Short Notes on Baroreceptors and chemoreceptors, Statocyst and Hygroreceptors and Phonoreceptors
Baroreceptors and chemoreceptors:
baros = weight +
receptor. Baroreceptors sense changes in pressure. Responses to pressure
changes have been identified in ocean dwelling copepod crustaceans,
ctenophores, jelly-fish medusa and squids. Some intertidal crustaceans
coordinate migratory activity with daily tidal movement possibly in response to
pressure changes accompanying water depth changes.
Chemoreceptors: They
pertain to chemistry and respond to chemicals. Protozoa have chemical sense.
They respond with avoidance behaviour to acid, alkali and salt stimuli.
Chemoreceptors of may aquatic invertebrates are located in pits or depression
through which water carrying the specific chemicals may be circulated. In
arthropods chemoreceptors are on antennae, mouthparts and legs in the form of
hollow hairs containing chemo sensory neusons. The types of chemicals which
invertebrates respond are closely associated with their life styles as humidity
detection, pH assessment, prey tracking, food recognition and mate location.
Statocyst:
Statocysts are
found in various gastropods, cephalopds, crustaceans, nemertines, polychaetes
and sayphozoans. These animals use information from statocysts in different
ways. For example burrowing invertebrates cannot rely on photoreceptors for
orientation, instead, they rely on georeceptors for orientation within the
substation. Most georeceptors are statocysts.
Statocysts
consist of a fluid filled chamber lined with cilia bearing sensory epithelium,
within the chamber is a solid granule called a statolith (stone). Any movement
of the animal changes the position of the statolith and moves the fluid, thus
altering the intensity and pattern of information arising from the sensory
epithelium. When an animal moves both the movement of the statolith and the
flow of fluid over the sensory epithelium provide information about animals
linear and rotational acceleration relative to the environment.
Hygroreceptors and Phonoreceptors:
Hygroreceptors: Hygro
= moist. They detect the water content of air e.g. some insects have
hygrorecepros that can detect small changes in the ambient relative humidity.
This sense enables them to seek environment with specific humidity or to modify
their physiology or behaviour with respect to ambient humidity (to control the
opening or closing of spiracles). These structures are found on antennae,
palps, under side of body and near spiracles of insects.
Phonoreceptors:
Phono = voice. They respond to sound and are demonstrated only in insects,
arachnids and centipedes, although other invertebrates seem to respond to sound
induced vibrations of the substratum e.g. crickets, grasshoppers and cicadas
possess phonoreceptors called tympanic or tympanal organs. This organ consists
of a flexible tympanum that covers internal sac that allows the tympanum to
vibrate when sound waves strike it. Sensory neurons attached to tympanum are
stimulated and produce generator potential.
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