Rhinophore
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Rhinophores ( ancient Greek ῥίς ( rhis ) = nose, φορος (phoros) = carrying) form an olfactory sensory organ that allows a species-dependent selection of chemical substances such as B. recognizes fragrances, flavors, pheromones. You kick u. a. in nudibranchs and sea slugs ( Opisthobranchia ) of the order of the nudibranch ( Nudisbranchia ), especially in the dorid nudibranch. The sensory organ consists of chemoreceptors, biological sensors with which substances are perceived, of input neurons to the nervous system, which transmit signals for perceived substances induced by the receptors, and a pair of feelers, which are in an exposed position on the top of the head and accommodate receptors such as input neurons .
Case study on Aplysia californica
The basic structure of rhinophores is described here using the example of the species Aplysia californica from the much-studied species of sea hare .
function
In the Alypsia, the rhinophores are used for remote perception of substances such as fragrances and flavors as well as rheoreception (perception of the flow of water).
A large number of chemoreceptors on the surface of the rhinophores enables a fine perception, with the help of which the snail finds food sources.
It could also be proven that they detect pheromones (lock and messenger substances) by means of the rhinophores .
construction
In Aplysia , the rhinophores are a pair of rod antennas that attach to the surface of the top of the head. Compared to the size of the animal, the rhinophores are usually quite small: in an adult Aplysia californica their length was only about 1 cm.
The rhinophores' physical center of perception is contained in a furrow at their tip. The perception occurs via specialized hair cells (ciliary cells) or protuberances (small protuberances) on the surface of the outer tissue. These hair cells are chemoreceptors for fragrances and flavors.
It enters the nervous system via neurons that are embedded in the tissue (epithelium) in the furrow space. The dendrites of these neurons are connected to the hair cells and protuberances. When substances are perceived by the receptor cells on the surface, the neurons are activated. The neurons then forward the input signal via their axons to the rhinophore ganglion (collection of nerve cells and processing center in the snail's nervous system ) ( projection ).
Rhinophore tip of an Aplysia californica
Electron microscope: low resolution
Scale: bars = 300 μm.
rg - rhinophore furrow
tip - rhinophore tip
Rhinophore furrows with ciliary cells on the epithelial surface
Electron microscope: medium resolution
Scale: bars = 100 μm.
f - folds
square - next section
Pores with and without emerging cilia.
Electron microscope: high resolution.
Scale: bars = 10 μm.
ci - cilia of various lengths
In the vicinity of the throat, the Aplysia californica have tentacles, which are also occupied by receptor cells and are used for sensory perception. However, one does not assume any function overlap, but rather believes that the tentacle receptors are more chemo or mechanoreceptors for contact perception.
Extensions
Based on the Alypsia californica, the main elements of olfactory perception by rhinophores have been shown: antenna - chemoreceptors - input neurons - nervous system - ganglia. These elements and the signal path remain the same for all snail species with rhinophores. However, there is variability in the forms that we now draw attention to.
Mobility of rhinophores
The above picture of Chromodoris coi suggests that rhinophores are not just rigid attachments. In fact, some snails can point their rhinophores in different directions.
The antenna shape of the rhinophores is good for the tasks to be performed, but at the same time makes them sensitive points of attack for their natural enemies: the rhinophores are easy to tear off, eat or eat away. To avoid this, most dorid nudibranchs are able to pull their rhinophores into pockets below the surface of the skin.
Olfactory perception
Compared to the sense of sight and hearing, olfactory perception shows some differences.
The sense of sight and hearing are based on waves (light, sound waves). Waves spread relatively quickly and evenly. The signal transmission follows the domino principle. If you hit a chain of dominoes, all dominoes stay in place, but change their state from “standing” to “fallen”, and the last falling stone tells the recipient that the sender has previously hit the chain. So physical states are physically transmitted, but not components. Furthermore, relatively few types of receptor cells are sufficient for perception. In the human eye, for. B. Rod cells are responsible for nocturnal light-dark vision and three types of cone cells are responsible for filtering out frequency bands (proportion of red, green, blue light) during daytime vision.
In olfactory perception, fluctuating molecules of chemical substances must be filtered out of the carrier medium (water) and assigned. Filtering out is often done by docking and entering into chemical bonds, which then trigger an internal signal chain. For the "recognition" of many substances, a sufficiently broad spectrum of receptor cells is required (a person has ~ 320 chemoreceptors , a German shepherd ~ 1200). Signals are transmitted via the physical transfer of molecules from the point of origin to the place of perception. However, molecules are quite large (e.g. compared to electrons) and are prone to barriers. On the other hand, they are subject to influences from the transport medium (e.g. currents) on the signal path. Chemical signals, if they are not very strong, are therefore diffuse and not as directional as light and sound waves.
From this one can establish general quality criteria for olfactory sense organs:
- there should be as many receptors as possible per type of chemoreceptor,
- If possible, the receptors should not be concentrated selectively, but rather spatially distributed sensibly
- the more types of chemoreceptors, the better the perception.
Well distributed receptor surfaces in the room with good penetration of different types are therefore desirable.
Shape of rhinophores
The shapes of rhinophores differ both in the shape of the sensory fields, in the position and in the shape of the antenna. The shapes of the rhinophores produced can be evaluated from the above points of view.
Many rhinophores have two rod antennas with attached sensory fields as their basic shape. Rod antennas are simple, flexible constructions. They can be inclined, rotated and extended / retracted in various directions for protection purposes. On the other hand, the antennas themselves are not very extensive.
The above pictures of Canthodoris pilosa , Chromodoris annulata and Chromodoris coi show attachments with sensory fields of different shapes, lengths and grooves. In the Chromodoris coi almost the entire rod is covered with spiral grooves, in the Canthodoris pilosa only the upper part. Furthermore, u. a. fields in brush form, feather form, documented with longitudinal folds and fields that fan out at the end of the rod. Brushes, feathers and fans are geometric shapes with large surfaces in a small space.
In addition to snails with pure rod antennas, there are snails (star snail Bornella stellifer ), in which the antennae are not head attachments , but rather come from branching tentacles.
etymology
The name rhinophores is derived from its function as an olfactory organ. "Rhino-" comes from the ancient Greek word ῥίς ( rhis ) for nose. "Phore" comes from the ( neo-Latin ) "phore" for wear , and from the Greek word φορος ( phoros what) supporting means.
literature
- Luise Schmekel, Adolf Portmann: Opisthobranchia of the Mediterranean: Nudibranchia and Saccoglossa. Springer-Verlag, Berlin Heidelberg New York 1982. Anatomy of the nudibranchia , rhinophores: p. 19 f.
- Adrian Wertz, Wolfgang Rössler, Malu Obermayer, Ulf Bickmeyer: Functional neuroanatomy of the rhinophore of Aplysia punctata . In: Frontiers in Zoology . tape 3 , no. 1 , April 6, 2006, ISSN 1742-9994 , p. 6 , doi : 10.1186 / 1742-9994-3-6 ( frontiersinzoology.com ).
Individual evidence
- ↑ a b c d e f Scott F. Cummins, Dirk Erpenbeck, Zhihua Zou, Charles Claudianos, Leonid L. Moroz, Gregg T. Nagle, Bernard M. Degnan: Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia . In: BMC Biology . tape 7 , no. 1 , June 4, 2009, ISSN 1741-7007 , p. 28 , doi : 10.1186 / 1741-7007-7-28 ( biomedcentral.com ).
- ^ Sea Slug: Forms of Rhinophores