Neurophysiology of Nerve Impulses Activity 1: The Resting Membrane Potential 1. Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels? Activity 2: Receptor Potential 2. You are at the dentist and the hygienist squirts really cold water on one of your teeth and you flinch. They ask you: "did that hurt?" and of course you say yes. Which of the following receptors was likely responding to the stimulus? a. Muscle Spindle b. Pacinian Corpuscle c. Olfactory receptor d. Free nerve ending 3. The amplitude of the receptor potential is proportional to the strength of the stimulus. a. True b. False Activity 3: Threshold 4. Failure to reach threshold voltage in an axon could be caused by which of the following? a. A graded potential that makes the axonal resting membrane potential less negative. b. A graded potential that is insufficient to depolarize the axon. c. Application of the correct stimulus type. d. Depolarization of the axon hillock that opens voltage-gated sodium channels.
Activity 4: Importance of Na+ Voltage-gated Channels After you recovered from the squirt of very cold water in the dentist office, the dentist applied lidocaine. When the cold water was administered again, the water had no effect. Explain the reason for this. Activity 5: Measuring Absolute and Relative Refractory Period 5. If the stimulus is strong enough a second action potential can be triggered during both the absolute and relative refractory periods? a. True b. False 6. What determines the length of the absolute refractory period? Activity 6: Coding for Stimulus Intensity 7. Sound, light, taste, touch and smell do not come in one level. We are able to describe the intensity of a stimulus (i.e. the loudness of a sound or the brightness of a cars headlight). What are the mechanisms used by the nervous system to communicate intensity via the following? Graded potentials: Action potentials: