The morphological basis to the mammalian vestibulo-ocular system: the influence of skull architecture locomotion and phylogeny

哺乳动物前庭眼系统的形态学基础：头骨结构运动和系统发育的影响

• 批准号: BB/D000068/1
• 负责人: Nathan Jeffery
• 金额: $ 29.36万
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FD000068%2F1
• 关键词: morphological; basis; mammalian; vestibulo; ocular

Fix your eyes on a distant object and walk towards it. As you walk, your eyeballs constantly move around to compensate for the movements of your head. The structures responsible for monitoring head movement and feeding this information to the muscles of the eyeball are the semicircular canals of the inner ear. There are three of these half-moon shaped canals, one for each rotation of the head (e.g. tip up-down, rotate left-right and tilt left-right). These supply information via the brain to three pairs of muscles that can move the eyeball in the opposite direction to that of the head (e.g. tip down-up, rotate right-left and tilt right-left). Both the canals and muscles pairs are critical to the lives of all vertebrates. Without rapid communication between the canals and the muscle pairs, the compensatory movements of the eyes would lag behind movements of the head during motion, the image on the eye's retina would blur, and you would soon feel dizzy and eventually fall over. These are the severely debilitating symptoms experienced by patients with conditions like Meniere's disease. Clearly the eye muscles must move quickly to counteract movements of the head sensed by the canals. You might therefore imagine that the plane through each pair of muscles is aligned with the plane of the semicircular canal providing the primary input (e.g. up-down canal lies parallel to the muscle pair that moves the eye down-up). That way the signal output would closely match the direction of action required (e.g. a computer cursor is most easily moved up and down by moving the mouse up and down rather than side to side or diagonally). Such close spatial matching of signal and action would minimize the need for time-consuming readjustments of the signal by the brain. Because an aligned arrangement would seem to be the simplest and most logical, people have assumed that the planes are indeed parallel, or near to parallel. Over decades this assumption has gradually gained in credence, even appearing in some textbooks and as the basis for mathematical models of inner ear and eye muscle function. However, it turns out that there is evidence, albeit very limited, to suggest that the planes are not parallel and that the brain must therefore do some processing of the signal arising from the canals. The problem is that because the eye muscles and canals are not generally accessible to physical inspection, the available data is too little to ascertain the extent of the difference between the planes and whether such differences are the same in all animals, particularly those used in research. This means several important questions remain unanswered: First and foremost, are the mathematical models used in research to understand, for example, motion sickness employing the appropriate numbers? Second, is the difference in orientation connected to whether you normally move around rapidly or slowly, or on two or four legs? Or, is it primarily due to differences in the position of the eyes within the skull: for example is the arrangement the same in cats where the eyes face forward as it is in rabbits where the eyes face sideways. To answer these and other questions I propose imaging the heads of 100 dead mammals and measuring the difference in the plane of each pair of eye muscles and the corresponding semicircular canal. Twenty to forty rhesus monkeys and rabbits will be examined to determine variations within species. The remaining 40-60 specimens will be sampled to represent a wide range of sizes, types of body movement and skull shapes. I propose imaging the mammals with a magnetic resonance imager (MRI). This will enable me to look into the head without physically damaging it. Associations of the divergence of the planes with body size, mode of body movement and skull architecture will be evaluated with a set of complex mathematical tools called geometric morphometrics.

眼睛盯着远处的物体，然后朝它走去。当你走路的时候，你的眼球不断地转动，以补偿你头部的运动。负责监测头部运动并将此信息传递给眼球肌肉的结构是内耳的半规管。这些半月形管道有三个，头部每次旋转一个（例如，上下倾斜、左右旋转和左右倾斜）。这些通过大脑向三对肌肉提供信息，这些肌肉可以使眼球以与头部相反的方向移动（例如，上下倾斜，左右旋转和左右倾斜）。运河和肌肉对所有脊椎动物的生命都至关重要。如果没有运河和肌肉对之间的快速沟通，眼睛的补偿运动将落后于头部运动，眼睛视网膜上的图像将模糊，你很快就会感到头晕，最终摔倒。这些是梅尼埃病等疾病患者所经历的严重衰弱症状。显然，眼部肌肉必须快速运动，以抵消由运河感觉到的头部运动。因此，你可以想象，通过每对肌肉的平面与提供主要输入的半规管平面对齐（例如，上下管平行于使眼睛上下移动的肌肉对）。这样，信号输出将紧密匹配所需的动作方向（例如，通过上下移动鼠标而不是左右或对角移动，计算机光标最容易上下移动）。信号和动作在空间上如此紧密的匹配，将使大脑重新调整信号的耗时最小化。因为排列整齐似乎是最简单和最合乎逻辑的，所以人们假设这些平面确实是平行的，或者接近平行。几十年来，这一假设逐渐得到了人们的信任，甚至出现在一些教科书中，并作为内耳和眼肌功能数学模型的基础。然而，事实证明，有证据表明，尽管非常有限，但这些平面并不平行，因此大脑必须对来自运河的信号进行一些处理。问题是，由于眼肌和眼管一般无法进行物理检查，因此现有数据太少，无法确定平面之间的差异程度，以及这种差异是否在所有动物中都是一样的，特别是那些用于研究的动物。这意味着几个重要的问题仍然没有答案：首先，研究中使用的数学模型是否使用了适当的数字来理解，例如，晕动病？第二，方向上的差异是否与你通常是快速还是缓慢地移动，或者是用两条腿还是四条腿移动有关？或者，这主要是由于在头骨内的眼睛的位置的差异：例如，是安排在猫的眼睛面向前方，因为它是在兔子的眼睛面向侧面相同。为了回答这些和其他问题，我建议对100只死亡哺乳动物的头部进行成像，并测量每对眼肌和相应半规管的平面差异。将检查20 - 40只恒河猴和家兔，以确定种属内的变异。剩下的40-60个标本将被取样，以代表广泛的大小，身体运动类型和头骨形状。我建议用磁共振成像仪（MRI）对哺乳动物进行成像。这将使我能够在不对头部造成物理损伤的情况下观察头部。将使用一套称为几何形态测量学的复杂数学工具来评估平面的发散度与身体大小、身体运动模式和头骨结构的关联。