Physiology Lecture 4 (Action Potentials) Flashcards Preview

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1

Membrane Potential

A charge difference across the membraneCaused by diffusion

Vm

2

Cell membrane potentials determine what about the cell?

Their exctibility

3

Excitable cells

Capable of generating electrochemical impulses at the membrane

lower resting potentials

Nerves and muscles

4

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

The kidneys

5

If a membrane was permeable only to K+...

...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)

6

If a membrane were only permeable to Na+...

...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)

7

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

The Equilibrium Potential

8

Resting Membrane Potential

-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

9

What is the resting potential similar to and why?

Potassium Membrane Potential (Ek)

B/c the membrane potential is more permeable to postassium

10

Goldman-Hodgekin-Katz Equation / Goldman Field Equation

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

11

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

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

12

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

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

13

What would happen if K+ plasma concentration is increased?

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

14

How can resting potential be changed?Is it advantageous?

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)

15

Nerve Action Potential

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

16

Depolariaztion

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

17

Repolarization

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

18

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

Fast - myelin sheaths allow for faster propagation

Slow - no myelin sheaths

19

What to ions typically initiate depolarization in a nerve cell?

Sodium - faster depolarization

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

20

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

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

21

What reestablishes the sodium-potassium gradient in a cell?

Sodium-Potassium ATPase (sensative to intracellular sodium)