quorum sensing

Examples of quorum sensing in the following topics:

• Signaling in Bacteria

  • Signaling in bacteria, known as quorum sensing, enables bacteria to monitor extracellular conditions, ensure sufficient amounts of nutrients are present, and avoid hazardous situations.
  • Because the number of cells present in the environment (the cell density) is the determining factor for signaling, bacterial signaling was named quorum sensing.
  • Quorum sensing uses autoinducers as signaling molecules.
  • Some species of bacteria that use quorum sensing form biofilms, which are complex colonies of bacteria (often containing several species) that exchange chemical signals to coordinate the release of toxins that attack the host.
  • Quorum sensing determines whether the bacteria should produce the luciferase enzyme.

• Reception

  • While it is helpful to this underwater predator, electrosensitivity is a sense not found in most land animals.
  • Senses provide information about the body and its environment.
  • Think for a moment about the differences in receptive fields for the different senses.
  • For the sense of touch, a stimulus must come into contact with body.
  • For the sense of hearing, a stimulus can be a moderate distance away.

• Tastes and Odors

  • The senses of taste and smell are related because they use the same types of receptors and are stimulated by molecules in solutions or air.
  • Compare that to mice, for example, which have about 1,300 olfactory receptor types and, therefore, probably sense many more odors.
  • The senses of smell and taste combine at the back of the throat.
  • Both smell and taste use chemoreceptors, which essentially means they are both sensing the chemical environment.
  • It is the sense of smell that is used to distinguish the difference.

• Balance and Determining Equilibrium

  • With hair cells in the inner ear that sense linear and rotational motion, the vestibular system determines equilibrium and balance states.
  • Along with audition, the inner ear is responsible for encoding information about equilibrium, or the sense of balance.
  • A similar mechanoreceptor—a hair cell with stereocilia—senses head position, head movement, and whether our bodies are in motion.
  • Head position is sensed by the utricle and saccule, whereas head movement is sensed by the semicircular canals.
  • The maculae are specialized for sensing linear acceleration, such as when gravity acts on the tilting head, or if the head starts moving in a straight line.

• Control of Homeostasis

  • The receptors sense changes in the environment, sending a signal to the control center (in most cases, the brain), which, in turn, generates a response that is signaled to an effector.
  • It may either increase or decrease the stimulus, but the stimulus is not allowed to continue as it did before the receptor sensed it.
  • When an animal has eaten, blood glucose levels rise, which is sensed by the nervous system.
  • Specialized cells in the pancreas (part of the endocrine system) sense the increase, releasing the hormone insulin.
  • This produces pain sensed by the nervous system.

• Transduction and Perception

  • Sensory receptors for the various senses work differently from each other.
  • They are specialized according to the type of stimulus they sense; thus, they have receptor specificity.
  • However, stimuli may be combined at higher levels in the brain, as happens with olfaction, contributing to our sense of taste.
  • This segregation of the senses is preserved in other sensory circuits.
  • When the sensory signal exits the thalamus, it is conducted to the specific area of the cortex dedicated to processing that particular sense .

• Plant Responses to Light

  • They can tell the time of day and time of year by sensing and using various wavelengths of sunlight.
  • The sensing of light in the environment is important to plants; it can be crucial for competition and survival.

• Reception and Transduction

  • Twelve million seems like a large number of receptors, but compare that to other animals: rabbits have about 100 million, most dogs have about 1 billion, and bloodhounds (dogs selectively bred for their sense of smell) have about 4 billion.
  • Both tasting abilities and sense of smell change with age.
  • In humans, the senses decline dramatically by age 50 and continue to decline.

• Blue Light Response

  • The protein-based receptors, phototropins and cryptochromes, sense blue light to alter plant physiology accordingly.
  • Like all plant photoreceptors, phototropins consist of a protein portion and a light-absorbing portion, called the chromophore, which senses blue wavelengths of light.
  • There is some evidence that cryptochromes work by sensing light-dependent redox reactions and that, together with phototropins, they mediate the phototropic response.

• Integration of Signals from Mechanoreceptors

  • The configuration of the different types of receptors working in concert in the human skin results in a very refined sense of touch .
  • Tactile-sense-related cortical neurons have receptive fields on the skin that can be modified by experience or by injury to sensory nerves, resulting in changes in the field's size and position.