Sensillum

from Wikipedia, the free encyclopedia
A cuticle and epidermis
1 epicuticle
2 exocuticle, 3 endocuticle
2 + 3 Procuticula
4 epithelial 5 basement membrane
6 epithelial cell, 6a pore channels
7 gland cell
8 Cuticulagrube (Bothrion)
9 Wärmerezeptive cells
10 nerve endings
11 trichobothrium
12 sensillum
13 glands openings

A sensillum (from Latin sensus 'sensation, feeling, sense'; plural: sensilla ), also sensille (plural: sensillen ), is an external hair-like sensory organ in physiology for the perception of environmental stimuli. In arthropods , sensilla are formed as part of the exoskeleton from a bristle hair or pores and two sensory cells ( receptors ) through the cuticle . In some reptiles , sensilla are found as hair-like scales, mainly on the tail. The chemical , thermal , optical or mechanical stimuli are transmitted via multiterminal ganglionic receptor cells.

arthropod

Layout and function

Different forms of the sensillum

Since arthropods have a rigid exoskeleton (exoskeleton), external mechanical stimuli, unlike vertebrates, for example, have to be directed to an excitable membrane . For this purpose, epithelial cells form a thin chitin thread , in the base of which at least one dendrite grows. This chitin thread transmits the mechanical stimulus with a sternite of the cuticle at the joint to the excitable membrane. The adequate stimulus is a transverse pressure on the dendritic membrane.

Depending on the type of stimulus, the shape of the stimulus transmitter can be modified in many ways: to pens, plates, caps, etc. (see illustration).

Types of Sensilla

Mechanosensilla

Hair sensilla

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

A hair sensillum is similar in function to a hair cell :

  • The outer limb of the dendrite resembles a rigid cilium and is densely covered with microtubules . Where it is squeezed into the chitin structures of the joint to transmit force, it forms a so-called tubular body (consists of a particularly large number of microtubules). The outer limb membrane is mechanically connected to the underlying microtubule jacket by means of molecular cones and to the outside with the dendritic sheath by bridges. The chitin structures of the joint, which transfer the leverage to the dendritic membrane, lie directly on the dendritic sheath. Mechanosensitive ion channels are located in the dendrite membrane, but their function has not yet been researched.
  • It reacts in a direction-specific manner, since transversal pressure leads to depolarization and transversal pull to hyperpolarization.
  • For the stimulus-specific outer limb, ion-tight connections with neighboring epithelial cells create a separate receptor lymphatic space, the ions of which are composed differently than in the hemolymph , which washes around the proximal (near-body) part of the sensory cell. This creates a direct voltage potential across the sensillum , which is modulated by the receptor current .
  • Sensilla react to even the smallest force. On the legs of insects, they respond to vibration amplitudes of a few nanometers. The electrical work at the excitation threshold is around 10 to 16 Ws. Similar to the deflection of the hair sensilla, particle movements through air or water, which move the hair through friction ( viscous coupling), are stimulated .
  • Hair sensors have a certain mass and stiffness, thus a certain mechanical resonance frequency , which is influenced by the type of lever joint and its own dynamic properties. This frequency is typically in the range from 100 to 200 Hz and results from:
    • the stiffness dependent on the deflection (10 to 12 N / rad),
    • the friction that depends on the speed of hair movement,
    • the acceleration-dependent mass action (9 to 10 mg per sensillum).

There are two types:

  • Filamentary hair: Activation by pushing or pulling, therefore direction-sensitive
  • Bristles: pure touch receptor

Bristle fields have the function of transmitting the joint positions. On many joints there are whole fields of such bristles, which are bent more or less depending on the position of the joint.

Dome or campanise villa

Sensilla in dome or campaniforms measure the deformation of the cuticle using mechanosensors and thus register even slight mechanical stimuli. They can be activated by transverse compression (load or muscle strength).

Scolopidialsensilla

Scolopidialsensilla end under the epithelium and respond to pressure or tension inside the body.

Cleft sensilla

Split or lyriform sensilla have the same tasks as domed sensilla , but they specialize in the vibration sense, especially in arachnids . They are formed by numerous parallel crevices in the exocuticle (extremely lying cuticle layer). In the center of each gap there is a so-called coupling cylinder, a cylindrical depression on which the dendrite ( cytoplasmic process of a nerve cell ) of the associated sensory cell attacks. Gap sensors are used to perceive ground vibrations and, when spinning, web vibrations, but also react to airborne noise in the frequency range between 100 and 2500 Hz (optimally between 300 and 700 Hz).

Chemosensillum

An olfactory sensillum is a sensillum for the perception of chemical stimuli of low concentration on the antennae of insects . These are cuticular sense organs. The odorous substances reach the 1 to 45 sensory cells via pores (150 to 50,000 per sensillum). A taste sensillum is a sensillum for the perception of chemical stimuli of higher concentration. You are

  • on the labellum (tip of the lower lip),
  • on the tarsus (foot),
  • on the labial and maxillary palps ( mouth parts of lips and upper jaw)
  • on the tip of the trunk ,
  • on the antennas as well
  • in the area of ​​the hypo- and epipharynx (appendages of the head capsule, false mouthparts).

Chemosensilla on their antennae enable ants ( Camponotus japonicus ) to distinguish between individuals in their own structure and those of others.

Hygro and thermosensillum

Some sansilla are sensitive to moisture and temperature.

Tubular sensillum

The function of the tubular sensilla is unclear.

Reptiles

In many geckos , some agamas and iguanas , hair-like receptors of the scaling can be found, especially on the tail. These are mechano or thermoreceptors, some are also associated with the development of noise. They are often assigned the function of determining the point where the tail is dropped in the event of danger and of initiating the twitching movements of the tail part. They have developed from the fine outgrowths of the scales, which have a lotus effect that reduce the ability to be wetted with water.

Individual evidence

  1. ^ HI Runion, PNR Usherwood: Tarsal receptors and leg reflexes in the locust and grasshopper. In: Journal of Experimental Biology 49, No. 2, 1968, pp. 421-436.
  2. ^ Rainer F. Foelix, I-Wu Chu-Wang: The morphology of spider sensilla I. Mechanoreceptors. In: Tissue and Cell 5, No. 3, 1973, pp. 451-460, doi: 10.1016 / S0040-8166 (73) 80037-0 .
  3. ↑ a b A. K. Bromley, JA Dunn, M. Anderson: Ultrastructure of the antennal sensilla of aphids. In: Cell and Tissue Research. 205, 1980, S., doi : 10.1007 / BF00232289 .
  4. ↑ Eric Hallberg, Bill S. Hansson: Arthropod sensilla: Morphology and phylogenetic considerations. In: Microscopy Research and Technique. 47, 1999, pp. 428-439, doi : 10.1002 / (SICI) 1097-0029 (19991215) 47: 6 <428 :: AID-JEMT6> 3.0.CO; 2-P .
  5. ↑ Andrew S. French, Päivi H. Torkkeli: Mechanotransduction in spider slit sensilla. In: Canadian Journal of Physiology and Pharmacology 82, No. 8-9, 2004, pp. 541-548, doi: 10.1139 / y04-031 .
  6. ↑ Friedrich G. Barth : A single cleft sense organ on the spider tarsus: its excitation depending on the parameters of the airborne sound stimulus. In: Journal for Comparative Physiology . 55, 1967, pp. 407-449, doi : 10.1007 / BF00302624 .
  7. ↑ Ulla Klein: Sensillum-lymph proteins from antennal olfactory hairs of the moth Antheraea polyphemus (Saturniidae). In: Insect Biochemistry 17, No. 8, 1987, pp. 1193-1204, doi: 10.1016 / 0020-1790 (87) 90093-X .
  8. ↑ Tamara Elmore, Rickard Ignell, John R. Carlson, Dean P. Smith: Targeted mutation of a Drosophila odor receptor defines receptor requirement in a novel class of sensillum. In: The Journal of Neuroscience 23, No. 30, 2003, pp. 9906-9912.
  9. ^ Mamiko Ozaki et al .: Ant nestmate and non-nestmate discrimination by a chemosensory sensillum. In: Science 309, No. 5732, 2005, pp. 311-314, doi: 10.1126 / science.1105244 .
  10. ↑ F. Yokohari: The sensillum capitulum, an antennal hygro-and thermoreceptive sensillum of the cockroach, Periplaneta americana L. In: Cell and Tissue Research 216, No. 3, 1981, pp. 525-543.
  11. ↑ Volker Hartenstein, James W. Posakony: A dual function of the Notch gene in Drosophila sensillum development. In: Developmental Biology 142. No. 1, 1990, pp. 13-30, doi: 10.1016 / 0012-1606 (90) 90147-B .
  12. ↑ Volker Storch, Robert P. Higgins, M. Patricia Morse: Ultrastructure of the body wall of Meiopriapulus fijiensis (Priapulida). In: Transactions of the American Microscopical Society 1989, pp. 319-331.
  13. ↑ Uwe Hiller: Morphology and electrophysiological properties of cutaneous sensilla in agamid lizards. In: Pflügers Archiv 377, No. 2, 1978, pp. 189-191, doi: 10.1007 / BF00582851 .
  14. ↑ Natalia G. Nikitina, Natalia B. Ananjeva: The skin sense organs of lizards of Teratoscincus Genus (Squamata: Sauria: Gekkonidae). (PDF) In: Herpatologia Petropolitana 2003, pp. 291–295.
  15. ^ AP Russell, AM Bauer: Caudal morphology of the knob-tailed geckos, genus Nephrurus (Reptilia, Gekkonidae), with special reference to the tail tip. In: Australian Journal of Zoology 35, No. 6, 1987, pp. 541-551, doi: 10.1071 / ZO9870541 .
  16. Jump up ↑ Anthony P. Russell, Erica K. Lai, G. Lawrence Powell, Timothy E. Higham: Density and distribution of cutaneous sensilla on tails of leopard geckos (Eublepharis macularius) in relation to caudal autotomy. In: J. Morphol. 2014, doi: 10.1002 / jmor.20269
  17. ↑ Aaron M. Bauer, Anthony P. Russell: Morphology of gekkonid cutaneous sensilla, with comments on function and phylogeny in the Carphodactylini (Reptilia: Gekkonidae). In: Canadian Journal of Zoology 66, No. 7, 1988, pp. 1583-1588, doi: 10.1139 / z88-231 .