Sensory receptor
Encyclopedia
In a sensory system
, a sensory receptor is a sensory nerve
ending that responds to a stimulus
in the internal or external environment of an organism
. In response to stimuli the sensory receptor initiates sensory transduction by creating graded potentials or action potential
s in the same cell or in an adjacent one.
that bind to specific chemicals. Odor receptors in olfactory receptor neuron
s, for example, are activated by interacting with molecular structures on the odor
molecule. Similarly, taste
receptors (gustatory receptors) in taste bud
s interact with chemicals in food to produce an action potential
.
Other receptors such as mechanoreceptor
s and photoreceptors respond to physical stimuli. For example, photoreceptor cells contain specialized proteins such as rhodopsin
to transduce
the physical energy in light into electrical signals. Some types of mechanoreceptors fire action potentials when their membranes are physically stretched.
The sensory receptor functions are the first component in a sensory system.
Sensory receptors respond to specific stimulus modalities. The stimulus modality to which a sensory receptor responds is determined by the sensory receptor's adequate stimulus
.
The sensory receptor responds to its stimulus modality by initiating sensory transduction. This may be accomplished by a net shift in the initial states of a receptor (see a picture of these putative states http://www.bio-balance.com/Receptor2.htm with the biophysical description http://www.bio-balance.com/Graphics.htm).
is the stimulus modality for which it possesses the adequate sensory transduction apparatus. Adequate stimulus can be used to classify sensory receptors:
Some tonic receptors are permanently active and indicate a background level. Examples of such tonic receptors are pain receptors, joint capsule
, and muscle spindle
.
.
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
, a sensory receptor is a sensory nerve
Sensory nerve
Sensory nerves are nerves that receive sensory stimuli, such as how something feels and if it is painful, smooth, rough, etc.They are made up of nerve fibers, called sensory fibers .Sensory neurons are neurons that are activated by sensory input Sensory nerves are nerves that receive sensory...
ending that responds to a stimulus
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
in the internal or external environment of an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
. In response to stimuli the sensory receptor initiates sensory transduction by creating graded potentials or action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s in the same cell or in an adjacent one.
Functions
The sensory receptors involved in taste and smell contain receptor moleculesReceptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
that bind to specific chemicals. Odor receptors in olfactory receptor neuron
Olfactory receptor neuron
An olfactory receptor neuron , also called an olfactory sensory neuron , is a transduction cell within the olfactory system. J. Rospars, Dendritic integration in olfactory sensory neurons: a steady-state analysis of how the neuron structure and neuron environment influence the coding of odor...
s, for example, are activated by interacting with molecular structures on the odor
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...
molecule. Similarly, taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
receptors (gustatory receptors) in taste bud
Taste bud
Taste buds contain the receptors for taste. They are located around the small structures on the upper surface of the tongue, soft palate, upper esophagus and epiglottis, which are called papillae. These structures are involved in detecting the five elements of taste perception: salty, sour,...
s interact with chemicals in food to produce an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
.
Other receptors such as mechanoreceptor
Mechanoreceptor
A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles...
s and photoreceptors respond to physical stimuli. For example, photoreceptor cells contain specialized proteins such as rhodopsin
Rhodopsin
Rhodopsin, also known as visual purple, is a biological pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light,...
to transduce
Transduction (physiology)
In physiology, transduction is the conversion of a stimulus from one form to another.Transduction in the nervous system typically refers to stimulus alerting events wherein a mechanical/physical/etc stimulus is converted into an action potential which is transmitted along axons towards the central...
the physical energy in light into electrical signals. Some types of mechanoreceptors fire action potentials when their membranes are physically stretched.
The sensory receptor functions are the first component in a sensory system.
Sensory receptors respond to specific stimulus modalities. The stimulus modality to which a sensory receptor responds is determined by the sensory receptor's adequate stimulus
Adequate stimulus
The adequate stimulus is a property of a sensory receptor that determines the type of energy to which a sensory receptor responds to with the initiation of sensory transduction....
.
The sensory receptor responds to its stimulus modality by initiating sensory transduction. This may be accomplished by a net shift in the initial states of a receptor (see a picture of these putative states http://www.bio-balance.com/Receptor2.htm with the biophysical description http://www.bio-balance.com/Graphics.htm).
by adequate stimulus
A sensory receptor's adequate stimulusAdequate stimulus
The adequate stimulus is a property of a sensory receptor that determines the type of energy to which a sensory receptor responds to with the initiation of sensory transduction....
is the stimulus modality for which it possesses the adequate sensory transduction apparatus. Adequate stimulus can be used to classify sensory receptors:
- Ampullae of LorenziniAmpullae of LorenziniThe ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...
respond to electric fields, salinity, and to temperature, but function primarily as electroreceptors - BaroreceptorBaroreceptorBaroreceptors are sensors located in the blood vessels of several mammals. They are a type of mechanoreceptor that detects the pressure of blood flowing through them, and can send messages to the central nervous system to increase or decrease total peripheral resistance and cardiac output...
s respond to pressure in blood vessels - Chemoreceptors respond to chemical stimuli
- Hydroreceptors respond to changes in humidity
- MechanoreceptorMechanoreceptorA mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion. There are four main types in the glabrous skin of humans: Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini corpuscles...
s respond to mechanical stress or mechanical strain - NociceptorNociceptorA nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...
s respond to damage to body tissues leading to pain perception - OsmoreceptorOsmoreceptorAn osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure. Osmoreceptors can be found in several structures, including the organum vasculosum of the lamina terminalis and the subfornical organ...
s respond to the osmolarity of fluids (such as in the hypothalamus) - Photoreceptors respond to light
- Proprioceptors provide the sense of position
- ThermoreceptorThermoreceptorA thermoreceptor is a sensory receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range...
s respond to temperature, either heat, cold or both - Electromagnetic receptors respond to electromagnetic waves
by location
Sensory receptors can be classified by location:- Cutaneous receptorCutaneous receptorA cutaneous receptor is a type of sensory receptor found in the dermis or epidermis. They are a part of the somatosensory system. Cutaneous receptors include e.g...
s are sensory receptors found in the dermisDermisThe dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
or epidermis. - Muscle spindleMuscle spindleMuscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. This information can be processed by the brain to determine the position of body parts...
s contain mechanoreceptors that detect stretch in muscles.
by morphology
Somatic sensory receptors near the surface of the skin can usually be divided into two groups based on morphology:- Free nerve endings characterize the nociceptorNociceptorA nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...
s and thermoreceptorThermoreceptorA thermoreceptor is a sensory receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range...
s and are called thus because the terminal branches of the neuron are unmyelinated and spread throughout the dermisDermisThe dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
and epidermis. - Encapsulated receptors consist of the remaining types of cutaneous receptors. Encapsulation exists for specialized functioning.
by rate of adaptation
- A tonic receptor is a sensory receptor that adapts slowly to a stimulus and continues to produce action potentialAction potentialIn physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s over the duration of the stimulus. In this way it conveys information about the duration of the stimulus.
Some tonic receptors are permanently active and indicate a background level. Examples of such tonic receptors are pain receptors, joint capsule
Joint capsule
An articular capsule is an envelope surrounding a synovial joint.-Layers:Each capsule consists of two layers:* an outer layer composed of avascular white fibrous tissue...
, and muscle spindle
Muscle spindle
Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. This information can be processed by the brain to determine the position of body parts...
.
- A phasic receptor is a sensory receptor that adapts rapidly to a stimulus. The response of the cell diminishes very quickly and then stops. It does not provide information on the duration of the stimulus; instead some of them convey information on rapid changes in stimulus intensity and rate. An example of a phasic receptor is the Pacinian corpusclePacinian corpuscleLamellar corpuscles or Pacinian corpuscles are one of the four major types of mechanoreceptor. They are nerve endings in the skin, responsible for sensitivity to vibration and pressure. Vibrational role may be used to detect surface, e.g., rough vs...
.
Innervation
Different sensory receptors are innervated by different types of nerve fibers. Muscles and associated sensory receptors are innvervated by type I and II sensory fibers, while cutaneous receptors are innervated by Aβ, Aδ and C fibersGroup C nerve fiber
-Location:C fibers are found in the peripheral nerves of the somatic sensory system. They are afferent fibers, conveying input signals from the periphery to the central nervous system.-Structure:...
.
See also
- SenseSenseSenses are physiological capacities of organisms that provide inputs for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception...
- Sensory neuronSensory neuronSensory neurons are typically classified as the neurons responsible for converting external stimuli from the environment into internal stimuli. They are activated by sensory input , and send projections into the central nervous system that convey sensory information to the brain or spinal cord...
- ProprioceptionProprioceptionProprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
- Receptor theoryReceptor theoryReceptor theory is the application of receptor models to explain drug behaviour. Pharmacological receptor models preceded accurate knowledge of receptors by many years. John Newport Langley and Paul Ehrlich introduced the concept of a receptor that would mediate drug action at the beginning of the...