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Multiple choice problems based on Neurochemistry involving sodium, potassium and calcium ions.

1. When considering nerve impulse generation across a cell membrane, potassium ions (K+), sodium ions (Na+) and calcium ions (Ca++) are the ions most involved in this process? By meaning these ions are defined as follows:

a.Potassium, K+, is a monovalent anion and is the major intracellular ion; Sodium, Na+, is a monovalent cation and is the major extracellular ion, and Calcium, Ca++, is a divalent cation found mainly outside of the cell.

b.Potassium, K+, is a monovalent cation and is the major extracellular ion; Sodium, Na+, is a monovalent anion and is the major intracellular ion, and calcium, Ca++, is a divalent cation found mainly outside of the cell.

c.Potassium, K+, is a monovalent anion and is the major intracellular ion; sodium, Na+, is a monovalent cation and is the major extracellular ion, and calcium, Ca++, is a divalent anion found mainly outside of the cell.

d.Potassium, K+, is a monovalent cation and is the major intracellular ion; sodium, Na+, is a monovalent cation and is the major extracellular ion; and calcium, Ca++, is a divalent cation found mainly outside of the cell.

e.None of the above answers are true or correct.

2.Select the best explanation of what a polarized membrane is:

a.A polarized membrane is one that has a different concentration of ions on one side of it versus the other side.

b.A polarized membrane is one that has a negative portion and a positive portion due to the difference in concentration of ions inside and outside of the cell membrane.

c.A polarized membrane is one that Kodak® holds the patent on and uses regularly in its instant photo technology.

d.A polarized membrane is one that has traveled to the Arctic Circle and returned unfrozen.

3.Select from the following choices the best and most true statement about the sodium-potassium pump during the repolarization of a cell membrane:

a.During repolarization, while pumping Na+ ions back out the cell and K+ ions back into the cell, the sodium-potassium pump carries on an even one-to-one ion exchange such that for every Na+ ion pumped out, there is one K+ ion pumped back in.

b.During repolarization, the sodium-potassium pump removes more positive ions from within the cell than it brings into it, resulting in the cell's interior becoming more negative, which makes the pump an electrogenic pump that creates a small potential across the cell membrane.

c.During repolarization the Hodgkin Cycle results in more repolarization of the membrane because more Na+ ions are pumped into the membrane.

d.During repolarization, the cell membrane becomes more permeable to Na+ ions than it was at its resting potential level, and the membrane becomes less permeable to K+ ions, resulting in the inner surface of the membrane to become negatively charged again.

e.None of the above.

4.During the period of repolarization of a nerve cell membrane, the membrane becomes more permeable to (1) _____ than it was at its resting potential level, making the membrane less permeable to (2) ______, causing the inner surface of the membrane to become (3) _________ charged again.

1.(1) = K+ ions, (2) = Na+ ions, (3) = positively.
2.(1) = K+ ions, (2) = Na+ ions, (3) = negatively.
3.(1) = Na+ ions, (2) = K+ ions, (3) = positively.
4.(1) = Na+ ions, (2) = K+ ions, (3) = negatively.
5.None of these answers work.

5.What is the importance of calcium ions (Ca++) in acetylcholine neurotransmitter release?

1.Ca++ causes the synaptic vesicles to release neurotransmitter ACh.

2.Ca++ results in the breakdown of ATP to ADP.

3. Ca++ ions play no important role at all in neurotransmitter release.

4.The effect of acetylcholine binding to receptors on the postjunctional membrane is:

a.ACh creates local increase in permeability of the postjunctional membrane to both sodium and potassium, thereby producing a local graded depolarization of the end-plate, creating an end plate potential (EPP), thereby leading to a muscle contraction.

b.ACh diffuses out of the synapses but is broken down before sufficient quantities can ever bind to receptors on the postjunctional membrane.

c.ACh creates local increase in permeability of the postjunctional membrane to chloride and acetyl CoA, thereby producing a local graded depolarization of the end-plate, creating an end plate potential (EPP).

d.None of the above.

7.We know that after a quanta of ACh is discharged into the synaptic gap, the end plate potential begins to rise from resting level (-70 mHz) toward ECRIT. Next, we know that the body usually releases additional quanta of ACh at this point, creating an "overkill" or additional unneeded release of ACh to ensure neuromuscular transmission results. This in turn creates a trophic effect. Select from the following choices the best answer that defines what trophic effect IS:

a.Trophic effect is a spontaneous discharge of ACh that provides a continual quantal release of ACh in quantities not sufficient to induce a postjunctional action potential but creates a minature end plate potential (mEPP) that is approximately 1 millivolt in magnitude, that occurs at a frequency of approximately once per second.

b.Trophic effect is rapid destruction of ACh by AChE which is found in the membrane of muscle cells, which inhibits nerve impulse conduction from axon terminals to the motor end plate.

c.Trophic effect is an atmospheric effect resulting after the passing of a hurricane in the tropics.

d.Trophic effect is the means by which a muscle cell membrane returns to a relaxed state, and involves the efflux of Ca++ ions.

e.None of the above.

8.When referring to STRIATION, such terms as myofibrils, sarcomeres and myofilaments are often discussed. To this extent, please identify the statement that best describes the relationship between actin and myosin in striation:

i.Myofibrils consist of both sarcomeres and myofilaments, and the myofilaments are either thin, called myosin, or thick, called actin, and it is this thick and think nature of the actin and myosin that gives the muscles its striated appearance and can only be seen in the H-Zone of relaxed muscle.

ii.In striated muscle, two myofilaments: actin, which is thin, and myosin, which is thick, overlap to form an anisotropic band (A-Band) which is a dark band that can polarize visible light; if only light strands of myofilament are being looked at, this light area is called an I-Band, and is comprised of actin, which forms the light areas of striation, and if only dark strands of myofilament are being looked at, this dark area is called an H-Zone, and is comprised of myosin which forms the dark areas of striation.

iii.Striated muscle is best seen in relaxed muscles because the relaxed muscle allows the A-Band to form, which means the actin and myosin overlap.

iv.Both answers (b) and (c) are correct.

v.Both answers (a) and (c) are correct.

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