Help finding Maximum Depolarization of the membrane above threshold.

In summary: The membrane potential can be found using the Nernst potentials and the given conductances. The membrane potential is -56.41mV.
  • #1
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Homework Statement


We will deal here with a certain identified synapse in the CNS of the mooncalf (Bos lunaris). The post synaptic cell has voltage-sensitive channels like the squid axon-- a rapidly depolarizing, inactivating channel which conducts only sodium ions, and a slowly depolarizing, non-inactivating channel which conducts only potassium ions. For our purposes, these are the only channels present in this neuron.
Ion concentrations for mooncalf blood and for the cytoplasm if this neuron are given below:
[Na] Cyto = 5mM
[Na] Blood = 500mM
[K] Cyto = 300mM
[K] Blood = 30mM

The membrane of this neuron at resting has a conductance to sodium ions, gNa, .1mS/cm2 and a conductance to potassium ions, gK, of 1mS/cm2.

After a large, rapid depolarization the maximum (peak) sodium conductance is 50 mS/cm2 and the peak potassium conductance is 50 mS/cm2.

What is the max depolarization of the membrane above threshold? (Your answer must be within +-2mV)
What is the max hyperpolarization of the axon below resting? (Within +-2mV)

What is the highest value of dV/dt -- the slope of the voltage curve -- that you could possibly observe the moment the voltage trace crosses 0mV during the depolarization phase of an action potential. Assume that the membrane capacitance = 1muF/cm2.

Homework Equations



ENa = [itex]\frac{RT}{zF}[/itex]*ln [itex]\frac{[Na]o}{[Na]i}[/itex]

The Attempt at a Solution



EK = -56.41mV
ENa = +112.83mV

I am self studying the materials posted at MIT OCW Cellular Neurobiology and this is from problem set #1 and I am using the text by Kandel et al. "Principles of Neural Science". I started by finding the Nernst potential of the ions using the concentration figures given. However I don't really know what value they are wanting, so I don't know where to proceed from here. I know what depolarization means, but I don't know what they are asking in the quantitative sense. Also I know what threshold means, but I could not find a "threshold" value for this neuron, so I really don't know the range of acceptable values. Thanks in advance.

Joe
 
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  • #2
After further searching and reading in another book, I think they are asking me to find the membrane potential using the Nernst potentials I found and the conductances given. This can be done using the equation for membrane potentials. Is it safe to assume a threshold which is roughly 5mV more positive than the resting potential?

Joe
 

Related to Help finding Maximum Depolarization of the membrane above threshold.

1. What is maximum depolarization of the membrane above threshold?

Maximum depolarization of the membrane above threshold refers to the point at which the membrane potential reaches its peak during an action potential. This is typically around +40mV.

2. How do you measure maximum depolarization of the membrane above threshold?

Maximum depolarization of the membrane above threshold can be measured using an electrode inserted into the cell's membrane, which detects changes in voltage. This is also known as an action potential recording.

3. What factors can affect the maximum depolarization of the membrane above threshold?

The maximum depolarization of the membrane above threshold can be affected by various factors, including the concentration of ions inside and outside the cell, the presence of neurotransmitters, and the activity of ion channels.

4. Why is it important to find the maximum depolarization of the membrane above threshold?

The maximum depolarization of the membrane above threshold is important because it is a critical step in the process of generating an action potential. It also allows researchers to study the functioning of neurons and the mechanisms of signal transmission in the nervous system.

5. How does the maximum depolarization of the membrane above threshold differ between different types of neurons?

The maximum depolarization of the membrane above threshold can vary between different types of neurons, as they may have different ion concentrations and ion channel properties. For example, neurons involved in motor coordination may have a higher maximum depolarization compared to sensory neurons.

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