Wednesday, October 29, 2008
Tuesday, October 28, 2008
Monday, October 27, 2008
Models of eel cells suggest electrifying possibilities
Engineers long have known that great ideas can be lifted from Mother Nature, but a new paper* by researchers at Yale University and the National Institute of Standards and Technology (NIST) takes it to a cellular level. Applying modern engineering design tools to one of the basic units of life, they argue that artificial cells could be built that not only replicate the electrical behavior of electric eel cells but in fact improve on them. Artificial versions of the eel’s electricity generating cells could be developed as a power source for medical implants and other tiny devices, they say.
The paper, according to NIST engineer David LaVan, is an example of the relatively new field of systems biology. “Do we understand how a cell produces electricity well enough to design one—and to optimize that design?” he asks.
Electric eels channel the output of thousands of specialized cells called electrocytes to generate electric potentials of up to 600 volts, according to biologists. The mechanism is similar to nerve cells. The arrival of a chemical signal triggers the opening of highly selective channels in a cell membrane causing sodium ions to flow in and potassium ions to flow out. The ion swap increases the voltage across the membrane, which causes even more channels to open. Past a certain point the process becomes self-perpetuating, resulting in an electric pulse traveling through the cell. The channels then close and alternate paths open to “pump” the ions back to their initial concentrations during a “resting” state.
In all, according LaVan, there are at least seven different types of channels, each with several possible variables to tweak, such as their density in the membrane. Nerve cells, which move information rather than energy, can fire rapidly but with relatively little power. Electrocytes have a slower cycle, but deliver more power for longer periods. LaVan and partner Jian Xu developed a complex numerical model to represent the conversion of ion concentrations to electrical impulses and tested it against previously published data on electrocytes and nerve cells to verify its accuracy. Then they considered how to optimize the system to maximize power output by changing the overall mix of channel types.
Their calculations show that substantial improvements are possible. One design for an artificial cell generates more than 40 percent more energy in a single pulse than a natural electrocyte. Another would produce peak power outputs over 28 percent higher. In principle, say the authors, stacked layers of artificial cells in a cube slightly over 4 mm on a side are capable of producing continuous power output of about 300 microwatts to drive small implant devices. The individual components of such artificial cells—including a pair of artificial membranes separated by an insulated partition and ion channels that could be created by engineering proteins—already have been demonstrated by other researchers. Like the natural counterpart, the cell’s energy source would be adenosine triphosphate (ATP), synthesized from the body’s sugars and fats using tailored bacteria or mitochondria.
Sunday, October 26, 2008
I recommend the following book; it contains many interesting facts and is extremely helpful to know the influence of sleep on well being.
About Sleep Debt:
A test for measuring sleep load was termed the Multiple Sleep Latency Test. The MSLT is the amount of time it takes for the person to fall asleep from (0 – 20). They found a direct linear relationship between the average amount of sleep lost and the average change in MSLT scores. They used this test to conclude another result,
“The brain keeps an exact accounting of how much sleep it is owed. In our first study, we restructed the sleep of 10 volunteers to exactly 5 hours each night for 7 nights and observed that the tendency to fall asleep increased progressively each successive day. For the first time in the history of sleep research, we discovered that the effect of each successive night of partial sleep loss carried over, and the effect appeared to accumulate in a precisely additive fashion. In other wods, the strength of the tendency to fall alssep was progressively greater during each successive day with exactly the same amount of sleep each night…” (Dement, 60).
However, this area still needs a more research because there are not enough studies on how long the brain retains an account of our sleeping debts.
The Sleep Cycle
The first round of REM comes after deep sleep.
Stage 1 and Stage 2: The theta waves of light sleep.
Stage 3 and 4: Deep sleep
“In a normal night's sleep, a sleeper begins in stage 1, moves down through the stages, to stage 4, then back up through the stages, with the exception that stage 1 is replaced by REM, then the sleeper goes back down through the stages again. One cycle, from stage 1 to REM takes approximately ninety minutes. This cycle is repeated throughout the night, with the length of REM periods increasing, and the length of delta sleep decreasing, until during the last few cycles there is no delta sleep at all”
Friday, October 24, 2008
The group designed a retinal implant that functions for the lost photoreceptors by electrically stimulating the remaining healty cells of the retina. These cells will create discrete points of light, leading to the perception of a shape.
This is a pair of glasses that captures an image with a camera, which is then converted into a pattern of electrical stimulations. There is a transmitting coil on the arm of the glasses that uses radiofrequency transmission to send information and power to the retinal implant. No need to have battery implants or wires going through body!
There is an array of stimulation electrodes in the implant that send current to appropriate areas of the retina corresponding to image.
Excerpt from site on progress of project... very cool stuff =]
"We have performed a total of six experiments on humans. These experiments were relatively brief (i.e. they lasted hours) and involved the surgical placement of an electrode array on to the surface of the retina. Very small electrical currents were delivered to the retina. Some of our patients who had been legally-blind for decades were able to see relatively small spots of light (i.e. like a "pea" as if viewed at arm's length) and occasionally were able to distinguish two spots of light from one another and "see" a line."
For more info! --> http://www.bostonretinalimplant.org
Wednesday, October 15, 2008
Tuesday, October 14, 2008
Source: Science News
Sunday, October 12, 2008
Patients affected with this disorder progressively lose their ability to control voluntary muscles, and in the later stages, become completely paralyzed. For most people, the muscles start to atrophy from their arms or legs, so there is difficulty performing everyday activities. Muscle atrophy causes the limbs to become thin and weak. The senses are not affected since this disease only attacks motor neurons, and there has been no proven effect on cognition. In later stages, paralysis spreads to the muscles affecting swallowing and breathing, eventually leading to death. 1
It still has not been found what the definitive cause of ALS is, and there is currently no cure.
Nothing has been found to reverse the effects of ALS, but there has been one federally approved drug (Riluzole) that can slow down the progression.
How bioelectricity helps us diagnose and understand ALS
- Detecting that a neuromuscular disease is Amyotrophic Lateral Sclerosis is hard, since many of its symptoms are found in other disorders. It is sometimes confused with Multiple Sclerosis, since both are neurological diseases usually affected the spinal cord. As mentioned in class, MS is a disease of myelin, not primarily of nerve cells. However, the principle characteristic in the pathology of ALS is loss of motor nerve cells. There is loss of large myelinated axons, but this is consequent to the loss of motorneurons, as compared to primary demyelination in MS.
- The Normal Diagnosis-Nerve conduction velocity (NCV) and electromyography (EMG) helps to diagnoses these disorders. With NCV, electrodes are placed on the skin over a nerve supplying a specific muscle. An electrical stimulus goes through the electrodes and the response of the muscle is measured and amplified. With ALS, the speed of the nerves is usually slowed, but compound muscle action potentials decreased. EMG measures the nerve impulses by placing electrodes in the muscles and observing electrical responses. Tracking of the electrical signals show that these responses are abnormal in cases of ALS.3
- But... As I mentioned earlier in this post, the senses are not affected. It is common to find normal sensory potentials, however a recent study (Mar. 4, 2008) showed that 6 patients had a reduced sensory nerve action potential (SNAP) amplitude or reduced conduction velocity (CV) or both. This first standardised multicentre study on sensory potentials show that mild sensory abnormalities should possibly be part of the diagnosis of ALS.
- What we know so far- ALS Mice with mutated human gene SOD1 - To test electrophysiological properties of motorneurons in mice, a wide range of electrical properties influencing motorneruon excitability was measured during current clamp. There weren't any differences in the resting potential, input conductance, action potential shape, or afterhyperpolarization between mutated genes and control motoneurons. The relationship between firing frequency and injected current was changed, and the slope of the relation was much greater. This shows that the hyperexcitability observed is induced by an aberration in the process of generating an action potential.7
HOPE for a cure!
For those who read until the end, sorry I had not intended for this post to be lengthy. I just want to shed some light on a rare disease that affects only one to two people out of 100,000, so you can imagine the difficult fight for the ALS community to raise funding for research. Especially in America, patients who are diagnosed with ALS are told by their doctors to live the years they have left and are discouraged from trying to stop the disease. But, families never want to give up on their loved ones and are always fighting for a way. I strongly believe one day we will find a cure, and in fact just recently we have hit two big milestones in ALS history. On October 2, 2008, a $5 Million ALS Research Bill was signed by President Bush, which will fund ALS reserachers across the country. The ALS Registry Act was also signed on Wednesday, October 8, which will establish the first national patient registry of people with ALS. This gives us a new tool and hopes that one day a cure will be found.
 Clinical Neurophysiology , Volume 119 , Issue 5 , Pages 1106 - 1110
 Andrew Eisen, Charles Krieger. Amyotrophic Lateral Sclerosis: A Synthesis of Research and Clinical Practice. Cambridge University Press.1998
Thursday, October 9, 2008
Kelvin argued that the key issue in the interpretation of the Second Law of Thermodynamics was the explanation of irreversible processes. He noted that if entropy always increased, the universe would eventually reach a state of uniform temperature and maximum entropy from which it would not be possible to extract any work. He called this the Heat Death of the Universe. With Rankine he proposed a thermodynamical theory based on the primacy of the energy concept, on which he believed all physics should be based. He said the two laws of thermodynamics expressed the indestructibility and dissipation of energy. He also tried to demonstrate that the equipartition theorem was invalid.
Thomson also calculated the age of the earth from its cooling rate and concluded that it was too short to fit with Lyell's theory of gradual geological change or Charles Darwin's theory of the evolution of animals though natural selection. He used the field concept to explain electromagnetic interactions. He speculated that electromagnetic forces were propagated as linear and rotational strains in an elastic solid, producing "vortex atoms" which generated the field. He proposed that these atoms consisted of tiny knotted strings, and the type of knot determined the type of atom. This led Tait to study the properties of knots. Kelvin's theory said ether behaved like an elastic solid when light waves propagated through it. He equated ether with the cellular structure of minute gyrostats. With Tait, Kelvin published Treatise on Natural Philosophy (1867), which was important for establishing energy within the structure of the theory of mechanics. (It was later republished under the title Principles of Mechanics and Dynamics by Dover Publications).