3 The resting membrane potential Flashcards
How is resting potential set up across cell membrane?
K+ channels open at rest, K+ flows out of cell along conc. gradient
as K+ leaves cell, it becomes more negative inside - attracting K+ not to move out - reaching equilibrium between concentration and electrical gradient
What is equilibrium potential for an ion and how is it reached? what is the resting membrane potential?
the concentration at which an ion’s electrical and concentration gradient is balanced
reached through more channels opened for that particular ion - the more open, the greater the membrane potential towards that ion
e.g. K+ is -95mV, but resting membrane potential is -90mV due to other ions (-75mV without K+)
How is the equilibrium potential for an ion calculated?
Nearnst equation
Ex = Equilibrium for ion x
Ex = 61/z log (10) [x] outside / [x] inside
z = valency e.g. Ca2+’s valency is +2
Outline how ligand-gated channels can give rise to synaptic potentials:
fast synaptic transmission: why is it called fast synaptic transmission?
What are the 2 types of fast synaptic transmission?
receptor is ligand-gated ion channel (NOT GPCR)
- excitatory post synaptic potentials (EPSP)
- inhibitory post synaptic potential (IPSP)
What is excitatory post synaptic potential (EPSP)?
depolarising transmitter (ligand signal) opens POSITIVE reversal potentials (makes cell less negative) lead to excitation of cell --> increase membrane potential --> closer to depolarising threshold selective for Na+, Ca2+ and other cations (positives)
What is inhibitory post synaptic potential (IPSP)?
hyperpolarising transmitters - opens channels which lead to NEGATIVE reversal potential - membrane more hyperpolarised (-ve)
e.g. K+ (out), Cl- (in) leading to inhibition
What is slow synaptic transmission and what are the 2 types of slow synaptic transmissions?
receptors isn’t an ion channel - signals to ion channel e.g. GPCR
- within the membrane
- intracellular messenger
Concept of selective permeability, and how it arises in cell membrane
selectivity: only 1 or few ions species let through e.g. K+, Na+, Cl-, Ca2+
ligand (ATP, nicotine) / voltage (Ca2+, Na+) gated - conformational change of protein channel
flow down electrochemical gradient - passive
regulate AP by opening / closing Na+/K+ channels
Describe how ‘within the membrane’ of slow synaptic transmission work
involves GTP binding protein
GTP binds to G-protein coupled receptor (activating it)
G-protein then travels along the membrane to bind to the protein channel on the membrane activating it
Describe how ‘intracellular messenger’ of slow synaptic transmission works
through signalling cascade, G-protein DOESN’T DIRECTLY bind to the protein channel e.g. close K+ channel
neurotransmitter binds to receptor
alpha subunit of G-protein dissociates, GTP binds to a-subunit
a-subunit binds to adenylate cyclase: ATP –> cAMP
cAMP activates PKA, phosphorylating K+ leak channels
K+ leak channels then shut preventing K+ form leaking (more +ve in)
When GTP phosphorylates to GDP then the a-subunit binds to beta + gamma
Define depolarisation and explain the mechanism that can lead to it
inside of cell becomes less negative (normally more neg than outside)
opening of Na+ and Ca2+ channels causing influx of Na+ and Ca2+ (enters cell along conc. gradient - passive)
Define hyperpolarisation and the mechanism that can lead to it
inside of cell even more negative than normal when compared to the outside of cell
opening of K+ channels (efflux) and Cl- channels (influx)
What is membrane potential?
the difference in voltage between inside & outside of cell
How is resting membrane potential measured?
using a microelectrode (fine pipette), penetrates membrane in conducting solution of KCl
What are the membrane potential range of values for muscle, nerve and animal cell?
muscle: -80mV to -90mV
nerve: -50mV to -75mV
animal cell: -20mV to -90mV
