DocBill

According to my friend Lynn Margulis, life has been at this now for almost 4 billion years 4^10. That's a lot of time to fix things. Bill

When a neuron is not being stimulated, it is at its resting potential, the charge at which no signal is transmit and the cell is at normally. The cytoplasm's charge is negative, and the surrounding fluid is positive. Average resting potentials in many animals are -70 milivolts (mV), meaning the inside of the cell has a negative charge of 70 milivolts. Resting potentials are maintained by the permiability of the plasma membrane. One way the membrane keeps the potential is to restrict large negativly charged molecules or proteins from leaving the cell. Another method is to utilize protein "pumps" to circulate certain types of molecules through the membrane. A good example of this "pumping" is in the regulation of potassium (K+) and sodium (Na+) ions. For an action potential to be generated, the cell's membrane (restricting Na+ ions from coming in, which are heavily concentrated outside of the cell..and K+ ions which are concentrated inside the cell) are allowed to freely diffuse to the outside (via pump transfer or gradient). Thus a buildup of positive charge outside (in the form of Na+), and the diffusion of positive charge from the cytoplasm to the outside (in the form of K+) make a more negative interior. Protein pumps (called sodium-potassium pumps) contribute by pumping controlled quantities of K+ and Na+ in and out of the cytoplasm. The pumps activly transport Na+ out of the cells (increasing the concentration outside) and pump K+ in. They pump more Na+ out than K+ in, thereby making the charge more negative inside. This process is the main method by which the cell's resting potential is maintained. The action potential itself is triggered by stimuli. In the case discussed in the previous post, the simuli may be the actual breaking of the plasma membrane. The plasma membrane immediately opens the Na+ channels, allowing the concentrated sodium to flow into the cell. K+ channels close, trapping the concentrated potassium inside the cell. Thus the charge increases until it reaches threshold potential, in many animals cells -50 mV. The threshold potential is the tripping point for the action potential. The action potential is triggered (the charge continues to increase and it causes more action potentials along the membrane), and the relative charge between the interior and exterior continues to increase. Average membranes reach their maximum charge at about +35 mV. The Na+ channels then close, the K+ channels reopen, and the charge decreases rapidly. It overshoots the resting potential briefly (because the K+ channels close slowly), and then returns to its resting state. As the action potential travels through the axon (its neuronal fiber beginning at the axon hillock), it comes to the synaptic knobs, the contacts that link axons together. The junction between two synaptic knobs, the synapse, which can be either electrical or chemical. Electrical synapses convey action potentials directly, while chemical synapses release chemicals across the divide between two axons to activate action potentials in the next axon (as the first poster above asked about). Nurotransmitter molecules from the stimulated axon attach to receptor proteins on the connected axon and trigger the opening of ion channels, which activate action potentials in the next axon. This continues in animals, where central nervous systems process the action potentials and respond. These NTM can be a single NT or in many cases, a double NT (as in the case of PNS using Acetacholine and Gabba). Please excuse any spelling errors. It has been a long day, and I have Dyslexia and no spell check. Bill

Any life form that is non-carbon based, say Silicon-oxygen, would be very heavy, and would have a difficult time maintaining a metabolizism (as we understand it) to feed a large compolex brain. However, if we remove much of the gravity, many issues disapear. The cosmos is vast beyond meassure, and what life exists in it is anyone's guess. Bill

Well, yes and no. Dating via Carbon 14 dating or Oxidizable Carbon Ratio Dating, often simply called "carbon dating" has a maximum reliabliity of about 60,000 years. Naturally occurring Carbon 14 decays to Nitrogen 14, with a half-life of 5,730 years. Because Carbon 14 has such a short half-life, it is useful in archaeology for dating artifacts (man-made objects) and the bones of animals up to 50,000 to 60,000 years old. However, it cannot be used on anything older than Middle Pleistocene Epoch in age. In order to date older fossils, scientists must use other radioactive isotopes. A commonly used technique is called Potassium-Argon dating. The element potassium is found in most rock-forming minerals, and the half-life of the radioactive isotope Potassium 40 is 1.25 billion years, allowing measurable quantities of Argon 40 (its decay element, known as the daughter element) to accumulate in potassium-bearing minerals of almost all ages. The amounts of potassium and argon isotopes can be measured accurately, even in very small quantities, making Potassium-Argon dating useful for both very young and very old rocks (and everything in between). Although radiometric dating is much more precise than relative dating, it does have its drawbacks as well. With the exception of Carbon dating, radiometric dating can only be used on igneous rocks, not sedimentary rocks or the actual fossils. Because fossils are found in sedimentary rock, paleontologists have to use radiometric dating information on igneous rocks found below and above the fossils in order to determine an age range for the sedimentary rocks. Bill