Action Potentials Flashcards
Where is the membrane potential charge
- This is only present in the cell membrane no the whole cell
where does the paracrine signalling act
- Act locally
what does the paracrine system include
ncludes neural; neurotransmitters(NT) released from nerves
- Some neurotransmitters can also be hormones such as adrenaline
- Also directed coupled cells via gap junctions (electrical and chemical coupling) such as cardiac and smooth muscle
Where does the endocrine system secrete
- Hormones released into the blood
What is the resting membrane potential
-70mv
what creates the negative voltage resting potential inside the cell
- at rest there is a small conductance(leakage of potassium ions down its concentration gradient (potassium ions to leave the cell) this creates a negative voltage which is the resting potential inside the cell
What is the difference in distribution between the intracellular fluids and the extracellular fluids
- in the inside Na+ 15nM, K+ 150mM, CL- 10nM, A- (protein)100nM
- in the outside NA+ 150nM, A- 0.2nM, K+ 5mM, Cl- 120mM
what would happen if the membrane is completely permeable
- if the membrane was complelety permeable then the natural concentration would be equal and we would not have this unequal distribution
How can ions move across the membrane
- passive ionic diffusion - leak channels
- facilitated diffusion
- active ionic diffusion
- gibbs-donnan equilibrium effect
what is passive diffusion for
leaks channels – this is mainly for water and gases, ions are usually to big
how does facilitated diffusion work
– pass down the channel, these are the leak channels, open all the time allow the passage of the ion down its concentration gradient, allows sodium to pass down pass through the open channel and get into the inside of the cell, opposite
How does active ionic diffusion work
– use energy move it against the concentration gradient, carrier channels move the ion against its concentration gradient, this is the sodium potassium ATPase, this moves sodium and potassium against its concentration gradient, sodium is pumped out from the inside of the cell
How does the Gibbs donnas equilibrium effect work
presence of charged impermeable ion(such as a protein this gets trapped inside the cell) on one side of a membrane (intracellular) which results in an asymmetric distribution of permeant charged ions, has negative charge, means that we have to balance the two negative charges with positive charges to create an electronetural situations on the inside and the outside of the cell
how does sodium enter through the cell membrane
Low intracellular Na+ compared to extracellular Na+ concentration so Na+ enters the cell by passive transport through non-gated (always open) Na+ channels.
what is the rate of sodium entry matched by
The rate of Na+ entry is matched by the active transport of Na+ out via Na+/K+ ATPase pump. This transports NA+ and K+ ions against their concentration gradient. The net result is intracellular Na+ is maintained low, even though Na+ continually enters
how is potassium moved across the membrane
Passive exit of K+ through non-gated K+ channels is matched by the active entry of K+.
what is the major contributor to the resting potential
sodium potassium pump is the major contributor
what is the 3 effects of the sodium potassium pump
- makes Na+ concentration high in extracellular space and low in intracellular space
- makes K+ concentration high in intracellular space and low in extracellular space
- Result = extracellular space has positive voltage with respect to intracellular space
what does the sodium potassium pump do
- Pump exchanges 3 Na+ ions from intracellular space for 2 K+ ions from extracellular spaces – contributes -4mV to resting membrane potential
How is the membrane potential generated
- More potassium leak channels then sodium, this moves the potassium out
- Fewer sodium channels moving sodium in
- Large negative charged proteins trapped in the cell
- Sodium and potassium pumps move 3 Na+ out for 2 K+ in - main thing that establishing the resting potential membrane, as it moves against the concentration gradient and against the electrochemical gradient
- All result in the inside being slightly more negative than the outside
- Measure in volts
- -70mv
How do you measure the charge across a membrane
- voltmeter
- a recording electrode is inserted into the cell and a reference electrode is inserted outside the cell
- by comparing the charge measured by these two electrodes
- transmembrane voltage is determined
what is a nearest equation
- Em=61.5log [concentration]0/[concentration]
what does the nerst equation measure
- Potential across the cell membrane at which the net diffusion of ions across the cell membrane due to the concentration gradient stops
- Relates Em the membrane potential to the concentration gradient
whats the constant for potassium
61.5
