## Time Constant

To consider the time constant, first consider a very simple thermal analog. Take the case where a block of metal that is initially at 25°C is placed on a hot plate that is at 50° C. Assume that the hot-plate temperature is constant. What will be the consequences of placing the block on the hot plate? It is obvious that over a period of time the temperature of the block will change from its initial value of 25° C to a final value of 50° C, but it will not do so instantaneously. It will take a certain period of time for the heat transfer to occur. If the temperature of the block is measured as a function of time, the temperature will change as an exponential function of time, approaching a final value of 50°C.

A similar phenomenon is observed in membranes when one applies an artificial depolarizing or hyperpo-larizing stimulus. This phenomenon is illustrated in Fig. 2. A nerve cell is impaled with one electrode to record the membrane potential and another electrode to depolarize or hyperpolarize the cell artificially (Fig. 2A). The cell is initially at its resting potential of —60 mV. At time zero, the stimulating electrode is connected to a battery. The size of the battery is such that the stimulus eventually will depolarize the cell by 10 mV (Fig. 2B). As a result, the membrane potential will change from its initial value of —60 mV to a final value of —50 mV. Note that even though the current flow (i.e., stimulating current) is instantaneous (and constant), the membrane potential does not change instantaneously. There is a period of time during which the membrane potential charges to its new final level of —50 mV. This charging process is an exponential

## Get Rid of Gallstones Naturally

One of the main home remedies that you need to follow to prevent gallstones is a healthy lifestyle. You need to maintain a healthy body weight to prevent gallstones. The following are the best home remedies that will help you to treat and prevent gallstones.

Get My Free Ebook