Chapter 12.2 : Electrical Potentials Flashcards
What are the four types of electrical potentials?
Resting Membrane Potentials
Local Potentials
Action Potentials
Receptor Potentials
All cells have a _____ membrane potential
resting
Nerves have resting potential when
not stimulated
Dendrites exhibit local potentials (similar to receptor potentials) after
stimulus moves resting potential towards threshold
Local potentials are
graded, decremental, reversible, and either excitory or
inhibitory
If stimulus great enough it spreads to the
trigger zone (axon hillock)
If a local potential stimulus reaches trigger zone then it initiates an action potential that
travels down axon (all or none and uni-directional)
Electrical potential
a difference in the concentration of
charged particles separated by a barrier (the unit membrane)
Voltage values may vary depending on
tissue type
Voltage
separation of ions
Electrical current
the flow of ions
in the body, currents created by movement of ions (e.g. Na+ or K+) through gated channels in the plasma membrane
gated channels
are opened or closed by various stimuli
(voltage / ligand / mechanical)
regulated gates enables cell to allow ____ ___ ___ /// results in _______ ______ /// creates mechanism that can be used to ______ cellular events
ions to flow ; electrical currents ; regulate
All living cells are polarized // called the
resting membrane potential (RMP)
resting membrane potential (RMP)
charge difference across the plasma
membrane
What number is the resting potential?
-70 mV RMP
negative value means
there are more
negatively charged particles on the inside of
the membrane than on the outside (like a little
battery)
nervous and muscle tissue may ____ their
resting membrane potential // sequentially
_______ and ______ gates to first
reverse then restore the charge across the
membrane // excitable tissue
alter ; opening ; different
RMP exists because of
unequal electrolyte distribution across
membrane
resting membrane is much less _______ to Na+
than K+
permeable
70% of the energy requirement of the nervous system is
used to power what pump
Na+/K+ ATPase pump
Na+/K+ ATPase pump
Transmembrane protein channels // moves out 3 Na+
and moves in 2 K+ for each ATP consumed
Local potential
Current movement across dendrite and soma
response is initiated at the dendrite then spreads
across the soma to trigger zone
If stimulus great enough then local potential reaches the trigger
zone /// achieves “threshold” and an _______ ______ results
action potential
Other names for local potentials are
end plate potential or receptor potential
Local potential occurs when a neuron
is stimulated by chemicals, light, heat or mechanical disturbance
Sodium ions move into neuron at dendrites or somas when a
neuron is
stimulated
depolarization
Voltage measured across the membrane
drifts toward zero
– Stimulus opens the Na+ gates and allows Na+ to rush in to the cell
– Na+ inflow neutralizes some of the internal negative charge
There are four characteristics that distinguish local potentials from the action potentials. What are they?
Graded
Decremental
Reversible
Either excitatory or inhibitory
Graded
- vary in magnitude with stimulus strength
- stronger stimuli open more Na+
gates
Decremental
- get weaker the farther they spread from the point of
stimulation - voltage shift caused by Na+ inflow diminishes rapidly
with distance
Reversible
- get weaker the farther they spread from the point of
stimulation - voltage shift caused by Na+ inflow diminishes rapidly
with distance
Either excitatory or inhibitory
- E.g. / the neurotransmitter glycine make the
membrane potential more negative - hyperpolarize membrane // less likely to
produce an action potential // inhibitory
Action potentialsis a more ______ change than local potential
dramatic
Does an action potential resemble a positive feedback loop or a negative feedback loop?
positive feedback mechanism
Produced by voltage-regulated ion gates in the plasma
membrane at
axon hillock
the axon hillock is the same thing as the
trigger zone
How many gates per um2 are on a soma?
50-75
How many gates per um2 are on a trigger zone?
350-500
Between the soma and the trigger zone, which one cannot generate an action potential and which one is where the action potential is generated?
soma cannot generate an action potential
trigger zone where action potential is generated
if local potential spreads all the way to the _______ // can
open gates at axon hillock and generate an _______
trigger zone ; action potential
action potential
is a rapid up-and-down shift in the membrane voltage
threshold
critical voltage which local potentials must reach in order to open the voltage-regulated gates at axon hillock
___mV is threshold value in neurons
-55
Action potential occurs so fast it is often referred to as a “____”
spike
Four Phases
Resting – Depolarization – Repolarization - Hyperpolarizing
In an action potential only a thin layer of the _____ next to the cell membrane is affected /// very few ____ are involved
cytoplasm ; ions
characteristics of action potential versus a local potential
all-or-none law
non-decremental
irreversible
all-or-none law
if threshold is reached, neuron fires at its maximum voltage
if threshold is not reached it does not fire
non-decremental
does not become weaker with distance
irreversible
once started goes to completion and can not be stopped
refractory period
the period of resistance to stimulation
during an action potential and for a few milliseconds after, it is
difficult or impossible to stimulate that region of a neuron to
fire again.
two phases of the refractory period
absolute refractory period
relative refractory period
absolute refractory period
- no stimulus of any strength will trigger AP
- as long as Na+ gates are open
- from action potential to RMP
relative refractory period
- only especially strong stimulus will trigger new AP
- K+ gates are still open and any affect of incoming Na+
is opposed by the outgoing K+
refractory period is occurring only at a _______ of the neuron’s membrane at one time. Other parts of the neuron can be
______ while the small part is in refractory period
small patch ; stimulated
for communication to occur, the nerve signal must
travel to the
end of the axon (reach synaptic knobs)
saltatory conduction
the nerve signal seems to jump from node to node
Saltatory Conduction is faster than conduction speed in an _______ fibers
unmyelinated
