President's Message: The Honeybee's Accelerometer
Thursday, July 01, 2010
By George B. Schramm, LIBC
President
If you own one of the new ‘smart phones’, like the iPhone, or had a chance to play with someone else’s, you have probably noticed that the phone responds to gravity. For example, the image on the screen will orient itself automatically in response to the position in which you hold the phone; hold it horizontally and the image will display horizontally; rotate the phone vertically and the image responds appropriately. This occurs because inside the phone there is a microelectromechanical device called an accelerometer. At the heart of the accelerometer is a tiny, flat, square-shaped weight with rods projecting out from the edges in each of the four directions. The weight is held in place by small springs at the end of each rod and each spring provides just enough resistance to gravity so that if you lay the phone flat the weight will be centered, but when you tip the phone the springs will allow the weight to move in the direction of gravity. Also projecting from each edge of the weight are tiny rod-shaped capacitors that move with the weight. Parallel to these are another set of rod-shaped capacitors but these are fixed to the phone. So as the weight moves the pairs of capacitors are moving past each other. The paired capacitors respond to the change in voltage that occurs depending on how much the capacitors overlap. If you stand the phone on end, the weight moves downward, making the weight-mounted capacitor at the bottom of the weight completely overlap the fixed capacitor. The tiny computer inside the phone senses the voltage change and tells the display to respond appropriately.
Honeybees use a similar type of mechanical device to sense gravity. Unlike humans and other mammals, honeybees do not have a vestibular apparatus (the arrangement of tiny fluid-filled semicircular tubes in the inner ear). The bee uses the position of its head to determine which way is down.
The outside surface of a honeybee is an articulated exoskeleton and at the joints between the body parts are hair plates. These plates have evolved in such a way that when one part, let’s say a leg, moves, it stimulates the hairs that are located around the joint where the leg is attached to the thorax. The movement of these hairs sends a signal to the bee’s central nervous system (similar to the signal your brain receives when the hairs on your arm move), and in this way the bee can perceive the position of it’s leg. These hair plates that signal the position of body parts are called proprioceptors (a fancy way of saying self-perception receptors).
At the joint where the bee’s head is attached to the thorax there are hair plates that have the specific function of determining the position of the head in response to gravity. The bee’s head is similar to the weight inside an accelerometer; gravity forces the head into a slightly different position when the bee is standing on a vertical surface, like hive comb, facing down than it does when facing up. And the hair plates on the bee’s neck are similar to the rod-shaped capacitors in that they sense the position of the head [weight] and relay that information back to the central nervous system [tiny computer]. This arrangement that allows the bee to sense gravity is called the proprioceptor gravity receptor system (or PGR system).
But the similarity doesn’t end there. A smart phone uses its accelerometer to control its fancy display and a honeybee uses its PGR system to put on a rather fancy display of its own. The waggle dance is the method by which a single honeybee can convey to other honeybees in the hive the distance and direction of a food source. During the dance the performing bee walks at a certain angle in relationship to gravity and waggles its abdomen (remember, all the bees are standing on the vertical surface of the comb). It is thought that the other bees that are witnessing the dance are able to transpose that angle of orientation with respect to gravity to an angle of orientation with respect to the sun. After witnessing the dance additional foraging bees can now find the new food source by flying in a direction that has that same angle of orientation to the sun. Performing the waggle dance to communicate with other bees is only possible because of the bee’s ability to sense gravity with its PGR system.
As I mentioned above, humans have a vestibular apparatus in the inner ear to detect the direction of gravity, but our brains also use two other methods: visual evidence perceived through the eyes and proprioception. The proprioceptors in humans produce results similar to the ones in honeybees, in that they convey the position of our body parts, but they operate differently. Humans have sensory neurons, like stretch receptors, in our muscles and joints that, almost imperceptibly, convey to our brains how are arms and legs are positioned in relationship to gravity. You can easily test your proprioceptors by closing your eyes, raising your left hand over your head, and trying to picture in your mind where your left hand is positioned. If, when you open your eyes, your left hand is where you thought it would be then your proprioceptors are working just fine. In rare cases of proprioceptor scotoma, patients have lost the use of their proprioceptor system and can only determine the position of their limbs by looking at them. Can you imagine closing your eyes while moving your right arm and having absolutely no idea where your iPhone is? Or, despite how much you waggle your abdomen, you still can’t find your honey? Scary.
For more information on the honeybee’s response to gravity, see “Form and Function in the Honey Bee” by Lesley Goodman (ISBN 978-0860982432), and for a compelling story on the consequences of losing the use of your proprioceptor system, see “A Leg to Stand On” by Dr. Oliver Sacks (ISBN 978-0684853956).
If you own one of the new ‘smart phones’, like the iPhone, or had a chance to play with someone else’s, you have probably noticed that the phone responds to gravity. For example, the image on the screen will orient itself automatically in response to the position in which you hold the phone; hold it horizontally and the image will display horizontally; rotate the phone vertically and the image responds appropriately. This occurs because inside the phone there is a microelectromechanical device called an accelerometer. At the heart of the accelerometer is a tiny, flat, square-shaped weight with rods projecting out from the edges in each of the four directions. The weight is held in place by small springs at the end of each rod and each spring provides just enough resistance to gravity so that if you lay the phone flat the weight will be centered, but when you tip the phone the springs will allow the weight to move in the direction of gravity. Also projecting from each edge of the weight are tiny rod-shaped capacitors that move with the weight. Parallel to these are another set of rod-shaped capacitors but these are fixed to the phone. So as the weight moves the pairs of capacitors are moving past each other. The paired capacitors respond to the change in voltage that occurs depending on how much the capacitors overlap. If you stand the phone on end, the weight moves downward, making the weight-mounted capacitor at the bottom of the weight completely overlap the fixed capacitor. The tiny computer inside the phone senses the voltage change and tells the display to respond appropriately.
Honeybees use a similar type of mechanical device to sense gravity. Unlike humans and other mammals, honeybees do not have a vestibular apparatus (the arrangement of tiny fluid-filled semicircular tubes in the inner ear). The bee uses the position of its head to determine which way is down.
The outside surface of a honeybee is an articulated exoskeleton and at the joints between the body parts are hair plates. These plates have evolved in such a way that when one part, let’s say a leg, moves, it stimulates the hairs that are located around the joint where the leg is attached to the thorax. The movement of these hairs sends a signal to the bee’s central nervous system (similar to the signal your brain receives when the hairs on your arm move), and in this way the bee can perceive the position of it’s leg. These hair plates that signal the position of body parts are called proprioceptors (a fancy way of saying self-perception receptors).
At the joint where the bee’s head is attached to the thorax there are hair plates that have the specific function of determining the position of the head in response to gravity. The bee’s head is similar to the weight inside an accelerometer; gravity forces the head into a slightly different position when the bee is standing on a vertical surface, like hive comb, facing down than it does when facing up. And the hair plates on the bee’s neck are similar to the rod-shaped capacitors in that they sense the position of the head [weight] and relay that information back to the central nervous system [tiny computer]. This arrangement that allows the bee to sense gravity is called the proprioceptor gravity receptor system (or PGR system).
But the similarity doesn’t end there. A smart phone uses its accelerometer to control its fancy display and a honeybee uses its PGR system to put on a rather fancy display of its own. The waggle dance is the method by which a single honeybee can convey to other honeybees in the hive the distance and direction of a food source. During the dance the performing bee walks at a certain angle in relationship to gravity and waggles its abdomen (remember, all the bees are standing on the vertical surface of the comb). It is thought that the other bees that are witnessing the dance are able to transpose that angle of orientation with respect to gravity to an angle of orientation with respect to the sun. After witnessing the dance additional foraging bees can now find the new food source by flying in a direction that has that same angle of orientation to the sun. Performing the waggle dance to communicate with other bees is only possible because of the bee’s ability to sense gravity with its PGR system.
As I mentioned above, humans have a vestibular apparatus in the inner ear to detect the direction of gravity, but our brains also use two other methods: visual evidence perceived through the eyes and proprioception. The proprioceptors in humans produce results similar to the ones in honeybees, in that they convey the position of our body parts, but they operate differently. Humans have sensory neurons, like stretch receptors, in our muscles and joints that, almost imperceptibly, convey to our brains how are arms and legs are positioned in relationship to gravity. You can easily test your proprioceptors by closing your eyes, raising your left hand over your head, and trying to picture in your mind where your left hand is positioned. If, when you open your eyes, your left hand is where you thought it would be then your proprioceptors are working just fine. In rare cases of proprioceptor scotoma, patients have lost the use of their proprioceptor system and can only determine the position of their limbs by looking at them. Can you imagine closing your eyes while moving your right arm and having absolutely no idea where your iPhone is? Or, despite how much you waggle your abdomen, you still can’t find your honey? Scary.
For more information on the honeybee’s response to gravity, see “Form and Function in the Honey Bee” by Lesley Goodman (ISBN 978-0860982432), and for a compelling story on the consequences of losing the use of your proprioceptor system, see “A Leg to Stand On” by Dr. Oliver Sacks (ISBN 978-0684853956).