6 - Resting Membrane Potential Flashcards
What are the resting membrane potentials for:
- Cardiomyocytes
- Neurones
- Skeletal myocytes
- Smooth myocytes
-80 mv
-70 mv
-90 mv
-50 mv
How is the membrane potential measure?
- 2 electrodes
- Microelectrode (fine glass pipette) filled with conducting solution (KCl) that can penetrate cell membrane
- Diamter of electrode 1 um
What is the resting potential?
The electrical charge across a membrane, expressed as the intracellular potential. (mV)
What is the range of resting potentials for animal cells and nerve cells and what cells have the largest resting potential?
- -20 to -90 mv
- Nerve -50 to - 75 mv
- Cardiac (-80) and Skeletal muscle (-90)
What are the concentrations of Na, Cl, A, K intracellularly and extracellularly?
Why is there a concentration difference extracellulary and intracellularly in ions?
Membrane is selectively permeable due to different ion channels
How is the resting potential generated?
- Membrane permeable to K+ as K+ channels open
- K+ diffuses out of the cell down it’s concentration gradient
- Anions cannot leave cell as membrane not permeable to them
- Generates electrochemical gradient, K+ reaches equillibrium due to electrochemical gradient
How do you work out the membrane potential for a particular ion at equilibrum and why is it not always equal to the actual membrane potential?
- Nernst equation (Ek)
- Membrane not selectively permeable to the one ion alone
What is the resting potential compared to Ek like in:
- Cardiac and Nerve cells
- Smooth muscle cells
- Skeletal muscle
ALL Ek -95mV
- Almost the same, membrane permeable to K+
- Lower, -50mV, membrane less permeable to K+
- In between Ek and Ecl as cells permeable to Cl too
What can changes in membrane potential do?
- Trigger AP
- Trigger and control muscle contraction
- Control secretion of hormones and neurotransmitters
- Post synaptic actions of fast synaptic transmitters
- Transduce sensory information into electrical activity
What are the equilibrium potentials for all of the main ions?
What changes membrane potential and what are the causes of hyper and depolarisation?
CHANGING IONIC PERMEABILITY
Hyper: Opening Cl- or K+ channels
De: Opening Ca2+ or Na+
What is a more accurate way of working out the membrane potential?
What are the characteristics of the acetylcholine receptor?
- Opened by acetylcholine
- Allows cations through, mainly Na, but not fully selective
- Moves membrane potential towards 0 as average of ENa and EK
How can membrane potential change?
Changing permeability of the membrane due to
- Ligand gated channels
- Mechanical gated channels
- Voltage gated channels
What happens during fast synaptic transmission?
What happens at a excitatory synapse?
- Ligand opens depolarising channels, Na and Ca
- Change in membrane potential is called EPSP (excitatory post synaptic potential)
- Longer than AP
- Graded by amount of neurotransmitter
- Acetylcholine and glutamate
What happens at an inhibitory synapse?
- Transmitter opens hyperpolarising channels so membrane permeable to K+ and Cl-
- IPSP
Glycine and GABA
What happens during slow synaptic transmission?
Receptor is not an ion channel, channel is signalled to open in other ways
What other factors can affect membrane potential apart from ion permeability?
- Ion concentration changes extracellularly (e/g eating bananas)
- Electrogenic pumps (Na/K ATPase)
What is bad about high potassium levels in the blood?
HYPERKALEMIA (above 4.5 mmol, 6 severe)
Leads to excitable cells as less K+ leaves cells as less of a concentration gradient so membrane potential less negative and closer to threshold
- Tachycardia
- Palpatations
- Muscle spasms
