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163 Cards in this Set
- Front
- Back
What do all living cells have that varies from moment to moment depending on the activities of the cell? |
Membrane potential |
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What is the membrane potential of an unstimulated cell? |
Resting membrane potential |
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What begins with a change in the resting membrane potential of a neuron? |
All neural activites |
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What is a typical stimulus that produces a temporary, localized change in the resting membrane potential called? |
Graded Potential |
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What decreases with distance form the stimulus? |
The effect of graded potential |
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What is created in the membrane of the axon if the graded potential is large enough? |
Action potential |
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What is propagated during an action potential along the surface of an axon? |
Electrical impulse |
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The electrical impulse in action potential does not ___________ as it moves away from its source. |
Deminish |
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Where does the electrical impulse in action potential travel to? |
One or more synapses |
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The integration of stimuli at the level of the individual cell is the simplest from of what in the nervous system? |
Information Processing |
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What two things do the response of the postsynaptic cell receiving the stimuli ultimately depend on? |
What stimulated receptors do and What other stimuli are influencing the cell at the same time |
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What processes do you need to understand to know how neurons deal with information and communicate with one another and with peripheral effectors? |
Resting potential, Graded potential, Action Potential, Synaptic Activity, Information processing |
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What is the first important concept regarding the membrane potential? |
The extracellur fluid (ECF) and intracellular fluid (cytosol) differ greatly. |
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What does the extracellular fluid (ECF contain high concentrations of? |
Sodium ions (Na+) and chloride ions (Cl-)
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What does intracellular fluid (cytosol) contain high concentrations of? |
Potassium ions (K+) and negatively charged proteins |
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What is the second important concept regarding the membrane potential? |
Cells have selectively permeable membranes |
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If the the plasma membrane were freely permeable, diffusion would continue until all the ions were evenly distributed across the membrane and what would exist? |
State of equilibrium |
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Why does an even distribution across a plasma membrane not occur? |
Because cells have selectively permeable membranes |
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What portion of the plasma membrane are ions unable to cross freely? |
Lipid |
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What is the only thing ions can enter or leave the cell through? |
Membrane channels |
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Many kind of membrane channels exist, each with its own what? |
Properties |
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Where do ions move through at the resting membrane potential, or membrane potential of an undisturbed cell. |
Leak channels |
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Leak channels are membrane channels that are always what? |
open |
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What do sodium potassium exchange pumps move? |
Specific ions into or out of the cell |
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What is the third important concept regarding the membrane potential? |
Membrane permeability varies by ion |
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What does not ensure an equal distribution of charges across its plasma membrane? |
The cell's passive and active transport mechanisms |
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Why does the cell's passive and active transport mechanisms not ensure an equal distribution of charges across its plasma membrane? |
Because membrane permeability varies by ion |
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What does membrane permeability very by? |
Ions |
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What forces act across the plasma membrane to determine the membrane potential at any moment? |
Both Passive and active |
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What to things are involved in the passive forces acting across the plasma membrane? |
Chemical and Electrical gradients |
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What do positive and negative charge do to one another? |
Attract
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What happens if nothing separates positive and negative charges? |
Oppositely charged ions will move together and eliminate the potential difference between them |
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What is a movement of charges to eliminate a potential difference called? |
Current |
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If a barrier (such as a plasma membrane) separates the oppositely charged ions, what does the amount of current depend on? |
How easily the ions can cross the membrane |
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What is a measure of how much the membrane restricts ion movement called? |
Resistance |
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If the resistance is high, the current is very small. Why is this? |
Because few ions can cross the membrane |
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If the resistance is low, the current is very large. Why is this? |
Because ions flow across the membrane |
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What can either reinforce or oppose the chemical gradient for each ion? |
Electrical gradients |
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What is the sum of the chemical and electrical forces action on a specific ion across the plasma membrane called? |
Electrochemical gradient |
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What are the primary factors affecting the resting membrane potential of most cells, including neurons called? |
The electrochemical gradients for K+ and Na+ |
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What is relatively high in intracellular concentration, but very low in extracellular concentration? |
Potassium (K+) ions |
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Because the potassium ions relatively high in intracellular fluid, their chemical gradients tend to do what? |
Drive them out of the cell |
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What does the electrical gradient do to the movement of (K+) potassium? |
It opposes movement |
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Why does the electrical gradient oppose the movement of (K+) potassium? |
Because (K+) inside the cell are attracted to negatively charges on the inside or the plasma membrane |
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What are k+ repelled by? |
The positive charges on the outside of the plasma membrane |
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Does the chemical gradient or the electrical gradient have more power? |
Chemical gradient |
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What weakens the force driving the K+ out of the cell? |
Electrical gradient |
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What would happen if the plasma membrane were freely permeable to K+ but impermeable to other positively charged ions? |
Potassium ions would continue to leave the cell until the electrical gradient was as strong as the chemical gradient. |
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What is the membrane potential at which there is no net movement of a particular ion across the plasma membrane called? |
Equilibrium potential |
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What is the mV for equilibrium for potassium ions? |
-90mV |
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What is the mV for resting membrane potential? |
-70mV |
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What is the difference in equilibrium potential and resting potential due to? |
Na+ leaking continuously into the cell |
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What does the equilibrium indicate? |
An ion's contribution to the resting membrane potential |
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What concentration is relatively high in extracellular fluid, but extremely low inside the cell? |
Sodium Ion (Na+) |
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What is the result of having a high concentration of sodium ion (Na+) outside of the cell? |
A strong chemical gradient is driving it into the cell |
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In addition, the extracellular sodium ions are attracted by the excess of __________ _______ on the inner surface of the plasma membrane |
Negative charges |
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What two things drive Na+ into the cell? |
Both electrical forces and chemical forces |
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If the plasma membrane were completely permeable to Na+ the ions would continue to cross until the interior of the cell contains enough excess positive charges to do what? |
Reverse the electrical gradient |
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Na+ movement across a freely permeable membrane would continue until the interior developed such a strongly positive charge that repulsion between the positive charges would prevent what? |
Any further net movement of Na+ into the cell. |
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What is mV for the equilibrium potential for Na+? |
+66mV |
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The resting membrane potential is nowhere near the equilibrium potential because resting membrane permeability to Na+ is very what? |
Low |
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What do ion pumps in the plasma membrane do to sodium ions? |
It ejects them as fast as they cross the membrane |
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What is an electrochemical gradient a form of? |
Potential energy |
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The potential energy is stored energy - the energy of ________, as exists in a stretched spring, a _______ battery, or water ______ a dam. |
Position, Charged, Behind |
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What would diffusion do without a plasma membrane? |
eliminate all electrochemical gradients |
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What does any stimulus that increases the permeability of the plasma membrane to sodium or potassium ions produce? |
sudden and dramatic ion movement |
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What does a stimulus that opens sodium on channels trigger? |
A rush of Na+ into the cell |
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Does the nature of the stimulus determine the amount of ion movement? |
No |
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What determine the amount of ion movement once the stimulus opens the door? |
Electrochemical gradient |
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At the normal resting membrane potential, the cell must bail out __________ ions that leak in and recapture _________ ions that leak out. |
Sodium, Potassium |
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The "bailing" takes place through the activity of an exchange pump powered by what? |
ATP |
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The ion pump involved in the "bailing" of sodium ions is the carrier protein called what? |
Sodium-potassium ATPase |
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How many sodium ions are exchange in the Sodium-potassium pump? |
3 intracellular sodium ions |
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How many potassium ions are exchanged in the Sodium-potassium pump? |
2 extracellular potassium ions |
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At what rate are sodium ions ejected from the sodium-potassium pump during normal resting membrane potential? |
As quickly as they enter the cell |
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Why does the resting membrane potential remain stable? |
Because the ionic concentration gradient are mainteined |
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Why does the resting potential exist? |
The cytosol differs from extracellular fluid in chemical and ionic composition, The plasma membrane is selectively permeable |
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Cells are dynamic structures that continually modify their what? |
Activities |
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How do cells continually modify specific functions? |
Either in response to external stimuli or to perform specific functions |
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The membrane potential is equally dynamic, doing what in response to temporary changes in membrane permeability? |
rising or falling |
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The changes in the membrane a result of what? |
Opening or closing of specific membrane channels |
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What controls the movement of ions across the plasma membrane? |
Membrane channels |
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What are the primary determinants of the membrane potential of many cell types, including neurons? |
Sodium and potassium ions |
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Sodium and potassium ion channels are one of which two things? |
Passive, and active |
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Whats another word for passive channel? |
Leak channels |
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Are leak channels A) Always open B) Always closed or C) they open and close? |
Always open |
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What can vary with leak channels from moment to moment? |
It's permeability |
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What makes up the leak channels? |
Protiens |
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What changes as the proteins that make up the leak channel responds to local conditions? |
Its shape |
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What are leak channels important in establishing? |
The normal resting membrane of the cell |
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What do plasma membranes have that open or close in response to specific stimuli? |
Active channels |
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What is another name for active channels? |
Gated channels |
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What are the three states in which each gated channel can be in? |
Closed but capable of opening, Open (activated), Closed and incapable of opening (inactivated) |
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What are the threeclasses of gated channels? |
Chemically gated or ligand-gated channels, Voltage-gated channels, Mechanically gated channels |
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Which class of gated channel opens or closes when they bind specific chemicals? |
Chemically gated channels or ligand-gated channels |
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How class of gated channel has receptors that bind acetycholine (ACH) at the neuromuscular junction? |
Chemically gated |
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Where are chemically gated channels most abundant? |
Dendrites and cell body of neuron |
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What occurs most at the dendrites and cell body of a neuron? |
Synaptic communication |
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Which class of gated channels open or close in response to changes in the membrane potential? |
Voltage-gated channels |
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A membrane capable of generating and propagating an action potential is called what? |
Excitable membrane |
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Examples of excitable membranes are the _____ of unipolar and multipolar neurons, and the __________ (including _________) of skeletal muscle cells. |
Axons, Sacrolemma, T-tubules |
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What are the three most important voltage-gated channels for the purposes of this chapter? |
Sodium channels, Potassium channels, Calcium channels |
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What are the two gates of the voltage-gated sodium channels? |
Activation gate, Inactivation gate |
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Which voltage-gated sodium channel opens on stimulation, letting sodium ions into the cell? |
Activation gate |
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Which voltage-gated sodium channel closes to stop the entry of sodium ions? |
Inactivation gate |
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Which class of gated channels opens or closes in response to physical distortion of the membrane surface? |
Mechanically gated channels |
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What are mechanically gated channels important in? |
Sensory receptors that respond to touch, pressure, or vibration |
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Are most gated channels open or closed at the resting potential? |
Closed |
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When gated channels open, what happens to the rate of ion movement across the plasma membrane, changing the membrane potential? |
It increases |
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What causes the rate of ion movement across the plasma membrane to increase? |
A gate channel opening. |
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When a gate channel opens and the rate of the ion movement across the plasma membrane increases, what changes? |
Membrane potential |
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The distribution of membrane channels ______ from one region of plasma membrane to another. |
Varies |
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What does the variance of distribution of membranes channels affect? |
How and where a cell responds to specific stimuli |
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What are wide spread channels on the surfaces of a neuron? |
Chemically gated sodium channels |
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What channels are abundant on the axon, its branches, and axon terminals? |
Voltage-gated sodium channels |
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What are voltage-gated sodium channels abundant on? |
Axon, Branches, Axon terminals |
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What channels are typically located only on the dendrites of sensory neurons? |
Mechanically gated channels |
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Where are mechanically gated channels typically located? |
Dendrites of sensory neurons |
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What are changes in the membrane potential that cannot spread from the site of stimulation? |
Graded potentials |
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What is another word for graded potentials? |
Local potentials |
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A graded potential is produced by any stimulus that does what? |
Opens a gate channel |
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During graded potential what enters the cell? |
Sodium ions |
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What are sodium ions that enter the cell during graded potential attracted to? |
The negative charges along the inner surface of the membrane |
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As additions positively charged sodium ions enter spread out, the membrane potential shifts towards what mV? |
0 |
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What is any shift from the resting membrane potential toward a more positive potential is called what? |
Depolarization |
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The term depolarization applies to changes in potential from ___ mV to smaller negative values, as well as to membrane potentials above ___ mV. |
-70, 0 |
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During depolarization membrane potential always becomes more what? |
Positive |
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As the plasma membrane depolarizes, sodium ions are released from where? |
Its outer surface |
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Where do the sodium ions released from its outer surface, along with other extracellular sodium ions, move toward? |
Open channels |
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What do the sodium ions released from its outer surface, along with other extracellular sodium ions, that move toward the open channels replace? |
Ions that have already entered the cell |
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What is the movement of positive charges parallel to the inner and outer surfaces of a membrane clled? |
Local current |
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In a graded potential, what decreases with distance away from the stimulation site? |
Degree of depolarization |
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One reason depolarization lessens with distance is because the cytosol offers considerable what? |
Resistance to ion movement
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Another reason depolarization lessens with distance is because some of the sodium ions entering cell then do what? |
Move back out across the membrane through sodium leak channels |
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What is undetectable at some distance from the entry point? |
The effects on the membrane potential |
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The maximum change in the membrane potential is proportional to the size of what? |
The stimulus |
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What determines the number of open sodium channels? |
The size of the stilmulus |
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The more open _________, the more _________ ____ enter the cell? |
Channels, Sodium Ions |
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The greater the membrane area affected, and the greater the what? |
The degree of depolarization |
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What does the membrane potential soon do when a chemical stimulus is removed and a normal membrane permeability is restored? |
Returns to resting membrane |
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What is the process of restoring the normal resting membrane potential after depolarization called? |
Repolarization |
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Repolarization typically involves a combination of what two things? |
Ion movement through membrane channels, The activities of ion pumps
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What does opening a gated potassium channel have the opposite effect from? |
Opening a gated sodium channel |
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What happens to the rate of potassium ion outflow when opening a gated potassium channel? |
It increases |
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What happens to the interior of a cell during the opening of a potassium gated channel? |
Loses positive ions |
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What effect does losing positive ions from the interior of the cell have? |
It becomes more negative? |
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What does the increase of negativity of the resting membrane potential and loss of positive ions produce? |
Hyperpolarizatoin |
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What distributes the effect to adjacent portions of the plasma membrane during hyperpolarization? |
Local current |
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A local current distributes the effect of hyperpolarization to adjacent portions of the plasma membrane, and the effect decreases with what? |
Distance from the open channel or channels |
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Graded potential occur in membranes of many cell types of cells - not just nerve and muscle cells. What are those other cell types? |
Epithelial cells, Gland cells, Adipocytes, Variety of sensory receptors.
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Graded potential often trigger specific what? |
Cell functions |
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An example of graded potential triggering a specific cell function would be when it triggers what at the surface of a gland cell? |
Exocytosis of secretory vesicles |
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At a neuromuscular junction, what does the graded depolarization of the motor end plate by ACh at trigger? |
An action potential in adjacent portions of the sarcolemma |
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What does the motor end plate support? |
Graded potentials |
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What does the sarcolemma consist of? |
Excitable membrane |
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What channels do excitable membranes have? |
Voltage-gated channels |
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The effect of graded potential decrease with what? |
Distance |
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In graded potential, the membrane potential is most changed where? |
At the site of stimulation |
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How does the effect of graded potential spread due to local currents? |
Passively |
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Graded potential effect spreads passively due to what? |
Local currents |
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Can graded potential be involved in both depolarization and hyperpolarization? If not, which one can it be involved in? |
Both |
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The properties and distribution of the membrane channels involved in graded potential determine what? |
The nature of the change |
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What increases with stronger stimulus during graded potential? |
The change in the membrane potential The affected area |