Physiology Lecture 4 (Action Potentials)

Question 1

Membrane Potential

Answer 1

A charge difference across the membraneCaused by diffusion

Vm

Question 2

Cell membrane potentials determine what about the cell?

Answer 2

Their exctibility

Question 3

Excitable cells

Answer 3

Capable of generating electrochemical impulses at the membrane

lower resting potentials

Nerves and muscles

Question 4

What maintains K+ and Na+ concentration levels in the body?

Answer 4

The kidneys

Question 5

If a membrane was permeable only to K+…

Answer 5

…K+ would diffuse down its concentration gradient until the electric potential down the cell membrane countered diffusion

This countering electric potential = K+ Equilibrium Potential (Ek)

The Potassium Nernst Potential (-94mV)

Question 6

If a membrane were only permeable to Na+…

Answer 6

…Na+ would diffuse down its concentration gradient until the electric potential down the cell membrane countered diffusion

This countering electric potential = Na+ Equilibrium Potential (ENa)
The Sodium Nernst Potential (+61mV)

Question 7

What is another name for the Potassium Nernst Potential (Ek)?

Answer 7

The Equilibrium Potential

Question 8

Resting Membrane Potential

Answer 8

-90mV

Caused by concentrations of K+ and Na+ inside and outside of the cell

The inside of the cell is always more negative than the the outside of the cell

Must use Goldman-Hodgekin-Katz Equation to determine Vm of the 2 ions

Question 9

What is the resting potential similar to and why?

Answer 9

Potassium Membrane Potential (Ek)

B/c the membrane potential is more permeable to postassium

Question 10

Goldman-Hodgekin-Katz Equation / Goldman Field Equation

Answer 10

Calculates the Vm of more than one ion

Used to determine the resting potential

Must know the charge of the ion, the concentration gradient, and the permeability of the membrane in order to determine Vm

Question 11

With a normal resting potential, how can the membrane potential become more positive?

Answer 11

By increasing the permeability of the membrane to sodium (i.e. opening gated sodium channels) = sodium rushes into the cell (depolarization)

Question 12

With a normal resting potential, how does the membrane potential become more negative?

Answer 12

By increasing the permeability of the membrane to potassium (i.e. opening gated potassium channels) = K+ rushes out of the cell)

Question 13

What would happen if K+ plasma concentration is increased?

Answer 13

It would cause a decrease in the gradient of potassium causing an increase in the resting potential allowing for easier depolarization

Question 14

How can resting potential be changed?Is it advantageous?

Answer 14

Resting potential can be changed by changing the concentration of extracellular ionsIt is not advantageous because it affects the bodies homeostasis. It is better to change the movement of already present ions (i.e. opening channels)

Question 15

Nerve Action Potential

Answer 15

A regenerating action potential of membrane potential that propagates along and excitable membrane

Stages - Resting Stage (Resting Membrane Potential = -90mV), Depolarization Stage, and Repolariztion Stage

Question 16

Depolariaztion

Answer 16

1) stimulation causes leakage of sodium into cell which increases the me,brane potential from -90mV to a range of -70 to -50mV
2) Voltage-gated sodium channels are activated (activated gate opens) and sodium rushes into cell changing the membrane potential to +35mV
3) Repolarization then occurs in order to reestablish the resting potential

Question 17

Repolarization

Answer 17

1) Once the action potential is reached through depolarization, the inactivated sodium gates close
2) Potassium voltage-gated show slow activation (open) but not inactivation
3) Potassium diffuses out of the cell to, once again, reach the resting potential (-90mV)

A cell cannot reach another action potential while it is in the repolarization state

Question 18

Conduction to skeletal muscles is ——- and to the autonomic muscles (heart, ect.) is ——–

Answer 18

Fast - myelin sheaths allow for faster propagation

Slow - no myelin sheaths

Question 19

What to ions typically initiate depolarization in a nerve cell?

Answer 19

Sodium - faster depolarization

Calcium - slower depolarization (also present in synaptic vessicle at the end of the exon during neurotransmitter release

Question 20

What allows for a faster propagation of an electrical signal in a nerve cell?

Answer 20

The presence of myelin sheaths as insulators. These sheaths allow for the signal to skip over them and only produce action potentials on areas between the sheaths

Question 21

What reestablishes the sodium-potassium gradient in a cell?

Answer 21

Sodium-Potassium ATPase (sensative to intracellular sodium)