su14_-_physiology_exam_1_20141210195301 Flashcards
What are often referred to as “excitable cells”? Why?
neurons (single nerve cells) and most muscle cells because their physiologic functions rely critically on electrical events in their plasma (surface) membrane
What are the 3 mechanisms of electrical events?
- mechanism of cell-to-cell (intercellular) communication2. mechanism for sensing environmental changes (light, sound, temperature, etc.)3. mechanism for triggering intracellular events
An electrical event that acts in cell-to-cell communication ____ (is/is not) very rapid, allows for ____, and allows for ____.
- is very rapid- allows precise timing of signals between cells- allows complex patterns of communication between cells
What is an example of an electrical event that acts to sense environmental changes?
stimuli from the environment affect receptors (ex. rods and cones of the retina) and cause electrical events to occur in the receptor cells
Electrical events in cells can trigger intracellular changes which ____ (are/are not) rapid or can ____.
- are rapid- accumulate over time
What is an example of an electrical event that triggers intracellular events that is rapid?
rapid changes in [Ca +2] in hear and skeletal muscle cells
What is an example of an electrical event that triggers intracellular changes that can accumulate over time?
changes in hippocampal cells involved in learning (memory formation)
What is the definition of excitation?
activation to initiate an event
What are the 3 compartments that are important for excitation in cells?
- extracellular fluid (interstitial fluid)2. intracellular fluid (cytosol)3. cell membrane
What is found in the extracellular fluid (interstitial fluid)? What is it similar to in respect to the ionic composition? What is in high concentration?
- primarily ions, proteins, and other molecules- similar to plasma with respect to ionic composition- high NaCl concentration
What is found in the intracellular fluid (cytosol)? What is in high concentration?
- ions, much higher concentration of proteins, and other molecules- predominant salt in cells is KCl
Describe the composition of the cell membrane.
phospholipid bilayer and proteins; about equal amounts of protein and lipid and a small (approx 5%) amount of carbohydrates (for cell recognition)
What is the definition of permeability?
an index of the ability of the ion to cross the membrane
Changes in permeability that are ____ and ____ are essential to excitation in cells.
- ion-specific- exquisitely timed
What are the 5 types of movements across membranes?
- simple diffusion2. mediated transport3. osmosis4. endocytosis5. exocytosis
What is the definition of simple diffusion?
random diffusion, diffusion down an electrical gradient or a concentration gradient (organic molecules or ions)
____ (polar/non-polar) organic molecuels diffuse rapidly through the membrane which is 50% lipid because their solubility in lipid is ____ (high/low). Energy ____ (is/is not) required.
- non-polar- high- is not
In simple diffusion, ions cross membranes through ____ which are proteins, often composed of several subunits and generally ion-specific (ex. K or Na channels).
channels
What are some examples (4) of non-polar substances?
oxygen, carbon dioxide, fatty acids, steroid hormones
What is the definition of flux?
amount of substance crossing a surface per unit of time
The diffusion of a substance between two compartments is always ____ (bidirectional/unidirectional).
bidirectional
What is the definition of net flux? When the net flux = 0, what is the system called?
- difference between the two unidirectional fluxes- in a state of “diffusion equilibrium”
What is the definition of mediated transport?
ligand binds to a transporter in the membrane, the transporter undergoes a conformational change, and the ligand is released on the other side of the membrane
What are the 2 types of mediated transport?
- facilitated diffusion2. active transport
What is the definition of facilitated diffusion? Is energy required?
- a membrane protein serves as a carrier to translocate a molecule across the membrane- NO energy is required
What is an example of facilitated diffusion?
diffusion of glucose across the plasma membrane; glucose is large and polar; all cells have glucose transporters only in muscle and adipose tissue
What are the only locations where cells with glucose transporters can be found?
muscle and adipose tissue
What is the definition of active transport? Does it require energy?
- molecule is bound to a transporter in the membrane; molecule moves UP its concentration gradient and/or up and electrical gradient- energy is required!
What are the 2 ways energy affects transporters in active transport?
- the affinity of the transporter for the ligand on one side of the membrane more than on the other side- rate of transporter conformational change
What is the difference between primary and secondary active transport?
- primary active transport: energy source is hydrolysis of ATP, transporter becomes phosphorylated, change in affinity for ligand solute, increases transporter rate- secondary active transport: energy source is ion concentration gradient across membrane, transporter has 2 binding sites (transport of amino acids uses [Na] gradient); this is like a revolving door bringing in fresh air to the building
What are the 3 steps in mediated transport?
- ligand binds to transporter2. transporter undergoes conformational change3. ligand is released on other side of the membrane
What 3 factors determine the rate of flux in active transport?
- number of transporters in the membrane- extent of transporter saturation which, in turn, is affected by transporter affinity and ligand concentration- rate of transporter conformational change
What are the 3 types of active transport channels?
- ligand-sensitive (“chemically-regulated”)- voltage-sensitive (“voltage-regulated”)- mechanosensitive (ex. atria of heart)
What is the definition of osmosis?
bulk flow of water across a membrane; can lead to cell swelling or cell shrinkage if flow is large
What are the channels through which water flows in osmosis called?
aquaporins
What is the definition of osmolarity?
the total solute concentration in a solution
1.0 mole glucose = ____ osmole1.0 mole NaCl = ____ osmoleosmolarity of extracellular fluid = ____ mOsm
- 1.0 osmole- 2.0 osmole- 300 mOsm
Isotonic solution = ____ mOsm of non-penetrating solutes -> ____ (change/no change) in cell volume
- 300 mOsm- no change
Hypotonic solution ____ (</>) 300 mOsm of non-penetrating solutes -> cells ____ (swell/shrink)
- <- swell
Hypertonic solution ____ (</>) 300 mOsm of non-penetrating solutes -> cells ____ (swell/shrink)
- >
- shrink
What is the difference between iso-, hypo-, and hypertonic solutions and iso-, hypo-, and hyperosmotic solutions?
- solutions that are “-tonic” only take into account the non-penetrating solutes- solutions that are “-osmotic” take into account ALL solutes
True or false: A solution can be hyperosmotic and isotonic at the same time.
true! the cell will initially shrink because water will leave with the concentration gradient of the penetrating solute, but as that solute enters the cell, water will flow back into the cell
Hypoosmotic solution ____ (</>) 300 mOsm of non-penetrating and penetrating solutes.
<
Hyperosmotic solution ____ (</>) 300 mOsm of non-penetrating and penetrating solutes.
>
What is the definition of endocytosis?
engulfment of fluid and particles from the extracellular space; macrophages engulf cellular debris
What are the 2 types of endocytosis? Describe each.
- pinocytosis: small particles with or without a small volume of extracellular fluid (ECF)- phagocytosis: large particles or cellular debris; specialized cells (phagocytes) do this
What is the definition of exocytosis? What are the 2 purposes of it?
- reverse of endocytosis- replaces membrane patches internalized through endocytosis and mechanism of release of molecules synthesized within cells (secretion)
Is K+ in a higher concentration intracellular or extracellular?
intracellular (124 mM) > extracellular (2.25 mM)
Is Na+ in a higher concentration intracellular or extracellular?
extracellular (109 mM) > intracellular (10.4 mM)
Is Cl- in a higher concentration intracellular or extracellular?
extracellular (77.5 mM) > intracellular (1.5 mM)
Is Ca+2 in a higher concentration intracellular or extracellular?
intracellular (4.9 mM) > extracellular (2.1 mM)Note: most of the intracellular Ca+2 is bound or sequestered; the free Ca+2 is very low (<0.1 mM) and free Ca+2 is usually what is important
Are organic anions (ex. proteins) higher in concentration intracellular or extracellular?
intracellular (74 mM) > extracellular (13 mM)
What is the definition of voltage (V)?
an electrical charge difference between the inside and outside of virtually all cells
What is the definition of resistance (R)?
the fact that a steady voltage exists across the plasma membrane indicates that the membrane has resistance
What is the definition of current (I)?
when the resistance changes, ions move across the membrane from the inside of the cell to the outside or from the outside to the inside and this ion movement is called current
What is Ohm’s Law?
V = IR
What is the definition of conductance (G)?
reciprocal of resistance
What does conductance (G) equal?
G = I/V
If the resistance decreases, the conductance ____. Conductance and resistance are ____ properties.
- increases- membrane
There is a greater concentration of X+ and Y- in compartment 1. However, because the number of cations in compartment 1 is the same as the number of anions in compartment 1, and the same is true for compartment 2, there is no ____ difference between the two compartments.
voltage
Equilibrium is defined by a ____ difference and a ____ difference between two compartments.
voltage and concentration
State the Nernst equation.
Ex = (58z) log10([X1]/[X2])z = valence of the ion[X1] = concentration of X in compartment 1[X2] = concentration of X in compartment 2
What does the Nernst equation give?
equilibrium potential (or equilibrium voltage) of a single ionic species; the voltage across a cell membrane that exactly balances the force in the concentration gradient of a PERMEABLE ion
log 10 (0.1) = ____log 10 (1) = ____log 10 (10) = ____log 10 (100) = ____
-1012
____ potentials can also exist. However, they can be ____ (they can disappear over time). They are due to ____ (an imbalance in the flow of an ion or several ions between 2 compartments).
- diffusion- transient- asymmetric ion flow*NOTE: this could happen during the flow of Na+ and Cl- between two compartments if membrane is permeable to both, but Cl- has greater mobility
A living, resting cell has a higher concentration of ____ inside the cell than outside and a higher concentration of ____ outside the cell than inside.
K+Na+
A living, resting cell has a membrane that is most permeable to ____. The Pk/Pna ratio is approximately ____. That is ____ ions diffuse across a typical cell membrane approximately ____ times more readily than do ____ ions when a cell is at rest.
- K+- 60- K+- 60- Na
What are the 6 things that make up the basis of the Resting Membrane Potential?
- there is a concentration gradient across the plasma membrane for K+ ([K+] is always greater inside the cell than outside)- Pk»_space; Pna- K+ ions move down their concentration gradient leading to the development of a diffusion potential- equilibrium is reached when the force in the concentration gradient for K+ ions to move out of the cell is balanced by the opposing force in the electrical gradient (which favors keeping K+ ions inside the cell). At this point, the membrane potential (approx -90 mV) is very close to the equilibrium potential for K+ (Ek = approx -100 mV)- the fact that the resting membrane potential is not exactly equal to Ek indicates that some other ion(s) is (are) contributing to the resting potential; the resting membrane is slightly permeable to Na+ ions; therefore, Na diffuses into the cell down both its concentration gradient and electrical gradient and this is what keeps the resting membrane potential slightly lower (less negative) than Ex- therefore, K+ ions diffuse out of the cell at rest and Na+ ions diffuse into the cell at rest
The resting membrane potential of living cells is ____ (hint: adjective, not number). Therefore, resting potential ____ (is/is not) a transient diffusion potential.
- steady- is notNote: This very important point illustrates the fact that the resting potential is NOT due to the instantaneous movement of ions; it is due to the fact that ions ahve moved across the membrane, specifically K+ ions
A change of the membrane potential toward 0 mV is referred to as ____ or less commonly, as ____.
- depolarization- hypopolarization
A change in membrane potential away from 0 mV, in the negative voltage direction, is referred to as ____.
repolarization
An increase in membrane potential from the resting value (ex. more negative) is referred to as ____.
hyperpolarization
The Na+/K+ ATPase pump is responsible for transporting ____ ions into the cell and ____ ions out of the cell. This protein is an enzyme that hydrolyzes ____ to do work. It is responsible for maintaining the ____ gradient for Na+ and K+ across the membrane.
- K+ ions- Na+ ions- ATP- concentration
Without the Na/K pump, the resting membrane potential would slowly become ____. This ____ transport mechanism counteracts the ____ diffusion of ions - an example of ____.
- 0 mV- active- passive- homeostasis
What is the definition of homeostasis?
the mechanisms that have, as their goal, the maintenance of the body’s internal environment
True or false: During periods of intense excitation, the extracellular and intracellular concentrations of the ion(s) that cross the living cell’s plasma membrane changes.
FALSE. The number of ions that cross the membrane is an extremely small fraction of the total number of ions.
What is the equilibrium potential (mV) of K? Of Na? Of Cl?
K = -101 mVNa = +59 mVCl = -99 mV
Cells spend most of their time at rest. However, there are large and very rapid changes in membrane potential during excitation. The most common change in membrane potential is referred to as ____.
action potential (AP)
What are the 2 most common sites of action potentials in the body?
- single nerve cells (“neurons”)- muscle cells (“muscle fibers”)
Action potentials are ____ events that are ____ over a distance.
- active- propagated
What are the 4 parts of a neuron?
- dendrites- cell body- axon- axon terminal
A change in the environment causes a change in the ____ potential of a resting cell in the ____ direction. This environmental change is called a ____.
- membrane- depolarizing- stimulus
What are some examples of stimuli?
light, temperature, and sources of pain
A stimulus triggers a change in the ion permeability of what ion typically?
Na
The change in membrane potential that is directly due to the stimulus occurs primarily in the ____ of the neuron. This eventually causes the cell body to ____
- dendrites- depolarize
The action potential usually first develops in the ____ and then travels down the axon.
initial segment of axon
Describe the 9 steps during the development and time course of an action potential.
- increase in the membrane permeability to Na+ ions2. Na+ ions enter the cell (Na conductance increases) through voltage-regulated (?) Na channels being driven by electrical and concentration gradients that exist across the plasma membrane of neurons; they carry a positive charge with them3. the membrane potential moves closer to 0 mV4. if the depolarization is sufficiently large, the threshold will be reached which will cause additional voltage-regulated Na channels to open5. more Na+ enters the cell (conductance of Na increases); positive feedback cycle during this phase of the action potential; this is called the “rising phase” of the AP6. the membrane potential very rapidly moves toward 0 mV and overshoots, reaching a peak at approx 40 mV7. K+ channels open because they too are voltage-regulated and K+ ions cross the plasma membrane from the inside to the outside (conductance of K increases)8. the membrane potential then abruptly reverses direction and rapidly returns to the resting value as K+ ions diffuse out of the cell, carrying positive charge with them; called “falling phase” of the AP; movement of K+ ions is driven by the concentration gradient and, initially, by the electrical gradient as long as the potential is positive; Na channels also close because they are voltage-regulated and the membrane is now becoming more negative (called “Na inactivation”)9. overshoot (“afterpolarization”) is a phase of hyperpolarization; the rapid depolarization and repolarization phases are usually complete in approx 1 ms, but the afterpolarization phase can last 10+ ms
True or false: When the Na/K pump is poisoned, several hundred APs can still occur in the same neuron.
true
Describe the positive feedback cycle of an action potential.
opening of voltage-gated Na channels in membrane -> increased membrane Na permeability -> increased flow of Na into cell -> decreased membrane potential (depolarization) -> opening of voltage-gated Na channels…
What is the peak membrane potential during an action potential?
approx 40 mV
Why does the peak of the AP (approx 40 mV) approach the equilibrium potential for Na (approx 58 mV)?
the permeability of Na is very high during the rising phase of the AP; therefore, Na is free to cross the membrane until its ionic gradient is in equilibrium with the membrane potential; the two forces that act on Na ions (the concentration gradient and electrical gradient) nearly balance each other at the peak of the AP, but because the K channels open, you never reach 58 mV
Why is the end of the repolarization phase close to the equilibrium potential for K+?
the permeability of K is very high during the rising phase of the AP; therefore, K is free to cross the membrane until its ionic gradient is in equilibrium with the membrane potential; the two forces that act on K ions (the concentration gradient and electrical gradient) nearly balance each other at the peak of the AP, but because there is a finite Na permeability, you will never reach equilibrium potential of K
What is the definition of a subthreshold stimulus? Threshold stimulus? Suprathreshold stimulus?
- subthreshold: if the strength of the stimulus that causes the initial depolarization is too low to cause the membrane potential to reach threshold- threshold: stimulus is just sufficient to cause the membrane potential to reach threshold- suprathreshold: stimulus which is greater than a threshold stimulus
What type of stimulus causes events that are confined to the immediate region of the membrane and do NOT move along the membrane? What are these events called?
- subthreshold stimulus- local responses
Local responses are called ____ because they are proportional to the stimulus strength.
graded responses
What type of stimulus causes an action potential to occur?
threshold or suprathreshold stimulus
The fact that once an action potential crosses the threshold level and continues to completion is referred to as ____.
“all-or-none”
True or false: All action potentials are “all-or-none.”
true
What is the definition of a graded potential?
a change in the membrane potential, initiated by a weak stimuli, that is not propagated
True or false: The amplitude of a graded potential is graded with the strength of the stimulus.
true
What are the 2 types of summation of graded potentials?
- temporal summation- spatial summation
What is the definition of an absolute refractory period? Relative refractory period?
- absolute refractory period: period of time after an action potential when a second threshold stimulus or even suprathreshold stimulus cannot elicit a second action potential- relative refractory period: a period of time that is even longer after an action potential when a suprathreshold stimulus can elicit another AP but a threshold stimulus still cannot
The refractory periods impose an upper limit on ____.
the frequency at which cells can fire action potentials
True or false: Action potentials often undergo summation.
FALSE. Action potentials CANNOT undergo summation.
Describe “adaptation” of the cell regarding stimuli and action potentials. Describe “accommodation.” What is the difference between the two terms?
- adaptation: a stimulus with a given magnitude is applied quickly and generates an AP; a stimulus with an identical magnitude is applied slowly and there is no AP generated- accommodation: the transition from the closed-state ion channel to the open-state is dependent on the rate of stimulus change- adaptation is a property of the neuron and it is due to the accommodation of the ion channels
What are the 4 important stimulus parameters?
- intensity (amplitude)- duration- rate of change- frequency (upper limit could be determined by the refractory periods)
In a stimulus strength-duration curve, what is the definition of rheobase?
the magnitude of the least intense stimulus that can elicit a response
In a stimulus strength-duration curve, what is the definition of utilization time?
the duration required to elicit a response by a stimulus with a rheobase magnitude
In a stimulus strength-duration curve, what is the definition of chronaxie? What is it used for?
-the duration required to elicit a response for a stimulus that has a magnitude that is twice the rheobase magnitude- can be used to compare the excitability of different cells
If you wanted to “blunt” the excitability of a cell, which way should the stimulus strength-duration curve move?
to the right so that it takes a longer time to excite
Action potentials that progress along the entire length of the axon of a neuron are called ____.
action potential propagation
What is the definition of an electrotonic current (“local current”)? Are they active or passive currents?
-currents that occur at the immediate site of the stimulating electrodes that are placed near a neuron- passive currents (they do not propagate)
Current flows from the ____ through the neuron to the ____. This is a flow of ____ charges.
- anode- cathode- positive
The potential change at the ____ is a depolarizing potential change. The potential change at the ____ is a hyperpolarizing potential change.
- cathode- anode
True or false: One action potential moves along the entire axon.
FALSE. Correctly speaking, one AP does not actually move along the entire axon. Rather, every site along an axon undergoes a change in membrane potential which is the AP, unless the axon is myelinated.
The initiation of an AP at each site is dependent on the ____ from the adjacent site which cause a depolarization of the membrane that opens ____ channels. This allows ____ ions to enter the cell, bringing a positive charge which causes additional depolarization and subsequent generation of an AP at that site.
- local currents- Na- Na+
Why is it that local currents go bidirectional, but action potentials only proceed in one direction?
because when the Na channels close, they cannot reopen again for a little while
____ surround the axons of neurons. These cells wrap an extensive layer of ____ around the axon, except at periodic nodes called ____.
- Schwann cells- plasma membrane- nodes of Ranvier
What are the layers of Schwann cell membrane called? What type of insulator are they?
- myelin- electrical insulator
True or false: Action potentials are generated between nodes of a myelinated axon.
FALSE. Action potentials are generated at the nodes.
Local currents inside the axon spread much further in the presence of myelin and this allows action potentials to be generated only at the nodes between the Schwann cell membranes. The AP “skips” along the axon, which is called ____. This generally increases ____.
- salutatory conduction- velocity of AP propagation along axons
Breakdown of myelin in myelinated neurons results in what?
gross motor abnormalities
Axons with larger diameters have ____ (higher/lower) velocities of conduction.
higher
The further the recording electrodes are from the stimulating electrodes, the ____ (more/less) the individual APs are discerned from each other.
more
Rank the nerves from largest diameter to smallest and from fastest velocity to slowest.
A(alpha) > A(beta) > A(gamma) > A(delta) > B > C(dorsal root) > C (sympathetic)diameter and velocity are directly related
True or false: In general, larger diameter neurons are usually myelinated while smaller are unmyelinated.
true
Do autonomic nerves usually have a large or small diameter? Myelinated or unmyelinated? High or low velocity?
- small diameter- unmyelinated- low velocity
What is the function of A(alpha) neurons? Of A(beta)?
- A(alpha): motor, proprioception- A(beta): touch, pressure
What is the function of A(gamma) neurons? Of A(delta)?
- A(gamma): muscle spindles- A(delta): pain, cold, touch
What is the function of B neurons?
preganglionic autonomic
What is the function of C dorsal root neurons?
pain, temperature, mechanoreceptors, reflexes
What is the function of C sympathetic neurons?
postganglionic sympathetic
