Sensing touch, movement & sound
Objectives
- To learn about the way insects sense their environment through touch and sound.
Topic Outline
- Part 1: Introduction and types of Mechanoreceptors
- Part 2: Setae
- Part 3: Campaniform Sensillae
- Part 4: Scolopidia and Chordotonal organs
- Part 5: Stretch receptors
Activities
- Minilecture on touch, movement and sound.
Part 1: Introduction
In this module we explore the way in which insects feel and hear the world around them. Insects have an exoskeleton. This makes the sensing of the outside world a challenge. To feel touch and sound through a hard outer casing requires the use of a different strategy than found in organisms with a soft skin. The solution is the use of nerve cells that connect with components of this ‘armor’. These can connect to single articulated spines or be embedded in the exoskeleton. Inside the body, stretch can be felt by mechanoreceptors attached to muscle or connective tissues.
Sound is monitored either through the movement of body spines or the flexing of a cuticular tympanum (ear-drum).
All of the forms of sense organs used to feel touch, movement and sound involve the principle of bending or stretching. (Reference: Chapman: chapters 23 and 26)
Right: Head of the European honeybee: note the numerous hairs even on the eye. Scanning electron micrograph [Image BW Cribb]
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Mini-lecture:
Variety and modifications of sense organs
There are 4 types of mechanoreceptors. Three have a bipolar form and are connected with the cuticle (exoskeleton). The fourth is multipolar and connected to muscle or connective tissue. Table 1 provides a summary of these details. We will investigate the structure and function of these types in more detail below.
Table 1. Types of mechanoreceptors
Type |
Formal name/s |
Primary function |
|---|---|---|
Hair-types seen externally |
Sensilla chaetica |
Touch; air movement; some sound (via air movement); body position (i.e. proprioception); and pressure (in aquatic insects) |
Dome-types seen externally |
Campaniform sensilla |
Shearing stresses in cuticle; body position monitoring (proprioception); pitch, yaw, roll and wingbeat in flight. |
Externally invisible but attached to the epidermis of the cuticle |
Scolopidia Chordotonal organs |
Displacement; pressure; and sound (insect ‘ears’): Involved a variety of ‘organs’ (subgenual organ; Johnston’s organ; tympanal organs) that respond to changes in air pressure and therefore sound. |
Externally invisible multipolar cells without associated specialized structures |
Multipolar stretch receptors |
Stretch of internal organs and muscles is involved in monitoring feeding, growth and reproduction. Monitoring of muscle tension is involved in proprioception. |
Go on to part 2: Setae