Effects of temperature on conduction velocity
We will now compare and contrast the effects of varied temperatures on the latency and conduction velocity of the ulnar nerve.
You will be recording latencies to stimulation of the elbow, after first setting the forearm to the following temperatures: 18, 25, 32, and 39. Stimulus strength in this experiment is fixed at 12 mA.
Please note that in a real-world experiment, the order of temperatures should be randomized to prevent order effects. However, for the purposes of this simulated laboratory, any order is suitable.
Set the bath to the desired temperature then immerse the entire arm in the bath.
Timer: 0:00:00
Once the arm is at the desired temperature, press Stimulate to record a CMAP response.
Stimulus strength: 12 mA
Temperature: ???
Perform three trials at each temperature and record your results in the table below.
| Temperature (°C) | Trial no. | Measured latency (ms) | Distance (mm) | Conduction velocity (m/s) |
|---|---|---|---|---|
| Lowest temperature (18°C) | ||||
| 18 | 1 | 300 | ||
| 18 | 2 | 300 | ||
| 18 | 3 | 300 | ||
| Room temperature (24°C) | ||||
| 24 | 1 | 300 | ||
| 24 | 2 | 300 | ||
| 24 | 3 | 300 | ||
| High temperature (29°C) | ||||
| 29 | 1 | 300 | ||
| 29 | 2 | 300 | ||
| 29 | 3 | 300 | ||
| Higher temperature (34°C) | ||||
| 34 | 1 | 300 | ||
| 34 | 2 | 300 | ||
| 34 | 3 | 300 | ||
| Highest temperature (39°C) | ||||
| 39 | 1 | 300 | ||
| 39 | 2 | 300 | ||
| 39 | 3 | 300 | ||
Graph of your results
Theory
The effects of temperature on Ulnar N CV that you observed in the simulation are most likely due to the sensitivity of voltage-gated Na+ channels (and other channels) to temperature.
As noted by Sarria and colleagues (see below for reference) as well as others, temperature significantly affects voltage-gated Na+ channels, influencing their activation, inactivation, and overall excitability.
Similarly, Ruff (1999) has shown in mammalian skeletal muscle fibres, that temperature changes the fraction of Na+ channels that were excitable at the resting potential., with only 30% of channels being excitable at the resting potential when temperature was 19°C, but this increased to 93% of Na+ channels being excitable at the resting potential when temperature was 37°C.
References:
- Sarria I, Ling J & Gu JG (2012) Thermal sensitivity of voltage-gated Na+ channels and A-type K+ channels contributes to somatosensory neuron excitability at cooling temperatures, J Neurochem 122(6), 1145-1154. doi.org/10.1111/j.1471-4159.2012.07839.x
- Ruff RL (1999) Effects of temperature on slow and fast inactivation of rat skeletal muscle Na+ channels Am J Physiol 277(5), C937-C947. doi.org/10.1152/ajpcell.1999.277.5.C937