Equilibrium Potentials And Resting Mem & Graded Potentials Flashcards
Nernst equation:
(+60 or -60)/zk (log [concentration out}/ [concenetration in]
Nernst equation: The concentrations of K+ inside and outside the cell account for the
chemical/concentration gradient
Nernst equation: zk that represents the
valence electrons accounts for the electrical driving forces
is reached when the movement of ions down their electrical gradient is equal and opposite in the direction to the movement of ions down their concentration (chemical) gradient
Electrochemical equilibrium
is the membrane potential in a cell when electrochemical equilibrium is reached
Equilibrium potentials
Equilibrium potentials for K+, Na+, Ca2+
K+= -89 mV
Na+= +60 mV
Ca2+= +134 mV
Differences in equilibrium potential for Na+, Ca2+, and K+
Na+ makes the cell inside slightly less negative, smaller gradient for Na+, less magnitude
What change has a larger effect: A 5 mM increase in the ECF of K+ vs. a 5mM increase in ECF of Na+
K+: because it has a greater effect from 5 to 10, then 150 to 155.
When you increase the ECF of K+, and the ICF remains the same, what is the effect of this?
It decreases the size of the concentration gradient more than Na+ concentration gradient.
In order for the cell to have a negative resting membrane potential it needs…
More K+ leak channels, allowing more movement of K+ down the gradient AND Na/K ATPase protein to maintain the gradient
Explain why the resting membrane potential is closer to EK than to ENa
more K leak channels (permeability) are open, therefore net movement of K down its concentration gradient out of the cell—leading to negative membrane potential
two reasons why changes in extracellular K + concentration have more dramatic effects on resting membrane potential than do changes in extracellular Na+ concentration
- charge difference of K+ flowing out and Na+ flowing in.
- larger K+ gradient
what the relative ion permeability (P) represents in the Goldman-Hodgkin-Katz equation
the ion permeability being rapidly variable due to ion channel gating
Explain which variables in this equation are generally quite stable in the Goldman-Hodgkin-Katz equation
The ion gradients (concentrations) due to Na+/K+ ATPase protein
What ions have the largest influence over the membrane potential
Large concentration gradients and high membrane permeability
K+ makes the membrane potential…
slightly more negative (hyperpolarize)
Na+ makes the membrane potential…
slightly less negative (depolarize)
Ca2+ makes the membrane potential…
slightly less negative (depolarize)
Cl- makes the membrane potential…
slightly more negative (hyperpolarize)
Direction of concentration gradients and electrical gradients for Ca2+:
Electrical gradient= inward (inside) the cell
Concentration gradient= inside the cell
Direction of concentration gradients and electrical gradients for K+:
Electrical gradient= inside the cell
Concentration gradient=outside
Direction of concentration gradients and electrical gradients for Na+:
Electrical gradient= inside the cell
Concentration gradient= inside the cell
Direction of concentration gradients and electrical gradients for Cl-:
Electrical gradient= outward (outside) the cell
Concentration gradient= inside the cell
Direction of concentration gradients and electrical gradients for Anions:
Electrical gradient= outward (outside) the cell
Concentration gradient= outside the cell
TOTAL number of particles per liter of water. The sum of
penetrating and non-penetrating molecules in a solution
osmolarity
how to calculate the osmolarity of solutions
Molarity (mol/L) x number of particles per molecule dissolved
Particles that ionize or dissociate are known as (ex. NaCl)
non-penetrating
does not dissolve or dissociate are known as
penetrating (urea, ethanol)
two mechanisms by which water can move across plasma membranes…
- Through simple diffusion
- By moving through aquaporins, integral membrane proteins function as water channels
Typical value of intracellular osmolarity of human cells
300 mOSM
able to pass through a membrane
penetrating solutes
Any solute present in the ECF that cannot effectively pass through a plasma membrane
Non-penetrating solutes
if two solutions have the same osmolarities (penetrating and nonpenetrating combination)
Iso-osmotic
the osmolarities of nonpenetrating solutes are the same on the inside and outside of the membrane
isotonic
Tonicity only depends on
non-penetrating
A solution with a higher osmolarity (more solute particles) than another solution
Hyperosmotic
A solution with lower osmolarity (fewer solute particles) than another solution
hypo-osmotic
Solution has a higher osmolarity of non-penetrating solute outside the cell than inside the cell
hypertonic
Hypertonic solution results in what H2O movement
outward
Solution has a lower osmolarity of non-penetrating solutes than inside the cell
hypotonic
Hyportonic solution results in what H2O movement
inward
If all solutes in the isosmotic solution are non-penetrating, then the solution is
isotonic
If RBC’s were placed in an iso-osmotic solution with only penetrating solutes, the penetrating solutes would
enter the RBCs on their own, hypotonic
If RBC’s were placed in an iso-osmotic solution with only non-penetrating solutes, the solution would be
isotonic
Predict what would happen to the volume of red blood cells if they were placed in a 1400 mOSM solution of NaCl…
The solution would be hypertonic and RBC would shrivel and die because the water moves out of the cell
Predict what would happen to the volume of RBCs if they were placed in a solution containing 700 mOSM of NaCl plus 700 mOSM of urea…
the RBCs would also shrink but less, because less water was needed to leave the cell
Explain how the presence of approximately 150 mM NaCl (saline) can prevent osmotic swelling of red blood cells in a solution that also contains some penetrating solute….
150 mM NaCl dissociates into 300 mOsm which is the same concentration inside the cell: solutions are isotonic
The higher the osmolarity= the __ the water concentration
lower
Two solutions with the same osmolarity have the
same water concentration
Adding solute, __ water concentration
decreases
As solute concentration increases, water concentration
decreases
what two events generate graded potentials…
a stimulus applied to sensory receptor and neurotransmitter synapse
sensory receptors contain what channel
transduction
characteristics of a stimulus
intensity, modality, location in body
determines how many channels are open and how long
intensity
type of stimulus: pain, touch, etc; that activates the receptor
modality
coding of the stimulus by the
size of the receptor potential
The larger the stimulus, __ transduction channels open, __ receptor potential
more, larger
if opening of transduction channels leads to a depolarizing potential, which ions would these channels likely to be permeable?
Only Na+
Only K+
Both, but more permeable to K+ then Na+
Na+
if opening of transduction channels leads to a hyperpolarizing potential, which ions would these channels likely to be permeable?
Only Na+
Only K+
Both, but more permeable to K+ then Na+
K+
peripheral endings of sensory neurons
Sensory receptors
have transduction channels that are opened by a specific type of stimulus (e.g. mechanical, thermal, chemical)
Sensory receptors
convert a stimulus into an electrical signal we call a graded potential (GP)
Sensory receptors
conversion of one type of stimulus energy (e.g. pressure) to an electrical signal (i.e. receptor potential)
sensory transduction
In sensory transduction what channel mediates it
gated channel
How does a sensory transduction occur? (with Na+ and Ca2+)
An influx of sodium and calcium causes a depolarizing receptor potential—stimuli opens channels.
How does a pacinian corpuscle work
if pushed on, the capsule deforms by a stimulus and the channels open
Thermoreceptors
have transduction channels that open when temp increases or decreases
Nociceptors have transduction channels that open when
exposed to extreme heat, intense mechanical stimuli, and chemicals released from cells that have been damaged
What channel determines resting membrane potential
Leak channels
Channel that randomly open and close, so at any given
time
leak channels
change a physical stimulus into an electrical event (i.e. change in membrane potential)
transduction channels
Size and duration of the receptor potential is determined by
how many transduction channels are opened by the
stimulus, and for how long they stay open
The modality of a sensory receptor is determined by
Type of transduction channel, structure where channel is located, location of receptor
The graded potentials that occur in sensory receptors
sensory receptor potential
