When we touch something hot, molecules in our body go to the surfaces of our nerve cells and open up signaling channels that start the pain message heading up the spine.

When our blood sugar increases, other molecules at the surfaces of our cells signal the pancreas to produce insulin.

In fact, there is hardly anything that our body does or reacts to that doesn't involve signals crossing the membranes of our trillions of cells.

This is the territory where Megan Spence lives, probing the fatty layer that separates the interior of a cell from its surroundings -- a membrane so thin that it would take more than a million of them to span an inch.

Because the membranes are so minuscule, Dr. Spence, a chemistry professor at the University of Pittsburgh, uses a powerful magnet to tease apart their secrets.

The 500-megahertz nuclear magnetic resonance machine, several times more powerful than hospital imaging scanners, has yellow and black warning tape on the floor around it to keep people with pacemakers or artificial joints from inadvertently stepping within its field.

The magnet's strong field allows Dr. Spence to detect what kind of molecules make up a given substance. When a radio signal briefly interrupts the magnet's hold on a biological sample, each type of molecule in it gives off a distinct frequency. She likens it to flicking the side of a compass and watching the needle vibrate until it returns to true north.

The NMR scanner, which sits in the basement of Chevron Science Center at Pitt, "lets you see all the different parts of a molecule," she said. "It can tell you the part that has a nitrogen on it from the part that has a carbon on it," and the higher the magnetic field, the better its eye for detail.

It's a daunting task, she said. One small protein may contain 100 amino acids, and each amino acid may give off five molecular signals.

While many scientists investigate the proteins and enzymes that do the cell's work, Dr. Spence has been particularly focused on the cell membrane itself and the 50 to 60 different kinds of fatty lipids that comprise it.

Recently, she has been trying to see whether her magnet can detect "lipid rafts" -- small islands of lipids within the membrane.

Most people have never heard of lipid rafts, but among cell biologists, they are a hotly debated issue. The classic view is that the lipids are evenly distributed in the membrane and simply provide scaffolding for the proteins that do the important work.

But a newer view theorizes that lipid rafts help organize the proteins, almost like a convoy vessel with attachments, and that sometimes, the rafts can malfunction and play a role in diseases, she said.

One whole line of research suggests that lipid rafts interact with proteins to cause the plaques seen in the brains of Alzheimer's disease patients.

The trouble is, she said, no one has actually proven that lipid rafts exist in groups of living cells. They are too small for any microscope to pick up, so NMR techniques like hers may offer the best hope of finding an answer.

Last year, Dr. Spence received a $650,000 early career grant from the National Science Foundation to purse that research. She was also helped, she said, by getting her magnet for a "discount" price of $750,000 because it had been the "demo model" for the manufacturer.

There are other molecule-scale events that have attracted her interest.

One is tarantula venom. The venom contains about 30 different toxins, she said. Some of them go directly to the surface of nerve cells and block their signaling channels, "just like a cork in a bottle," leading to paralysis of the victims.

Other tarantula toxins slide into the cell membrane, and may change its shape, she said.

She is also intrigued by the work of University of Toronto researcher Shana Kelley, who has created small molecular chains called peptides that can go through a cell membrane without rupturing it, seek out the cell's power plant, known as the mitochondrion, and cause it to explode.

That holds promise as a cancer treatment, she said, and she is interested in finding out how these peptide chains can go through the cell membranes without harming them, but then wreak havoc on the mitochondria.

Other peptides might be able to serve as a new form of antibiotic. When they encounter the cell membrane of a bacterium, for instance, "they interact with the membrane and they lyse it -- they make a little hole and that lets water travel through, killing the cell, so that's a natural antimicrobial action."

She does all this research while also caring for her 1-year-old baby boy. Her husband, software engineer Paul Drielsma, works for the local office of Apple.

Recently, she said, he revealed to her that he had written the software for one of the programs on the new iPad. "He'd had to keep it secret," she said. "When they announced the iPad, he said, 'Actually, I've had one since September.' "

That's Fascinating, where Mark Roth spotlights the odd and the interesting in everyday life, is featured exclusively in the Opinion section on PG+, a members-only web site from the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.