SLE1/MODULE 2- Activation Signals Flashcards
neuron is a type of ____
cell
where do neurons sit
extracellular fluid (ECF)
concentration gradient
refers to the movement of ions, into/out of the neuron
membrane potential
the change in potential across a cell membrane
resting membrane potential
no active signaling is occuring
-cell is at resting state
how do cells communicate
through membrane potential changes + movement of ions
resistance
how hard it is for an ion to cross the membrane
if there are a lot of doors/channels for the ion to go through, there is low/high resistance
LOW resistance
-high resistance if there are few channels
movement of ions causes ____
depolarizaition/hyperpolarization
depolarization
becoming more positive
hyperpolarization
becoming more negative
what does cell depolarization/hyperpolarizaiton do
modulates the chances of neuronal discharge
the neuron rests at a positive/negative membrane potential
negative
how is resting membrane potential (RMP) disrupted
ionic flow
ionic flow
the diffusion of ions
ions typically flow in what direction
high to low concentration
-different if energy is inputted into the system
through what does diffusion occur
via resting channels that are constantly open
if a bunch of positive ions enter a cell, we have depolarized/hyperpolarized
depolarized
if a bunch of positive ions exit a cell, we have depolarized/hyperpolarized
hyperpolarized
if negative ions enter a cell, we have depolarized/hyperpolarized
hyperpolarized
if negative ions exit a cell, we have depolarized/hyperpolarized
depolarized
Na+ goes into/out of cell
into (influx)
K+ goes into/out of a cell
out of (efflux)
why do nerve + muscle cell membranes generate potential differences
to pass current or to store charged particles
what does the membrane consist of
-lipids
-proteins
what is the membrane also called
phospholipid bilayer
phospholipid bilayer is permeable/impermeable
almost impermeable
-very tightly bound + almost impermeable to ions
-ions that CAN cross the membrane do so through specialized proteins, called ion channels
another name for ion channels
conductors
conductors enable nerve + muscle cells to do what
transmit changes in membrane potential
lots of ion channels/conductors = low/high resistance = low/high conductance
low resistance + high conductance
if ions pass through ion channels in a certain direction, what will happen
memrbane potential will change
3 properties of ion channels
-conduct ions rapidly
-recognize + select specific ions
-most of them open + close (gating) in response to specific electrical, mechanical, or chemical stimuli
are channels specific to specific ions
YES
-only recognize specific ions
-won’t let just any ion through
4 primary types of ion channels
-ligand-gated
-phosphorylation-gated
-voltage-gated
-stretch or pressre-gated
ligand-gated ion channel
binding of a chemical transmitter
-chemical transmitter binds to ion channel to open/close
phosphorylation-gated ion channel
phosphorylation of protein
-protein gets a phosphate added on
voltage-gated ion channel
change in membrane potential
-open/close in response to changes in membrane potential
-MOST IMPORTANT
stretch or pressure-gated ion channels
mechanical stimulus
-mechanical stimulus occurs + the channel is responsive to that particular stimuli
ligand-gated channels
open when a chemical ligand binds to a receptor site to allow ion flow
voltage-gated channels
open when a voltage changes to allow ion flow
2 types of voltage-gated channels
-Na+ channels
-K+ channels
Na+ channels are slow/fast to open
fast
K+ channels are slow/fast to open
slow
leak channels
channels without gates
-ions can move however they like, freely
-cell can be at resting membrane potential with these channels because as things go in, the same amount go out at rest
leak channels are ____ at rest
active
leak channels are largely responsible for establishing what
resting membrane potential
leak channels have selective permeability to ____
K+
-but also some Na+ and Cl-
are leak channels enough to re-establish concentrations of ions after muscle activation on their own
no
-if an AP happened, concentrations deviate from normal + leak channels ARE NOT enough to re-establish the original concentrations prior to the AP
equation for calculating resting membrane potential
Goldman Hodgkin Katz equation (GHJ)
Goldman Hodgkin Katz equation considers what 3 primary ions
-sodium
-potassium
-chloride
THESE IONS ALL IMPACT RMP
why do we frequently see squid nerve in physiology
because it’s nervous system is very simplistic
what unit is cell membrane potential measured in
mV
concentration is indicated by what
[brackets]
what unit is concentration measured in
millimoles
cytoplasm
inside cell
extracellular fluid
outside cell
equilibrium potential
the ion’s “happy place”
-when the chemical + electrical forces are balanced for a given ion
KNOW THIS
resting membrane potential for most neurons
about -65 or -70 mV
what sets the RMP
combination of all the equilibrium potentials of each ion (K+, Na+, Cl-, Ca2+, A)
-KNOW that not just one of these ions creats the RMP but all of them do + each have different levels of say in contributing
what ion has a BIG say in determining RMP compared to other ions
K+
-all contribute, but K+ has a stronger say
K+ equilibrium potential
-75
Na+ equilibrium potential
+55
Cl- equilibrium potential
-60
Ca2+ equilibrium potential
+145
whic equation calculates the equilibrium potential of an ion
Nernst equation
Nernst equation
includes concentration of ion inside the cell, concentration of ion outside the cell, temperature, constants
-the sign of the ion is taken into account
when we have active signaling, what does the resting membrane potential become
membrane potential
-no longer resting
resting membrane potential is calculated by ___
GHK
resting membrane potential is influenced by what
the equilibrium potentials of indivdual ions
equilibrium potentials of individual ions are calculated by ____
Nernst
the movement of K+ and Na+ are active/passive at RMP
passive
at RMP, the diffusion of K+ and Na+ is called what
leak currents
-aka through leak channels
current
the flow of positive charges
-both the influx of Na+ into the cell + efflux of Cl- out of the cell
both the influx of Na+ into the cell + efflux of Cl- out of the cell are described as ____
inward currents
know that current refers to POSITIVE charges
the diffusion of an ion across the membrane depends on what
balancing 2 forces
-chemical force
-electrical force
chemical force
due to the concentration gradient
-ex: how much sodium there is inside vs outside
electrical force
electrostatic force due to potential difference across the membrane
-has to do with the CHARGE
net driving force
combination of chemical + electrical driving forces
-magnitude of force acting on an ion
net driving force equation
NDF = membrane potential - equilirbium potential
sign of net driving force indicates what
direction
negative net driving force
ions are moving IN
-influx
positive net driving force
ions are moving out
-efflux
electro-chemical gradients:
flux of K+ ions across resting membrane depends on what
balance of outward chemical force + inward electrical force, as well as K+ membrane conductance (# of resting channels)
if there is a lot more K+ on inside than out…
chemical force is outward for K+ at rest
-K+ concentration gradient drives K+ out of the cell
if the inside of the cell is negative and K+ is positive…
there is an inward electrical force for K+
-since opposites attract with electrical charges
cation
positive ion
*See slide 17, image could be used on quiz
opposites ___
attract
-likes repel
conductance
has to do with # of channels/conductors
-impacts permeability aka ability of an ion to move across a membrane
-therefore has a say in membrane potential
K+ has low/high conductance
high
Na+ has low/high conductance
low
Cl- has low/high conductance
medium
Cl- current
no current because - charge
-current is only + charges
leak channels are also called
resting channels
are leak/resting channels enough to help re-establish concentrations of ions after muscle activation on their own
no
-needs sodium potassium pump
KNOW THIS
what % pumps are active under resting conditions
5%
concentration gradients generate what
RMP
what does a cell need to passively diffuse its ions indefinitely
a mechanism to maintain the gradients
-like the sodium potassium pump
Na+/K+ pump (sodium potassium pump)
a transmembrane protein that returns the ions to their regions of high concentration using ATP for energy
active signaling
refers to an AP
4 steps of sodium potassium pump
-the sodium potassium pump binds 3 sodium ions + a molecule of ATP
-the splitting of ATP provides energy to change the shape of the channel; the sodium ions are driven through the channel
-the sodium ions are release to the outside of the membrane + the new shape of the channel allows 2 potassium ions to bind
-release of the phosphate allows the channel to revert to its original form, releasing the potassium ions on the inside of the membrane
sodium potassium pump:
the unequal transfer of the ions is in what net direction
net outward current
sodium potassium pump:
the ELECTROGENIC action of the pump
the unequal transfer of the ions results in a net outward current that maintains the negative charge on the inside of the membrane
sodium potassium pump location on membrane
spans entire membrane
sodium potassium pump: binding sites for K+ are on outside/inside
outside
sodium potassium pump: binding sides for Na+ are on outside/inside
inside
sodium potassium pump: binding sites for ATP are on outside/inside
inside
sodium potassium pump: what happens to ATP each cycle
ATP is hydrolyzed each cycle of the sodium potassium pump
-3 Na+ are removed from inside
-2 K+ are returned to inside
sodium potassium pump moves K+ in/out and Na+ in/out
K+ in, Na+ out
what causes the net outward current of the sodium potassium pump
the UNEQUAL transfer of K+ and Na+ ions
-this returns us back to the negative charge of the of the resting membrane
RMP in mV
-65 or -70 mV
threshold
the voltage the cell must get to in order to develop an AP
EPSP
excitatory post-synaptic potential
what happens right before AP returns to resting potential
big negative overshoot
all or none
while a stimulus below the threshold will not produce a signal, all stimuli above the threshold will produce the same signal
-the amplitude + duration does not change
-a stimulus that doesn’t get to threshold will not produce any signal
-anything that hits threshold will 100% produce an AP
steps of an AP
RMP ->
threshold level ->
depolarization ->
repolarization ->
hyperpolarization
what happens at the threshold level step of an AP
-local potential change
-graded potential
what happens at depolarization stage of an AP
opening of voltage gated Na+ channels
what happens at repolarization stage of an AP
-closure of Na+ voltage gated channels
-opening of K+ voltage gated channels
what happens at hyperpolarization stage of an AP
vtolage gated K+ channels remain open after the potential reaches resting level
-this is what causes the graph to dip BELOW threshold level
depolarization is excitatory/inhibitory
excitatory
-membrane becomes less negative
how does depolarization happen
-POSITIVE charged ions carry the current on the inside of the membrane so that the potential difference across the membrane is reduced
-enhances the ability of postsynaptic cell to generate an AP
how does hyperpolarization happen
-NEGATIVE charged ions carry the current on the inside of the membrane so that the potential difference across the membrane is amplified
-decreases the ability of postsynaptic cell to generate an AP
what is the primary communication system between the neuromuscular system + beyond
APs
FDI
first dorsal interosseous muscle
-we love studying this muscle in humans because small size + doesn’t affect other muscles
neuromuscular propagation
transformation of the nerve action potential into a muscle fiber AP
what assists the propagation of the descending command
myelin
signal down brain descending center -> spinal cord -> muscle contraction is ____
unilateral direction
voluntary contractions have unilateral/bilateral direction
unilateral
voluntary contractions have ____
refractory period
refractory period
think of slug analogy
-there is a period for APs where no other APs can occur until fully reset
-because things in nervous system move so fast, there is no problem with this
continuous conduction
signals have no blocks/bumps/nodes to jump over
saltatory conduction
signals jump from 1 node to another to another
-comes from word “saltar” in Spanish- to jump
-looks like signal is jumping from parts of the neuron
-not ACTUALLY jumping, just looks like it because there are little nodes or segments of myelin that helps propagate signals faster/slower based on how much myelin there is
*do we need to memorize Nernst equation? and GHK equation?
IF SO- see slide 27
