Flashcards in Physiology Lecture 4 (Action Potentials) Deck (21)
A charge difference across the membraneCaused by diffusion
Cell membrane potentials determine what about the cell?
Capable of generating electrochemical impulses at the membrane
lower resting potentials
Nerves and muscles
What maintains K+ and Na+ concentration levels in the body?
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)
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)
What is another name for the Potassium Nernst Potential (Ek)?
The Equilibrium Potential
Resting Membrane Potential
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
What is the resting potential similar to and why?
Potassium Membrane Potential (Ek)
B/c the membrane potential is more permeable to postassium
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
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)
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)
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
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)
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
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
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
Conduction to skeletal muscles is ------- and to the autonomic muscles (heart, ect.) is --------
Fast - myelin sheaths allow for faster propagation
Slow - no myelin sheaths
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
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