Where can you find sensory receptors

Broadly, sensory receptors respond to one of four primary stimuli:. A schematic of the classes of sensory receptors : Sensory receptor cells differ in terms of morphology, location, and stimulus. All sensory receptors rely on one of these four capacities to detect changes in the environment, but may be tuned to detect specific characteristics of each to perform a specific sensory function.

In some cases, the mechanism of action for a receptor is not clear. For example, hygroreceptors that respond to changes in humidity and osmoreceptors that respond to the osmolarity of fluids may do so via a mechanosensory mechanism or may detect a chemical characteristic of the environment.

Sensory receptors perform countless functions in our bodies. During vision, rod and cone photoreceptors respond to light intensity and color. During hearing, mechanoreceptors in hair cells of the inner ear detect vibrations conducted from the eardrum.

During taste, sensory neurons in our taste buds detect chemical qualities of our foods including sweetness, bitterness, sourness, saltiness, and umami savory taste. During smell, olfactory receptors recognize molecular features of wafting odors. During touch, mechanoreceptors in the skin and other tissues respond to variations in pressure. Adequate stimulus can be used to classify sensory receptors. Somatic sensory receptors near the surface of the skin can usually be divided into two groups based on morphology:.

In addition, bitter agonists administered to the stomach activate the nucleus tractus solitarii, and via vagal nerve activation, slow gastric emptying in human volunteers. Glendinning et al.

Activation of TAS2Rs leads to smooth muscle relaxation in many different tissue types, providing therapeutic targets to treat diseases like pulmonary hypertension, reactive airway disease including asthma , and bladder spasms. Studies showing vascular relaxation are limited to vessels in the brain and gastrointestinal tract; however, additional studies should be conducted to determine changes to peripheral and cardiac vasculature. Therefore their use presents high potential for side effects caused by unintended receptor activation.

Future research should focus on receptor-specific therapeutic medications to limit such effects. These receptors also contribute to progression of pathologic conditions, such as airway inflammation and asthma, and metabolic diseases of the pancreas, such as diabetes.

The most significant role that TAS1Rs might have in the future is treatment for gastrointestinal diseases and obesity. In contrast to bitter receptor activation, sweet sensation promotes food intake. Obesity decreases both bitter and sweet receptor expression in the duodenum and in areas of the murine brain involved in energy homeostasis.

TAS1R3 is downregulated in the stomachs of obese patients Widmayer et al. These obesity effects suggest that TAS1R agonists may provide a therapeutic target to limit excess food intake. Like bitter taste receptors, TAS1Rs are also involved in bacterial recognition and immune cell function. Stimulation of the innate immune response by altering sweet receptor expression may benefit those chronically infected or unresponsive to traditional anti-bacterial medications.

These taste receptors may hold potential as therapeutic targets to treat these diseases, but this possibility requires investigation. The discovery of nonvisual opsins in non-classic sensory organs prompts us to question whether these receptors can be engaged for therapeutic potential. The discovery that OPN4 receptors and TRPC channels in subcutaneous fat mediate a light-induced lipolytic activity suggests that blue-wavelength light might be used to reduce subcutaneous fat in a safe, noninvasive manner Ondrusova et al.

Since subcutaneous white adipose tissue is the main fat deposit in the human body, this could have big implications to aid in fat deposit regulation and the associated metabolic disorders. Some applications of photoreceptors are already being explored for skin health, such as the use of directed light therapy on the skin to treat acne Jung et al.

Regarding these applications, OPN3 has been suggested to take part in melanogenesis, but no known photoreceptor has been associated yet with the acne reduction in response to blue or red light. Furthermore, blue light exposure was shown to have a positive effect on hair growth, an effect mediated by OPN3.

These results suggest that exposure to blue light may be a safe treatment for alopecia Buscone et al. The idea of using light to control the function of specific brain regions and to treat neurologic disorders has led to the field of optogenetics Deisseroth, Fiber-optic cables targeted to specific regions of the brain or other tissue can serve as the switch activators.

The limitations of this technology are 1 the need to transfect the light-activated switches using viral vectors and 2 the need for light-directing cables to be implanted in specific areas. With regard to the first limitation, the need for transfecting channels can be bypassed by recruiting the endogenously expressed OPNs in each tissue, or endogenous optogenetics.

The second limitation of using fiber optic cables can also be circumvented. Whereas blue light, the wavelength that activates the OPN3 and 4 receptors, has very limited tissue penetrance, NIR light has the potential for deep tissue penetration, including bone.

Upconverting nanocrystals, nanoparticles coated in rare earth lanthanides, can convert 2 photons of NIR light to 1 photon of blue light Christ and Schaferling, The delivery of these crystals in tissues might therefore allow the use of NIR light to stimulate and activate endogenous OPN receptors by up-conversion to blue light Chen et al.

Given the expression of these OPN receptors in blood vessels and several brain tissues, this process may open up a potential light-based therapeutic path for the treatment of a wide variety of diseases. As discussed previously, the phototherapeutic approach of using directed blue light delivery along with GRK2 inhibition can effectively induce sustained vascular relaxation by activating OPN3 and OPN4, while preventing receptor desensitization by GRK2.

This treatment has been demonstrated to alleviate both chronic and acute PH in rat models, though its application could be extended to other cardiovascular diseases characterized by abnormal vasoconstriction Barreto Ortiz et al. Additionally, this phototherapy has the potential of inducing vasodilation in acute vascular obstruction events easily and safely, possibly buying precious time for a patient experiencing a cardiovascular episode such as a stroke or heart attack and allowing blood flow to the affected areas until surgical procedures to remove the obstruction can be performed.

Further research on the clinical applicability of phototherapy in vascular relaxation is therefore crucial. As ORs comprise the largest gene family in the genome, opportunities likely exist to leverage these receptors to modify physiologic and pathophysiologic processes. Such aspirations are currently limited by the fact that many ORs remain orphan receptors, with no known ligand. Because the most obvious strategy for commandeering these receptors for therapy would be to use agonists or antagonists, it is necessary that ligands be clearly identified for each of the ORs.

Although past efforts to identify ligands have been hampered by technical hurdles regarding OR trafficking in vitro , recent studies have made progress in this area Saito et al.

ORs may lend themselves to being leveraged therapeutically in several potential areas, but we should caution that in all areas, future work is warranted to establish the feasibility and efficacy of potential interventions.

OR51E2 has been shown to modulate proliferation and cytoskeletal remodeling in ASM from both asthmatics and non-asthmatics, implying that modulation of OR51E2 signaling may be beneficial in asthma Aisenberg et al. A number of studies in several different systems have pointed to a potential role of ORs in controlling the growth of cancer cells. Hence, modulating OR signaling might offer the possibility to inhibit cancer cell growth. However, the same OR has also been shown to stimulate cancer cell invasiveness Sanz et al.

In addition, OR2J3 activation induced apoptosis and inhibited cell proliferation in a non-small-cell lung cancer cell line Kalbe et al. Olfr has been reported to play a role in the regulation of glucagon secretion Kang et al. In addition, Olfr modulates renal glucose handling by modulating Sglt1 Shepard et al. Of note, Sglt1 is similar in function to Sglt2, a current drug target used to reduce blood glucose in type 2 diabetes. The suggestion that bourgeonal may act through an OR to help direct the sperm in the direction of the egg to aid in fertilization Spehr et al.

Olfr78 increases renin secretion by the kidney and also plays a role in modulating vascular tone Pluznick et al. Activation of OR51E1 has been associated with negative chronotropic and inotropic effects on the heart Jovancevic et al. Activation of OR2AT4 has been shown to promote cell proliferation and migration in keratinocytes Busse et al.

When transgenic mice for MOR23 were crossed with dystrophic mice, mechanical stress caused less damage to the muscles from dystrophic mice with elevated MOR23 than to muscles from dystrophic mice with normal MOR23 levels Pichavant et al.

In conclusion, receptors traditionally believed only to identify and interpret light, sound, and taste also contribute to normal functions within many if not all other organ systems.

Determining the function of sensory receptors in these organ systems and their roles under normal and pathophysiologic conditions has become a primary research focus with the potential to identify novel therapeutic targets to treat and possibly cure many medical diseases.

DB edited the final manuscript, contributing sections for novel therapeutic potential. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Adappa, N. T2R38 genotype is correlated with sinonasal quality of life in homozygous DeltaF cystic fibrosis patients.

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Broadly, sensory receptors respond to one of four primary stimuli: Chemicals chemoreceptors Temperature thermoreceptors Pressure mechanoreceptors Light photoreceptors A schematic of the classes of sensory receptors : Sensory receptor cells differ in terms of morphology, location, and stimulus.

Classification of Sensory Receptors Adequate Stimulus Adequate stimulus can be used to classify sensory receptors. Sensory receptors with corresponding stimuli to which they respond. Receptor Stimulus Apmullae of Lorenzini primarily function as electroreceptors Electric fields, salinity, and temperature Baroreceptors Pressure in blood vessels Chemo receptors Chemical stimuli Electromagnetic radiation receptors Electromagnetic radiation Electroreceptors Electrofields Hydroreceptors Humidity Infrared receptors Infrared radiation Magnetoreceptors Magnetic fields Mechanoreceptors Mechanical stress or strain Nociceptors Damage or threat of damage to body tissues leads to pain perception Osmoreceptors Osmolarity of fluids Photoreceptors Visible light Proprioceptors Sense of position Thermoreceptors Temperature Ultraviolet receptors Ultraviolet radiation.

Location Sensory receptors can be classified by location: Cutaneous receptors are sensory receptors found in the dermis or epidermis. Muscle spindles contain mechanoreceptors that detect stretch in muscles.

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 nociceptors and thermoreceptors. Other overlooked senses include temperature perception by thermoreceptors and pain perception by nociceptors. Within the realm of physiology, senses can be classified as either general or special.

A general sense is one that is distributed throughout the body and has receptor cells within the structures of other organs.

Mechanoreceptors in the skin, muscles, or the walls of blood vessels are examples of this type. General senses often contribute to the sense of touch, as described above, or to proprioception body position and kinesthesia body movement , or to a visceral sense , which is most important to autonomic functions. A special sense discussed in Chapter 15 is one that has a specific organ devoted to it, namely the eye, inner ear, tongue, or nose.

Each of the senses is referred to as a sensory modality. Modality refers to the way that information is encoded into a perception. The main sensory modalities can be described on the basis of how each stimulus is transduced and perceived. The chemical senses include taste and smell. The general sense that is usually referred to as touch includes chemical sensation in the form of nociception, or pain. Pressure, vibration, muscle stretch, and the movement of hair by an external stimulus, are all sensed by mechanoreceptors and perceived as touch or proprioception.

Hearing and balance are also sensed by mechanoreceptors. Finally, vision involves the activation of photoreceptors. Listing all the different sensory modalities, which can number as many as 17, involves separating the five major senses into more specific categories, or submodalities , of the larger sense. An individual sensory modality represents the sensation of a specific type of stimulus. For example, the general sense of touch, which is known as somatosensation , can be separated into light pressure, deep pressure, vibration, itch, pain, temperature, or hair movement.

In this chapter we will discuss the general senses which include pain, temperature, touch, pressure, vibration and proprioception. We will discuss the special senses, which include smell, taste, vision, hearing and the vestibular system, in chapter Somatosensation is considered a general sense, as opposed to the submodalities discussed in this section. Somatosensation is the group of sensory modalities that are associated with touch and limb position.

These modalities include pressure, vibration, light touch, tickle, itch, temperature, pain, proprioception, and kinesthesia. This means that its receptors are not associated with a specialized organ, but are instead spread throughout the body in a variety of organs. Many of the somatosensory receptors are located in the skin, but receptors are also found in muscles, tendons, joint capsules and ligaments. Two types of somatosensory signals that are transduced by free nerve endings are pain and temperature.

These two modalities use thermoreceptors and nociceptors to transduce temperature and pain stimuli, respectively. Temperature receptors are stimulated when local temperatures differ from body temperature.

Some thermoreceptors are sensitive to just cold and others to just heat.