Neurophys Midterm 1 Flashcards
Stretching of muscle requires relatively little force until the PRELOAD reaches ___ μ
3.2 μ
Compare Osmolarity with Tonicity
Osmolarity:
- A physiochemical property
- Is a way of expressing [] of particles in a solution
Tonicity:
- Is a property OF a certain solution
- Determines whether it will make a cell shrink, swell, or maintain its original size
Water flux measured by diffusion of ______ed _____ (“___”) allows the diffusion coefficient of water to be measured
Water flux measured by diffusion of TRITIATED WATER (THO)
allows the diffusion coefficient of water to be measured
[Na+] much higher in/outside?
Outside
The means by which an AP “jumps” from one Node of Ranvier to the next is?
via Graded Potentials
During an Iso_____ contraction, the muscle develops FORCE and SHORTENS
IsoTONIC contraction
The distribution of proteins in a phospholipid bilayer is called…?
The Fluid Mosaic Model
The nerve axon axial resistance (Rax) is much LESS than…?
The membrane resistance, Rm
What happens to a RBC placed in a solution of 145 mM NaCl (σ<span>NaCl</span> = .9)?
ISOTONIC
(2 x 145= 290 mM)
The gates of which channels (Na+ or K+) open faster?
Because K+ channel’s “N“gates OPEN MUCH MORE SLOWLY
than Na+ channel’s “M” gates
Thus, Na+ channels are open before the K+ channels are
The density of capillaries in a tissue is dependent on what?
Give 2 examples
…the metabolic rate of the tissues
- Metabolic rate in heart is HIGH, therefore TONS of capillaries in myocardium
- Metabolic rate in SK muscle is LOW, therefore LOW density of capillaries
What is the take-home message of the Time Course of Diffusion (the “Einstein relationship”)?
Diffusion is a FAST process over SHORT distances
Diffusion is a SLOW process over LONG distances
When a substance diffuses, the distance is NOT a LINEAR function of time
In an Isotonic contraction, the load lifted by the muscle when it shortens is called the…?
“Afterload”
What could happen if the membrane were impaired?
Equilibrium would be lost
Cell could BURST
To what point do Graded Potentials have to depolarize the membrane above in order to generate an AP?
aka what is the Threshold Voltage?
Above -55 mV
Graded Potentials: Describe EPSPs
Excitatory Postsynaptic Potential (EPSP)
Is the DE-polarization of a Graded Potential on the the post-synaptic membrane
Define ELECTROLYTES
= Substances that dissociate into cations (+) and anions (-) when they dissolve in water
What causes HYPERpolarization to occur?
K+ channels are open as long as the membrane is depolarized
Once membrane hits resting potential, K+ channels start to close, but do so SLOWLY
The extra K+ ions that sneak in before it closes cause the “undershoot“
When Na gate opens, K+ flows OUT of the cell, hyperpolarizing the membrane BACK to its resting potential
The inside of the cell is usually ______ in relation to the outside
NEGATIVE
Inside (-)
Outside (+)
Most cells are within ___μM of a capillary
100μM
Increased stiffness of proteins like Titin & Nebulin helps, at high preloads, to prevent what?
Muscle overstretching
Time course of diffusion (Einstein relationship) explains why animals require…?
a circulatory system
(diffusion is too slow over long distances)
The duration of a “twitch” is greater than the duration of …?
An AP
During an AP, the membrane potential in a neuron, Em, will always be between which two values?
Between -90mV and +60mV
Ohm’s Law during an AP
*Remember: During an AP, the cell is NOT in what?
IK + INa ≠ ?
NOT in “steady state”
IK + INa ≠ 0
Differentiate:
Channel proteins vs Carrier proteins
CHANNEL proteins:
- Create a water-filled pore
- Form an open “channel” b/t the two sides of the membrane
CARRIER proteins:
- NEVER FORM AN OPEN CHANNEL b/t both sides of the membrane!!
What happens that causes the Na channel to inactivate?
H gate closes
(Na channel is closed)
What is the typical Resting Membrane potential NOT equal to?
Resting membrane potential (-70 mV) is NOT equal to:
EK or ENa
If a solute (e.g. sucrose) is IMPERMEABLE to the cell membrane, ie σ = 1.0 :
A solution that is _hypo-osmotic_ to the cell contents will be…?
HYPOTONIC
Formula for Fick’s Law of Diffusion (WITH partitioning)
J = Kp ⋅ D ⋅ ΔC / Δx
- J = Flux
- Kp = partition coeff.
- ΔC = [] difference, C1-C2
- Δx = membrane thickness, usually 7.5nm
- D = diffusion coeff
Ions, such as __, __, and __, can NOT diffuse through the plasma membrane
Cl-, K+, Na+
What are 3 common types of Aquaporins, and where are they found?
- AQP1*
- AQP4*
- AQP9*
Found in the BRAIN
What happens to a RBC placed in a solution of 290 mM sucrose?
σsucrose = 1
Isotonic
(no net mvmt)
Van’t Hoff formula for a SINGLE solution = ?
Solutions of higher [] have higher/lower Posmotic?
Δπ = nRTC
(just using “C” instead of “ΔC”)
∴ solutions of HIGHER [] have HIGHER Posmotic
The brain has no ________ system, therefore brain edema fluid is eliminated how?
No LYMPHATIC system
Eliminated into the ventricular CSF and through the BBB
pH in ECF = ?
7.4
Define “Eion“
The membrane potential (Em) at which the sum of the electrical and chemical forces on an ion is zero
The Nernst equation solves for Eion
______ potentials:
Depolarizations or hyperpolarizations whose
Strength is proportional to the strength of the triggering event
Graded potentials
(not the case in AP’s)
INCREASED Unsaturated FA’s = ________ed membrane fluidity
= Increased membrane fluidity
(due to kinks in HC tail)
What type of fluid (hyper-, hypo-. hyper-) could reduce the swelling of the brain following traumatic injury?
HYPERTONIC fluid
Strength-duration curve:
What is the Rheobase?
The minimum current , I, that can cause an AP
Large, UNcharged polar molecules, such as _____ and _____, can NOT diffuse across the membrane
Glucose, Sucrose
Strength-duration curve:
What is the Chronaxie?
The minimum stimulus TIME, T, that will cause an AP
…using a current 2X the value of the rheobase
[K+] in ECF = ?
4 mM
In Isometric contractions, contractions produced by successive ____’s can ______
contractions produced by successive AP’s can summate
Resting membrane potential is a _____ state, but NOT an _______ state
Why is this?
Resting membrane potential is a STEADY state, but NOT an EQUILIBRIUM state
This is bc the cell can only remain at resting membrane potential because the Na+/K+ pump is running (this requires energy!!!)
Hence, this is a steady state, not an equilibrium
What’s the main difference b/t a PORE and a CHANNEL?
Pores AREN’T regulated
Channels ARE regulated
If a solute (e.g. sucrose) is IMPERMEABLE to the cell membrane, ie σ = 1.0 :
A solution that is _isosmotic_ to the cell contents will be…?
ISOTONIC
Describe [] difference, ΔC, diffusion, and voltage difference, Em, across the cell when:
Cell (below) is IMPERMEABLE to both K+ and Cl-
No [] difference, ΔC = 0
No diffusion of K+ OR Cl-
No potential (voltage) difference, Em = 0
During an IsoTONIC contraction, the VELOCITY of shortening is inversely proportional to what?
Inversely proportional to the AFTERLOAD
Both the ECF & ICF are electrically…?
…electrically NEUTRAL
What happens to a RBC placed in a solution of 580 mM sucrose?
σsucrose = 1
Hypertonic
(water moves OUT of cell,
cell shrinks, ie is “crenated”)
[K+] much higher in/outside?
Inside
If a solute (e.g. sucrose) is IMPERMEABLE to the cell membrane, ie σ = 1.0 :
A solution that is _hyper-osmotic_ to the cell contents will be…?
HYPERTONIC
What is the Chord Choductance equation?
How does it relate to the Transference equation?
Define “Tonicity”
= the [] of particles in a solution OUTSIDE the cell which CANNOT CROSS the membrane
Do ENa & EK change during an AP?
Why/why not?
NO
…because the number of ions which move are so small that NO concentration change can be detected
The force produced during an Isometric contraction (also) depends on the # of what?
Depends on the # of muscle fibers activated
A solution with LESSER osmolarity than another is said to be…?
“Hypo-osmolar”
What causes potassium conductance, gK, to change during an AP?
Changes because of movement of the N gate
When the Na channel is closed and NOT available for activation,
what has to happen to make it AVAILABLE for activation?
What happens after that?
Membrane potential must return to about -80 mV
Then, M gate closes, and H gate opens
- Now, channel is STILL CLOSED, but AVAILABLE for activation*
- (same state it was in before the AP arrived)*
TNa + TK = ?
TNa + TK = 1
gNa and gK DO change during an AP,
therefore what also changes?
TNa and TK
Describe [] difference, ΔC, diffusion, and voltage difference, Em, across the cell when:
Cell is PERMEABLE to K+ but _not_ to Cl-
- [K+] difference exists
- ΔC = ( .1 - .01) = .09
-
K+ diffuses OUT of cell, down [] gradient
- Extra negative charges (Cl-) INSIDE
- Extra positive charges (K+) OUTSIDE
- Potential difference forms
- Causes interior of cell to become negative wrt cell exterior
EQUILIBRIUM HAS NOT YET BEEN REACHED
An IsoTONIC contraction consists of what 3 phases?
- It contracts isoMETRICALLY
- Until the force developed is equal to the “Afterload”
- It shortens isoTONICALLY
- At a constant velocity
- Until it shortens as much as possible
- It contracts isoMETRICALLY
- Until it begins to relax
On which part of the post-synaptic membrane do Graded Potentials summate?
The Trigger Zone
In Diffusion, how much of the random molecule mvmt is related to HEAT in the solution?
NONE!
What happens to a RBC placed in a solution of:
145 mM NaCl and 290 mM urea (σ<span>NaCl</span> = .9 and σurea = .2 )?
ISOTONIC
(Both ≤ 290 mM)
If there are NO BARRIERS, the process of diffusion results in what?
In equilibrium
[]s the same everywhere
Since Van’t Hoff equation only solves for osmotic pressure of IMPERMEABLE membranes, what happens if you’re given a question where the membrane is PARTIALLY permeable?
Here, the actual Posmotic will be:
BETWEEN ZERO & the Posmotic predicted by Van’t Hoff’s Law
CHO composes ~___% of all membrane lipid
What does it do to the membrane? (2)
CHO is ~19-50% of all membrane lipid
- It stabilizes the membrane
- It reduces the mobility of complex lipids in the membrane
During an IsoTONIC contraction, the AMOUNT of shortening is inversely proportional to what?
Inversely proportional to the AFTERLOAD
Small, uncharged polar molecules, such as ____, ____, and _____ can diffuse through the membrane
H2O, Glycerol, Indole
What would the osmolarity of a .15 M NaCl solution?
= .15 * 2 molecules (Na + Cl)
= ~.3 osm
What causes excess urination in diabetics?
Excess glucose in renal tubular fluid DRAWS WATER OUT,
into the tubules, and eventually into the urine
(Osmotic balance of renal fluids)
What happens to a RBC placed in a solution of 145 mM sucrose?
σsucrose = 1
HypOtonic
(Cell swells, but doesnt burst)
Hydrophilic solutes require _____s or _____s, because they CAN’T diffuse across the phospholipid bilayer
Channels or Pores
“Osmotic pressure differences cause water to move through pores in a membrane just like _______ ________ would”
“…just like HYDROSTATIC PRESSURE would”
REGARDLESS of the osmolarity of the solution,
if the reflection oefficient is LESS than 1 ( σ < 1 ), the cell will be…?
- Why is this the case?
- When is the only time you’d need to take into account if the solute is an electrolyte (and then solve for osmolarity)?
If σ ISOTONIC!!!
- This is true because it will always EVENTUALLY reach equilibrium and thus be “isotonic”
- it is only when the solute is IMPERMEABLE (σ = 1) that you need to take into account if it is an electrolyte, and then solve for osmolarity
What is the tonicity of SWEAT?
Why?
HYPOTONIC
Has a lower [] of electrolytes than the cells of sweat glands
∴ WE become hypertonic; need ISOTONIC fluids (e.g. Gatorade) to replenish the lost electrolytes
In an Iso_____ contraction, the total length of the muscle does NOT change
IsoMETRIC contraction
What does an AP in a neuron look like graphically?
Include: Resting potential, Threshold potential, Depolarization, Repolarization, Hyperpolarization, Refractory period
NaCl is effectively IMPERMEABLE to RBCs (σ=1)
∴ an ISOTONIC solution of NaCl is ____mM (__%)
Isotonic solution of NaCl=
154 mM (.9%)
Graded or Action Potential?
“Merge on a membrane and summate algebraically”
(Spatial & temportal summation)
= Graded Potentials
A solution with GREATER osmolarity than another is said to be…?
“Hyperosmolar”
Describe Absolute Refractory Period
A second AP cannot be generated no matter how strong a stimulus is used
- Not enough Na+ channels available to trigger another AP.
- They are either all already in use, or have been inactivated.
What is the formula for the Nernst equation?
What is it used to calculate?
Used to calculate the voltage where the ion is in equilibrium
Solves for Eion
” used to calculate the membrane potential where the electrochemical potential of an ion will be the same on both sides of a membrane with the given concentrations”
Formula for Fick’s Law of Diffusion (WITHOUT partitioning)
J = D ⋅ ΔC / Δx
- J = Flux
- ΔC = [] difference, C1-C2
- Δx = membrane thickness, usually 7.5nm
- D = diffusion coeff
What types of fluids (hyper-, hypo-, or isotonic) should be consuded to rehydrate following aerobic exercise?
ISOTONIC fluids
e.g. Gatorade
How thick is the plasma membrane (in nm)?
Due to its thickness, the membrane is “mechanically ____”
7.5 nm
Hence, plasma membrane is “mechanically weak”
The contractile force produced by a SINGLE AP is called a…?
“Twitch contraction”
Can (non-water) solutes get through Aquaporins?
NO!
Aquaporins extremely specific for water– water ONLY gets through
NaCl is effectively IMPERMEABLE to RBCs (σ=1)
∴ an ISOTONIC solution of NaCl is ____mM (__%)
Isotonic solution of NaCl=
154 mM (.9%)
If a solute (e.g. Urea) is PARTIALLY PERMEABLE to the cell membrane, ie σ < 1:
A solution that is _hypo-osmotic_ to the cell contents will be…?
HYPOTONIC
What happens to a RBC placed in a solution of 290 mM urea (σurea = .2)
ISOTONIC
(Urea can easily pass through membrane; won’t be isotonic initially but will be within milliseconds)
AQP2 is abundant where, and what hormone targets it?
AQP2 found in collecting duct of KIDNEYS
Is the target of ADH
What causes sodium conductance, gNa, to change during an AP?
gNa changes due to movement of M and H gates
In an Isometric contraction, the initial length of the muscle PRIOR to contraction is called the…?
“Preload”
Channels can be regulated by what 2 things?
Voltage
Binding of certain small molecules
K+ channels have how many gates?
Where will you find many K+ channels?
Just one gate, the “N” gate
What does the Van’t Hoff equation solve ?
The osmotic pressure across a membrane (Δπ)
- …when solutions are dilute and the membrane is*
- absolutely IMPERMEABLE to the solute*
“Van’t Hoff equation quantifies osmotic pressure across a membrane”
Efferent neurons conduct APs down what type of nerve, resulting in what?
Efferent neurons conduct APs down motor nerves,
resulting in SK muscle contraction
What do Graded Potentials precede?
Action Potentials
Describe [] difference, ΔC, diffusion, and voltage difference, Em, across the cell when:
Cell is IMPERMEABLE to both K+ and Cl-
- [K+] difference!
- ΔC = ( .1 - .01) = .09
-
NO diffusion of K+ OR Cl-
- Because membrane is impermeable to both
- No potential (voltage) difference, Em = 0
______ potentials decay spatially
Graded potentials
(AP’s do NOT dimish spatially)
Fick’s Law of Diffusion:
Equation using PERMEABILITY = ?
What do (+) values indicate wrt movement in/out of cell?
J = P(Cin - Cout)
Positive values mean there is a net OUTWARD flux of solute from a cell
What are the 2 “modulators” of cell excitability?
-
Low extracellular Ca2+
- Makes Na+ channels more easily activated
- THIS MAKES THE CELL MORE EXCITABLE
-
High extracellular K+
- Depolarizes cell
- Inactivates Na+ channels
- Activates some K+ channels
- THESE CHANGES MAKE THE CELL LESS EXCITABLE
Na+ channels have what gates?
What needs to happen for Na+ channels to be open?
Activation gate, “M” gate
Inactivation gate, “H” gate
The channel is open only if BOTH gates are open
What does the Na+ channel’s M gate require to open up?
a very tiny current, called the Gating Current
[Ca2+] much higher in/outside?
Outside
[Na+] in ECF = ?
142 mM
During “Solvent Drag,” why dont the permeable solutes just cross the membrane on their own?
Solvent drag is FASTER!
Hydrophobic molecules, such as ___, ___, and ___, can diffuse through the membrane
O2, CO2, and N2
While it can vary according to cell type, the voltage difference is usually between what values?
Between -50mV and -90mV
If two solutions have the SAME OSMOLARITY, they are said to be…?
“Iso-osmolar”
What does the Strength-Duration curve of a nerve stimulus look like graphically?
What is the formula that explains this relationship?
Hyperbolic curve
Q = IT
- Q = Charge placed on membrane
- I = Current of stimulus
- T = Duration of stimulus
NONelectrolytes are lipo_____
lipoPHILIC
Describe “Undershoot”
- Because so many K+ channels are open,*
- the K+ transference, TK, becomes large enough to make the membrane potential, Em, even more negative than the normal resting potential.*
- This hyperpolarized phase is called the “undershoot”*
Van’t Hoff formula = ?
Explain each component
Δπ = nRTΔC
- Δπ = Difference in Posmotic across an impermeable membrane
- n = # of particles the solute dissociates into
- 1 for nonelectrolytes
- 2 for NaCl
- 3 for MgCl2
- R = universal gas constant, .0821
- T = temperature, 273 + celsius temp
- ΔC = difference in molar [], C2-C1
[Cl-] much higher in/outside?
outside
pH:
ECF vs ICF
ECF is slightly ALKALINE (basic)
while ICF is closer to NEUTRAL
[H+] in ECF = ?
40 nM
Resting membrane potential:
There can be NO potential difference (“voltage difference”) unless….?
Unless the membrane is permeable TO AT LEAST ONE ION!
The force produced during an Isometric contraction depends on what 3 things?
- The Preload
- i.e. the overlap b/t thick & thin filaments
- The # of muscle fibers activated
- The frequency of APs generated
The phenomenon of different solubility of a solute in OIL as opposed to WATER is called…?
“Partitioning”
Graded Potentials: Describe IPSPs
Inhibitory Postsynaptic Potential (IPSP)
Is the HYPER-polarization of a Graded Potential on the the post-synaptic membrane
Where do Graded Potentials occur?
Occur in all tissues which spontaneously generate or conduct APs
For example:
- In cell bodies and dendrites of neurons
- In cells electrically coupled by gap junctions (e.g. cardiac myocytes)
- On post-synaptic membranes
How is cell volume regulated by movement of solutes across the membrane?
By the transport of ions (via active transport)
Define “Solvent Drag”
When water is moving across a multicellular “membrane” by osmosis,
PERMEABLE solutes get caught up in the flow and are swept along
Kp is equal to…?
Therefore, Kp > 1 indicates?
Kp = solubility in OIL / solubility in WATER
Kp > 1 means it’s LIPOPHILIC/ HYDROPHOBIC
(diffuses across membrane more quickly & easily)
Ohm’s Law during an AP:
What component of the formula changes during different phases of an AP?
gNa & gK
[Ca2+] in ECF = ?
1 mM
Why don’t K+ channel INACTIVATE?
K+ channels are open as long as the membrane is _________?
Because they dont have any INACTIVATION gates (unlike Na channels)
K+ channels are open as long as the membrane is DEpolarized
[Cl-] in ECF = ?
105 mM
In Na+ channels, what determine the inward Na+ current?
Determined by:
the driving force on Na+, (Em - ENa)
the sodium conductance, gNa
What happens to a RBC placed in a solution of:
580 mM urea (σurea = .2 )?
ISOTONIC (?)
Compare osmolarity values for ECF & ICF
Usually EQUAL to e/o
Channels are made up of one or more of what?
Integral membrane proteins
What causes TETANY (intermittent muscular spasms) in muscles?
LOW extracellular Ca2+
Carriers for what type of carrier-mediated transport can “come back empty?”
What exactly does that mean?
FACILITATED DIFFUSION
- = Empty carriers can REORIENT themselves*
- from ONE face of the membrane to the OTHER*
(e. g. extracellular face ⇋ cytosolic face)
The force produced during an Isometric contraction depends on the…?
PRELOAD
Describe Relative Refractory Period
- A second AP CAN be generated but a stronger stimulus*
- (greater voltage) must be used.*
- There are not as many Na+ channels available as normal to trigger another AP because many are inactivated.
- Also, many more K+ channels are open, so it is more difficult to depolarize the membrane to threshold.
Describe IK and INa at REST
IK + INa = 0
At rest, both IK and INa are small
What happens to a RBC placed in a solution of PURE WATER?
VERY HYPOTONIC
(Water moves into cells, CELL BURSTS!!)
Osmolarity in ECF = ?
290 mOsm/L
(“milliosmoles”)
If a neuron has an absolute refractory period of 1.25mS,
what is the maximum firing rate (in Hz)?
Maximum firing rate = 1 S/ 1.25mS = 1000mS/1.25mS = 800 (Hz)
(convert seconds to milliseconds, then divide)
What causes ankle edema (swollen ankles)?
What can pts do to relieve their symptoms?
= EXCESS FLUID
Reducing the amount of SALT in your food ofter relieves edema
What happens to a RBC placed in a solution of 290 mM NaCl (σ<span>NaCl</span> = .9)?
HYPERTONIC
(2 x 290= 580 mM)
What is it called when membrane potential, Em, becomes positive and approaches ENa?
“Overshoot”
In AP conductance, the positive charge that enters the nerve cell is carried by ___ and is called the “________ current”
Carried by K+
Called the Axoplasmic current, or iax
In AP conductance, the positive charge that LEAVES the nerve cell through membrane channels is called the ________ current, or …?
Membrane current, or im
In both myelinated AND unmyelinated axons, increasing the ______ will leads to increased conduction velocity
Diameter
Time constant, τ, is the time at which…?
It is a measure of what?
Formula = ?
Time at which it reaches 63% of the final voltage
it is a measure of how rapidly a voltage disturbance SETTLES DOWN
τ = Rm Cm
Length constant, λ, is the distance where…?
What is it a measure of?
Is the distance where the voltage is only 37% of the voltage where x=0
It is a measure of HOW FAR ALONG the axon a voltage disturbance is felt
In a MYELINATED axon, the length constant, λ, and conduction velocity, V, are directly proportional to..?
Diameter
In an UNMYELINATED axon, the length constant, λ, and conduction velocity, V, are directly proportional to..?
√ Diameter
Only the ____ channels at the nodes of ranvier need to be activated, which saves _____ and increases _____
Na channels
saves time
increases speed of propagation
Do myelinated or unmyelinated axons have more LOCAL CIRCUIT PATHS?
Unmyelinated
