BME365R Homework #6

Due October 12, 2004

1. The Boston Globe (Monday, August 5, 1985, p. 39) in a section called In The News, contained the following seven paragraph article:

Live squid have become essential to the study of nerve cells. Since 1936, schools of these curious creatures with a beak like a parrot, tentacles like an octopus and an eye like a human have attracted hundreds of scientists to Cape Cod’s shores.

“A whole technology has been developed around the squid,” said William J. Adelman Jr., a National Institutes of Health laboratory chief at the Marine Biological Laboratory at Woods Hole. “We now have a fairly good understanding of how (certain parts of the squid nerve cell) work.”

Evolution has maintained the chemical formula for these structures since they first evolved. The primary difference is that more complex animals have constructed the nerve cells into more sophisticated structures. The squid’s nerve cell, though thousands of times larger, is very similar to the human nerve cell. It has the same basic mechanism.

Electrical signals enter the nerve cell as a chemical reaction through root-like structures called dendrites. This stimulates tiny gates in the immediate area of the nerve wall to open, letting in positively charged sodium particles and letting out negatively charged potassium particles.

This stimulates a chain reaction that runs the length of the cell. When it reaches the nerve endings, the electrical pulse is converted back into a chemical reaction, which either stimulates muscle or the next nerve cell.

As the signal passes along the cell it becomes positively charged. However, it must be made negative again before another signal can pass along it. The cell does this by using sodium-potassium pumps a few molecules in size.

Scientists say the would like to know how sodium-potassium pumps work, and they have begin to study the chemical reactions that take place as the signal is transferred from cell to cell.

Focus on paragraph 6, which contains the author’s description of the mechanism of nerve excitation and conduction in squid neurons. Write a concise critique of the mechanism presented in this paragraph. Please stick to the main issues raised in this paragraph; do not give a general discussion of nerve excitation and conduction. Keep the discussion to 50 words or less.

2. The figure below shows results from two separate experiments, Experiments 1 and 2, on the giant axon of a squid. One set of traces shows the effect on the action potential of changing intracellular sodium concentrations; the other shows the effect of changing extracellular potassium concentration.

1. Which experiment shows the results of changing intracellular sodium concentration? Describe the feature or features of the waveforms that indicate changes in intracellular sodium. Which waveform corresponds to the highest concentration of intracellular sodium? Why?
2. Which experiment shows the results of changing extracellular potassium concentration? Describe the feature or features of the waveforms that indicate changes in extracellular potassium. Which waveform corresponds to the highest concentration of extracellular potassium? Why?