifer L, Pabst D Ann
Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina 28403, USA.
J Morphol. 2008 Dec;269(12):1520-38. doi: 10.1002/jmor.10668.
Most mammals possess stamina because their locomotor and respiratory (i.e., ventilatory) systems are mechanically coupled. These systems are decoupled, however, in bottlenose dolphins (Tursiops truncatus) as they swim on a breath hold. Locomotion and ventilation are coupled only during their brief surfacing event, when they respire explosively (up to 90% of total lung volume in approximately 0.3 s) (Ridgway et al. 1969 Science 166:1651-1654). The predominantly slow-twitch fiber profile of their diaphragm (Dearolf 2003 J Morphol 256:79-88) suggests that this muscle does not likely power their rapid ventilatory event. Based on Bramble's (1989 Amer Zool 29:171-186) biomechanical model of locomotor-respiratory coupling in galloping mammals, it was hypothesized that locomotor muscles function to power ventilation in bottlenose dolphins. It was further hypothesized that these muscles would be composed predominantly of fast-twitch fibers to facilitate the bottlenose dolphin's rapid ventilation. The gross morphology of craniocervical (scalenus, sternocephalicus, sternohyoid), thoracic (intercostals, transverse thoracis), and lumbopelvic (hypaxialis, rectus abdominis, abdominal obliques) muscles (n = 7) and the fiber-type profiles (n = 6) of selected muscles (scalenus, sternocephalicus, sternohyoid, rectus abdominis) of bottlenose dolphins were investigated. Physical manipulations of excised thoracic units were carried out to investigate potential actions of these muscles. Results suggest that the craniocervical muscles act to draw the sternum and associated ribs craniodorsally, which flares the ribs laterally, and increases the thoracic cavity volume required for inspiration. The lumbopelvic muscles act to draw the sternum and caudal ribs caudally, which decreases the volumes of the thoracic and abdominal cavities required for expiration. All muscles investigated were composed predominantly of fast-twitch fibers (range 61-88% by area) and appear histochemically poised for rapid contraction. These combined results suggest that dolphins utilize muscles, similar to those used by galloping mammals, to power their explosive ventilation.
大多数哺乳动物都具备耐力，因为它们的运动系统和呼吸（即通气）系统在机械上是耦合的。然而，宽吻海豚（瓶鼻海豚）在屏气游泳时，这两个系统是解耦的。只有在它们短暂浮出水面进行呼吸时，运动和通气才会耦合，此时它们会进行快速呼吸（在大约0.3秒内可达肺总量的90%）（里奇韦等人，1969年，《科学》166:1651 - 1654）。宽吻海豚膈肌主要由慢肌纤维组成（迪尔洛夫，2003年，《形态学杂志》256:79 - 88），这表明该肌肉不太可能为其快速通气提供动力。基于布兰布尔（1989年，《美国动物学》29:171 - 186）对奔跑哺乳动物运动 - 呼吸耦合的生物力学模型，有人提出假设，认为宽吻海豚的运动肌肉起到为通气提供动力的作用。进一步的假设是，这些肌肉将主要由快肌纤维组成，以促进宽吻海豚的快速通气。对宽吻海豚的颅颈（斜角肌、胸头肌、胸骨舌骨肌）、胸部（肋间肌、胸横肌）和腰骨盆部（腹下肌、腹直肌、腹外斜肌）肌肉（n = 7）的大体形态以及选定肌肉（斜角肌、胸头肌、胸骨舌骨肌、腹直肌）的纤维类型分布（n = 6）进行了研究。对切除的胸部肌肉单元进行了物理操作，以研究这些肌肉的潜在作用。结果表明，颅颈肌的作用是将胸骨和相关肋骨向颅背侧牵拉，使肋骨向外侧扩张，并增加吸气所需的胸腔容积。腰骨盆部肌肉的作用是将胸骨和尾肋向尾侧牵拉，减少呼气所需的胸腔和腹腔容积。所有研究的肌肉主要由快肌纤维组成（面积占比范围为61 - 88%），并且在组织化学上似乎易于快速收缩。这些综合结果表明，海豚利用与奔跑哺乳动物类似的肌肉来为其快速通气提供动力。
