Week 5: membrane potentials and action potentials Flashcards
Potassium concentrations in/out of nerve cell
Potassium is high concentration in nerve fiber membrane
low concentration outside cell membrane
How does electropositivity occur outside cell membrane
Ions flow out and carry positive electrical charge with them
Effect of positive ion outflow of cell membrane
Diffusion potential decreases (until is ceases)
Diffusion potential at which K+ diffusion ceases (from in–>out of cell)
-94 mV
Diffusion of sodium in/out of cell and overall membrane potential
Sodium diffuses into cell (positive charge) and creates overall potential +61mV
Nerst equation explaination
Greater ration of ions = greater tendency for ion do move in one direction = greater Nerst potential REQUIRED to PREVENT additional diffusion
The Nerst equation explores
The relation of diffusion potential to ion concentration difference
Sodium concentration (inside vs outside of cell)
High outside of membrane, low inside
Nerst Potential refers to inside or outside of membrane?
Inside of membrane
Nerst potential assumes that potential of extracellular fluid =
0
Nerst potential of a membrane is positive if
Ion diffusing in—>out is negative
Nerst potential of a membrane is negative if
ion diffusing from inside—- out is positive
The Goldman Equation
Calculates the diffusional potential when membrane is permeable to many ions
The Nerst equation assumes that
A membrane is only permeable to one ion
The Goldman Equation factors in: (3)
- Polarity of electrical charge of each ion
- Permeability of the membrane (K+ is more permeable than Na+)
- Concentration of ions on the inside and outside
What ions are most important for developing membrane potentials in nerve and muscle fibers?
Na, K, Cl
_______ is the key for determining voltage
Permeability
Which ions have changing permeability during action potentials?
Na and K
Which ions have fixed permeability during action potentials
Cl
Resting membrane potential of nerves(calculated from goldman equation)
-70 mV
2 Factors that account for the negative membrane potential
- Sodium-Potassium pump pumps more + ions out than in (3 Na out, 2 K in)
- K+ leak channels out
more positives out of cell than into cell = negative
Does Na or K have a higher magnitude inside:outside ratio
Potassium
K+ inside: K+ outside = 35
Na+ inside: Na+ outside = 0.1
How do neuron action potentials begin?
Sudden change from resting negative membrane potential —> positive potential
Once a neuron’s action potential starts, it
moves along the nerve fiber until the fiber’s end
Action potential stages:
- Resting
- Depolarization
- Repolarization
Depolarization definition and cause
Potential rapidly rises (becomes less negative)
cause: membranes become more permeable to sodium
Repolorization definition and cause
Re-establishment of normal negative resting potential
Cause: Sodium channels close and potassium channels open (K+ rapidly diffuses out of cell)
Once action potential threshold is met:
It always fires and always goes the length of the neuron
Sodium permeability is facilitated by
Activation/Inactivation gate
Sodium gate at rest (neuron action potentials)
Gate is closed, prevents entry of sodium ions into nerve fibers
What happens to trigger activation of depolorization?
membrane potential becomes less negative
What is the trigger range (mV) for depolarization
-70 - -50 mV
What happens to sodium gates when action potential depolarization threshold is met?
It has a conformational change and Na+ permeability rapidly increases
What causes the increase in mV that lead to activation of depolarization
Na+ outflow by sodium-potassium pump (3+ out, 2+ in = more positive on the outside)
Inactivation of Na+ gate
Voltage quickly increases with inflow of Na+ and gate quickly shuts
(happens within a few 10,000ths of a second)
Repolorization of membrane potential
Sodium channels close (no more + flows in) and Potassium channels open (more + flows out)
At rest, potassium channels are
Closed
As the membrane becomes more positive, potassium channels
Open and potassium diffuses out
During depolarization, __________ flows in _____
During depolarization, Na+ flows in rapidly
During repolorization, ______ flows in_____
During repolarization, K+ flows out slower
During conductance, at rest K concentration is ____ than sodium (inside cell)
greater than
During action potential, sodium conductance _____
Increases 5000 fold
How does Ca+ contribute to membrane potential becoming positive?
Voltage gated channels allow Ca+ to flood in, increasing overall + charge
Deficits in Ca+ lead to______. Why?
highly excitable neurons
Neuron can’t get all the way to resting potential - it does not repolarize all the way
What is the threshold for action potential?
-65 mV?
Propagation means
impulse travels in all directions
Action potentials follow an _______ principle
all-or-nothing
Schwann cells create
myelin sheath in myelinated axons in PNS
Myelination _____ speed of transmission
insulates and increases speed of tranmission
Ions flow through _____
Nodes of Ranvier
Electrical currents flow through
Extracellular fluid and axoplasm
Myelination ____ velocity of nerve transmission
increases nerve transmission
Oligodendroytes
Similar to myelination, but in central nervous system
What factors change sodium ion diffusion/cause excitation (3)? Examples?
- Mechanical (pressure distorts membrane)
- Chemical (i.e excitatory neurotransmitters/ligands bind and open Na+ gate)
3.Electrical (membrane potential increases, action potential starts)
Membrane stabilizing factors _____ excite ability
Decrease
Examples of membrane- stabilizing factors
- calcium ions
2.Procaine and tetracaine (Na channels more difficult to open)
What can create acute local potentials?
Small electrical stimulations
Refractory period
Membrane needs to return to resting potential before it fires again
acute sub-threshold potentials
Do not trigger a full action potential
Saltatory conduction
Action potentials occur node to node jumping
