Lab #3 Chapter 7 Neurophysiology of Nerve Impulses Lab #3 Activity #1 The Resting Membrane Potential Lab Report
Discuss the relative permeability of the membrane to Na+ and K+ in a resting neuron.
Membrane permeability of a resting neuron to K+ is four to five times greater than for Na+
The membrane has open K+ channels and changing extracellular K+ concentration results in a change in membrane potential. Changing the extracellular Na+ concentration does not significantly change the membrane potential. What did your results suggest about the number or the state (open or closed) of Na+ channels in the resting membrane of a neuron
Na+ channels are mostly closed
Which way would Na+ move across the membrane if there were open Na+ Channels
Na+ would diffuse into the cell
Explain why increasing extracellular K+ causes the membrane potential to change to a less negative value.
Resting membrane potential is negative because the negative charge inside the cell is greater than the positive charge outside the cell. Increasing extracellular K+ increases the positive charge outside the cell. This decreases the difference between the inside and outside of the cell.
What is the approximate concentration of K+ inside a typical cell (intracellular concentration)?
150 mM
What is the approximate concentration of Na+ outside a cell (extracellular concentration)?
150 mM
What is the approximate concentration of K+ outside a cell (extracellular concentration)?
5mM
What is the approximate concentration of Na+ inside a cell (intracellular concentration)?
5mM
Discuss how a change in Na+ or K+ conductance would affect the resting membrane potential.
A change in K+ conductance would have a greater effect on resting membrane potential than a change in Na+ conductance because the membrane is more permeable to K+.
Explain why a change in extracellular Na+ did not alter the membrane potential in the resting neuron.
A change in extracellular Na+ results in little change to resting membrane potential because the plasma membrane of a neuron is only slightly permeable to Na+ because it contains relatively few Na+ leakage channels. This inhibits net diffusion of Na+ into or out of the cell.
what caused a change in membrane potential from -70 to -40 in the cell body?
an increase in extracellular K+
What had the most negative voltage
between the inside of the axon and the outside of the axon with control K+ ECF
A negative membrane potential was recorded when the tip of the microelectrode was
both inside the cell body and inside the axon
what effect does increasing extracellular K+ have on the net diffusion of K+ out of the cell
it decreases net diffusion of K+
What is the polarity of the resting membrane potential (voltage)
negative
The membrane of most cells, including neurons, contains passive, open, K+ leak channels. Given the normal K+ concentrations and the resultant concentration gradient, which direction would K+ be expected to move (diffuse) through these leak channels
out of the cell
what does it mean that the voltage just inside the membrane is negative?
there are more negative charges than positive charges just inside the membrane
Explain why increasing extracellular K+ reduces the net diffusion of K+ out of the neuron through the K+ leak channels.
There is usually more K⁺ inside the cell relative to the extracellular environment. Increasing extracellular K⁺ reduces the concentration gradient, thus reducing net diffusion of K⁺.
