May 1969 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
John Frye, creator of fictitious electronics repair shop owner Mac McGregor and his sidekick technician, Barney, must have been an amateur student of brainology[sic]. This episode in a 1969 issue of Electronics World, and a recent story titled, "Biological Effects of Electrical Shock," which appeared in the May 1973 edition of Popular Electronics are proof of that. A very good introduction to the workings of nerve cells, axons, synapses, dendrites, etc., is given here. In a role reversal, Barney is educating Mac this time based on a psychology course he is taking at the community college. He goes beyond the "your brain is a computer" pitch to describing how sensory signals are detected and transmitted to and from body extremities. I have also been a decades-long reader of interest regarding neurological discoveries, mainly in publications like Scientific American and Discover magazines - not JAMA. Medicine has come a long way since 1969, but it is amazing how much was already known at the time.
Mac's Service Shop: Electronics and Psychology
By John Frye
A background in electronics is a great help in understanding neurophysiology.
Barney, how are you doing with that psychology course you're taking at the university extension center over at Kokomo?," Mac asked his assistant working at the service bench beside him. "Great, boss," Barney replied. "I'm the most interested student in the class."
"And so refreshingly modest," Mac retorted sarcastically. ''I've never figured out, though, why you selected that subject. I'd have thought you'd have gone for math or physics or something like that. Why did you pick psychology?"
"Maybe I'd better let my mother tell you," Barney said with a grin. "While I was studying in the living room last evening, I heard a neighbor ask her that same question out in the kitchen. 'That boy,' Mom explained, 'has been taking things apart to see what makes them tick ever since he learned to toddle, and I just suppose he finally got around to wondering what makes him tick.'
"That's about as good an answer as I can give you, but let me straighten you out on that 'modesty' bit: I didn't say I was the best student in the class; I said I was the most interested. And the reason I'm interested is that we're studying the nervous system and I keep discovering oodles of exciting similarities between this system and the electronic components and circuits with which we work."
"Oh come on! You're not going to resurrect that tired old analogy of how much the brain is like a computer, are you?
"Not yet, but give me time. Remember this is only Psychology 1. I'm talking about comparisons on a component-to-component and function-to-function basis."
Mac leaned back against the wall and lit his pipe. "All right," he said as he blew out the match with an air of exaggerated resignation, "get it out of your system. You're busting to do so, and you're not going to be any good at the bench until you've had a chance to tell what you've learned."
"That's what I like - an understanding boss," Barney answered, dropping the test prods with alacrity and heaving himself up on the bench. "To start, psychology uses our 'black box' approach to acquiring information. The psychologists call it behaviorism, but it employs the same principles we use to determine: (a) what components exist inside all opaque sealed box, and (b) how these components are wired together. We do this by feeding various types of currents into the box and examining the currents and voltages that come back out.
"For centuries before 1913 it had been taken for granted that a person knows what goes on in his own mind directly, that he is conscious of his own consciousness. In that year John B. Watson cleaned house and threw out mental processes from psychology. He said the only thing a psychologist could be sure of is what a man or animal does - in short, how he behaves. Watson denied the scientific value of introspection, the direct observation of one's own mental processes: He felt this was about as trustworthy as having a bank examine its own books. Behaviorism, which he founded, treats the mind and body as a black box. Stimuli can be observed going into it, or selected stimuli can be deliberately fed into it, and the resulting behavior can then be observed. From this, educated guesses can be made as to what takes place inside."
"Do all psychologists agree with this?"
"Oh you dreamer! A consensus among psychologists on a theory is as rare as one among fashion designers on the proper height for skirts."
"You mentioned components in the nervous system that reminded you of electronic components. Tell me about those."
"Okay, but I don't think I need belabor the similarity between auditory receptors and microphones, visual receptors and photocells, or heat receptors on the skin's surface and thermocouples. In each instance the sensory nerve and the electronic device change, respectively, sound, light, and heat into electrical impulses. In the body these impulses travel along nerves or neurons, and I find tracking an impulse along such a pathway as fascinating and as full of surprises as reading a good whodunit.
"In the first place, it takes about ten billion neurons to 'wire' a human being. They are microscopic in cross section but vary in length from a fraction of a millimeter to more than a meter. They are packed together by the thousands to form the macroscopic structures of nerves, spinal column, and brain. A neuron is like a diode in that it allows an impulse to pass through it in only one direction. At the input end are one or more fibrils called dendrites. A single fibril going out of the sending end is called an axon."
"Hold it!" Mac interrupted. "Are you saying a nerve and a neuron are not the same thing?"
"That's right. A neuron is the single cell body, while a nerve is made up of a bundle of the long fibers that grow out of the cell bodies - dendrites or axons or both. You can think of nerves as being the laced cables that tie together the units of the neuron switchboard."
"And I suppose an impulse, being electrical, zips along these nerves and neurons the way it would along any other conductor.
"It's not all that simple. The impulse is both an electrical and chemical change that sweeps across the neuron at a fast but limited speed. But more about that later. It doesn't travel the same way in a dendrite that it does in a cell body or axon. A dendrite conducts 'decrementally.' That means it acts like a lossy transmission line; the impulse is attenuated as it moves along the dendrite. Unless the impulse is strong to begin with, it may disappear altogether before it reaches the cell body. The cell body and axon, however, work on the all-or-none principle. When excited enough to fire, they expend all their accumulated energy without decrement. The difference is that between a bow and arrow and a shotgun. With the former, the harder you pull the bowstring, the harder you shoot; but the shotgun shoots just as hard whether you jerk the trigger or squeeze it gently."
"That axon must fire the way a gaseous voltage-regulator tube does," Mac observed. "It's also an all-or-none conducting device."
Nature of the Impulse
"Precisely!" Barney applauded. "Now I've got you doing it. To get back to the speed of a neural impulse, let's take a closer look at the nature of the impulse. Picture the axon as a long tube of permeable material that, at rest, has positive sodium ions on the outside and negative ions on the inside. When an impulse comes from the cell body, the positive sodium ions near the neuron permeate the sheath and reduce the inside-outside potential to zero. To be painfully exact, there is a little overshoot in this process, and the potential actually reverses polarity briefly. This wave of sodium ion penetration moves out along the axon, while behind the traveling wavefront the sodium ions move back out of the axon to restore the normal resting state.
"This brings up an amusing circumstance. Psychologists do not know how the sodium ions are moved back out of the axon; so they 'invented' a sodium pump and say it moves them out! Remember how scientists, when they needed to explain how radio waves could travel through space, 'invented' the medium of ether to conduct the waves?"
"Yes, I suppose the sodium pump, the ether, and the purple cow all belong in the same imaginary museum. But for the last time: how fast does this impulse travel?"
"The speed varies from 1 meter a second in a small fiber to 120 meters a second in a large fiber."
"How does an impulse move from one neuron to another?"
"This takes place at junctions called synapses. Sometimes the synapse occurs where the axon of one neuron contacts a dendrite of another; in other instances the axon bypasses the dendrites and goes through a synapse directly to the cell body. The axon is branched and may contact several different neurons. In any event, the synapse is a variable-resistance conducting device. Not only does the resistance vary from synapse to synapse, but apparently the resistance of a given synapse can be varied by the learning process.
"Let me give you a ferinstance: suppose I burn my finger and the pain stimulus travels up an afferent neural path to the sensory portion of the cortex, then across through various internuncial paths in the brain to the motor area, and finally down an efferent path to muscles that produce an action. Let's say one time the action is to put my finger in my mouth. Another time I stick the finger under a stream of cold water. This last feels better; so all the synapses in the long-loop stimulus-response path that produced the cold water treatment are lowered in resistance, while the ones along the stick-the-finger-in-the-mouth path are increased in resistance. Of two possible responses to the painful stimulus, one has been reinforced by quicker escape from pain while the other has been inhibited by the longer duration of pain. This is one form of learning."
"If I understand you correctly, an axon connects through synapses with several different neurons. Through learning, it comes to fire only one of these. It is as though the axon were working through a multi-position single-pole switch that could be set by experience."
"Hey, you learn fast. Of course you understand this is a vastly over-simplified explanation. Let me tell you just one more thing I learned and then I'll get back to work.
The Arousal System
"The brain has a defense against distraction called the arousal system that has an uncanny similarity to the squelch circuit in a CB receiver. You know how you can set the squelch level so skip stations and other weak signals are kept from actuating the speaker; yet a strong wanted signal opens the squelch and is clearly heard. Well, the brain needs a squelch circuit, too. Without it every faint smell, every tiny sound, every body sensation - in short, all the important and unimportant information constantly bombarding the senses - would drive a person crazy, just as listening to an unsquelched CB receiver on Channel 9 these days will drive you nuts.
"A sensory impulse divides into two functions at the base of the brain. One, the cue function, is relayed on to the sensory portion of the cortex supposed to receive that particular sensation. The other, the arousal function, is fed to the arousal system deep in the brain stem. Its job is to provide a kind of adjustable bias to the sensory portion of the brain so that signals below a selected amplitude cannot get through. For example, the arousal state is very low when you're asleep, and faint or familiar sounds make no impression on the consciousness. But when the person is awake, alert, and vigilant, the arousal state is high and the smallest sound registers on the consciousness. You might say 'he is running with his squelch wide open.'''
"You've convinced me you're an interested student," Mac said, knocking the ashes from his pipe on the heel of his hand. "Now if you will just follow your psychology course with one in karate, you should be able to handle both our wily and our obstreperous customers! But now I think it's time for us to get back to work."
Posted April 20, 2018
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive stories was the brainchild of none other than John T.
Frye, creator of the Carl and Jerry series that ran in
Popular Electronics for many years. Mac's Radio Service Shop began life
in Radio & Television News
magazine (which itself started as simply Radio News), and then changed
its name to Mac's Service Shop after the magazine became
World. 'Mac' is electronics repair shop owner Mac McGregor, and Barney
is his eager, if not somewhat naive, technician assistant. 'Lessons' are taught
in story format with dialogs between Mac and Barney.