~Sam~
09-15-2004, 06:43 PM
It, firstly, is a term coined by Arthur T. Winfree, author of "The Geometry of Biological Time" and Professor at Purdue University.
It is secondly, an experiment. Zhabotinsky Soup, a chemical reaction that supports waves of excitation remarkably like the electrical waves that trigger the heartbeat. But it's much simpler than a real heart - it's not even alive - and it has no muscles or motion of any kind. It's an idealized arena for exploring excitable wave propagation in its purest form. In that way, it plays the same role for heart waves that fruit flies play for genetics: a convenient simplification that captures the essense of more complicated phenomena.
Normally, the most amusing outcome you can hope for in a chemistry experiment is a puff of smoke or a noxious odor. In comparison, Zhabotinsky Soup offers nonstop entertainment. When brewed according to its original recipe, it acts like a spontaneous oscillator, the chemical analog of pacemaker cells. It changes colors back and forth, rhythmically alternating between sky blue and rusty red dozens of times, before eventually relaxing to equilibrium about an hour later. At the molecular scale, the performance would appear even more impressive, if only we could see it: trillions of coupled oscillators, hoofing in perfect sync, the largest line dance ever assembled.
In its new, more subtle recipe, the reaction is excitable. At first it looks disappointingly inert. The oscillations are gone. But if you pour a thin layer of the red soup into a petri dishand then prick it with a silver wire or a hot needle, it suddenly launches a blue circular wave that expands and spreads like a grassfire. This is a chemical wave, a pulse of propagating excitation in which the reaction switches from a reduced state to an oxidized one. (This analogy is not perfect, however. The chemicals recover more rapidly than the prairie; a second wave can follow right behind.)
Chemical waves are completely different from the waves studied in traditional physics courses, like sound waves or the ripples on a pond. When a chemical wave spreads by diffusion, the surface of the liquid does not bob up and down. It remains motionless. What moves is a pattern of excitation, a kind of chemical contagion. Nor do these waves weaken like sound or ripples as they travel away from their origin. Each patch of the medium provides a fresh source of energy that refuels the wave, preventing it from damping out.
Now suppose you detonate two chemical waves at two different points in the petri dish. The blue circles expand and creep toward each other. When they collide, they do not interpenetrate or add up: They annihilate. And they do so for the same reason that onrushing grass fires snuff each other out: Neither can burn through the other's ashes. In this metaphor, the ashes correspond to a region of exhaustion, a refractory zone in the wake of the wave. The chemical medium needs time to recover before it can become excited again.
In many ways, this chemical medium behaves like the human sexual response. Sexual arousal and recovery depend on the properties of nerve tissue, which, like Zhabotinsky soup, belongs to a general class of systems called excitable media. A neuron has three states: Quiescent, excited, and refractory. Normally a neuron is quiescent. With inadequate stimulation, it shows little response and returns to rest. But a sufficiently provocative stimulus will excite the neuron and cause it to fire. Next it becomes refractory (incapable of being excited for a while) and finally returns to quiescence. The parallels with chemical waves extend to action potentials, the electrical waves that propagate along nerve axons. They too travel without attenuation, and when two of them collide, they annihilate each other. In fact, all of these statements are equally true of electrical waves in another excitable medium: the heart. That's the beauty of this abstraction - the qualitative properties of one excitable medium hold for them all. They can all be studied in one stroke. The family resemblance among Zhabotinsky soup, nerve tissue, and heart muscle persists right on down to the structure of the mathematical equations that govern their nonlinear dynamics. The analogy runs deep.
But Zhabotinsky soup offers a number of advatages, especially for a beginning experimenter. No animals need to be sacrificed. There's no confusing anatomy, like the intricate tangle of neural networks or the twisted-fiber architecture of the heart muscle. Best of all, the waves are visible to the naked eye and they move slowly, so there's no need for any elaborate recording equipment. In contrast, the visualization of waves on the heart remains a formidable technical challenge to this day, even for labs with huge budgets, requiring voltage-sensitive dyes, multielectrode arrays, and other state-of-the-art technology.
With the help of Zhabotinsky soup, scientists have begun to unravel the secrets of wave propagation in excitable media. In particular, it was in Zhabotinsky soup that a new kind of wave was discovered: a rotating, self-sustaining wave shaped like a spiral. Although its geometry is graceful, its consequences are destructive. Rotating spiral waves on the heart are the culprits behind tachycardia and, in the worst case, ventricular fibrillation followed by sudden cardiac death.
The discovery of Zhabotinsky soup and its remarkable spiral waves is a tale of dogma, dissappointment, and ultimate vindication. Of course, Zhabotinsky soup is not its real name - that's just what Winfree always called it. Today it's know as the BZ reaction, for Belousov and Zhabotinsky, the Russian scientists who invented it and refined it, respectively.
So why do I identify with Zhabotinsky soup? I feel that an inert, chemical media, that, when stimulated by an electrical impulse organizes itself into a wave propagation comparable to Life functions is pretty damned kewl by any stretch of the imagination. I also identify with; "A tale of dogma, disappointment, and ultimate vindication." It's the story of my life.
I'll be back to continue with this tale of Zhabotinsky soup later in the day. Now I have to take the pup to the Vet's.
It's technical, I know... but then so am I... it's how I think, and feel and learn to weigh my reactions in this life. "I yam what I yam..." Zhabotinsky Soup...
OK, OK.... Later Baby.
It is secondly, an experiment. Zhabotinsky Soup, a chemical reaction that supports waves of excitation remarkably like the electrical waves that trigger the heartbeat. But it's much simpler than a real heart - it's not even alive - and it has no muscles or motion of any kind. It's an idealized arena for exploring excitable wave propagation in its purest form. In that way, it plays the same role for heart waves that fruit flies play for genetics: a convenient simplification that captures the essense of more complicated phenomena.
Normally, the most amusing outcome you can hope for in a chemistry experiment is a puff of smoke or a noxious odor. In comparison, Zhabotinsky Soup offers nonstop entertainment. When brewed according to its original recipe, it acts like a spontaneous oscillator, the chemical analog of pacemaker cells. It changes colors back and forth, rhythmically alternating between sky blue and rusty red dozens of times, before eventually relaxing to equilibrium about an hour later. At the molecular scale, the performance would appear even more impressive, if only we could see it: trillions of coupled oscillators, hoofing in perfect sync, the largest line dance ever assembled.
In its new, more subtle recipe, the reaction is excitable. At first it looks disappointingly inert. The oscillations are gone. But if you pour a thin layer of the red soup into a petri dishand then prick it with a silver wire or a hot needle, it suddenly launches a blue circular wave that expands and spreads like a grassfire. This is a chemical wave, a pulse of propagating excitation in which the reaction switches from a reduced state to an oxidized one. (This analogy is not perfect, however. The chemicals recover more rapidly than the prairie; a second wave can follow right behind.)
Chemical waves are completely different from the waves studied in traditional physics courses, like sound waves or the ripples on a pond. When a chemical wave spreads by diffusion, the surface of the liquid does not bob up and down. It remains motionless. What moves is a pattern of excitation, a kind of chemical contagion. Nor do these waves weaken like sound or ripples as they travel away from their origin. Each patch of the medium provides a fresh source of energy that refuels the wave, preventing it from damping out.
Now suppose you detonate two chemical waves at two different points in the petri dish. The blue circles expand and creep toward each other. When they collide, they do not interpenetrate or add up: They annihilate. And they do so for the same reason that onrushing grass fires snuff each other out: Neither can burn through the other's ashes. In this metaphor, the ashes correspond to a region of exhaustion, a refractory zone in the wake of the wave. The chemical medium needs time to recover before it can become excited again.
In many ways, this chemical medium behaves like the human sexual response. Sexual arousal and recovery depend on the properties of nerve tissue, which, like Zhabotinsky soup, belongs to a general class of systems called excitable media. A neuron has three states: Quiescent, excited, and refractory. Normally a neuron is quiescent. With inadequate stimulation, it shows little response and returns to rest. But a sufficiently provocative stimulus will excite the neuron and cause it to fire. Next it becomes refractory (incapable of being excited for a while) and finally returns to quiescence. The parallels with chemical waves extend to action potentials, the electrical waves that propagate along nerve axons. They too travel without attenuation, and when two of them collide, they annihilate each other. In fact, all of these statements are equally true of electrical waves in another excitable medium: the heart. That's the beauty of this abstraction - the qualitative properties of one excitable medium hold for them all. They can all be studied in one stroke. The family resemblance among Zhabotinsky soup, nerve tissue, and heart muscle persists right on down to the structure of the mathematical equations that govern their nonlinear dynamics. The analogy runs deep.
But Zhabotinsky soup offers a number of advatages, especially for a beginning experimenter. No animals need to be sacrificed. There's no confusing anatomy, like the intricate tangle of neural networks or the twisted-fiber architecture of the heart muscle. Best of all, the waves are visible to the naked eye and they move slowly, so there's no need for any elaborate recording equipment. In contrast, the visualization of waves on the heart remains a formidable technical challenge to this day, even for labs with huge budgets, requiring voltage-sensitive dyes, multielectrode arrays, and other state-of-the-art technology.
With the help of Zhabotinsky soup, scientists have begun to unravel the secrets of wave propagation in excitable media. In particular, it was in Zhabotinsky soup that a new kind of wave was discovered: a rotating, self-sustaining wave shaped like a spiral. Although its geometry is graceful, its consequences are destructive. Rotating spiral waves on the heart are the culprits behind tachycardia and, in the worst case, ventricular fibrillation followed by sudden cardiac death.
The discovery of Zhabotinsky soup and its remarkable spiral waves is a tale of dogma, dissappointment, and ultimate vindication. Of course, Zhabotinsky soup is not its real name - that's just what Winfree always called it. Today it's know as the BZ reaction, for Belousov and Zhabotinsky, the Russian scientists who invented it and refined it, respectively.
So why do I identify with Zhabotinsky soup? I feel that an inert, chemical media, that, when stimulated by an electrical impulse organizes itself into a wave propagation comparable to Life functions is pretty damned kewl by any stretch of the imagination. I also identify with; "A tale of dogma, disappointment, and ultimate vindication." It's the story of my life.
I'll be back to continue with this tale of Zhabotinsky soup later in the day. Now I have to take the pup to the Vet's.
It's technical, I know... but then so am I... it's how I think, and feel and learn to weigh my reactions in this life. "I yam what I yam..." Zhabotinsky Soup...
OK, OK.... Later Baby.