The normal membrane potential inside the axon of nerve cells is –70mV, and since this potential can change in nerve cells it is called the resting potential. When a stimulus is applied a brief reversal of the membrane potential, lasting about a millisecond, occurs. This brief reversal is called the action potential
<span>A stimulus can cause the membrane potential to change a little. The voltage-gated ion channels can detect this change, and when the potential reaches –30mV the sodium channels open for 0.5ms. The causes sodium ions to rush in, making the inside of the cell more positive. This phase is referred to as a depolarisation since the normal voltage polarity (negative inside) is reversed (becomes positive inside). </span>
<span>Repolarisation. At a certain point, the depolarisation of the membrane causes the sodium channels to close. As a result the potassium channels open for 0.5ms, causing potassium ions to rush out, making the inside more negative again. Since this restores the original polarity, it is called repolarisation. As the polarity becomes restored, there is a slight ‘overshoot’ in the movement of potassium ions (called hyperpolarisation). The resting membrane potential is restored by the Na+K+ATPase pump.</span>
The immune system has many kinds of white blood cells to fight infections. HIV finds the white blood cells, called CD4 cells. But with cancer the white blood cells are being killed off.
Marshes give off saturated soil: "Marshes, also known as wetlands, are frequently inundated (flooded) with water. Plants found in marshes such as the common cattail, lily pads, and duckweed are adapted to the saturated soil conditions. Animals commonly seen in a marsh are otters and muskrats. There are many different types of marshes including coastal, inland, fresh water, salt water, riparian, and more. Marshes get their water from surface water (rain/runoff) and ground water." (Gundersen Envision,p.1)
They have plants and food for living animals there to eat.
There are fish for humans to use as food for.
They Drain common water from floods.
Most have fresh water (Meaning its drinkable)