Crayfish Lab Report

November 9, 2012

Dr. Marvin

Results:

Figure 1. Firing Rate of Tonic Receptor in Response to Stretch. The correlation between Firing Rate and Stretch of the slow adapting crayfish receptor for four different sets of data is represented in this figure. The recordings are taken at stretches of 2, 4, 6, 8, and 10 mm of the crayfish tail. The best fit lines for the different sets of data are as follows: Ali and Emily- Linear best fit line, Dave and Laura- Exponential best fit line, Jimmy and Amina-Exponential best fit line, Tala and Jen-Linear best fit line).

Figure 2. Class Average for Firing Rate of Tonic Receptor in Response to Stretch. The firing rate of the slow-adapting receptor neuron in response to stimulus, which in this experiment is the stretching of the Crayfish tail at 2, 4, 6, 8 and 10 mm.

Figure 3. Rate of Adaptation of Tonic Receptor held at Constant Length (6mm). The best fit line for the rate of adaptation of the Tonic receptor is Logarithmic. At a constant stimulus, the initial firing rat drops and levels off at a constant firing rate representing the presence of a stimulus.

R2 Values for Linear, Exponential and Logarithmic Lines for each Data Set | Curve Type| R^2|

Tala, Jen| Linear| 0.982|

| Exponential| 0.982|

| Logarithmic| 0.982|

Dave, Laura| Linear| 0.982|

| Exponential| 0.982|

| Logarithmic| 0.746|

Jimmy, Amina| Linear| 0.950|

| Exponential| 0.976|

| Logarithmic| 0.824|

Ali, Emily| Linear| 0.988|

| Exponential| 0.934|

| Logarithmic| 0.965|

Class Average| Linear| 0.995|

| Exponential| 0.966|

| Logarithmic| 0.920|

Discussion:

3. Frequency vs Stretch

a) In our classroom experiment, after dissecting and preparing our crayfish tail, we sucked up a MRO receptor neuron with our electrode to record firing of the nerve as we adjusted the length of the crayfish tail using a string attached to both the micromanipulator and the end of the tail. Unlike our classroom experiment, the methods for Delcomyn and Krnjevic and Van Gelder’s experiment dealt directly with the MRO strand, to be more specific –the isolated abdominal stretch receptors of the crayfish. In Delcomyn’s experiment, the MRO strand was held at each end by forceps and a microelectrode was inserted into the cell body of the sensory neuron. Gentle manipulations of the forceps caused a stretch in the MRO generating a generator potential in the strand that caused a spike potential in the sensory neuron. As stated earlier, methodically, Krnjevic and Van Gelder’s experiment didn’t differ significantly because they too interacted directly with the MRO receptor neuron. The independent variable in each experiment was the stretch applied to the neuron. The dependent variable for our classroom experiment and Delcomyn’s experiment was the firing rate, but Krnjevic and Van Gelder’s experiment contained an additional dependent variable—tension (which is linearly related to the firing rate).

b) According to Krnjevic and Van Gelder’s Figure 7, stretch and tension are linearly related. The graphs reveal that with increasing tension, firing rate and tension increase progressively faster. The relationship of both tension and firing rate to stretch are exponential (Krnjevic and van Gelder, 1961). Because of the differences in our methodical approaches, our classroom experiment is not directly comparable to Delcomyn or Krnjevic and van Gelder’s. The author’s data is much more comparable because Delcomyn and Krnjevic applied stretch directly to the MRO strand, so the stretch in mm is directly comparable for the two. In our classroom experiment, we have a much bigger range because we dealt with the entire crayfish tail, so much of the movement in millimeters goes into lifting the tail itself.

c)

The best-fit curve for my results of firing rate vs. stretch applied is exponential. Similarly to Delcomyn’s results, my stretch...