Short Notes on Propioreceptors, Tactilereceptors and Thermoreceptors and Lateral line system and Electrical sensing
Propioreceptors:
Propio = self.
Propioreceptors
commonly called “stretch receptors” are internal sense organs that respond to
mechanically induced changes caused by stretching, compression, bending or
tension. These receptors give an annual information about the movement of its
body parts and their position relative to each other. Proprioreceptors have been
most thoroughly studied in arthropods where they are associated with appendage,
joints and body extensor muscles. In these animals the sensory neurons involved
in proprioreception are associated with and attached to some part of the body
that is stretched. These parts may be specialized muscle cells, elastic
connective tissue fibres or various membranes that span joints. As these
structures change shape, sensory nerve endings of the attached nerves distort
accordingly and initiate a generator potential.
Tactilereceptors and Thermoreceptors:
Tactilereceptors:
Tactile = touch. Tactilereceptors are derived from modification of epithelial
cells associated with sensory neurons. Most tactile receptors of animals
involve projection from the body surface e.g. various bristles, spines, setae
and tubercles. When an animal contracts an object in the environment these
receptors are mechanically deformed. These deformations activate the receptor
which in turn activates underlying sensory neurons initiating a generator
potential. Most tactile receptors are also sensitive to mechanically induced
vibrations propagated through water or a solid substrate. Tube dwelling
polychaetes bear receptors that allow them to retract quickly into their tubes
in response to movements in their surroundings. Web building spiders have
tactile receptors that can sense struggling prey in webs through vibrations of
the web threads.
Termoreceptors: Thermo
= heat. They respond to temperature changes. Some invertebrates can directly
sense differences in environmental temperatures. Protozoa paramecium collects
in areas where water temperature is moderate and it avoids temperature
extremes. A heat sensing mechanism draws Leeches and ticks to warm blooded
hosts. Certain insects, some crustaceans and horse shoe crab (limulus) can also
sense thermal variations.
Lateral line system and Electrical
sensing:
Specialized
organs for equilibrium and gravity detection, audition and magnetoreception
have evolved from the lateral line system of fishes. The lateral line system
for electrical sensing is in the head and body areas of most fishes some
amphibians and platypus. It consists of sensory pores in the epidermis of the
skin that connect to canals leading into electroreceptors called ampullary organs.
These organs can sense electrical currents in the surrounding water. Most
living organisms generate weak electrical fields. The ability to detect these
fields helps a fish to find mates, capture prey or avoid predators. This is
valuable sense in deep musky water, where vision is of little use. In fact some
fishes actually generate electrical fields and then use their electroreceptors
(electro communication) to detect how surrounding objects distort the field.
This allows these fishes to navigate in musky waters.
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