Lecture 32 - Action Potentials Flashcards
Which of the following is not a GATED ion channel?
leak channels
Which ion channels are responsible for the repolarization phase??
K+
In the CNS, which cell type produces myelin??
Oligodendrocytes
the cell membrane acts as a
selective filter
describe the structure of the cell membrane
phospholipid bilayer stippled with transport channels and proteins
what are the 3 types of gated ion channels
- voltage-gated
- ligand-gated
- mechanically-gated
what gate responds to a change in membrane potential. give an example.
voltage-gated
Na+/K+ channels
what gate responds to the binding of a neurotransmitter. give an example.
ligand-gated
NMDA
what gate responds to a physical change in the membrane. give an example.
mechanically-gated
mechano-receptors in skin
T/F: leak channels are always open
TRUE
cations
positive charge
anion
negative charge
____ is the main extracellular cation while ____ is the main anion
Na+; Cl-
the main intracellular cation is ____
K+
what two gradients are there
- concentration
- electrochemical
the sodium-potassium ATPase pump transports what in and out of the cell
3 Na+ out
2 K+ in
what is the function of the sodium-potassium ATPase pump
stabilize membrane potential
what is the resting membrane potential? what is this value in neurons?
the electric potential difference across plasma membrane when non-excited
-70mV
Describe electrochemical equilibrium
as potassium leaks out of the cell, the intracellular fluid becomes more negative and thus attracts the potassium back to the cell
*opposing forces acting on potassium crossing the plasma membrane
The nerst equation signifies
the relationship of electrical and chemical forces acting on any ionic species across a semipermeable membrane
explains the electrochemical potential
temporal summation
effect when impulses received at the same place on the neuron add up
spatial summation
effect when simultaneous impulses received at different places on the neuron add up
what is the threshold potential
value at which an action potential can be triggered
-50-55mV
T/F: action potentials are short-lived and are considered all-or-none signals
TRUE
Depolarize
getting closer to zero
Repolarize
potassium in charge
bringing back to -70mV
What are the 4 phases of action potentials
- resting state
- depolarization
- repolarization
- hyperpolarization
Summarize the resting phase of action potentials
all gated Na+ and K+ channels are closed
resting membrane potential maintained
Summarize the depolarization phase of action potentials
Na+ channels open
Na+ influx causes more depolarization
at the threshold of positive feedback causes a large spike (+30 mV)
Summarize the repolarization phase of action potentials
Na+ channels inactivate, K+ channels open and go down their gradient
returns to resting potential
Summarize the hyperpolarization phase of action potentials
some K+ channels remain open allowing efflux and membrane dips slightly below resting voltage
What is the refractory period
period in which the cell is incapable of repeating an action potential
absolute - cannot generate
relative - possible, greater stimulus
Pacemaker cells
noncontractile cells that spontaneously depolarize in heart
3 parts of action potential in pacemaker
- Pacemaker potential: K+ channels closed, Na+ open. the interior becomes more positive
- Depolarization: Ca2+ channels open (-40mV) contributing to rise of potential
- Repolarization: K+ channels open, allowing efflux, and becomes more negative
summarize a contractile cardiac action potential
- depolarization opens Na+ channels (rise AP from -90mV to +30mV)
- depolarization by Na+ leads to opening of Ca2+ channels (at +30mV Na+ channels close)
- after 200ms, Ca2+ channels close and K+ channels open. RMP achieved
myelin sheaths ____ conduction velocity and _____ energy efficiency
increase; improve
