Neurophysiology of Nerve Impulses
A C T I V I T Y 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.
Increasing the extracellular potassium reduces the concentration gradient, and less potassium diffuses out of the neuron and into the cell.
2. Explain why increasing extracellular K_ causes the membrane potential to change to a less negative value. How well did the results compare with your prediction? _______________________________________________________________________ A lesser amount of Potassium ions diffuse out across the membrane, leaving behind a less negative charge. The membrane potential became less negative because less potassium diffused out, so it is more positive (K+) = less negative. ______________
3. Explain why a change in extracellular Na_ did not alter the membrane potential in the resting neuron. __________________________________________________ In a resting neuron, there are fewer sodium leakage channels than potassium leakage channels, , and more of the potassium channels are open.
4. Discuss the relative permeability of the membrane to Na_ and K_ in a resting neuron. _____________________________________________________________________ Potassium is more permeable than sodium in a resting neuron. Membrane permeability to sodium is very low because there are only a few sodium leakage channels.
5. Discuss how a change in Na_ or K_ conductance would affect the resting membrane potential. ________________________________________________ A change in permeability would affect the intercellular and extracellular concentration of ions during resting membrane potential. The concentration of Na+ and K+ ions inside and outside the cell are the primary factors that produce the resting membrane potential.
A C T I V I T Y 2 Receptor Potential
1. Sensory neurons have a resting potential based on the efflux of potassium ions (as demonstrated in Activity 1). What passive channels are likely found in the membrane of the olfactory receptor, in the membrane of the Pacinian corpuscle, and in the membrane of the free nerve ending? ______________________________ Olfactory Receptor: Na+ ion channels
Pacinian Corpuscle: K+ leakage channels
Free Nerve Ending: Na+ ion channels
2. What is meant by the term graded potential? _______________________________ A graded potential, or local potential, depends on stimulus intensity. With an appropriate stimulus, the amplitude of the receptor potential increases with stimulus intensity.
3. Identify which of the stimulus modalities induced the largest amplitude receptor potential in the Pacinian corpuscle. How well did the results compare with your prediction? The high pressure modality induced the largest amplitude receptor potential in the Pacinian corpuscle. It had anamplitude response of 40mv.
4. Identify which of the stimulus modalities induced the largest-amplitude receptor potential in the olfactory receptors. How well did the results compare with your prediction? The high chemical modality induced the largest amplitude receptor potential in the olfactory receptors. It had a peak value response of -45 mv and an amplitude response of 25 mv.
5. The olfactory receptor also contains a membrane protein that recognizes isoamyl acetate and, via several other molecules, transduces the odor stimulus into a receptor potential. Does the Pacinian corpuscle likely have this isoamyl acetate receptor protein? Does the free nerve ending likely have this isoamyl acetate receptor protein?
Neither the Pacinian corpuscle, nor the free nerve ending contain the isaomyl acetate receptor protein. The Pacinian corpuscle and the free nerve ending are not likely to have the isoamyl acetate receptor because they did not respond to chemical stimuli.
6. What type of sensory neuron would likely respond...
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