World Library  
Flag as Inappropriate
Email this Article

Chemoreceptor

Article Id: WHEBN0000489289
Reproduction Date:

Title: Chemoreceptor  
Author: World Heritage Encyclopedia
Language: English
Subject: Trace amine-associated receptor, Tentacle, Control of ventilation, Carotid body, Mayer waves
Collection: Analytical Chemistry, Gas Sensors, Respiratory Physiology, Sensory Receptors, Vomiting
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Chemoreceptor

A chemoreceptor, also known as chemosensor, is a sensory receptor that transduces a chemical signal into an action potential. In more general terms, a chemosensor detects certain chemical stimuli in the environment.

Contents

  • Classes 1
  • Sensory Organs 2
  • In Physiology 3
    • Control of Breathing 3.1
    • Heart rate 3.2
  • See also 4
  • References 5
  • External links 6

Classes

There are two main classes of the chemosensor: direct and distance.

  • Examples of distance chemoreceptors are:
    • pheromones. The current view, however, is that both systems can detect odorants and pheromones.[1] Olfaction in invertebrates differs from olfaction in vertebrates. For example, in insects, olfactory sensilla are present on their antennae.[2]
  • Examples of direct chemoreceptors include:
    • Taste buds in the gustatory system: The primary use of gustation as a type of chemoreception is for the detection of tasteants. Aqueous chemical compounds come into contact with chemoreceptors in the mouth, such as taste buds on the tongue, and trigger responses. These chemical compounds can either trigger an appetitive response for nutrients, or a defensive response against toxins depending on which receptors fire. Fish and crustaceans, who are constantly in an aqueous environment, use their gustatory system to identify certain chemicals in the mixture for the purpose of localization and ingestion of food.
    • Insects use contact chemoreception to recognize certain chemicals such as cuticular hydrocarbons and chemicals specific to host plants. Contact chemoreception is more commonly seen in insects but is also involved in the mating behavior of some vertebrates. The contact chemoreceptor is specific to one type of chemical.[2]

Sensory Organs

  • Olfaction: In vertebrates, olfaction occurs in the Nose. Volatile chemical stimuli enter the nose and eventually reach the olfactory cleft (where the main olfactory epithelium is located). Embedded in the olfactory epithelium are three types of cells: supporting, basal, and olfactory sensory neurons (OSN's). While all three types of cells are integral to the olfactory pathway, only OSN cells make contact with the stimulus. After the stimulus is received by the cilia protruding from the OSNs, the signal activates an action potential which then travels through the bony cribiform plate to the glomeruli within the olfactory bulb. While the proximity of the olfactory cleft to the brain is close, the signals are often slow to illicit response and often require numerous molecules to trigger the corresponding action potential. In insects, antennae act as distance chemoreceptors. For example, antennae on moths are made up of long feathery hairs that increase sensory surface area. Each long hair from the main antenna also has smaller sensilla that are used for volatile olfaction.[3] Since moths are mainly nocturnal animals, the development of greater olfaction aids them in navigating the night.
  • Gustation: In many vertebrates, the savory. The salty and sour tastes work directly through the ion channels, the sweet and bitter taste work through G protein-coupled receptors, and the savory sensation is activated by glutamate.
  • Contact Chemoreception: Contact chemoreception is dependent on the physical contact of the receptor with the stimulus. The receptors are short hairs or cones that have a single pore at, or close to the tip of the projection. They are known as uniporous receptors. Some receptors are flexible, while others are rigid and do not bend with contact. They are mostly found in the mouthparts, but can also occur on the antennae or legs of some insects. There is a collection of dendrites located near the pores of the receptors, yet the distribution of these dendrites changes depending on the organism being examined. The method of transduction of the signal from the dendrites differs depending on the organism and the chemical it is responding to.
  • Cellular antennae: Within the [4]

When inputs from the environment are significant to the survival of the organism, the input must be detected. As all life processes are ultimately based on chemistry it is natural that detection and passing on of the external input will involve chemical events. The chemistry of the environment is, of course, relevant to survival, and detection of chemical input from the outside may well articulate directly with cell chemicals.

Chemoreception is important for the detection of food, habitat, conspecifics including mates, and predators. For example, the emissions of a predator's food source, such as odors or pheromones, may be in the air or on a surface where the food source has been. Cells in the head, usually the air passages or mouth, have chemical receptors on their surface that change when in contact with the emissions. It passes in either chemical or electrochemical form to the central processor, the brain or spinal cord. The resulting output from the CNS (central nervous system) makes body actions that will engage the food and enhance survival.

In Physiology

Control of Breathing

Particular chemoreceptors, called ASICs, detect the levels of carbon dioxide in the blood. To do this, they monitor the concentration of hydrogen ions in the blood, which decrease the pH of the blood. This can be a direct consequence of an increase in carbon dioxide concentration, because aqueous carbon dioxide in the presence of carbonic anhydrase reacts to form a proton and a bicarbonate ion.

The response is that the respiratory centre (in the medulla), sends nervous impulses to the external intercostal muscles and the diaphragm, via the intercostal nerve and the phrenic nerve, respectively, to increase breathing rate and the volume of the lungs during inhalation.

Chemoreceptors that regulate the depth and rhythm of breathing are broken down into two categories.

  • central chemoreceptors are located on the ventrolateral surface of medulla oblongata and detect changes in pH of cerebrospinal fluid. They have also been shown experimentally to respond to hypercapnic hypoxia (elevated CO2, decreased O2), and eventually desensitize . These are sensitive to pH and CO2.
  • peripheral chemoreceptors: consists of aortic and carotid bodies. Aortic body detects changes in blood oxygen and carbon dioxide, but not pH, while carotid body detects all three. They do not desensitize. Their effect on breathing rate is less than that of the central chemoreceptors.

Heart rate

The response to stimulation of chemoreceptors on the heart rate is complicated. Stimulation of peripheral chemoreceptors directly activates the medullary vagal center and slows the heart rate. However, a number of other factors are usually at play in this situation which obscure this response. These factors include activation of stretch receptors due to increased ventilation and the release of circulating catecholamines. Hence, although the stimulation of peripheral chemoreceptors causes bradycardia, this may not be the net result.[5]

See also

References

  1. ^ Shi, P.; Zhang, J. (2009). "Extraordinary Diversity of Chemosensory Receptor Gene Repertoires Among Vertebrates". Chemosensory Systems in Mammals, Fishes, and Insects. Results and Problems in Cell Differentiation 47. pp. 57–75.  
  2. ^ a b Chapman RF (1998) "Chemoreception" in The Insects: structure and function 4th edition. Cambridge University Press, Cambridge. 639.
  3. ^ http://www.ncbi.nlm.nih.gov/books/NBK55976/
  4. ^ Satir, Peter; Christensen, Søren T. (2008). "Structure and function of mammalian cilia". Histochemistry and Cell Biology 129 (6): 687–93.  
  5. ^ Levy, MN; AJ Pappano (2007). Cardiovascular Physiology 9ed. Philadelphia USA: Elsevier. pp. 89–91. 

External links

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.