LAB 5 - Michele Ahmadi: Systems Physiology Lab 5 Tues-...

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Michele Ahmadi: Systems Physiology Lab 5 Tues- 6:40-10:00, Jen Results Electrical stimulation was administered from the spinal-end of the nerve at 0.2V, 0.5V, 1.0V, 1.75V, and 2.0V. Subsequent changes in electrical potential caused by the nerve’s impulse were measured by electrodes at the distal-end of the nerve. A threshold of 0.2V was provided as well as maximum stimulation amplitude of 2.0V. Amplitude of response was generated in two-cursor mode by subtracting minimum from maximum voltages. The relationship between stimulus strength and amplitude of response continued as such: a stimulus of 0.2V yielded response of 0.039V, a stimulus of 0.5V yielded response of 0.039V, a stimulus of 1.0V yielded a response of 0.042V, a stimulus of 1.75V yielded a response of 0.156V and a stimulus of 2.0V yielded a response of 0.156V(Fig.1). As the amplitude of the stimulus increased, larger responses were generated. Plateau and threshold voltages, already provided, were labeled accordingly. Figure 1: Graph of Stimulus Amplitude and Response Amplitude. Measurements taken with iWorks electronic stimulator.
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Speed of conduction was measured by dividing a change in distance by a change in time of two sweeps. Sweep one had a distance of 0mm while sweep two had a distance of 5mm (0.005m). The difference in time taken for an impulse to travel down the sciatic nerve in situ and at a 5mm altered distance was 0.001sec. Thus 0.005m was divided by 0.001sec to give a conduction velocity of 5m/s. Results were taken by superimposing the two sweeps in one image and then using two-cursor mode to make measurements. Discussion The response amplitude of a large compound nerve such as the sciatic depends on the type and number of individual axons which are recruited by the stimulus. Furthermore, the action potentials that results from axon recruitment is dependent on the unequal distribution of ions –mainly sodium (Na +) and potassium (K + ), as well as the functioning of both chemically and electrically gated ion channels. Using extracellular fluctuations in the ions of a frog nerve (sciatic / Rana catesbeiana) as compared to the intracellular fluctuations, a relationship between magnitude of stimulus and magnitude of response was analyzed and graphed. When stimulated, sodium channels on the neuron open and sodium rushes into the axon, causing a region of positive charge within the axon, known as depolarization. The region of positive charge causes nearby voltage gated sodium channels to close. Just after the sodium
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This note was uploaded on 04/03/2008 for the course EX SCI 01:146:357 taught by Professor Merrill during the Spring '08 term at Rutgers.

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LAB 5 - Michele Ahmadi: Systems Physiology Lab 5 Tues-...

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