How Does Helmholtz Measure The Speed Of The Neural Impulse

Speed of the Human Neural Impulse
Helmholtz (1821-1894) was a German scientist. In 1850, he measured the neural impulse in frogs. By strapping down the frogs and putting electrical voltage into their legs, Helmholtz measured the time it took for the frogs’ leg to twitch. Helmholtz used a galvanometer to measure the neural impulse. He found that the neural impulse in frogs was 83-90 ft/s. Afterwards, Helmholtz went on to test the neural impulse in humans. He put a low grade electrical voltage to humans’ legs and measured the time it took for his participants to press the button (meaning they felt the voltage). He found that the neural impulse in humans was 165-300 ft/s. His results showed that even though neural impulses seem instantaneous,
The participants sat on the floor of a classroom in a circle, and all were approximately an arm’s length away from each other. No informed consent was necessary because the study was low-risk and being used for demonstration purposes. To calculate the speed of the neural impulse, first the time it took to feel pressure needed to be calculated. The timer was an ambidextrous female volunteer from the group of participants. The timer used a laptop to record the time; she started the time while simultaneously squeezing the left shoulder or ankle of the person to the right of her with her right hand to begin a trial. The participants were seated cross-legged when the shoulder condition was being tested, and with their feet flat on the ground with knees up for the ankle condition. Before the initial trials, two practice runs of each condition were completed. Afterwards, the group of participants completed eight trials, alternating between each of the two conditions, in a counter-clockwise manner, with each participant squeezing the next participants body part with their right hand. This hand was chosen because the majority of the participants were right-handed and the alternation between the shoulder and the ankle condition was done to eliminate practice effects. Additionally, the participants had their eyes closed to reduce anticipation
See table one for the times of each trial. The mean time for the ankle condition was 5.27 s, and the mean time for the shoulder condition was 4.53 s. A t-test indicated this difference to be significant, t(7)=-7.28, p=.00. As hypothesized, the ankle condition took significantly longer than the shoulder condition. The second hypothesis was that the speed of a human neural impulse would be faster than the frogs and within the range of Helmholtz’s research. Speed was calculated by dividing distance by time. The distance was the sum of the measurements from the participants ankle to shoulder (976.88 in.). The time was the difference between the average of the ankle and shoulder condition (.73 s). After being calculated and converted, the speed was 110.76 ft/s. The data partially support the hypothesis. The speed was faster than the frogs (83-90 ft/s), but not within Helmholtz’s range for humans (165-300