Neurophysiology Flashcards
5 steps of neurons responding to stimuli and communicate with distant cells
Resting membrane potential
Graded potential
Action potential
Synaptic activity
Information processing
Resting membrane potential is what
transmembrane potential of resting cell
description of how ions are distributed
at resting membrane potential, what is the inside relative to the outside
negative
graded potential is what
temporary, localized changes in transmembrane potential
cell becomes less or more negative than before
to be meaningful, what change has to occur at a graded potential
a changed caused by a stimulus
when does an action potential occur
if the stimulus is great enough
what happens at action potential
reversal of membrane potential, so the inside is positive relative to the outside
what do action potentials continue along
the axon
what is synaptic activity
occurs once action potentials reach the terminal bouton, then neurotransmitters are released
information processing step has what
when neurotransmitters binds to receptor, then changes occur in postsynaptic cell
What does the cell membrane separate
charges
so ICF (-) and ECF (+)
the membrane is polarized
where does RMP occur
only in thin layer along cell membrane
what is the RMP in neurons or muscle fibers (mV)
-70 mV
what are the 2 points measured between for voltage
reference electrode and recording electrode
Is Na + ICF or ECF
ECF
is K+ ICF or ECF
ICF
What are the passive forces across membranes
chemical gradient
electrical gradient
electrochemical gradient
what is chemical gradient
a concentration gradient
where particles move down the conc gradient
what is the potassium chemical gradient
out
when does electrical gradient occur
if charges are separated
what is the electrochemical gradient determine
the direction that the ion moves if a channel opens
What can small electrical differences offset
large chemical differences
K electrical gradient is
IN
K concentration gradient is
OUT
K electrochemical gradient is
OUT
Na electrical gradient is
IN
NA concentration gradient is
IN
NA electrochemical gradient is
IN
If allowed, how do particles move
down their electrochemical gradient
Ions only cross a membrane if what
if channel or carrier is present in membrane
steps of resting membrane potential
na tends to leak in
k tends to leak out
lots of channels for Cl - to move near equilibrium
anionic proteins are trapped inside cell
examples of active transport
Na/K pump
what does the Na/K pump use and to do what
uses ATP to move ions againnst electrochemical gradients
what is the equilibrium potential used to determine
the directio of electrochemical gradient
equilibrium potential def
the transmembrane potential at which no net movement of a particular ion across the cell membrane
equilibrium potential simple def
net movement in=net movement out
electrical gradient is equal and opposite to the what for an ion in the equilibrium potential
to the chemical gradient
if the channel opens, where do ions move
in the direction that pulls Vm toward E
What is changing membrane potentials def
alter membrane potential by changin membrane permeability to certain ions
how do neurons and muscle cells change permeability
by opening or closing channels in membrane
what are the 3 gated channels
ligand gated
voltage gated
mechanically regulated
ligand gated channels are what
chemical that binds
when binding occurs in ligan gated channels, what happens
the channel opens
what breaks down acetylcholine
acetycholine esterase.
AchE breaks down Ach so that the channel closes
voltage gated channels, what happens at RMP
the activation gate is closed but the inactivation gate is open
if increase vM, what happens to gates
both gates open
if a lot of sodium enters a cell what happens
the pos voltage is achieved and this causes inactivation gate to close
mechanically regulated channels is what
distorting cell membrane by physically pressing on it so that the channel opens
transmembrane potential exists across cell membranes because why?
ICF and ECF have different chemical/ion balances
Graded potention is a deviation from what
RMP due to stimulus
Magnitude is proportional to what
Stimulus intensity
when the cell is stimulated, what happens
na channels open,
so na rushes in
cell becomes more positive/less negative
what type of changes does graded potential enact
local changes only
how far does graded potential travel
short distances
where do sodium ions sit
they dont, they diffuse along membrane
depolarization is what
when Vm becomes less negative/more positive
what channels open during depolarization
sodium channels open so that Na rushes in
OR
potassium channels close so that less K exits out
what happens during hyperpolarization
Vm becomes more negative/less positive
what channels open during hyperpolarization
potassium channels open so that K exits the cell
OR
sodium channels close so that less sodium enters the cell
why do transmembrane potentaisls change
due to altered membrane permeability in response to stimuli
action potentials are what
rapid, dramatic change in transmembrane potental
what happens ruing action potentials
Vm becomes positive, leads to a series
magnitude is similar
propagated without decrement
are action potentials depolarization or hyperpolarization
depolarization … Vm becomes less negative
what is a thrshold stimulus
a stimulus large enough to depolarize axon hillock to -60 mV
what happens if graded potential is smaller?
Bigger?
smaller - no AP is generation
bigger- yes able to generate AP
what does depolarizaing the cell membrane to threshold result in
the generation of an action potential
how long does the action potential feedback loop occur until
until all voltage-gated sodium channels open
what causes the rapid reversal of membrane potential to +50 mV
action potential
how does membrane potential move to +50 mV
all voltage gated sodium channels need to open
pulling Vm toward ENA+
why doesn’t the membrane potential reach ENA+
because voltage gated Na channels start to close when Vm reaches +30 mV
when do voltage gated K+channels open
when Vm reaches about +30 mV
At peak, waht happens to K+ and NA_-+
K+ begins rushing out and NA+ movement across membrane stops mostly
what happens when K+ rushes out
it rushes out down its electrochemical gradient and toward EK+
what is EK+
-90 mV
what is the refractory period
time from beginning of action potential to return to resting state
will membrane respond normally to additional stimulus during the refractory period
no
can a 2nd AP be generated during absolute refractory period
no
what happns during the relative refractory period
2nd AP can be generated, but it requires a larger stimulus and not as big as a normal AP
Sodium channels during Absolute refractory period
sodicum channels open or inactivated
cell is still depolarizing, therefore…cant respond
is additional AP possible during Absolute refractory period
not possible
Gates reset at about - 4o mV
steps of a voltage regulated channel
RMP
threshold voltage where activation gate opens
inactivation gate closes, and activation gates still remains open
what happens to the membrane potential during the relative refractory period
membrane potential is amost normal (between -40 mV and RMP)
Stimulus information during relative refractory period
stimulus greater than threshold can initiate action potential
but a normal stimulus will not
this is because some NA+ channels haven’t reset yet
this counters efflux of K+
what is the propagation of action potentials
series of action potentials along axon toward synaptic knob
what is continuous conduction caused by
unmyelinated axons
5 steps of continuous conduction
- AP depolarizes membrane to +30 mV
- local current depolarizes adjecent membrane to threshold (voltage gated Na channels open)
- generation of another AP
- cycle repears
- AP travles 1 m/sec
why does Na move along membrane
to remove electrical gradient
where is the location of voltage gated sodium channels
between cell body and axon
steps of saltatory conduction (myelinated axons)
- action potential depolarizes membrane to +30
- local current depolarizes adjacent node to threshold (voltage gated Na open)
- generation of another action potential
- cycle repears
- AP travels 50 m/sec
one way propagation of action potentials means what
as next area develops an action potential , the previous area is in refractory period
transmembrane potential reverses if what
if threshold stimulus is reached
series of AP are propagated toward what
axon terminal
properties of AP result in what
one way nerve conduction
what happens at the cholinergic synapse/what are they
all neuromuscular junctions with skeletal muscle
many synapses in CNS
all neuron to neuron synapses in PNS
all neuromuscular and nuroglandular junctions is PSNS
what is the most common neurotransmitter
cholinergic synapse
what is a chemical synapse example
its a neurotransmitter… ex is acetylcholine
do reflexes have less or more synapses
less to make it faster
what are the events at cholinergic synapse… 5
AP arrives at synaptic end knob
Depolarization of synaptic end knob
voltage gated Ca++ channels open
Ca++ enter synaptic knob
Trigger exocytosis of ACH
ACh binds to receptors on postsynaptic membrane
depolarization of postsynaptic membrane
AChE breaks ACh into acetate and choline
what is the delay Cholinergic synapse
0.2 to 0.5 seconds
what happens when AP arrives at synaptic end knob
sodium channels open
what is it called when transmembrane potetential Vm becomes positive
Depolarization
Ca++ influx moves how
down its electrochemical gradient
what does cytoplasmic Ca++ cause synaptic vessicles to do
move along microtubules and fuse with cell membrane
how whcih does ACHE break down ACH
within 20msec of binding to receptors
as ACh drop in synaptic gap, what happens
they are not able to remain attached to its receptor
what do nuerotransmitter direct
effects via ligand gated channels
what is nicotinic
a chemical in cigarrettes that is addictivve
what happens when ACh binds a receptor,
Na channels open, and then Na enters…. causing depolarization
what are the 3 indirect effects via G proteins
- receptor binding of ligand activates G protein
- Activated G protein binds enzyme thus altering its activity
- production of second messenger
what do G proteins do
bind GTP - active which can make GDP - inactive
what do activated g proteins do
turns on or off
where does cAMP accumulate
in cytoplasm
how do enzymes change cell metabolism and activity
by adding/removing phosphates
what does Nuerpiphrine bind
receptors
what happens during the information processing stage
postsynaptic cell can recienve multiple stimuli
why cna one cell receive multiple stimule
bcuz multiple presynaptic cells are coming in contact with it
excitatory postsynaptic potential is what
depolarization: graded potential
inhibitory postsynaptic potential is what
hyperpolarizaiton :graded potential
what is summation
the summed influence of multiple inputs to determine if an AP occurs in postsynaptic cell
what is spatial summation
simultaneous stimuli from multiple synapse
what is temporal summation
send stimuli in rapid succession at single synapse
what is the simplest form of information processing in the nervous system
a change in transmembrane potential that determines whether or not AP’s are generated
What is An excitatory postsynaptic potential (EPSP)
is a temporary depolarization of the postsynaptic membrane that occurs when a neurotransmitter binds to receptors on a neuron
what is An inhibitory postsynaptic potential (IPSP)
is a change in the electrical potential of a postsynaptic neuron that decreases the likelihood of an action potential:
