Sensors and Effectors

The human body is a marvelous piece of work - an intricate network of 206 bones, 900 ligaments, 4000 tendons, 100 organs, and more than 600 muscles (about 40% of the body’s total mass)  It is serviced by a vast plumbing arrangement of veins, arteries and capillaries totaling around 60,000 miles.  Input from 5 familiar sensors - taste, smell, sight, sound and touch - must be processed rapidly in order to synchronize this complex system.  It’s no wonder it has been such a challenge to reverse-engineer.

Consider the not-so-simple task of walking, which requires coordination of 200 or more muscles. It is an oft-used idiom that people lacking basic intelligence and coordination cannot “walk and chew gum at the same time.”   The phrase originated with President Lyndon Johnson in reference to then Representative Gerald Ford.  (Johnson actually substituted “walk” with another more colorful word)  The President’s intent nevertheless remained the same - walking is complex enough to require extra concentration for certain folks.

Research shows that the average human brain is perfectly capable of multi-tasking some basic activities including walking and chewing gum - such combinations can actually improve stability and coordination.  Some physicians are using the "walk and chew gum" test, with varying tasks, to assess cognitive function and potential dementia risk. I know of no robots that can pass this test.

While walking requires a chorus of muscles to work in synchronicity, the gum chewing task is limited to a single muscle, the masseter (jaw muscle) that happens to be the strongest in the body.  If you’ve ever bitten your tongue or cheek, you can appreciate that the system differentiating gum from flesh is not flawless.   Most of the time, however, the masseter performs without incident.

One of the questions that reverse engineers sometimes ask themselves is “What’s this thing for?”.  While our brains are gathering information from various sensors and sending out signals to our muscles, it is important to note that some of these effectors are “no longer in service.”  One such vestigial muscle is the pyramidalis in the abdomen.  Another, the palmaris longus, connects the wrist to the elbow and contributes to grip strength.  The auricular muscles, which change the shape of the outer ear, might once have been helpful for distinguishing sounds but haven’t been used for millions of years.  As over-ear headphones and earbuds proliferate, the auriculars are unlikely to be called out of retirement.

Jacked, pumped, ripped, ropy - all conjure the image of an unusually muscular individual.  While biceps and triceps are the eye-catching ones, the heart is the essential muscle that makes it all possible.  Humans, hamsters and elephants all have different lifespans, yet each will have around 3 billion heartbeats from start to finish.  Much like the human heart, there is another busy group of muscles (six per eye) that make human vision possible.  Although the eye itself is a wonder of ingenuity, it requires the coordinated activity (about 3 movements per second) of these sextets in order for us to see.  The blurry motion between focal points is anticipated and removed by our brains.  The eye is the most crucial of our sensors - it can compensate for the other four and helps form 80% of our impressions of the world around us. 

Every time a muscle contracts, it produces heat, providing about 85% of the body’s total warmth.  The hypothalamus is responsible for monitoring body temperature and will confine blood flow to the deep veins to preserve heat if necessary.  If that doesn’t work, random signals will be sent to the skeletal muscles, contracting them and helping to warm us - what we call shivering is just the body taking care of itself.

Simone Biles, the most decorated gymnast in history, has incredible muscular strength, and she also knows a thing or two about proprioception.  While performing on the world stage at the 2020 Olympics, Simone experienced a condition known to gymnasts as “the twisties” - a temporary loss of communication between brain and body which compromises “air awareness.”  Can you imagine what it must feel like to be in the middle of the “Biles II” maneuver and lose track of where you are?  Neither can I.  I’m just happy to come close when my doctor asks me to close my eyes and touch my fingertips together. 

Reverse engineering of the human body is not just a simple problem involving sensors and effectors.  The muscles themselves (effectors) also have a critical sensor function in helping to determine our position in space.  Taste and smell sensors might not be as important, unless you are building a humanoid sommelier.  Hearing sensors are an established technology, and AI Chatbots are frighteningly good at interpreting and responding to their input.  Our touch sensors remain a bit of a mystery, contributing as they do to sensations of temperature, pressure, texture, pain and even proprioception.  These sensors are crucial for navigating and understanding our environment, from interacting with soft, comfortable objects to avoiding sharp, hard ones.

So how does one build a humanoid robot?  To begin, construct a human figure. Ensure that it stands at a height of 4 cubits and has a circumference of 2 cubits.  Then create the rest.

Author Profile - Paul W. Smith - leader, educator, technologist, writer - has a lifelong interest in the countless ways that technology changes the course of our journey through life.  In addition to being a regular contributor to NetworkDataPedia, he maintains the website Technology for the Journey and occasionally writes for Blogcritics.  Paul has over 50 years of experience in research and advanced development for companies ranging from small startups to industry leaders.  His other passion is teaching - he is a former Adjunct Professor of Mechanical Engineering at the Colorado School of Mines. Paul holds a doctorate in Applied Mechanics from the California Institute of Technology, as well as Bachelor’s and Master’s Degrees in Mechanical Engineering from the University of California, Santa Barbara.