A) determine the change in sodium and potassium ion concentrations (both interna

ID: 3478401 • Letter: A

Question

A) determine the change in sodium and potassium ion concentrations (both internal and external) after 1,000 action potentials.

- you can ignore chloride for this problem

- use reasonable values for initial sodium and potassium ion concentration

- assume the neuron is a cylinder with an average diameter in the midrange for class A fibers; the neuron length is 100 mm

- the neuron is contained in a 10 ml environment

- use typical ion conductance values for resting and excitation states

- use this info: sodium influx = 4.33 picomoles per sq. cm per AP

potassium efflux = 4.26 picomoles per sq. cm per AP

B) use the values from A to determine the change in resting membrane potential after 1,000 APs

Sodium ion concentration Internal- 15Mmol/l

Potassium ion concenytation internal- 150mmol/l

Sodium ion concentration external- 150mmol/l

Potassium ion concenytation external- 5Mmol/l

class A fiber diameter 12-20 micrometer

since length is 100 mm the surface area is 1 0 sq.cm

length- 100 mm

sodium influx = 4.33 picomoles per sq. cm per AP

potassium efflux = 4.26 picomoles per sq. cm per AP

so if sodium influx is 4.33 per sq.cm per AP

for 1000 AP it is 43.300 picomoles

So sodium inside is 4.3 mmol

so if potassium efflux = 4.26 picomoles per sq. cm per AP

for 1000 AP it is 42.600 picomoles

So potassium outside is 4.26mmol/l

Hence Resting membrane potential after 1000 AP is around 33 mv

Because of repeated AP sodium conductance will be increased thereby increasing the resting membrane potential.

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