Match the information on the right with the term on the left. Use each answer on

Question

Match the information on the right with the term on the left. Use each answer only once.

Unmyelinated axons

      [ Choose ]            always open            conduction velocity of 110 m/s            conduction velocity of 1 m/s            opened by positive charge      

K+ leak

      [ Choose ]            always open            conduction velocity of 110 m/s            conduction velocity of 1 m/s            opened by positive charge      

myelinated axons

      [ Choose ]            always open            conduction velocity of 110 m/s            conduction velocity of 1 m/s            opened by positive charge      

Na+

      [ Choose ]            always open            conduction velocity of 110 m/s            conduction velocity of 1 m/s            opened by positive charge      

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Question 21 pts

When measurements are taken along an unmyelinated axon, we see a decrease in voltage as we move down the axon. Why do we see this decrease?

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Question 31 pts

Action potentials propagate as invariant (stereotyped) signals. What does the word "invariant" in this statement mean?

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Question 41 pts

During depolarization, the dominant channel that is open is the                            [ Select ]                       ["Voltage gated Na+ channels", "Voltage gated K+ channels", "K+ leak channels", "Voltage gated Ca2+ channels"]         . During repolarization, the dominant channel that is open is the                            [ Select ]                       ["K+ leak channels", "Voltage gated K+ channels", "Voltage gated Na+ channels", "Voltage gated Ca2+ channels"]         .

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Question 51 pts

***This is an example of a test question***

The concentration of Na+ on the inside of the cell exceed the concentration of Na+ on the outside of the cell at which of the following voltages?

Explanation / Answer

ANSWER 1 : (a) In unmyelinated axons conduction speed is about to 1 m/s. Because it not covered with myelin sheath. That protects the lose action potential in axon necessary for maintaining constant speed of conduction through nerve fibre.

(b) K+ leak channels are non gated channel that remain always open. Because voltage-gate are not necessary for their working and oftenly found in resting potential membrane. so also called as passive channel.

(c) In myelinated axons conduction velocity is about 110 m/s. Because it is covered with a myelin sheath that enhances the speed of conduction via saltatory conduction ( from Ranvier node to subsequent node).

(d) Na+ opened by a positively charged ion (K+) through sodium- potassium ion pump, during depolarisation Na+ gate open that cause influx of Na+ and pushing out of K+ .

ANSWER 2 : In unmyelinated axon, a decrease in voltage is often seen, because it is not unshielded ( myelin is absent throughout axon). So the electric charge that maintain a constant voltage in axon leaves through voltage-gated Na+ channels to other neuronal membrane that present in surrounding.

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