Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Canada.
J Exp Biol. 2013 Mar 15;216(Pt 6):1003-11. doi: 10.1242/jeb.067231.
The ability of an animal to detect and respond to changes in the environment is crucial to its survival. However, two elements of sensorimotor control - the time required to respond to a stimulus (responsiveness) and the precision of stimulus detection and response production (resolution) - are inherently limited by a competition for space in peripheral nerves and muscles. These limitations only become more acute as animal size increases. In this paper, we investigated whether the physiology of giraffes has found unique solutions for maintaining sensorimotor performance in order to compensate for their extreme size. To examine responsiveness, we quantified three major sources of delay: nerve conduction delay, muscle electromechanical delay and force generation delay. To examine resolution, we quantified the number and size distribution of nerve fibers in the sciatic nerve. Rather than possessing a particularly unique sensorimotor system, we found that our measurements in giraffes were broadly comparable to size-dependent trends seen across other terrestrial mammals. Consequently, both giraffes and other large animals must contend with greater sensorimotor delays and lower innervation density in comparison to smaller animals. Because of their unconventional leg length, giraffes may experience even longer delays compared with other animals of the same mass when sensing distal stimuli. While there are certainly advantages to being tall, there appear to be challenges as well - our results suggest that giraffes are less able to precisely and accurately sense and respond to stimuli using feedback alone, particularly when moving quickly.
动物检测和响应环境变化的能力对其生存至关重要。然而，感觉运动控制的两个要素——对刺激做出反应所需的时间（反应速度）和刺激检测及反应产生的精度（分辨率）——本质上受到周围神经和肌肉空间竞争的限制。随着动物体型的增加，这些限制变得更加明显。在本文中，我们研究了长颈鹿的生理学是否找到了独特的解决方案，以维持其极端体型下的感觉运动表现。为了研究反应速度，我们量化了三个主要的延迟来源：神经传导延迟、肌肉机电延迟和力产生延迟。为了研究分辨率，我们量化了坐骨神经中神经纤维的数量和大小分布。我们发现，长颈鹿的测量结果与其他陆地哺乳动物的尺寸相关趋势大致相当，而不是拥有特别独特的感觉运动系统。因此，长颈鹿和其他大型动物与小型动物相比，必须应对更大的感觉运动延迟和更低的神经支配密度。由于它们非常规的腿长，长颈鹿在感知远端刺激时，与同质量的其他动物相比，可能会经历更长的延迟。虽然高大有其优势，但也存在挑战——我们的结果表明，长颈鹿在单独使用反馈来精确、准确地感知和响应刺激方面的能力较差，尤其是在快速移动时。
