Neuronal Biophysics Flashcards
(63 cards)
Ohm’s Law:
1) I = ?
2) G = ?
3) I = ?
I=GV
G= 1/R
I= V/R
What describes the relationships between current (I), voltage (V), conductance (G) and resistance (R)?
Ohms law
According to ohm’s law if voltage increases what happens to current?
What if resistance increases?
Current increases
Current decreases
What is the Nernst equation?
What is the simplified version at 37*C?
Ex = RT/zF ln [x]o/[x]i
Ex = 61.5 log [x]o/[x]i
What are the extracellular and intracellular concentrations of Cl-?
Ex 123mM
In 4.2 mM
Remember that valency and charge affect the Nernst eq. What are the equations for Ca2+ and Cl-?
Eca = RT/2F ln [X]o/[X]i
Ecl = RT/F ln [X]i/[X]o
What happens to the ratio of extracellular to intracellular ion conc in the Nernst eq if the ion is negatively charged?
Inverted
What eq shows contribution of different ions to resting potential?
Goldman-Hodgkin-Katz
If membrane permeable to Na and K what’s is the GHK eq at 37*C?
Vm = 61.5log (Pk[k]o + Pna[na]o)/(Pk[k]i + Pna[na]i)
What creates an asymmetric distribution of ions across the membrane?
Integral membrane proteins: Ion channels, pumps and transporters
What is an important feature of an ion channel?
Selective permeability
What’s different between the movement of ions through ions channels and transporters compared to pumps?
Channels/transporters move ions down electrochemical grad
Pumps move ions AGAINST electrochemical grad
What part of a VG ion channel contains the selectivity filter?
Pore
Structure of pore determines which ions pass
VG ion channels have a gate which controls the pore but what controls the gate?
Voltage sensor
Movement of sensor causes conformational changes in channel protein cause gate to open
Describe the structure of a VG ion channel
4 identical subunits/domains
Each domain contains 6 transmembrane alpha helices (s1-s6. S4 is voltage sensing)
How does the K+ selectivity filter work?
Interactions between K+ and waters if hydration replaced by interactions with O2 atoms lining pore that bind K+
Why can’t Na+ pass K+ selectivity filter?
Too small
Can’t contact O2 atoms on both side of filter, not thermodynamically efficient to remove waters of hydration
How do Na channel gates work? (Activation and inactivation gates)
Activation gate (m) opens upon depolarization Inactivation gate (h) blocks pore 5ms after depolarization
How do Na channel gates contribute to refractory period?
Inactivation gate (h) remains blocking pore for a short time after depolarization Further Na influx not possible
What is mainly responsible for setting resting Vm?
What else contributes?
Background K+ activity
Na+ and K+ ATPase
Activation of which channels depolarise the membrane and is therefore excitatory?
Na+
Ca2+
Non selective cation channels
Activation of which channels hyperpolarize membrane and are inhibitory?
K+
Cl-
What are the Nernst potential for: K, Na, Ca, non-selective cation and Cl-?
Ek= -90mv Ena= +65 mv Eca = +110 mv Ecat = 0 mv Ecl= varies, in adult CNS usually -90mv
What is the equation for driving force of an ion?
Driving force = Vm - Eion
