Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Lecture Notes

HumanBody

NerveImpulses

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Nerve ImpulsesGoals

• Biology: To learn about nerve impulses propagating along motor nerves and understand why eye-foot and eye-hand reaction times are different.

• Physics: To calculate the average propagation speed of the nerve signals along motor nerves.

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Nerve ImpulsesBig Ideas

• Biology: Upon being subjected to stimuli the brain sends electro/chemical signals along motor nerves to the part of the body where a response is desired.

• Physics: The difference in eye-foot and eye-hand reaction times can be attributed to the finite propagation speed of the nerve impulse along the nerve.

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Nerve ImpulsesReaction Times

• On line reaction time tests athttp://getyourwebsitehere.com/jswb/rttest01.html

• Typical eye-hand reaction time is 0.28 s.[1]

• Eye-foot time is more important for emergency braking: typically 0.45 s. [1]

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Nerve ImpulsesReaction Times

•A small portion of the reaction time is due to the time it takes the brain to process the visual signal and to send out the signal to move.

•The remainder of the time is taken for the signal to travel down the nerves to the hands/feet.

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Nerve ImpulsesReaction Times

• The difference between eye-hand (0.28 s) and eye-foot (0.45 s) reaction times is due to the difference in distance that the signal has to travel.

• The distance from your brain to your hands is approximately 1 meter, and from your brain to your feet is approximately 1.6 meters.

• What are the average signal speeds?

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Nerve ImpulsesCalculation

• The extra distance the nerve impulse has to go from your brain to your feet is approximately 0.6 m longer than the distance to your hands.

• It takes (0.45 s - 0.28 s) = 0.17s longer for the signal to reach your feet so the speed of the signal propagating along the nerves is (0.6 m/0.17 s) = 3.5 m/s.

Signal Propagation • Note that this is an average

speed of a signal traveling along one neuron.

• The actual time it takes for the signal to travel along the axon of one neuron can be greater than 25 m/s but to relay the signal to the next neuron across the synapse is about 1000 times slower.

• Here the signal must also cross the synapses by chemical diffusion.

Physics and Astronomy Outreach Program at the University of British ColumbiaPhysics and Astronomy Outreach Program at the University of British Columbia

Nerve ImpulsesBibliography

[1] Journal of the American Optometric Association,   2000, vol. 71, no12, pp. 775-780 (32 ref.)[2] Image from http://upload.wikimedia.org/wikipedia/en/a/a6/Chemical_synapse_schema.jpg