Equilibrium Potentials And Resting Mem & Graded Potentials Flashcards by Mia Sassano

Nernst equation:

(+60 or -60)/zk (log [concentration out}/ [concenetration in]

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Nernst equation: The concentrations of K+ inside and outside the cell account for the

chemical/concentration gradient

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Nernst equation: zk that represents the

valence electrons accounts for the electrical driving forces

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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

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is the membrane potential in a cell when electrochemical equilibrium is reached

Equilibrium potentials

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Equilibrium potentials for K+, Na+, Ca2+

K+= -89 mV
Na+= +60 mV
Ca2+= +134 mV

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Differences in equilibrium potential for Na+, Ca2+, and K+

Na+ makes the cell inside slightly less negative, smaller gradient for Na+, less magnitude

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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.

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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.

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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

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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

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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

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what the relative ion permeability (P) represents in the Goldman-Hodgkin-Katz equation

the ion permeability being rapidly variable due to ion channel gating

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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

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What ions have the largest influence over the membrane potential

Large concentration gradients and high membrane permeability

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K+ makes the membrane potential…

slightly more negative (hyperpolarize)

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Na+ makes the membrane potential…

slightly less negative (depolarize)

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Ca2+ makes the membrane potential…

slightly less negative (depolarize)

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Cl- makes the membrane potential…

slightly more negative (hyperpolarize)

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Direction of concentration gradients and electrical gradients for Ca2+:

Electrical gradient= inward (inside) the cell
Concentration gradient= inside the cell

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Direction of concentration gradients and electrical gradients for K+:

Electrical gradient= inside the cell
Concentration gradient=outside

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Direction of concentration gradients and electrical gradients for Na+:

Electrical gradient= inside the cell
Concentration gradient= inside the cell

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Direction of concentration gradients and electrical gradients for Cl-:

Electrical gradient= outward (outside) the cell
Concentration gradient= inside the cell

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Direction of concentration gradients and electrical gradients for Anions:

Electrical gradient= outward (outside) the cell
Concentration gradient= outside the cell

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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...

1. Through simple diffusion 2. 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