Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 04 table of contents.
We have surveyed the five senses described by Aristotle: vision, audition, olfaction, gustation, and touch. All five are directed outward to receive stimuli from the outside world. Two other important senses, kinesthesis and equilibrium, involve sensitivity to internal events: position and motion of the body. Kinesthesis and equilibrium are proprioceptive senses, from the root proprio, which means belonging to the body. Kinesthetic receptors detect change in body position.
What is kinesthesis? What does proprioceptive mean?
Nerve impulses "code" the angle of a limb.
The kinesthetic sense monitors the position and movements of muscles, bones, and joints. Through the sense of kinesthesis you can tell, even with your eyes closed, where your arms are located. When you play any sport, when you drive a car, when you move around, you need to know where your limbs are located so you can move them to the right positions. Receptors in the joints and tendons send the brain information about the angle of your limbs.
How is the angle of an arm coded into neural impulses?
For example, a neuron connected to kinesthetic receptors in the elbow fires a certain number of impulses when the arm is outstretched. If the arm is at a 45-degree angle, the cell might fire 40 impulses per second. If the arm is at an angle of 60 degrees, the cell might fire 90 impulses per second.
Where are the kinesthetic receptors located, and what do they detect?
Kinesthetic receptors are primarily stretch receptors located in the muscles, joints and tendons. To activate a knee-jerk reflex, a doctor taps the tendon below the kneecap with a rubber hammer. The tap of the hammer momentarily stretches the patellar tendon, which runs from the patella (kneecap) to the muscles of the lower leg. When the tendon is tapped, stretch receptors send impulses to the spinal cord, activating motor neurons in the spine and sending impulses back to the muscle of the leg, making it twitch. This reflex system helps keep us upright; when we lean, stretch receptors activate leg muscles to correct the lean and pull us back into a vertical position.
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Copyright © 2007-2011 Russ Dewey