THE ISLAND SYNDROME
Part 2: A Link Between Biology and Technology
(September 15, 2010)
Within the body, it is necessary for "messages" to be passed from one location to another, so different parts of the body can interact with one another. There are two basic ways in which this is done.
First, one part of the body can create a substance that is released into the bloodstream. Once the substance starts circulating it will, within a few heart beats, travel just about everywhere in the body. As this happens, the substance will encounter cells that are sensitive to its particular shape and structure. Those cells then change their behavior in some way. In this way, one part of the body can "broadcast" a message that is detected and acted upon remotely by cells that are sensitive to that particular message.
When describing this system, we call the part of the body that secretes the substance a "gland". The substance itself is called a "hormone". As an example, the pancreas (a gland) secretes insulin (a hormone) which acts upon cells in the liver, muscle, and fat. There are many different glands in the body that work in this way and, collectively, we refer to them all as the "endocrine system". Doctors who specialize in this area are called endocrinologists.
The second way in which messages are passed from one location to another is via hard-wired, electrochemical connections. These connections are formed by specialized cells called "neurons". Within the brain (which is the focus of our attention), each neuron connects to one of more other neurons. Such connections are called "synapses", and each synapse consists of a tiny gap, into which chemicals can be released. Here is how it works.
In this way, signals are transmitted quickly and dependably from one part of the brain to another.
Consider a single neuron that is connected, via synapses, to several other neurons. (Imagine a thin electrical wire with a head and a tail. At the tail end, the wire connects to the heads of several other wires.) When the "head" of the neuron is stimulated, a tiny electric current travels (in one direction only) down the length of the neuron. When the current reaches the "tail", the electrical stimulation causes the release of tiny amounts of a specific chemical, called a "neurotransmitter" into the synapses. The neurotransmitter molecules travel across the gap quickly, where they stimulate the nearby neurons, which then fire off their own electrical signal. In this way, signals are transmitted quickly and dependably from one part of the brain to another.
Collectively, we refer to all the neurons in the body as the "nervous system". The "central nervous system" or CNS consists of the brain and spinal cord. The "peripheral nervous system" consists of all the neurons outside the CNS. Doctors who specialize in this area are called neurologists.
(At this point, you might pause for a moment and consider an analogy between the body and a computer network. The various parts of the body communicate with one another in two different ways. The endocrine system uses glands that secrete hormones that travel everywhere; the nervous system uses neurons that connect directly to one or more other neurons. Similarly, a computer network can use either wireless connections, that broadcast radio waves throughout the immediate vicinity, or cables that create hardwired connections between specific computers.)
As you might imagine, the endocrine and nervous systems are very complicated. For our purposes, however (understanding the link between biology and technology), all I want you to know are the names of the most important hormones and neurotransmitters, so we can talk about them. What's interesting is that some these chemicals are used as both hormones (to send messages all over the body) and neurotransmitters (to send messages from one part of the brain to another).
The hormones and neurotransmitters we will be concerned with are as follows:
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