Sensing touch, movement and sound
Part 5: Stretch receptors
There is a fourth type of receptor present in insects. This is the unspecialized stretch receptor. The structure is a multipolar neuron with free nerve endings.
Schematic stretch receptor [Diagram BW Cribb] |
Such nerve endings are necessary to monitor stretch in the gut, swelling of reproductive organs such as the bursa copulatrix, mouthparts, legs and wings. They are found across muscle fibres and embedded in connective tissues. Stretch receptors are a principle method of sensing stretch in soft-bodied dipterous larvae (maggots) and perhaps in other insects with unsclerotized cuticle where they effectively form a kind of neural net to monitor body shape. Cyclorrhaphan fly larvae have 24 to 30 per segment. Stretch receptors associated with muscles are present in all insects. This is especially the case for the abdomen. They are also associated with mouthparts, legs and wings. |
The stretch receptors associated with muscles fire in a tonic pattern under sustained stretching that is proportional to the amount of stretching. Rate of stretching can also be monitored with a faster rate of firing of action potentials for a higher rate of stretch.
Mechanism
Stimulation of mechanoreceptors (e.g. by stretching the dendrite membrane) results in opening of ion channels. The ion channels are permeable to cations (e.g. sodium, calcium and magnesium). They are called the transient receptor potential or TRP ion channel superfamily.
Reference and review: Kernan M. J. 2007 Mechanotransduction and auditory transduction in Drosophila. European Journal of Physiology 454,703–720.
Go on to the next module: Sensing Taste and odours.