Please answer all questions clearly In order to study the characteristics of a n
ID: 89281 • Letter: P
Question
Please answer all questions clearly In order to study the characteristics of a nerve message in a achillian reflex before and after it passes through the spinal cord, we use the experimental set up presented in document 1 and we realize the experiments described below. The experimental set up document 1 shows the location of the stimulating electrodes on the afferent fibers and that of recording electrodes O1 permits recording the effect of stimulations of one or more afferent fibers;Oscilloscopes O2 and O3 permit recording the electric responses of motor neurons M1 and M2 respectively at the level of the implantation cone. Oscilloscope O4 permits recording the electric activity at the level of the axon of motor neuron M1. Experiment 1: We apply two successive effective stimulations on one of the afferent fibers Fa1, and we vary the time between these two stimulations. The results, recorded by O2, are shown in document 2. 1- Interpret the results obtained in document 2. Experiment 2: We apply stimulation of increasing intensities on the afferent fibers and we record the results on the four oscilloscopes (document 3). 2- Explain the recordings obtained by O1. 3- Compare the recordings obtained by O2 and O4. Draw out the corresponding characteristics of the nerve message. 4- Indicate the type of summation which is revealed by experiment 2 at the level of the motor neuron M1. Justify the answer. Each of the motor neurons M1 and M2, innervates a muscle intervening in the achillian reflex that possible extension of the foot. 5- Specify, by referring to documents 1 and 3, and by using the acquired knowledge, the motor neuron innervating the flexor muscle. Justify the answer.
Explanation / Answer
1) The axon potential in a motor neuron begins when the depolarisation reaches the threshold limit. In the document 2, they have described about the electrical activity in a motor neuron following two different electrical stimulus. In the beginning, two electrical stimulus were at an intreval of 5 ms. Gradually the time intreval was reduced successively. Finally, when the time intreval between the two stimulus decreased to a critical level, the threshold limit of depolarisation is reached and the action potential is generated.