Intro to CNS Flashcards
Biological membranes are essentially impermeable to ions
This is because the internal region of the bilayer is very hydrophobic and ions are hydrated by water
Protein families have evolved that function to allow ionic passage across the membrane
- ATPase driven pumps
- Transporters
- Ion channels: some generalities
a) Integral membrane proteins
b) Multiple membrane-spanning domains
c) Form a hydrophobic channel in the center
ion channels
Selective for ions and regulated by :
changes in the cellular environment
Ion Channels have______gene products; multiple subunits and are Glycosylated on the
Multiple
extracellular side
Ion Channels have Consensus sequences for
kinases
non-gated, always open
Passive:
gated; the closed and open states of the channel are regulated
Active
Gating mechanisms
Membrane potential differences
small extracellular molecules (NT)
membrane proteins
intracellular molecules
this type of ion channel is open at RMP and can be either active or passive
leak chanel
all passive channels are
leak channels
intracellular proteins are predominately
anions
leak channels in the plasma membrane allow _____ and _____ movement across the membrane
K+ and Cl-
Conductance of _____ is 20 times greater then to Na
K+
Due to unequal conduction potentials, we see ______ distribution of Cl, K and Na across the membrane
unequal
____ is high inside and low outside
K+
____ and ____ are high inside and low outside
Na and Cl
We have both ____ and ______ for Na, Cl and K across the membrane
chemical and electrical potential
Ena =
+55mV
Ek =
-75 mV
Ecl=
-69mV
Some of the leak is opposed by the NaK ATPase pump that moves _____ions out of the cell and ____ions into the cel
Na
K
ion channels for a ______ channel in the center
hydrophyilic
is the membrane potential at which an ion is in electrochemical equilibrium across membrane
Nerst potential
As we increase conductance to Na we start to depolarize the membrane which leads to
voltage gate Na channels opening
These are more gradual opening and slower inactivation
Voltage gated K+ channels
Action potentials are
all or none; get to 100 mV in amplitude in 1-10 msec
Action potential is propagated down the axon through
cycles of depolarization and repolarization
Mechanisms by which initial change in membrane potential occurs to begin an action potential
Synaptic potential
Synaptic potential have what type of change in membrane potential
graded, short and small
the are LOCAL
and able to summate
graded, short and small
the are LOCAL
and able to summate
Synpatic potential
Two types of synaptic potentials
EPSP and IPSP
membrane potential becomes more positive; if it increases enough, threshold will be reached
Excitatory, postynaptic potential
EPSP can occur by increased conductane of
Na or Cl bc both push for depolarization
– such as Nicotinic chlinergic R or Glutamate receptor
EPSP can occur by decreased conductance of
closing a channel that is open at resting membrane potential; these are slower onset changes that last longer
closing a channel that is open at resting membrane potential; these are slower onset changes that last longer
example of EPSP via decreased conductance
Example of decreaed conductance causing EPSP
Closing a leak channel for K+
see changes in phosphorylation of the channel or regulated by second messenger cascades such as GCPR
Ligand gated chloride channel such as a GABA R is an excample of
IPSP
a) Increased conductance of the membrane to either potassium or chloride
Following are examples of what:
(a) Via direct interactions between the channel protein and G protein
(b) As a result of changes in phosphorylation state of closed K channels (mediated by second messenger cascades)
G protein coupled receptor activation can result in the opening of K channels
causes IPSP
G protein coupled receptor activation can result in the opening of K channels in two ways
through direct interactiosn btwn G protein and K+ channel
as a result of change in phosyphorylation state of K channels that are closed
Resting potential relies of
Channel specificity:
Channel specificity: non gagted K and Cl- channels; some nongated Na
Gating mechanism for resting potential
none
Properties of Resting potential
Usualy steady from -35 to -70 mV
Action potential channel specificity:
Independently gated Na and K channels
Gating mechanism for Action Potential channels
voltage gated
Properties of Action potential
all or none, 100 mV in amplitude; 1-10 msec in duration
Increased conductance EPSP channel specificity:
non-volatge gated channels; nonselective for univalent cations
Incrased conductance EPSP gating mechanism
chemical with extracellular site binding
Properties of increased conductance EPSP channels
graded, fast, several msec in duration and several mV in amplitude
Increased conductance IPSP channel specificity
non-voltage gated chans for K+ or Cl-
Gating mech for increased IPSP
Chemical with extracell binding site
Properties of increased conductance IPSP
graded, fast, severeal msec in duration and several mV in amplitude
Decreased EPSP channel specificity
Potassium leak channesl
Decreased EPSP gating mechanism
Chemical: GPCR then 2nd messenger
Properties of decreased EPSP
graded, fast, several msec in duration and several mV in amplitude
