Sensillum

Sensillum is a term from the physiology of arthropods and denotes various sense organs to carry out chemical, optical or mechanical stimuli. Here, a sensillum always consists of a hair or pores and two sensory cells (receptor ) is formed. The forwarding of the stimuli via multi- terminal ganglionale receptor cells.

Function of sensilla

Since arthropods have a rigid exoskeleton ( external skeleton ), external mechanical stimuli must otherwise be performed as for example in vertebrates of the excitable membrane. These epithelial cells form a thin Chitinfaden, in its base waxing at least a dendrite. This Chitinfaden transmits the mechanical stimulus with the cuticle of the body at the joint on the excitable membrane. Depending on the type of stimulus this stimulus carrier can be modified in many ways to pins, plates, caps, etc.. The adequate stimulus is a transverse pressure on the dendritic membrane. In many joints are whole fields of such bristles are bent more or less depending on joint position.

A Haarsensillum similar in function very a hair cell:

• The outer member of the dendrite resembles a rigid cilium and is provided with dense microtubules. Where it is constrained for power transmission in Chitinstrukturen of the joint, it forms a so-called Tubularkörper ( consists of a lot of microtubules ). The outer member membrane is mechanically connected to the underlying shell by microtubule molecule pin ( cones ) and outwardly with Dendritenscheide by bridges. The Chitinstrukturen of the joint, which transmit the leverage on the dendritic membrane lying directly on the Dendritenscheide. In the dendritic membrane are mechanosensitive ion channels, but which are not yet explored in their function.
• It reacts a specific direction because the transverse pressure to depolarisation and transversal train leads to hyperpolarization.
• For the stimulus-specific outer member is formed by ion- tight connections with neighboring epithelial cells separate Rezeptorlymphraum whose ions are put together differently than in the hemolymph, which bathes the proximal ( proximal ) part of the sensory cell. Is produced across the sensillum a DC potential which is modulated by the receptor power.
• Sensilla respond to even small forces. They respond to the legs of insects already on vibration amplitudes of a few nanometers. The electrical work on the excitation threshold is about 10 to 16 Ws Similarly for the deflection of the hair sensilla irritate particle movement through air or water, through friction ( viscous coupling) move the hair.
• Hair sensilla have a certain mass and stiffness, hence a certain mechanical resonance frequency is influenced by the nature of the lever joint and the dynamic properties of their own. Typically, this frequency is in the range of 100 to 200 Hz and is derived from: dependent on the deflection stiffness (10 to 12 N / rad),
• Dependent on the speed of movement of hair friction
• Dependent on the acceleration of mass action (9 to 10 mg per sensillum ).

Types of sensilla

Geruchssensillen

A Geruchssensillum is an organ for the perception of chemical stimuli of low concentration in the antennae of insects. It involves cuticular sense organs. The Fragrance access via pores (150 to 50,000 per sensillum ) to 1 to 45 sensory cells.

Geschmackssensillen

A Geschmackssensillum is an organ for the perception of chemical stimuli higher concentration. You are

• On the labellum ( top of the lower lip )
• On the tarsus (foot),
• On the labial and Maxillarpalpen ( mouthparts on the lips and maxillary )
• On the snout tip,
• On the antennas and
• In the area of ​​hypo-and nasopharynx ( Annexes to the head capsule, fake mouthparts ).

Hair sensilla

Typical mechanoreceptors are represented by the hair sensilla. They cover the entire body, but especially the legs. They are mostly simple whiskers and specialized trichobothria that respond to air movements and also on sound pressure waves.

There are two types:

• Thread hair: Activation by pressure or train, so sensitive to direction
• Bristles: pure touch receptor

Bristle fields have a very important function because they transmit joint positions.

Kuppelsensillen

In dome or campaniform sensilla Mechanosensors measure the deformation of the cuticle and register so even tiny mechanical stimuli. They are activated by cross- compression ( stress or muscle strength ).

Scolopidialsensillen

Scolopidialsensillen end beneath the epithelium and react inside the body to pressure or train.

Slit sensilla

Gap or Lyriforme sensilla have the same tasks as Kuppelsensillen, but they are specialized in the vibration sense particularly in spiders. They are formed by a plurality of parallel columns in the exocuticle ( extremely lying layer of skin). In the center of each gap there is a so-called coupling cylinder, a cylinder- shaped depression at the dendrite ( of cytoplasm of a nerve cell ) engages the associated sensory cell. Slit sensilla are used for the perception of soil and spiders of network vibrations, but also respond to airborne sound in the frequency range 100-2500 Hz (optimum between 300 and 700 Hz).

Tubularsensillen

The function of the Tubularsensillen is unknown as yet.

• Anatomy (eddy lots)