Lecture 7: Resting Membrane and Action Potentials Flashcards
Why do cells become excited and what are excitable tissue?
Cells become excited so that they are able to communicate with their interior or other cells.
Nerves and muscle.
How do cells become excited?
Prior to cells becoming excited, they begin at their resting membrane potential. In order for them to become excited, a signal is needed to activate and transmit it.
RMP changes from rest based on
Changes in charge across the membrane due to
- Different ions
- Different electrochemical gradients
Muscles rely on changes in resting membrane potential to do what?
They rely on signals received from motor neurons to initiate contraction in a process called excitation- contraction coupling.
Are all signals the same?
No. Some are graded potentials and some are action potentials.
Skeletal muscle concentrations of K+
Inside: 155mM
Outside: 4.5mM
Skeletal muscle concentrations of Na+
Inside: 12mM
Outside: 145mM
Skeletal muscle equilibrium potential for K+
-95mV
Skeletal muscle equilibrium potential for Na+
+67mV
In skeletal muscle, which has a higher concentration inside the cell: K or Na+.
K+ (155 inside/4.5 outside)
Na+ has a higher concentration outside (145 outside/12 inside)
How do we get a RMP?
K+ is higher inside the cell and Na+ is higher outside, resulting in a RMP that is (-).
This is due to the K+ leak channels and the Na/K ATPases.
K+ will flow out of the cell via K+ leak channels and be brought back in through Na+/K+ ATPases, which will move 3 Na+ out while bringing 2 K+ in.
RMP is primarily due to the permeability of the plasma membrane to ____________ ions.
K+
Is the membrane permeable to K+, Ca2+ or Na+
The membrane is somewhat permeable to K+, but not to Na+ or Ca2+.
Movement across the membrane to establish the RMP is controlled by what?
- K+ leak channels
2. Na/K ATPases.
Na+/K+ ATPases move how many Na and K?
3 Na+ out
2 K+ in
K+ leak channels
K+ leak channels are open all of the time and permit the unregulated passage of cells.
They are present at a 100:1 ratio compared to Na+ leak channels.
Is K+ more likely to leave the cell? or Na+ to enter?
K+ to leave the cell.
RMP for skeletal and cardiac muscle
-80 to -90 mV
RMP for neurons
-60 to -70 mV
RMP for smooth muscle
-60 mV
What forces allow us to develop a membrane potential?
- Chemical gradient (diffusion forces)
2. Electrical gradients (electrical gradients)
Diffusion forces
Diffusion forces help to establish a membrane potential. Ions will move from a high concentration to a low concentration.
Electrical forces
Opposite charges will attract, like charges repel. As ions move to either side, a charge will develop and prevent further movement of that ion.
What is the combined force that determines the movement of ions (development of a membrane potential)?
Electrochemical gradient (diffusion force + electrical force).