graded potential physio question.

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Ice2remember

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need help with this question.

transmission of impulses from the motor nerve to the muscle cell regularly produces.

a.an action potential in the muscle cell.
b.a graded potential in the muscle cell.
c.hyperpolarization of the muscle cell.
d.hypopolarization of the muscle cell.
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Hi friend,

I guess the correct answer is a.
ACh is stored in vesicles and is released when an action potential in the motor nerve opens Ca2+ channels in the presynaptic terminal. ACh diffuse across the synaptic cleft and opens Na+ and K+ channels in the muscle end plate, depolarizing it ( but not producing an action potential). Depolarization of the muscle end plate causes local currents in adjacent muscle membrane, depolarizing the membrane to threshold and producing action potential.

plz correct me if im wrong.
Thanks
 
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jennifertrn said:
Hi friend,

I guess the correct answer is a.
ACh is stored in vesicles and is released when an action potential in the motor nerve opens Ca2+ channels in the presynaptic terminal. ACh diffuse across the synaptic cleft and opens Na+ and K+ channels in the muscle end plate, depolarizing it ( but not producing an action potential). Depolarization of the muscle end plate causes local currents in adjacent muscle membrane, depolarizing the membrane to threshold and producing action potential.

plz correct me if im wrong.
Thanks
Click to expand...

Yea, i would've a guessed (a) action potential.
obviously (d) isn't it.
(c) can't be it because of the word "impulse" which I take to mean that depolarization is occuring. Hyperpolarization is to bring normalize any "impulses" in the membrane potential.
(b) isn't it because
(c) can't be it because a graded potential is a gradient of transmembrane potential difference along a length of cell membrane. Graded potentials are particularly important in neurons that lack action potentials, such as some types of retinal neurons.
(a) is likely the best choice and to continue on what happens after Ach is released into the motor end plate.... it stimulates and action potential that travels down T-tubules which in turn causes the sarcoplasmic reticulum to release Ca+2. The Ca+2. binds to troponin which removes the tropomyosin off the muscle fiber. I think it allows ATP to bind to the myosin heads and intiate contraction. I'm not sure about this. If someone could tell me what;s up... much appreciated.
 
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Ice2remember said:
need help with this question.

transmission of impulses from the motor nerve to the muscle cell regularly produces.

a.an action potential in the muscle cell.
b.a graded potential in the muscle cell.
c.hyperpolarization of the muscle cell.
d.hypopolarization of the muscle cell.

i feel both choice a and c are correct,since exitatory is depolarization (choice a)and inhibitory is hyperpolarization (choice c).since graded potential occurs in neuron it is'nt choice b.any inputs?
Click to expand...

The answer is a, but in a side note...

The transmission of impulses starts from the motor end plate to the the muscle cell, from which impulses generated from the chemical synapse can initiate an action potential in the muscle cell

By definition graded potentials are changes in membrane potential confined to a small region of a plasma membrane. Magnitude of these potentials is related to the magnitude of the initiating stimulus. They initiate a signal.http://en.wikipedia.org/wiki/Postsynaptic_potential
 
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Ice2remember said:
need help with this question.

transmission of impulses from the motor nerve to the muscle cell regularly produces.

a.an action potential in the muscle cell.
b.a graded potential in the muscle cell.
c.hyperpolarization of the muscle cell.
d.hypopolarization of the muscle cell.
Click to expand...
Evil Ibanez is back. :meanie:

1. GRADED POTENTIAL IS NOT JUST SEEN IN CASE OF NEURONS, but also POST-SYNAPTIC TERMINAL OF A NEUROMUSCULAR JUNCTION (MUSCLE, that is.)

2. END PLATE POTENTIAL IS A GRADED POTENTIAL. AND NOT ACTION POTENTIAL. MANY MEPPs (Miniature EPP) ARE GENERATED ON THE MEMBRANE (POST-SYNAPTIC membrane) and together they produce EPP.

3. The summation of MANY MEPPs at post-synaptic terminal/membrane will cause depolarization in the muscle cell. And now this depolarization will pass onto adjacent muscle tissue and so forth creating AN ACTION POTENTIAL. (Only if the EPP generated is more than the threshold value of a membrane, an action potential is produced. ALL OR NONE.)


Having said that and moving towards answering the question... I think I should list the keywords used in the question that will help us answer it: :idea:

MUSCLE CELL
REGULARLY


Now, the option 2 says "Graded potential" (re-read my point 1 and 2).
GRADED POTENTIAL develops only at the POST-SYNAPTIC TERMINAL; AND NOT THE ENTIRE MUSCLE TISSUE.
But if the question was framed in a way, say, "The transmission of impulses from motor neurons at neuromuscular junction regularly produces: " and if the options given were like

a Action Potential
b Graded Potential
c Hyperpolarization
d Hypopolarization

In such a case the answer will be "GRADED POTENTIAL" . Because MEPPs are REGULARLY PRODUCED and the summation of MEPPs (EPP) can be below the threshold level. IF below the threshold, there will be no Action Potential generated (like say for example in some neural disorder/degeneration/disease state).

AND ACTION POTENTIAL IS NOT PRODUCED AT POST SYNAPTIC TERMINAL OF A NM JUNCTION.

Moving on, the option 3 says: Hyperpolarization. Hyperpolarization is NOT A REGULARLY occuring phenomenon at NM junction. Though if the NT secreted at the NM junction is an inhibitory one then it results in Hyperpolarization and therefore there is NO MUSCLE CONTRACTION. 👎

Hyperpolarization may be a REGULAR phenomenon in a DISEASED STATE ONLY.
REMEMBER THERE ARE MANY EXCITATORY NTs BUT ONLY FEW INHIBITORY ONES.:idea:
SO ONLY FEW INHIBITORY IMPULSES (IPSPs; inhibitory post-synaptic potentials) AT NM junction.

The question is general and so you can take the NT as an excitatory one; its not framed specifically to test the knowledge of effect of an inhibitory NT at NM junction.

Option 4: Hypopolarization; there's no such thing as hypopolarization.


Option 1 is the bandicoot. Kill it!


Now Im tired 😴 and hope I was of some help 😱 else I know some Guru Ghantals "The Popats".😎


Mayank.

PS Most of the above text is guaranteed, the rest is my evil thinking... *Shoo Mayankie shoo* -shrugs- :meanie:
 
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jennifertrn said:
Hi friend,

I guess the correct answer is a.
ACh is stored in vesicles and is released when an action potential in the motor nerve opens Ca2+ channels in the presynaptic terminal. ACh diffuse across the synaptic cleft and opens Na+ and K+ channels in the muscle end plate, depolarizing it ( but not producing an action potential). Depolarization of the muscle end plate causes local currents in adjacent muscle membrane, depolarizing the membrane to threshold and producing action potential.

plz correct me if im wrong.
Thanks
Click to expand...
Read my post above, you've missed something important happening at the Neuromuscular junction 😛 😀
 
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briansle said:
Yea, i would've a guessed (a) action potential.
obviously (d) isn't it.
(c) can't be it because of the word "impulse" which I take to mean that depolarization is occuring. Hyperpolarization is to bring normalize any "impulses" in the membrane potential.
(b) isn't it because
(c) can't be it because a graded potential is a gradient of transmembrane potential difference along a length of cell membrane. Graded potentials are particularly important in neurons that lack action potentials, such as some types of retinal neurons.
(a) is likely the best choice and to continue on what happens after Ach is released into the motor end plate.... it stimulates and action potential that travels down T-tubules which in turn causes the sarcoplasmic reticulum to release Ca+2. The Ca+2. binds to troponin which removes the tropomyosin off the muscle fiber. I think it allows ATP to bind to the myosin heads and intiate contraction. I'm not sure about this. If someone could tell me what;s up... much appreciated.
Click to expand...
Read my reply above. 🙂
 
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The net passive potassium ion current through a cell membrane can be reduced to zero by:

A) enhancing the activity of the sodium-potassium pump
B)depolarizing the membrane potential to 0mV
C)increasing the concentration of of potassium ions inside the cell
D)decreasing the concentration of potassium ions outside the cell
E)hyperpolarising the membrane to potassium ion equilibrium potential
 
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nisreen said:
The net passive potassium ion current through a cell membrane can be reduced to zero by:

A) enhancing the activity of the sodium-potassium pump
B)depolarizing the membrane potential to 0mV
C)increasing the concentration of of potassium ions inside the cell
D)decreasing the concentration of potassium ions outside the cell
E)hyperpolarising the membrane to potassium ion equilibrium potential
Click to expand...

Answer is E because when membrane reaches equilibrium potential of specific ion, net current/flow of that ion reduces to zero that is no net flow.
 
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nisreen said:
The net passive potassium ion current through a cell membrane can be reduced to zero by:

A) enhancing the activity of the sodium-potassium pump
B)depolarizing the membrane potential to 0mV
C)increasing the concentration of of potassium ions inside the cell
D)decreasing the concentration of potassium ions outside the cell
E)hyperpolarising the membrane to potassium ion equilibrium potential
Click to expand...
I've already explained membrane potentials in another thread... but anyway I will explain the relevant stuff here or I can copy paste 😛 :idea:


During the UPSTROKE of the action potential (ASCENDING LIMB of AP), the depolarizing wave rapidly opens the ACTIVATION GATES of the Na+ channels. This results in movement of Na+ inside the cell (making the AP more POSITIVE near the equilibrium potential of Na+ --> +65 mV).

(This is also the brief period when the AP is positive.)

Remember that since the resting membrane potential is NEGATIVE (-70 mV),
Depolarizing wave, now, will make it POSITIVE (between 0 and +65 mV mark; approaches Na+ eq. potential, 3 Na+ moves IN and 2 K+ OUT... 3+ IN and 2 + OUT= +ive INside).

DEPOLARIZATION= CELL INTERIOR IS LESS NEGATIVE.

(Depolarization also closes the INACTIVATION gates but it takes time for the gates to close and they close later during repolarization. The closure of inactivation gates, during repolarization, will block the Na+ entering inside.)

For a wave of AP to propagate, the membrane potential has to come back to its resting state (so that it can be depolarized again; like a cyclic thing). REPOLARIZATION now begins by OPENING OF K+ channels (plus the inactivation gates of Na+ are also closing). Gradually the membrane potential will decrease towards resting state.(0 --> -70mV).
because for every 2 K+ that enters inside, 3 Na+ moves out.


(And after REPOLARIZATION, there's a brief period of HYPERPOLARIZATION (Afterpotential) when the AP approaches the eq. potential of K+ --> -85mV. (HYPERPOLARIZATION= MORE NEGATIVE)

This is because the membrane is more permeable to K+ than Na+ at rest. (Eq potential of K+ is near resting membrane potential !!!)


AT EQUILIBRIUM POTENTIAL THERE IS NO NET DIFFUSION OF THAT ION. SO K+ ION REACHES ITS (or approaches) EQUILIBRIUM POTENTIAL DURING HYPERPOLARIZATION. (Relative Refractory Period)


OPTION no. 5 (E) is the correct answer.


Let me explain the other options aswell:

a. Enhancing the Na-K pump.
Keyword in the question is NET "PASSIVE" DIFFUSION. Na-K pump is an example of PRIMARY ACTIVE TRANSPORT. It requires ATP as the movement of Na+ and K+ is against their electrochemical gradient.

b. Depolarizing the membrane potential to 0 mV
As already expalined above, 0 mV membrane potential is more positive than resting membrane potential of -70 mV. (During Upstroke)

DEPOLARIZATION WILL CAUSE THE ACTIVATION GATES OF Na+ CHANNEL TO OPEN. THUS THERE WILL BE MORE MOVEMENT OF Na+ than K+. (remember for every 3 Na+ that moves out, 2K- moves in)

c. Increasing the concentration of K+ inside the cell
This is what happens in Repolarization. Na+ channels are closing and K+ channels are opening and this will bring down the Action potential from some positive value (Upstroke/Depolarization) near the resting membrane potential.

This option seems correct but the BEST OPTION is E.

d. Decreasing the K+ conc outside the cell
Similarly this option doesn't specifically point at equilibrium. (DOES NOT QUANTIFY, like option c)


😴


Mayank.

PS Its 4 am and Im not quite poetic 😱
 
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As in all clear? All erased off your memory? Brain-washed? 😛

Nevermind you're welcome!! 🙂
 
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hi.. thanks a lot for replying dentstu and ibanez, and thank you very much for the explanation.. really appreciated...sorry you had to re- explain all of it ... i figured the answer was option e..just wanted to get the whole concept clear...and understand how and why the other options aren't correct...
 
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nisreen said:
hi.. thanks a lot for replying dentstu and ibanez, and thank you very much for the explanation.. really appreciated...sorry you had to re- explain all of it ... i figured the answer was option e..just wanted to get the whole concept clear...and understand how and why the other options aren't correct...
Click to expand...
No Problemo! 🙂
 
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Ibanez said:
Evil Ibanez is back. :smuggrin:

1. GRADED POTENTIAL IS NOT JUST SEEN IN CASE OF NEURONS, but also POST-SYNAPTIC TERMINAL OF A NEUROMUSCULAR JUNCTION (MUSCLE, that is.)

2. END PLATE POTENTIAL IS A GRADED POTENTIAL. AND NOT ACTION POTENTIAL. MANY MEPPs (Miniature EPP) ARE GENERATED ON THE MEMBRANE (POST-SYNAPTIC membrane) and together they produce EPP.

3. The summation of MANY MEPPs at post-synaptic terminal/membrane will cause depolarization in the muscle cell. And now this depolarization will pass onto adjacent muscle tissue and so forth creating AN ACTION POTENTIAL. (Only if the EPP generated is more than the threshold value of a membrane, an action potential is produced. ALL OR NONE.)


Having said that and moving towards answering the question... I think I should list the keywords used in the question that will help us answer it: :idea:

MUSCLE CELL
REGULARLY


Now, the option 2 says "Graded potential" (re-read my point 1 and 2).
GRADED POTENTIAL develops only at the POST-SYNAPTIC TERMINAL; AND NOT THE ENTIRE MUSCLE TISSUE.
But if the question was framed in a way, say, "The transmission of impulses from motor neurons at neuromuscular junction regularly produces: " and if the options given were like

a Action Potential
b Graded Potential
c Hyperpolarization
d Hypopolarization

In such a case the answer will be "GRADED POTENTIAL" . Because MEPPs are REGULARLY PRODUCED and the summation of MEPPs (EPP) can be below the threshold level. IF below the threshold, there will be no Action Potential generated (like say for example in some neural disorder/degeneration/disease state).

AND ACTION POTENTIAL IS NOT PRODUCED AT POST SYNAPTIC TERMINAL OF A NM JUNCTION.

Moving on, the option 3 says: Hyperpolarization. Hyperpolarization is NOT A REGULARLY occuring phenomenon at NM junction. Though if the NT secreted at the NM junction is an inhibitory one then it results in Hyperpolarization and therefore there is NO MUSCLE CONTRACTION. 👎

Hyperpolarization may be a REGULAR phenomenon in a DISEASED STATE ONLY.
REMEMBER THERE ARE MANY EXCITATORY NTs BUT ONLY FEW INHIBITORY ONES.:idea:
SO ONLY FEW INHIBITORY IMPULSES (IPSPs; inhibitory post-synaptic potentials) AT NM junction.

The question is general and so you can take the NT as an excitatory one; its not framed specifically to test the knowledge of effect of an inhibitory NT at NM junction.

Option 4: Hypopolarization; there's no such thing as hypopolarization.


Option 1 is the bandicoot. Kill it!


Now Im tired 😴 and hope I was of some help 😱 else I know some Guru Ghantals "The Popats".😎


Mayank.

PS Most of the above text is guaranteed, the rest is my evil thinking... *Shoo Mayankie shoo* -shrugs- :smuggrin:
Click to expand...
this is the most awesome explanation ever!!!
 
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