Cooper E, Diamond J
J Physiol. 1977 Jan;264(3):695-723. doi: 10.1113/jphysiol.1977.sp011690.
We have investigated by physiological means the characteristics and organization of the mechanoreceptors in the skin of the salamander hind limb. A controlled mechanical stimulator with a tip diameter of a few microns was used to activate single mechanoreceptors, and afferent impulses were recorded from whole spinal nerves. 2. The mechanoreceptors of the skin are rapidly adapting. When random spots on the skin were tested, the stimulus strength needed to evoke an impulse varied from one location to another. The histogram of percentage occurrence of these critical stimuli in a given skin has the same form whether the sampled spots are 50 mum apart and are all included in a small area, or whether the spots are sampled as much as 1 mm apart across the entire limb. The histogram is skewed, with the highest-percentage occurrence in the low-threshold range. 3. One interpretation of the findings is that there is a single population of mechanoreceptors, of uniform threshold, spaced far enough apart for a stimulator of small diameter to be situated between them. By locating a low-threshold spot, and then determining the increase in stimulus required to excite it at a known distance away, it was possible to estimate the relationship between the strength of the stimulus and the receptive field size of such a population of receptors; we were then able to infer the average receptor spacing and receptive field size. The values are approximately 250 and 75 mum respectively. 4. From appropriate maps of detailed systematic surveys of the skin sensitivity to touch it was possible to define discrete low-threshold areas. These areas had approximate radii in the range 50-75 mum, and their centres were about 200-250 mum apart; these values are consistant with those predicted above. We conclude that the experimentally determined sensitive areas represent the receptive fields (at threshold) of individual mechanosensory endings. There are approximately twenty to thirty of them per square millimetre. 5. Receptive fields of single mechanosensory axons (i.e. of sensory 'units') were measured by an occlusion technique using two prodders. These fields vary from 0-05 to 2-5 mm2, and are generally organized as discrete areas with only a little overlap among them. Individual axons supply from five to seventy-five mechanoreceptors. 6. The findings provide a basis for quantitative studies of plasticity involving the mechanosensory system of the salamander skin.
我们通过生理学方法研究了蝾螈后肢皮肤中机械感受器的特性和组织。使用尖端直径为几微米的可控机械刺激器来激活单个机械感受器，并从整个脊神经记录传入冲动。2. 皮肤的机械感受器具有快速适应性。当测试皮肤上的随机点时，引发冲动所需的刺激强度因位置而异。在给定皮肤中，这些临界刺激出现百分比的直方图具有相同的形式，无论采样点相隔50微米且都包含在一个小区域内，还是采样点在整个肢体上相隔多达1毫米。该直方图呈偏态分布，在低阈值范围内出现百分比最高。3. 对这些发现的一种解释是，存在单一群体的机械感受器，其阈值均匀，间隔足够远，使得小直径刺激器能够位于它们之间。通过定位一个低阈值点，然后确定在已知距离处激发它所需的刺激增加量，就有可能估计刺激强度与这类感受器群体的感受野大小之间的关系；然后我们能够推断出平均感受器间距和感受野大小。这些值分别约为250微米和75微米。4. 从对皮肤触觉敏感性的详细系统调查的适当图谱中，可以定义离散的低阈值区域。这些区域的近似半径在50 - 75微米范围内，它们的中心相距约200 - 250微米；这些值与上述预测值一致。我们得出结论，实验确定的敏感区域代表单个机械感觉末梢的感受野（在阈值时）。每平方毫米大约有二十到三十个这样的区域。5. 使用两个探针通过遮挡技术测量单个机械感觉轴突（即感觉“单位”）的感受野。这些感受野的大小从0.05到2.5平方毫米不等，并且通常组织为离散区域，它们之间只有少量重叠。单个轴突为五到七十五个机械感受器提供神经支配。6. 这些发现为涉及蝾螈皮肤机械感觉系统可塑性的定量研究提供了基础。
