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Flashcards in Physiology Test 2 Deck (207):

What is the most abundant extracellular cation?



What is the most abundant extracellular anion?



What is the most abundant intracellular cation?



What is the most abundant intracellular anion?

inorganic phosphate


What molecule is a co-factor for almost all chemical reactions?



What is a byproduct of the kreb cycle and what type of metabolism is it a result of?

CO2, aerobic metabolism and its comes from a carboxyl group


What is the function of ribosomes?

protein synthesis


What are the average extracellular and intracellular concentrations of sodium(Na+)?

140 mEq/L and 14 mEq/L


What are the average extracellular and intracellular concentrations of potassium(K+)?

4 mEq/L and 140 mEq/L


What are the average extracellular and intracellular concentrations of calcium(Ca2+)?

2.4 mEq/L and 0.0001 mEq/L


What are the average extracellular and intracellular concentrations of magnesium(Mg2+)?

1.2 mEq/L and 58 mEq/L


What are the average extracellular and intracellular concentrations of chloride(Cl-)?

103 mEq/L and 4 mEq/L


What are the average extracellular and intracellular concentrations of inorganic phosphate(HPO4)?

4 mEq/L and 75 mEq/L


What are the average extracellular and intracellular concentrations of glucose?

90 mg/dL and 0-20 mg/dL


What are the average extracellular and intracellular concentrations of pO2?

35 - 40 mmHg and ~20 mmHg


What are the average extracellular and intracellular concentrations of pCO2?

40 - 45 mmHg and ~45 - 50 mmHg


What are the average extracellular and intracellular concentrations of Amino Acids?

30 mg/dL and 200 mg/dL


What are two major categories by which molecules move across the cell membrane?

1. Simple diffusion
2. Active transport


What is another name for diffusion?

passive transport


How does simple diffusion occur?

molecule moves with the gradient, from higher to lower gradient(down the hill), does not utilize ATP


How does active transport occur?

molecule moves against the gradient from lower to higher gradient(up the hill)


What drives active transport?

energy is taken from ATP to drive the active process


What substances diffuse directly through the cell membrane by simple diffusion(4)?

carbon dioxide


Molecules that diffuse directly across the cell membrane, are what soluble?

lipid/fat soluble substances


What types of molecules needs help transversing the cell membrane? And what types of channels do they move through(still referring to simple diffusion)?

1. those that are water soluble(cell membrane is made up of lipids) and those that are electrically charged(anions and cations--->the cell membrane is polar)
2. protein channels


What is the main characteristic of a protein channel?

its selectively permeable


What are the three factors that determine the selective permeability of each protein channel?

1. size
2. shape
3. electrical charge within the channel


What are two types of protein leak channels?

1. sodium leak channel
2. potassium leak channel


What is the characteristic of a leak channel?

Leak channels are always open allowing substances to move across the cell membrane from a higher gradient to a lower gradient


What is the characteristic of a sodium leak channel?

sodium diffuses with the gradient from outside of the cell to the inside of the cell, sodium has a {} outside of the cell


What is the characteristic of a potassium leak channel?

potassium diffuses with the gradient from the inside of the cell to the outside of the cell.


Is the influx and output of Na+ and K+ evenly matched in and out of the cell, or does one come in or go out more? and why?

More potassium diffuses out of the cell than sodium leaks into the cell. Sodium molecules are surrounded by water which makes them larger which makes them not diffuse as rapidly as potassium which are smaller


What types of gradient determines the movement of solutes/molecules in protein leak channels?

electrical gradient
concentration gradient
or both


What are the characteristics of gated protein channels.

1. channels can be alternately opened and closed
2. channels allow diffusion only when gate is open


What are two types of Gated Protein Channels?

1. Ligand(chemical) Gated Channels
2. Voltage Gated Channels


What is the neurotransmitter(Ligand) that opens the Ligand(chemical) Gated Channel and allows Na+ to enter the cell?

acetylcholine binds to the receptor site


Once the Ligand is removed from the receptor site, what happens to the gate?

It closes


What is the name of the enzyme that removes acetylcholine from the receptor site of the Ligand Gated Channel?



What is the characteristic of a Voltage Gated Channel.

a change in the voltage across the cell membrane opens the voltage channel. for example if the voltage changes by 30 mV it opens the gate.


What's the difference between a fast voltage channel and a slow voltage channel?

fast voltage gated Na channel only takes about 30 mV, where as a slow voltage channel such as potassium voltage channel takes about a 90 mV change to open the gate. so Fast Voltage Na Channel 30 mV versus a Slow Voltage Potassium Channel 90 mV

*****As the sodium gates are closing...the potassium gates are just beginning to open*****


What amount of voltage change is required to open and close the Voltage Gated Channels?

~30 mV change to open the gate
~90 - 100 mV change to close the gate


What type of transport describes ALL types of diffusion?



What types of Sodium/Potassium channels are there(3/2)?

Sodium/Potassium Leak Channels
Ligand Gated Sodium channels
Voltage Gated Sodium/Potassium Channels


What type of diffusion is Facilitated(Carrier Mediated) Diffusion?

All types of diffusion is PASSIVE!


How is a molecule transported across the cell membrane by facilitated diffusion?

The molecule that needs to cross the cell membrane binds to a receptor site, once the saturation point has been reached the channel opens allowing the molecule to cross to the other side


What is a Major example of molecule/substance that crosses the cell membrane by facilitated diffusion?



Glucose transporters are an example of what type of transport?

facilitated diffusion


How is insulin involved in facilitated cell transport?

insulin regulated the number and activity of glucose transporters(GLUT)


What cells are not dependent upon insulin to regulate glucose transporters to enter the cells(5)?

1. neurons
2. hepatocytes(insulin does increase glucose transport into hepatocytes
3. Proximal tubules of the kidneys
4. small intestines
5. exercising skeletal muscle fibers require less insulin for glucose transport than resting skeletal muscle fibers


What is a major characteristic of facilitated diffusion?

a saturation point! If there is more glucose outside the cell wanting in than there are protein channels that can take it in what happens? They stay outside the cell and the person is hyperglycemic.


How does the surface area of the cell membrane affect rate of diffusion(all types of diffusion)?

The larger the surface area membrane the faster the rate of diffusion


How does the permeability of the cell membrane to a specific solute affect the rate of diffusion(all types of diffusion)?

The more permeable the membrane is to a specific solute the faster the rate of diffusion


How does the thickness of the cell membrane affect the rate of diffusion(all types of diffusion)?

The thicker the membrane the slower the diffusion, the thinner the membrane the faster the diffusion. The thicker the membrane the more resistance there is to diffusion!


How does lipid solubility affect the rate of diffusion across the cell membrane(all types of diffusion)?

Solutes that are highly lipid soluble diffuse faster than those that are less lipid soluble(more water soluble)


How does the number of protein channels for a specific solute affect diffusion across the cell membrane(all types of diffusion)?

as the number of channels increase, the number of solutes that can diffuse increases--->increased rates of diffusion!


How does temperature affect the rate of diffusion across the cell membrane(of all types of diffusion)?

As temperature increases...rate of diffusion increases


How does molecular weight of substances affect the rate of diffusion across the cell membrane(all types of diffusion)?

lower molecular weight substances diffuse faster than higher molecular weight substances


How does saturation point of protein transporters affect diffusion(for facilitated diffusion)?

The saturation point is the limit of diffusion...if all the channels are being used...any more substances can't diffuse across cell membrane at that time...the saturation point has been reached


What are three types of gradients that affect diffusion across the cell membrane?

1. concentration gradient
2. electrical gradient
3. pressure gradient

***for a given membrane there maybe more than one of these occurring at the same time*****

The equilibrium point is the net affect of how the gradients are all affecting at one time(i.e. more than one gradient may be at work at any one time--->so the equilibrium is determined by the net affect of all the gradients at any one time)


Transport by diffusion that is based on a concentration happens how? and what determines equilibrium?

molecules move inside cell via a protein channel from area of higher concentration to lower concentration. Equilibration happens when the concentration is equal on both sides of the cell membrane.


Transport by diffusion that is based on an electrical gradient happens how? and what determines equilibrium?

molecules move from one side of the cell to the other via protein channels. They are propelled through the protein channel attracted by similarly charged ions on the opposite side. The equilibrium point is not based on number of molecules on either side, rather it is an electrical equilibrium. When there is an equal charge on both sides.


Transport by diffusion that is based on a pressure gradient happens how? and what determines the equilibrium?

molecules move from one side of the cell membrane to the other from area from higher pressure to lower pressure. One the pressures become equal on both sides...the equilibrium point has been reached.


What is osmosis?

The movement of WATER across a SEMIPERMEABLE membrane from an area of lesser concentration of solutes to an area of higher concentration of solutes(from area of more water to an area of less water)

Osmosis is a faster rate of movement than that of just simple diffusion of water across a semipermeable membrane.


What is a mole?

Avogadro's number of particles(atoms, ions, molecules)


What does 1 mole =?

Avogadro's number 6.02 x 10^23


What is a millimole?

1 mole = 1000 millimoles(6.02x10^23/1000)


What is an osmole(osm)?

refers to the number of particles in solution

***1 osmole = 1 mole(Avogadro's number of particles) in 1 liter or 1 kg of water***


What is a milliosmole(mOsm)?

1/1000 osmole(6.02x10^23/1000)


What does the atomic number refer to on the periodic table?

number of the protons/electrons in the nucleus/orbitals


What does the atomic weight refer to on the periodic table?

weight of protons and neutrons in the nucleus


What does the group number tell you of the periodic table?

It tell you how many electrons there are in the outer most orbital
for example Na atomic number is 11 so it has 11 protons/electrons. Its group number is 1 so you know it only has 1 electron in the outer most orbital.


What does the periods tell you about the molecules on the periodic table?

It tells you how many orbitals there are. For example Na has 3 orbitals because its in the 3 period


If Na+ atomic weight is 23 what does that say?

Thats the weight of the protons and the neutrons in the nucleus


Potassiums atomic number is 19, it is in group 1 period 4 and its atomic weight is 39. What does all this mean?

19 protons and electrons
1 electron in the outermost orbit
4 total orbits
the total weight of protons and neutrons is 39


Chloride's atomic number is 17, it is in group 3 period 7 and its atomic weight is 34.45. What does all this mean?

17 protons and electrons
3 electrons in the outermost orbit
7 total orbits
the total weight of protons and neutrons is 34.45


What is an ionic bond?

Its a very weak bond caused when two element bind together to have 8 electrons in their outermost orbit. i.e. sodium chloride(1+7=8) or potassium chloride(1+7=8)


When an atom looses an atom and is no longer neutral what do we call it?

an Ion


When chlorine adds an extra atom what happens to its name? When they go from an atom to an ion.

chlorine becomes chloride
bromine becomes bromide
for example


Ionic bonds are very weak...true or false?



Which is the atom; chlorine or chloride?

Chlorine; chloride is the ion


What happens when a NaCl molecule is in water?

The negative poles of water attract the positive Na, the positive poles of water attract negative Cl, and the ionic bond of NaCl is broken--->ions are formed(cation: Na+, anion Cl-)


If one mole of NaCl is added to water, what is the resulting mole/moles?(Na+ atomic weight is 23/Cl- atomic weight is 35.5) What is the molecular weight of NaCl? What type of chemical bond is NaCl?

-NaCl dissociates in water into 1 mole of Na+ and 1 mole of Cl-
-2 X Avogadro's number of ions
-1 mole NaCl contributes 2 osm(2 X Avogadro's number of particles) to 1 liter or 1 kg of water
-molecular weight of NaCl is 58.5
-1 mole NaCl = 58.5 mg
-ionic boind


Do organic molecules, such as glucose, dissociate in water?



One mole of glucose contributes how many osmole?

1 osmole(Avogadro's number of particles) to 1 liter or 1 kg of water


One mole NaCl equals how many osmole/osmoles?

2 osmoles


If container A and container B are separated by a semipermeable membrane, A has 1 mole glucose and B has 1 mole NaCl, which way is the osmolar gradient?

from A to B
-Lesser concentration of 1 osm(glucose/water) to higher concentration of 2 osm(NaCl/water)--->water goes toward the higher number of particles


What is osmotic pressure?

-the point in which osmosis of water ceases because of changes in hydrostatic pressure


What is osmolaity?

Number of osm or mOsm/kg H20


What is osmolarity?

Number of osm or mOsm/liter H20


T/F: For this physiology class, Osmolality = osm or mOsm/liter H2O?



T/F: The size of particles, not the number of particles in a solution determines osmolality/osmolarity?

False: the number of particles determines it
-Every particle, regardless of size, makes an equal contribution to osmolality/osmolarity


What is Colloid Osmotic Pressure(Oncotic Pressure)?

-the contribution of proteins to osmolality/osmolarity of body fluids(plasma interstitial fluid)
-The normal, primary protein that contributes to osmolality/osmolarity is albumin, which is primarily found in plasma.


What is the primary protein found in plasma?



Why does albumin stay inside the blood vessel?

the molecules are too large to travel anywhere else


What is the average albumin level?

4 g/dl


If vascular fluid is moving into interstitial fluid compartments, which has higher osmotic pressure?



T/F: Plasma osm-interstitial osm=intracellular osm(intracellular osm=extracellular osm under normal conditons?)

-True, under normal conditions
-About 300 mOsm/L
-most remain within very narrow ranges for physiologic homeostasis and normal cell function


What is the energy source active transport across the cell membrane?



What is Primary Active Transport?

-energy from ATP is used to drive the solute against a natural concentration gradient


Sodium/Potassium ATP pump is an example of which type of cell membrane transport?

Primary active transport


What is the enzyme inside the intrinsic protein Sodium/Potassium ATP pump?

-it allows protein to cleave an ATP, break it down into ADP and an inorganic phosphate
-12000 calories of energy released


How many Na+ receptor binding sites intracellular on the Na+/K+ ATP pump?

3 (sodium inside is 14/outside 140--->against the gradient)


How many K+ receptor binding sites extracellular on the Na+/K+ ATP pump?

2 (potassium inside is 140/outside is 4---> against the gradient)


Simultaneously, how many and which way are Na+ and K+ ions transported across cell membrane with each cycle of the Na+/K+ ATP pump(one ATP used)?

-3 Na+ pumped out of the cell at the same time 2 K+ are pumped into the cell
-3 cations pumped out while 2 cations are pumped in


What is the purpose of the Na+/K+ ATP pump?

-it prevents Na+ buildup within the cell from the Na leak mechanism
-prevents too much K+ loss from the cell
-maintains the electrolyte concentration of Na+/K+ within the cell
-maintains the water volume/pressure/osmality within the cell
-maintains the integrity of the cell


What kind of transport is used in Calcium pumps?

Primary active transport


What is the role of calcium pumps within cell membranes?

-as soon as calcium is used for muscle contractions, they pump calcium ions across the cell membrane from intracellular to extracellular compartments
-Pumps calcium ions from cytoplasm to endoplasmic reticulum
-keeps Ca levels in narrow limits


What is Secondary Active Transport?

-active transport that does not DIRECTLY use energy from ATP
-use ATP INDIRECTLY to keep the transport mechanism going
-all of them require the Na+/K+ ATP pump


How does the Na-Glucose co-transporter secondary active system work? and where in the body might this be seen?

-Due to 3 Na+ normally being pumped out of the cell by the Na/K pump, and electrochemical Na gradient is formed causing Na to be pumped into the cell through its binding sites. Glucose molecules bind to Na outside the cell and rides it into the cell against its(glucose) concentration gradient.
-only in very selective cells
-small intestines, renal cells and the tubular cells of the kidneys


How are amino acids transported across cell membranes?

-the secondary active co-transport
-they travel with Na+(that goes with its natural gradient) against the amino acid gradient


What is the secondary active counter-transport? and what is an example?

-opposite transport across cell membrane
-indirectly uses ATP(from Na+/K+ pump)
-Na+/K+ pump creates a gradient to pump more Na+ into cells and substances inside the cell is pumped out at the same time
-H+ is transported out of the cell as Na+ is transported into the cell...utilized in renal cells to control acid base balance


What is pinocytosis?

-cell drinking
-type of endocytosis
-incorporated vesicles filled with water, water is dissolved within in order to get INTO cell


What is phagocytosis?

-incorporates large particles to inside the cell
-enzyme of lysosome breaks down the substrates
-ex. macrophages, neutriphils


What is exocytosis?

-a vesicle inside the cell is extruded outside the cell into extracellular fluid
-(ex.) usually anything that is excreted from a cell(hormones, neurotransmitters, ect.)


What is the molecular weight of glucose(C6H12O6)?

On the periodic table the atomic weight of carbon = 12, the atomic weight of hydrogen = 1, and the atomic weight of oxygen =
C-12 X 6 = 72
H-1 X 12 = 12
O-16 X 6 = 96
1 mole of glucose = 180 gm(Avogadro's number of molecules)


What is hydrostatic pressure?

The pressure at which water pushed against the wall of a water diffuses across a semi-permiable membrane, the hydrostatic pressure in the compartment its leaving decreases and the hydrostatic pressure of the compartment its moving to increases.
-hydrostatic=water change


If in compartment A the mOsm is 1200 and in compartment B the mOsm is 2800 what is happening to water and what is happening to the osm? Also what will happen when the osm equilibrates on the 2 sides? The amount of ___ ___ in B that stops osmosis of water is the ___ ___. Which side has the largest size particles?

-Water is moving from a lower mOsm to a highr mOsm(A to B) from an area of less particles to an area of more particles(osm of compartment A is increasing as water goes to compartment B)
-When this osm equilibrates on both sides the movement of water stops
-hydrostatic pressure, osmotic pressure
- it was a way to know that


Does albumin make a greater contribution to osmotic pressure of body fluids than Na+ or K+?



In shock with vascular to interstitial leak resulting in third spacing what is the first and primary response of the caregiver?

treat whatever is causing the hole in the vascular allowing capillary leak THEN give albumin to draw the interstitial fluid back to the vascular.


How does the sodium/potassium ATP pump contribute to the electrical gradient of the inside of the cell?

It makes the inside electrical gradient of the cell more negative.
a positive deficit inside the cell


What is the descriptive word used to describe the ATP electrical difference between the inside/outside of the cell related to the Na/K pump?

electrogenic pump


Na/K ATP pump transports against or with their natural gradient?



What are two examples of endocytosis?

1. pinocytosis
2. phagocytosis


What are the two major categories of transport across the cell membrane?

Passive transport
Active Transport


What is another name of passive transport across the cell membrane?



Does diffusion by passive transport utilize energy from ATP?



What category of transport utilizes energy from ATP?

active transport


Which types of transport moves WITH the gradient?

passive transport(diffusion) higher to lower gradient


What type of simple diffusion is the most simple?

directly across the phospholipid membrane(applies to lipid soluble substances)
O2, CO2, Nitrogen, alcohol


What are two types of leak channels?

Sodium Leak channels
Potassium Leak channels


Do Sodium Leak channels allow much sodium to leak into the cell or not? and why?

Sodium docent allow much leak because it holds on to water and so the molecules are larger


In what direction does the Potassium Leak channel leak?

inside to out


What are two types of Gated Channels?

1. Ligund Gated Channels
2. Voltage Gated Channels

***these still transport by diffusion***


What is an example of a ligund Gated Channel?

acetylcholine-sodium channel(acetylcholine binds with the receptor site opening the gate allowing sodium to enter the cell with its electrochemical gradient outside to inside)


What closes the Ligund Gated Channel?

When the Ligund(for example acetylcholine) is removed from the receptor site.


What are two types of Voltage Gated Channels?

1. Sodium Voltage Gated Channel
2. Potassium Voltage Gated Channel


How do Voltage Gated Channels work?

They open and close in response to voltage changes across the cell membrane


How many mV change has to occur for the Sodium Voltage Gated Channel to open?

~30 mV change(?990 to 960?)


What causes Sodium Voltage Gated Channels to close?

An even greater voltage change has to occur to close the Sodium Voltage Gated Channel?

Voltage gated sodium channels close when full amplitude depolarization achieved (at +20mV to +35) from -60 when they open to +20 is a change of 80 and to _35 is a change of 95.That what you mean? I think he leaned more to 95


How many mV opens the Potassium Voltage Gated Channel?

~90 mV change to open the gate for potassium.


Which voltage gated channels are called fast voltage gated and which are called slow voltage gated?

Sodium is a fast voltage gated channel
Potassium is a slow voltage gated channel


In relation to the voltage gated channels, of sodium and potassium which open first?

As the sodium gates are closing...the potassium gates are just beginning to open


When does the Potassium Voltage Gated Channels close?

When there is a return to depolarization????


What is an example of Facilitated Diffusion?

-glucose transporters in the cell membrane
-glucose molecule moves part way into the channel there it binds with receptor causing the channel to open to the other side of the cell membrane and then is released from the binding site(moves from higher to lower concentration)--->associated with a saturation point


What characteristic does Facilitated Diffusion work by that other types do not have?

Facilitated Diffusion works by a saturation point--->only so many receptor binding sites that can be accommodated at one time


Is Facilitated Diffusion an example of passive or active transport?



Does Facilitated move with the gradient or against the gradient?

With the gradient


With Facilitated Diffusion what happens when the saturation point is reached?

The molecules accumulate on the outside of the cell--->glucose for example


What does insulin do to glucose transporters?

Insulin increases the number of glucose transporters into the cell membrane--->facilitates getting more glucose into the cells


What type of transport is the Sodium Potassium ATP pump?

Active transport and it used ATP(energy) to transport against the gradient---> up the hill(from low to high)


How many sodiums are pumped out of the cell using the Sodium Potassium ATP pump?

3 sodiums out


How many potassium are pumped into the cell using the Sodium Potassium ATP pump?

2 potassiums in


What is the contribution of the Sodium Potassium Pump to the electrochemical gradient of the cell?

3 cations out 2 cations in--->keeping the inside of the cell slightly more negative


How does the Sodium Potassium Pump affect the cell in response to the Sodium Potassium Leak Channels?

If there were no active transport the cell would leak out all of its potassium and would be filled with sodium making it swell with water and being destroyed through lysis.


What would stop first if the cell should run out of ATP?

The Sodium Potassium ATP Pump


What are two examples of Secondary Active Co-Transport?

1. Sodium-Glucose
2. Sodium-Amino Acid


What is happening with Sodium-Glucose Secondary Active Co-Transport?

Sodium is moving WITH its electrochemical gradient
Glucose is moving AGAINST its {} gradient


Do all cells take up glucose via the Secondary Active Co-Transport mechanism?

No-normally glucose is transported by Facilitated Diffusion from higher to lower gradient.


Which cells receive glucose via the Secondary Active Co-Transport mechanism?

cells in the small intestines, renal cells and the tubular cells of the kidneys.


Do the cells that receive glucose via the Secondary Active Co-Tranport mechanism require insulin?

No; they need lots of glucose very quickly!


What determines the osmolality of a solution?

The number of particles/solutes it has


Do the size of the particles or the number of particles determine the osmolality?

The number of particles


A mole of an unassociated molecule to a liter of water, how many osmoles does it add to the liter of water?



A mole that is held together by an ionic bond such as NaCl, what will happen when it is added to water?

the bond will be broken


How many moles will result when 1 mole of NaCl is added to a liter of water? how many osmoses will result?

2 moles, 2 osmoles


1 mole of calcium chloride(CaCl2) when added to water. how many moles will result?

ionic bond will be broken
will result in 3 moles and 3 osmoles


What cells have membrane potentials?

All cells have membrane potentials(only some are excitable and can conduct actual potentials)


How are action potential quantified in relation to the cell membrane?


If its -90 mV, that means that it is 90 mV more negative as compared with the outside of that same cell membrane.

If its +30 mV, the inside of the cell membrane is 30 mV more positive compared to the outside of that membrane.


What would you expect the resting membrane potential to be?

-90 mV; thus the INSIDE of the cell membrane is 90 mV more negative relative to the OUTSIDE of that cell membrane.


What contributes to the resting membrane potential(4)?

1. K+ leak channels
2. Na+ leak channels
3. Na+/K+ ATP pump
4. Accumulation of negatively charged proteins along the inside of the cell membrane

***potassium leak channels is the biggest contribution***


During depolarization is the flow of amplitude positive or negative of the membrane potential?



During repolarization what is happening to the membrane potential?

It is becoming progressively more negative until it reaches its original resting membrane potential of -90 mV


What is the purpose of the refractory period with an action potential?

A Safety mechanism with the purpose of the refractory period is to repolarize back to the resting potential before depolarization again.


What are the 3 types of refractory periods?

1. Absolute
2. Relative
3. Supernormal/Vulnerable


Which part of the action potential do these various refractory period correspond with?



Define the Absolute Refractory Period

When the cell membrane is in absolute refractory period and it receives a very strong stimulus.

***It will not depolarize again while in the absolute refractory period***


Define the Relative Refractory Period

It is the period when if stimulated by a very strong stimulus to the cell membrane it may cause it to depolarize again.

***this is abnormal***


Define the Supernormal/Vulnerable Refractory Period

The period in which a mild stimulus may cause the cell membrane to depolarize again.

***this is abnormal***


What is the objective of the action potential repolarization?

The objective is to repolarize all the way back to resting before depolarizing again


What are the 3 categories of stimuli that initiates moving from a resting potential towards depolarization and what are examples of each?

1. chemicals--->neurotransmitters
2. electrical--->heart fibers
3. mechanical--->touch, pressure


If the initial stimulus increases the influx of Na+ enough to move the membrane potential in a less negative direction by 30 mV, what is that called and what will happen?

It is a threshold potential.
The Na+ voltage gated channels will open and depolarize...once this starts nothing can stop it...depolarization will occur.


At the full amplitude of depolarization, what 2 event occur simultaneously?

Voltage gated Na+ channels will close and the K+ gated channels will open.
As the influx of Na+ stops and outfox of K+ begins rapidly. As K+ is rapidly moving out of the cell, the cell membrane becomes more and more negative, rapidly depolarizing back to its original resting potential.


How do benzodiazepines affect the cell membrane action potential?

Benzos suppress the nerve impulses. They bind with GABA receptors which open the chloride channels. The direction of movement of chloride through these channels is from the outside to the inside of the cell membrane. Chloride anions(neg charges) come into the cell making it more negative(hyper polarized). It's really hard to get from way negative(hyper negative) all the way up and over the threshold of depolarization. This results in fewer action potentials and fewer nerve impulses.


How does hyperkalemia affect the action potential of the cell membrane?

Hyperkalemia HYPO POLARIZES the resting potential(making it less negative). When voltage gated Na+ channels open, the influx of Na+ is SLOWER than it normally should be, so the upstroke of depolarization is slow. Amplitude of depolarization is lower than normal, which is then followed by a rapid repolarization back to resting.

On EKG tall T waves--->repolarization is faster than normal decreased amplitude of QRS and widening of the QRS complex


How does hypokalemia affect the action potential of the cell membrane?

Hypokalemia HYPER POLARIZES the resting membrane(making it more negative). So it's hard to get from resting to threshold, but if the initial stimulus is strong enough to hit the resting threshold, then the influx of Na+ is fairly normal and depolarization is fairly normal followed by a slow/long repolarization back to resting.

During hypokalemia, repolarization is longer than normal, so refractory periods are longer than normal. INCREASED REFRACTORY PERIODS = increased opportunity for IRRITABLE DYSRHYTHMIAS

EKG: bradycardia, long flat T waves followed by a U wave


How does hypocalcemia affect threshold potential?

Hypocalcemia makes it EASIER TO OPEN voltages gated Na+ channels. It moves the threshold down closer to resting.***VOLTAGE GATED NA+ CHANNELS OPEN FASTER, Na+ FLOWS IN FASTER MAKING IT EASY TO DEPOLARIZE***

Hypocalcemia is generally worse clinically than hypercalcemia!!!


How does hypercalcemia affect threshold potential?

Hypercalcemia moves the threshold up further away from resting, making it MORE DIFFICULT to depolarize making it ***LESS EXCITABLE***

Hypercalcemia has to be really severe before it is going to have any major, devastating effects.


What potential does Potassium imbalances affect?

Potassium imbalances affect the cell membrane's resting potential


What potential does Calcium imbalances affect?

Calcium imbalances affect the threshold potential


What is the membrane potential?

it is the electrical potential or electrical difference across the cell membrane


Are intracellular and extracellular fluids polarized?

NO they are electrically neutral


What all parts of the cell does the membrane potential refer to?

Just "right on" the cell membrane....nothing else is referred to as positive or negative


What are 5 examples of cell that transmit electrical impulses using the action potential?

1. nerve fibers
2. skeletal muscle fibers
3. smooth muscle fibers
4. cardiac muscle fibers
5. cardiac electrical fibers


What are the 4 components of an action potential?

1. resting membrane potential
2. threshold potential
3. depolarization
4. repolarization


With a stimuli when sodium starts entering the cell what happens when the normal resting membrane potential goes from -90 mV to the threshold potential of -60 mV(a 30 mV change)?

The voltage gated Na+ channels open allowing an inward flood of Na+. The membrane rapidly becomes more positive as the sodium is a cation. This helps lead to depolarization.


What is the electrical charge at the zenith of depolarization?

~ 35 mV


What happens during repolarization?

As the Voltage-Gated sodium channels start to close, the Voltage-Gated potassium channels open allowing an influx of potassium leading to a return of resting membrane potential.

resting polarity of the cell membrane is re-established


What happens at the threshold potential?

The voltage gated channels of Na open


What are two ways in which extracellular substances regulate cell?

1. Through membrane-bound receptors
2. Intracellular receptors

*or a combination of both*


What does solubility have to do when talking about intracellular receptors?

They have to be lipid soluble to cross the cell membrane.


Describe the big picture cascade event once 1 ligand stimulates 1 cell receptor.

Once for example a hormone binds to a receptor site, G proteins are activated, they in turn activate an enzyme(adenylate cyclase), this in turn activates the second messenger cAMP which then activated protein kinase enzymes

***1 to many***


Describe the cascade event as related to the GDP and G protein complex.

In the resting phase alpha subunit of the G protein complex is attached to GDP. When the ligand binds with the receptor it activates the G protein. The GDP on the alpha subunit is replaced by GTP, which gives it more energy. The alpha subunit also has a phosphatase enzyme build into its subunit. The phosphate phosphorylates GTP back to GDP. This brings it back to it original resting state.


What is the function of phosphodiesterase?

It inactivates the cGMP


What are the three subunits attached to G protein?



Removal of the ligand from the receptor has what effect?

it ends the response as well as the phophodiesterase that phophorates the cAMP.


If you administer a medication that inhibits the phosphodiesterase enzyme that phosphoraltes the cAMP what happens?

The messenger stays active longer, the protein kinase stays active longer and the target cell response last longer.


With hormone receptors how long does it take for target cell response?

hours to days...slow response....last for a long time on the target cell.