PPP - excitable cells Flashcards
How would you measure the potential of a single ion channel?
patch clamping
What are the ranges in a waveform for intracellular, extracellular and patch clamp electrode recording?
intracellular = -70 - +40 (110mV)
extracellular = 0.1mV
patch clamp = 1pA
What establishes electrochemical gradient?
sodium-potassium pump
How does the cell membrane act like a capacitor?
stores ionic charges on it’s surface
What is capacitance of a membrane?
ability of a membrane to hold charge
What is the membrane potential?
the work required to separate charges on the inner and outer surfaces
What is the equilibrium potential?
when the concentration gradient is balanced by electrical gradient in the opposite direction (no net ion movement)
How can you determine the equilibrium potential?
using the Nernst equation:
E = 58 x log([C]out/[C]in)
What is the average resting membrane potential?
-70mV
What is the equilibrium potential of potassium and sodium?
Ek = -90mV Ena = + 50
Why is the resting membrane potential closer to Ek than Ena?
the membrane is 50x more permeable to K+ than Na+
What determines the driving force of an ion?
Vm-Eeq
What determines permeability of a membrane to an ion?
number of open channels for that ion
What is a problem with the Nernst equation, and how can this be overcome?
- doesn’t account for relative permeabilities of ions
- can use the Goldman Hodgkin Katz equation
Why is a threshold required for an action potential?
as Pk is much greater than Pna at rest, so the flow of K+ can counteract the flow of Na+
What is resistive current?
when current comes from ions moving through a channel
What is capacitive current?
when current comes from ions approaching 1 side of the membrane and another being expelled from the other side
What effect does thin axons have on speed of conduction?
decreases the speed
How do action potentials spread in cardiac cells?
through intercalated discs
What happens at neuromuscular junctions?
- VGCC in pre-synpatic cleft open when cell depolaries
- calcium causes vesicles to release neurotrasmitter into synapse
- Ach binds channels on skeletal muscle causing Na+ to enter and K+ to leave the cell
What is the end plate potential?
The voltage which causes depolarisation of skeletal muscle fibres
Name some drug agonists for neurotransmitter (NT) release?
L-DOPAa - acts as precursor
black widow venom - stimulates NT release
nicotine - stimulates post synaptic receptors
clondine - increases NT synthesis and release
cocaine - blocks Ach reuptake
physostigmine - inactivates acetylcholinesterase
Name some drug antagonists for neurotransmitter (NT) release?
reserprine - prevents vesicles storing NT
botox - inhibits release from vesicles
curane/atropin - blocks postsynaptic receptors
PCPA - inhibits NT synthesis
apomorphine - inhibits synthesis and release of NT
What are miniature end plate potentials (MEPP)?
small depolarisations at the neuromuscular junction which summate to form the end plate potential
What is the excitatory neurotransmitter in the knee jerk reflex?
glutamate
What is the inhibitory neurotransmitter in the knee jerk reflex?
glycine
What is conductance (g)?
the ease with which ions flow
What is capacitance measured in?
farads
