Stretch Receptors
Stretch receptors able of perception of muscle tension or stretch are distributed in the connective tissue related with muscles of many groups of animals. This contains a multi-polar neuron with free nerve endings embedded in the fibrous connective tissue. Stretch of the muscle is capable of stimulating this receptor. Several insects have a fine membrance or tympanum stretched across a cavity with air on both sides. In the locust, for instance, a pair of such tympanal organs is present in the first abdominal segment, the inner side of the membrance held over the air sac of the tracheal system. Against the inner side of the tympanum are held a group of mechanoreceptors. Sound waves among 500-11,000 c/s causing vibration of tympanum can produce impulses in the tympanal membrane. You will be surprised to know that many insects such as moths are even sensitive to ultrasound which we cannot perceive.