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Old 04-21-2011
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Question Transport Mechanism of Sodium flux in action potential

I read this question but confused on answer........
Na flux during an AP is an example of what transport mechanism??
1) carrier mediated diffusion
2) paracellular
3) primary active antiport
4) secondary active symport
5) simple diffusion

I think its 1) but answer says 5)
any explanations???
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Old 04-21-2011
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During an Action Potential the Na+ influx is caused by Voltage Gated Ion Channels. These channels are not carrier mediated. They operate on the principal of electrochemical gradient. By elimination you can rule out all other answers, and simple diffusion by electrochemical gradient is the answer.
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simple diffusion occurs down a concentration or electrochemical gradient n thts wt happens in action pot. Na+ influx into the cell thru the voltage gated channels
thanx fr putting up the q.
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Quote:
Originally Posted by qurat21 View Post
simple diffusion occurs down a concentration or electrochemical gradient n thts wt happens in action pot. Na+ influx into the cell thru the voltage gated channels
thanx fr putting up the q.
ok I'm confused, carrier mediated and facilitated diffusion are the same right? Doesn't it occur down the concentration gradient through the carrier?
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yup! carrier mediated includes facilitated diffusion , primary active n secondary active transport
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Old 04-21-2011
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So sodium passing along the concentration gradient through its channel won't be facilitated diffusion rather than simple diffusion?
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Quote:
Originally Posted by doctorsmonsters View Post
So sodium passing along the concentration gradient through its channel won't be facilitated diffusion rather than simple diffusion?
Simple diffusion
  • simple diffusion is the random movement of particles (molecules) from a region of high concentration to a region of low concentration.
  • this process will continue until a dynamic equilibrium reached.
  • example - diffusion of oxygen from the alveoli into the adjacent blood capillaries.

Facilitated diffusion
  • facilitated diffusion is the passive movement of molecules or ions down a concentration gradient.
  • the process involves special pore proteins (channel proteins) or specific carrier proteins in the plasma membrane.
  • the particular molecules combine with the specific active site of the carrier protein. The carrier protein changes its shape to allow the molecules to pass through to the other side of the plasma membrane. After assisting the movement of molecules to the other side of the plasma membrane, it is free to bind with other molecules.
  • example- the reabsorption of glucose and amino acid from the villi into the blood capillaries.

Source:
http://biology-stmark.blogspot.com/2...1_archive.html
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Quote:
Originally Posted by doctorsmonsters View Post
So sodium passing along the concentration gradient through its channel won't be facilitated diffusion rather than simple diffusion?
basically, think of it this way -

facilitated diffusion is for particles that are not permeable so they need a carrier protein that helps them go across the membrane.

simple diffusion is for permeable substances that can cross a membrane freely without need a carrier protein.

both the diffusions occur down a concentration gradient
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Old 04-21-2011
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Thanks for the explanation, very well put.
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