Flashcards in Excitable cells Deck (87):
activation to initiate an event
Extracellular fluid is also referred to as:
what is the composition of interstitial/extracellular fluid?
- primarily ions, proteins
- similar to plasma in ion content
- High NaCl level
what is the composition of intracellular fluid (aka cytosol)
-much higher [ ] of proteins
- Main salt in cytosol- KCl
CHanges in permeability, that are ________ and ________ are essential to excitation in cells
ion-specific and exquisitely timed
random diffusion, diffusion down electrical gradient or concentration gradient
-organic molecules or ions
________ organic molecules diffuse rapidly through the membrane. why is this?
non-polar organic molecules
- this is because they are readily soluble in the lipid membrane
Ions cross membranes through ______
what is flux?
amount of substance crossing a surface per unit of time
________ is the difference between the two unidirectional fluxes
what happens during mediated transport?
-ligand binds to a transporter in the membrane
-transporter undergoes a conformational change
-ligand is released on other side of membrane
what are the 2 types of mediated transport?
1) facilitated diffusion
2) active transport
what are the three factors that determine the rate of flux?
1) number of transporters in the membrane
2) extent of transporter saturation
3) rate of transporter conformational change
what are the types of channels involved in mediated transport?
total solute concentration in a solution
1 mole NaCl = ______ osmoles
what is the osmolarity of extracellular fluid?
what is the mOsm of an isotonic solution? hypertonic? hypotonic?
isotonic- 300 mOsm
hypotonic- less than 300 mOsm
hypertonic- greater than 300 mOsm
a hypoosmotic solution contains what?
less than 300 mOsm of non-penetrating plus penetrating solutes
what is a hyperosmotic solution?
greater than 300 mOsm of non-penetrating plus penetrating solutes
What is endocyctosis? Pinocytosis? phagocytosis?
Endocytosis- engulfment of fluid and particles
Pinocytosis- small particles with/without small volume of ECF
Phagocytosis- large particles or cellular debris
Voltage (V) = ________
current (I) x resistance (R)
Conductance (G) = ________
Current (I) divided by Voltage (V)
conductance is the _______ of resistance
current across cell membranes is an _________
actual flow of electrons
what is the definition of equilibrium?
balance of voltage and concentration
-note: voltage and concentrations can differ between the 2 solutions and they can still be in equilibrium
the nernst equation yields the __________ of a single ionic species
equilibrium potential (AKA the equilibrium voltage)
diffusion potentials occur due to an _______
asymmetric ion flow- an imbalance in the flow of an ion between 2 compartments
a _________ can also be maintained at a steady level over time
there are higher concentrations of ______ inside the cell, and higher concentrations of _____ outside
Potassium (K) - higher inside the cell
Sodium (Na) - higher outside the cell
there is a ____________ across the plasma membrane for potassium
Pk (permeability of K+) is much higher than ____
at what voltage is the membrane potential when equilibrium is reached for potassium?
-70 to -90 mV
(this is close to the equilibrium potential for K+…. -100mV)
Na+ diffuses into the cells own both of its _______ and ________
concentration gradient and electrical gradient
at rest, what ion diffuses out of the cell and what ion diffuses into it?
K+ goes out of the cell
Na+ goes into the cell
change of the membrane potential toward 0mV is referred to as "________"
what is hyper polarization?
increase in membrane potential from the resting value
- becoming MORE negative
without the Na/K ATPase pump, what would happen to the resting membrane potential?
it would slowly dissipate to 0 mV
T/F: even large changes in membrane potential will not effect the overall concentration of ions
true- an extremely small fraction of total ions moving can cause a large membrane potential
the most common change in membrane potential is referred to as the _________
where are the most common sites of action potentials in the body?
neurons and muscle cells
action potentials are _______ events that are _______ over a distance
propagated over a distance
action potentials usually first develop in the ___________ of the axon
what is the first step in the development of the action potential?
increase in the membrane permeability to sodium ions
sodium enters the cell, being driven by what?
the electrical and concentration gradients
as sodium rushes across the cell membrane, what happens to the membrane potential?
it moves closer to 0 mV
if the depolarization is sufficiently large, a point will be reached, the "______", which causes additional Na channels to open
the Na channels that open during a threshold depolarization are know as _______-regulated
during an action potential, the membrane potential overshoots 0mV and reaches a peak at what voltage?
after a peak of 40 mV has been reached, ____ channels open
-K ions move across the plasma membrane from the inside to the outside
what happens to the cell during the "falling phase"?
- K+ ions diffuse out of the cell, carrying the positive charge with them
- membrane potential abruptly reverses directly and returns to resting value
T/F: the afterpolarization phase can last much longer than the polarization/depolarization phases
the peak of the action potential (at 40 mV) approaches the equilibrium potential for what ion?
the end of the repolarization phase is close to the equilibrium potential for ______
the latency period precedes the _____ of the AP which is that portion of the rising phase before threshold is reached
what is a stimulus that is greater than the threshold stimulus?
T/F: local responses move along the membrane
they do NOT move along the membrane
what happens to a AP after a supra threshold stimulus is reached?
the action potential continues to completion and propagates along the entire length of the axon
how does a graded potential differ from an action potential?
a graded potential's amplitude is proportional to the strength of the stimulus (its not "all-or-none")
what is the difference between the absolute refractory period and the relative refractory period
absolute- cell cannot propagate another AP
relative- a suprathreshold stimulus can still elicit an AP, but a normal threshold stimulus cannot
Important stimulus parameters for neurons:
1) intensity (amplitude)
3) rate of change
what is "adaptation" of a neuron?
the transition from from closed-state to the open-state of the channels is dependent on the rate of stimulus change
basically, a nerve cell will respond to a quickly applied stimulus, but not a slowly applied one
_______ is a property of the neuron and its due to __________ of ion channels
adaptation of the neuron
accommodation of the ion channels
T/F: passive currents will propagate
current flows from the _____, through the neuron, to the ________
anode --> cathode
the cathode causes cations to move toward int, in both the ______ and __________
extracellular fluid and inside the cell
the stimulus that occurs at the site of a cathode will result in what?
a depolarizing potential change at that site
-will cause local currents around that site
-cause depolarization of adjacent regions
T/F: one AP does not actually move long the entire axon
-every site along an axon undergoes a change in membrane potential
the initiation of the AP at each site of the neuron is dependent on what?
local currents from the adjacent site
-cause a depolarization of the membrane that opens Na+ channels
_______ cells surround the axons of neurons
what are the names for the periodic nodes found along a myelinated nerve cell
nodes of ranvier
the action potential "skipping" along the axon of a myelinated cell is known as what?
loss of myeline prolongs the __________. what will this cause?
- will lower the maximal AP firing frequency
a peripheral nerve will express a _______ of several Action Potentials, due to its composition of axons of many neurons
composite of several AP's
the _______ of an action potential is dependent on the diameter of the axon
Velocity dependent on diameter
T/F: axons with larger diameters will have slower velocities of conduction
larger diameter= higher velocity
what is the sequence of events from an AP in a motor neuron to the fusion of neurotransmitter to the motor endplate?
- AP travels along motoneuron axon
- AP invades presynaptic terminal
- Calcium ion influx into presynaptic terminal
- vesicle fusion with membrane of presynap terminal
- release of ACh from fused vesicle
- diffusion of ACh across cleft
- binding of ACh to AChR (receptor) in postysnap membrane (motor endplate)
once ACh receptors are activated on the motor plate, what happens?
- Opening of Na+ and K+ channels
- Na+ influx and small K+ efflux across motor endplate
- generation of ENDPLATE potential
- opening of voltage-regulated Na+ channels in SARCOLEMMA immediately surrounding endplate
- AP is initiated in SARCOLEMMA
T/F: endplate potentials are graded, are not all-or-none in amplitude, do no not propagate, and can undergo summation
_______ are small EPP's that occur spontaneously and result from release of ACh
(miniature endplate potentials)
T/F: MEPP's and EPP's can be spontaneous
only MEPPs are spontaneous
are EPPs or MEPPs confined to the end-plate region?
BOTH are confined to the end-plate region
what is the role of acetylcholinesterase? (AChE)
creates acetic acid and choline
how does the botulinum toxin differ from curare and organophosphates?
botulinum toxin blocks ACh release
Curare- blocks AChR's
organophosphates- block AChE
what is a “Rheobase”?
“Rheobase”: magnitude of least intense stimulus that can elicit a response.
__________ is the duration required to elicit a response by a stimulus with a rheobase magnitude.