1. You conduct an experiment to examine the effect of temperature on conduction
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Question
1. You conduct an experiment to examine the effect of temperature on conduction velocity in the frog nerve. In the first measurement at room temperature of 22°C determine the conduction velocity is 40 meters/sec. Then you cool the nerve to 10°C and determine the conduction velocity is now 25 meters/sec. What accounts for the difference in conduction velocity?
2. You perform an experiment with the frog sciatic nerve in a nerve chamber. Remember that in the frog nerve the axons are not bundled together as they are in human nerves. You stimulate the nerve at one end and record the compound action potential (CAP) in mV at the other end. You repeat this experiment and increase the stimulus voltage by 0.1 V each time and record your results for each stimulus in the table below (total of 18 stimuli).
Stimulus No.
Stimulus (V)
CAP (mV)
Stimulus No.
Stimulus (V)
CAP (mV)
1
0.0
0.0
10
0.9
1.99
2
0.1
0.0
11
1.0
2.29
3
0.2
0.28
12
1.1
2.11
4
0.3
0.54
13
1.2
2.20
5
0.4
0.79
14
1.3
2.16
6
0.5
1.08
15
1.4
2.25
7
0.6
1.40
16
1.5
2.25
8
0.7
1.58
17
1.6
2.25
9
0.8
1.89
18
1.7
2.25
Action potentials are all or none usually producing a voltage of about 30 mV.
a. Why did the amplitude of the voltage recorded from the nerve increase as we increased the stimulus intensity in this experiment?
b. Why does the CAP value stop increasing once the stimulus strength reaches 1.4 mV?
Stimulus No.
Stimulus (V)
CAP (mV)
Stimulus No.
Stimulus (V)
CAP (mV)
1
0.0
0.0
10
0.9
1.99
2
0.1
0.0
11
1.0
2.29
3
0.2
0.28
12
1.1
2.11
4
0.3
0.54
13
1.2
2.20
5
0.4
0.79
14
1.3
2.16
6
0.5
1.08
15
1.4
2.25
7
0.6
1.40
16
1.5
2.25
8
0.7
1.58
17
1.6
2.25
9
0.8
1.89
18
1.7
2.25
Explanation / Answer
1.Conduction velocities are affected by a factors, including age, sex, and various medical conditions like temperature.we calculate conduction velocity in mm/ms .Low temperature cause slower nerve conduction velocities (NCVs), and increases amplitudes of muscle and nerve potentials.which leads to difference in conduction velocity.
2.(a) as the amplitude increased as the stimuli increased. This occurred because of the differing sizes and thresholds of nerve fibres within the whole nerve. Larger nerve fibres have low threshold stimuli than smaller ones, hence larger fibres were activated first, followed by smaller ones. As stimulus strength increased, the larger nerve fibres began firing followed by the activation of the smaller ones,This was because all the nerve fibres were to be activated.
(b) as the increasing stimulus strength increases response amplitude. thus increasing the level of stimulus causes more single nerve fibres to reach threshold and fire action potentials, thereby increasing the amplitude of the CAP. it is called maximal stimulus .As the stimulus strength increased there was an increase in response amplitude as a consequence of the number of action potentials generated, and it continued to increase until a maximum value was reached.further increases in stimulus result caused no changes in response amplitude (at 1.4mV)
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