ionic movement, membrane potentials and action potentials Flashcards
the amount of ions able to cross a membrane is based on what?
number and activity of transport proteins
Conductance of ions is based on what?
-the number of channels that are open
what are the two kinds of exclusion ion channels have because they are so specific?
- size exclusion
- charge exclusion
how does charge exclusion work?
-interior of the channel will be lined with charged amino acids prevent like ions from crossing
what are leak channels open?
-they are always open
what is an example of leak channels?
K+ and Cl- channels
what are gated channels?
closed until a stimulus opens them
what can act as a stimulus for gated channels?
- ligands
- second messenger
- voltage
- light
when is a ligand gated channel open and when does ir close?
- opens when proper ligand binds to it
- remains open until ligand is removed
what is an example of second messenger gated channels?
- calcium channels in smooth muscle cells
- Angiotensin II binds to its receptor and causes the production of IP3
- IP3 binds to and opens calcium channels
what is an example of a voltage gated channel?
-sodium channel in muscles
which type of channel would have the most rapid effect on ionic flow?
ligand gated
which type of channel could lead to a more varied cellular response?
2nd messenger gated
what happens when ions move down a concentration gradient?
they generate a current
movement of ions continues until when?
-when they reach their equilibrium potential
what is the equilibrium potential?
-potential difference required to stop ion movement
what do ions move in response to?
concentration and charge
what would you use the Nernst equation for?
determining the equilibrium potential
the sign of the equilibrium potential is with respect to what?
the interior of the cell
what is RMP?
- resting membrane potential
- charge difference across cell membranes due to concentration gradients of permeant ions
what is the RMP in neurons? in skeletal muscle?
- 70 in neurons
- 90 in skeletal muscle
increasing permeability of what to 100% would cause the greatest change in RMP?
calcium
what is an action potential?
- rapid changes in membrane potential
- depolarization from and repolarization to RMP
are all action potentials for the same cell type the same?
-yea hella similar
what does it mean by all action potentials are propagated?
-they have to move from one site to the next!
what does it mean by all action potentials are all or nothing?
-if they reach specific voltage, then it will occur
what happens are local depolarization?
- membrane moves closer to zero mV
- losing polarity
what is the threshold?
- about -60mV
- point at which AP has to occur
what is overshoot?
-interior becomes positive relative to the outside
what is repolarization?
-membrane begins to move back towards zero and more negative
what is hyperpolarization?
-membrane becomes more negative past the RMP
RMP is maintained by what?
K+ leak currents (K+ conductance)
what is necessary for RMP? what is moved?
- Na-K ATPase
- 3 Na+ out for 2 K+ in to make inside more negative
in what cells is RMP not stable?
-rhythm generating cells (intestine and heart cells)
what is the major contributor to the RMP?
K+ current through leak channels
what is responsible for the depolarization of action potentials?
voltage gated Na+ channels
local depolarization is stimulated by what?
ligand gated Na+ channels
local hyperpolarization is stimulated by what?
ligand gated Cl- channels
