What is flow in neuroscience
movement of ions
Why can`t ions pass across the lipid bilayer membrane (in biological liquids)
ions are always enveloped by a hydrate layer
dipole characteristics of water molecules
Ohm´sche law (Resistance)
Voltage(U) = R * Current(I)
Voltage = elektrische Spannung in Volt
Current = elektrischer Strom in Ampere
R = elektrischer Widerstand in Ohm
Name the equation of the capacitance of the membrane?
And what is consequences of thinner membrane
C = e0*e*A*d^-1
e0= dielectricity constant of vacuum
e = dielectricity constant of the membrane
A = membrane area
d = membrane thickness
thinner membrane -> larger membrane area & higher the dielelectricity constatn -> more changes can be stored
What is the NA+K+pump ?
major drain of energy in an organism
for each ATP-> 3 sodium ions(Na+) to outside & 2(K+) postassium-ions inside
maintain major chemical gradients in cells
also called ATPase
What are ion channels? And how are they achieved?
transmembrane proteins that form a hydrophilic pore across the membrane
charged amino acids in center of large 3D protein that form a charged tunnel which allows ions to pass
Are ion channels selective or not?
both
if selective ->entrance of channel carries charges that repel the wrong charges & center of pore has diameter that restrict the passenger further
How does the opening and closing of channel happen? And how does change can be induced?
results from a change in the 3D-dim form of the protein
binding of a ligand
mechanical forces
changes in electric field
What is the donnan experiment?
System with 2 chambers & 1 semipermeable membrane
freely diffusable salt is put into 1 chamber -> equilibrium
1 side with non-diffusable anion is added -> anion will push out other anions & kepp cations on its side -> both side neutral because still equal num of pos an dneg charges
-> for given ion this diff. is theromdynamically bad (2.law -> all substances reach homogeneous distribution in space)
what are the consequences if membrane channels for K+ exist?
if k crosses membrance, it decreases its chemical gradient across membrane
charge gradient is built up -> voltage across membrane -> the more k ions cross membrane the higher voltage gete -> becomes major hindrance of further K ions to cross
given equilibrium point : chemical gradient & voltage gradient cancel each other out -> resulting in zero netto-diffusion across membrane
How can the resulting voltage be computed? (chemical & electrical gradient are in balance & enough time is given)
equate osmotic work and electrical work
Wel = nFE
Wosm = RT*ln(K+a/K+i)
-> E = (RT/nF)ln(K+a/K+i) (Nernst equitation)
R = gas costant; T = temperature in Kelvin; n = number of charges per ion; F = Faradayconstant
How can you simplify the Nernst-equitation?
E = 58log(Kation+a/ Kation+i)
What is the nernst equitation?
Voltage one ion would want the membrane to be at so its a equilibrium
What is the Goldman equilibrium?
The actual membrane voltage resulting from all relevant ions, weighted by permeability.
On what does the contribution of each ion type depend?
conductance
Goldmann equation
Why is the resting potential close to nernst potential of postasium?
Because resting permeability of membrane for potassium is ca 100 times the resting pot. for sodium
What is the cell potential dependetn on?
nernst potentials of all ions & their permeability
Where does the action potential occur
between the nernst potential of ions
How do voltage-gated channel change their form?
voltage across the membrane is altered
open at specific voltage value (threshold)
above -> channel open, below -> closed
How does the voltage-gated sodium(natrium) channel work
possesses 2 gates
1 is controlled by voltage across membrane
if gat opened -> triggers the closing of 2 gate (1ms afterwards)
refreshing channel takes time
Why does the membran potential change during actionpotential
Because permeability change
What happens during resting potential?
Small permeability changes for any ion lead to small changes of the membrane potential
What is the reson for the large dynamic membrance potential change of action potential
at certain threshould all voltage-gated sodium channel open at once & shortly afterwards
When is the sodium permeability the highest?
At the peak, the membrane is mostly permeable to sodium, which is why the potential is close to the sodium equilibrium potential
Name a -e
a = resting potential
b = depolarization
c = upstroke
d = plateau
e = repolariztaion & afterhyperpolarization
What is the result of the still decreasing “possibility to open sodium-channles by voltage” after action potential
refractory period where cell is first not excitable & theny only by strong depolarization
summar of action potential
A neuron is at resting potential.
Sodium channels open (e.g., by binding a ligand such as a neurotransmitter)
A sodium influx results that depolarizes the neuron.
As soon as the threshold of the first voltage-gated (vg) sodium channel is reached, it opens and additional sodium flows in that depolarizes the cell further.
5. A positive feedback couples opening of vg sodium channels, sodium influx and further depolarization and leads to a fast increase in sodium permeability.This eads to the upstroke of the action potential.
6. The voltage-gated sodium channels close after ca 2 msec (GNa goes back to 0).
Now potassium permeability is increased through opening of delayed vg potassium channels that were activated in parallel to the vg sodium-channels.
Inactivation of vg sodium channels and delayed opening of vg potassium channels lead to a repolarization.
After the action potential, the membrane potential temporarily falls beneath theregular resting potential, since both leak channels and vg channels for potassium are open; this is called an afterhyperpolarization.
Only after the vg potassium channels have closed after a delay (closing caused by the voltage returning to resting potential, the former resting potential is reached.
What is refractroy period?
Delayed closing of the v.g. potassium channels
What is absolute PR
too few vg sodium channels are regenerated
positive feedback can not occur
cell is non ecxitable
What is relative PR
num of vg sodium channels that can again be activated is high enough to sustain pos reinforcement
cell needs to be depolarized stronger & resulting sction potential is smaller than regular action potential
What is the Strömchentheorie and why can't the action potential travel backward?
Strömchentheorie (Hermann, 19th century): Early idea that electrical "currents" from excited nerve areas flow to neighboring regions, triggering further excitation.
Modern view: This local current flow contributes to the propagation of the action potential along the axon.
No backward travel: The previously excited area is in the refractory period, so it cannot be re-excited immediately — ensuring one-way signal flow.
Name the 2 different tyoes of potential conductance in neurons
passive
not regenerative & decreases with time and distance
conduction velocity is fast
actively regenerated potential
gen. by vg channels of neuron
propagation of action potential slow (signal needs to be regenerated at each membrane)
Passive eletronic propagation in neurons
Neurotransmitter binds to ligand-gated sodium channel
through the open channels, sodium flows into the cell
the current spreads through the cell
signal strength decreases with distance in the cell
Propagation of passive signals
a long longitudinal axis, decrease of signal is observed
decrease caused by both electric resistance along axis & membrane
stength & time course of signal is altered over distance
How can the range of depolarization be increased
increase membrane resistance by isolation
decrease of inner resistance relative to Rm
Two solution to accelerate AP propagation
giant fibers
isolation of the fiber increases Rm and decreases the capacitance of membrane
Why does the electronic signal propagation loose conduction speed of action potential
Depolarization of next membrane compartment depends on length constant of the fiber
Name factors that determine conduction speed
temperature
time constant
length constant
When is conduction speed fastest
smaller time constant & larger lenght constant
What consequences does electrical isolation of axon have
increases resistance across membrane
decreases the capacity
What is the disadvantage of thick fibers
smaller resistance along the fiber than resistance across the membrane
Where can you find electronic potentials
in dendritic cells
What two structures does the snypase have? And what is the transmitter between them?
pre- and postsynaptic
acetylcholine
What effect a neurotransmitter has at the postsynaptic membrane depends on
trasnmitter
receptor for the transmitter
ion gradients ar postsynpatic membrane
What leads to depolarization and hyperpolarization
depolarization: openingn of channels for soidum or calcium
hyperpolarization: opening of channel for postassium or chloride
what are spines
small computational modules where changes in synaptic strengh can take place (area of memory fomation & learning)
Function of spines
spines are postsynaptic to 1-2 axonal terminals
both biochemical and electrical compartments
What is the difference between EPSCs/IPSCs and EPSPs/IPSPs?
EPSC/IPSC (Post-Synaptic Currents):
Represent ion flow (current), measured in picoamperes (pA)
Require voltage clamp to measure
Can be added algebraically
Reflects instantaneous channel activity
EPSP/IPSP (Post-Synaptic Potentials):
Represent membrane voltage changes, measured in millivolts (mV)
Require current clamp to measure
Summation is non-linear, shaped by membrane properties
Reflects integrated effect of current over time
How can dendrites be changed?
by activity
by excitation spreading back from soma
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