Receptors- Definition, Structure & Functions

Receptors: definition, meaning, Functions, Types, Topics

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:52 PM IST

Receptors are specialized structures in the body that detect and respond to various stimuli, such as light, sound, temperature, and chemicals. They are present in sensory organs and play a crucial role in transmitting signals to the nervous system for processing. In this article, receptors, types of receptors, function of receptors, intracellular receptors, and cell surface receptors are discussed. Receptors is a topic of the chapter Neural Control and Coordination in Biology.

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Definition of Receptors
Types of Receptors
Function of Receptors
Intracellular Receptors
Cell Surface Receptors

Receptors: definition, meaning, Functions, Types, Topics

Definition of Receptors

Receptors are highly specialised proteins found either on or inside the cells that change conformation upon specific molecule binding. They form an integral part of physiological processes and mediate interactions between the cell and its environment.

Receptors are proteins that participate in detecting signals, among them hormones, neurotransmitters, and sensory stimuli, and acting accordingly. They allow the cell to respond to the changes and thus maintain homeostasis; they participate in growth, immune responses, and sensing.

Types of Receptors

Receptors can be classified in several ways. Knowing the classifications is associated with the functions and mechanisms connected with the different kinds of receptors.

Classification Based on Location

Cell Surface Receptors: These are present on the plasma membrane and the receptor binds to the extracellular molecules.
Intracellular Receptors: These are present inside the cell and the receptors bind to those molecules which can cross the plasma membrane.

Based on Function

Sensory Receptors: These are sensitive to light, sound, temperature, etc.
Neurotransmitter Receptors: These mediate the actions of neurotransmitters within the nervous system.
Hormone receptors: These bind with the hormone and mediate a diversity of physiological processes.

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Function of Receptors

Protein molecules called receptors that are present in the target cell or on its surface perform a number of tasks, such as:

It controls the binding of cells.
It facilitates the transmission of signals.
It regulates the channels in the membrane.
Additionally, it has a role in immunotherapy and immunological responses.
Cell metabolisms such as growth, division, and death are induced by it.

Intracellular Receptors

The internal receptors include-

Growth factor receptors

Growth factor receptors are crucial for controlling the division, differentiation, and growth of cells. Among the receptors are:

Vascular endothelial growth factor receptors, neurotrophin receptors, fibroblast growth factor receptors, EGF receptors, epidermal growth factor receptors, insulin-like growth factor receptors, PDGF receptors, platelet-derived growth factor receptors, VEGF receptors, and cytokine receptors

Cytokine receptors

Through their ability to react to signals produced by other organelles, cytokine receptors let cells connect with the extracellular environment. Additionally, it plays a role in cell cycle modifications, mediator release, gene expression, etc.

Cell Surface Receptors

The cell surface receptors include-

B Cell Receptors

B cells or B lymphocytes are other names for these cells. They circulate in the blood and lymph after being formed in the bone marrow. A B cell's primary job is to make antibodies that defend the body from invaders or foreign substances. These cells are essential for both the start of allergic reactions and adaptive immunity.

T Cell Receptors

One type of lymphocyte that is produced in the thymus gland is the T cell. They are in charge of clearing the body of infections.

Granulocyte Receptors

During allergies, infections, and asthma, this granule-containing immune cell type helps release enzymes. Three categories of granulocyte receptors exist: White blood cells, including neutrophils, eosinophils, and basophils

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Frequently Asked Questions (FAQs)

1. What is the general role of the receptors in the body?

Receptors detect and respond to a wide range of signals, allowing cells and hence activities to communicate and coordinate in homeostasis maintenance and physiological process regulation.

2. What is the mechanism of action of G Protein-Coupled Receptors?

GPCRs are associated with extra-cellular ligands. The latter triggers associated intra-cellular G proteins. In turn, the latter initiates the execution of downstream signalling pathways and consequent cellular responses.

3. What are cell surface receptors versus intracellular receptors?

Cell-surface receptors stay in the plasma membrane and act through signal molecules outside the cell. In contrast to the intracellular receptors, which are centrally located in the cell, they act through molecules that diffuse freely across the membrane.

4. How do sensory receptors contribute to perception?

Sensory receptors detect environmental stimuli and convert them into electrical impulses interpreted by the nervous system to mediate the perception of touch, temperature, light, sound, and chemicals.

5. What do the hormone receptors of the endocrine system do?

The hormone receptors bind its specific hormone and initiate signal transduction pathways, which then mediate growth, metabolism, reproduction, and many other physiological processes.

6. What is the role of olfactory receptors in our sense of smell?

Olfactory receptors are chemoreceptors located in the upper part of the nasal cavity. They bind to specific odor molecules, triggering electrical signals that are sent to the olfactory bulb in the brain. Different combinations of activated receptors allow us to distinguish between thousands of different odors.

7. How do chemoreceptors contribute to our sense of taste and smell?

Chemoreceptors detect specific chemicals in the environment. In taste buds, they bind to dissolved substances in food, while in the nose, they bind to airborne molecules. This binding triggers electrical signals that the brain interprets as different tastes or smells.

8. How do receptors in the tongue detect different tastes?

Taste receptors (taste buds) on the tongue contain specialized cells that detect five basic tastes: sweet, sour, salty, bitter, and umami. Each taste bud can detect all five tastes, but some are more sensitive to certain tastes than others. The combination of activated taste buds creates our perception of flavor.

9. What is sensory transduction, and how do receptors accomplish it?

Sensory transduction is the process by which receptors convert environmental stimuli into electrical signals (action potentials) that can be interpreted by the nervous system. Receptors accomplish this through various mechanisms, such as opening or closing ion channels, which changes the cell's membrane potential and can trigger an action potential.

10. How do stretch receptors in the lungs contribute to breathing regulation?

Stretch receptors in the lungs detect the degree of lung inflation. When the lungs are fully inflated, these receptors send signals to the brain stem, triggering the switch from inhalation to exhalation. This helps regulate the rhythm and depth of breathing.

11. What are receptors in the context of neural control and coordination?

Receptors are specialized cells or structures that detect and respond to specific stimuli from the environment or within the body. They convert these stimuli into electrical signals (action potentials) that can be processed by the nervous system.

12. What is the difference between a receptor and a sensory neuron?

A receptor is a specialized cell or structure that detects specific stimuli and converts them into electrical signals. A sensory neuron is a nerve cell that transmits these signals from receptors to the central nervous system. In some cases, like with olfactory receptors, the receptor itself is a sensory neuron. In other cases, like with taste receptors, the receptor cell is separate from but closely associated with sensory neurons.

13. How do receptors in plants differ from those in animals?

While plants don't have a nervous system like animals, they do have various receptors that detect environmental stimuli. Plant receptors are typically proteins that can detect light, touch, chemicals, or temperature. Unlike animal receptors, which often generate electrical signals, plant receptors usually trigger chemical signaling cascades that lead to responses such as growth towards light (phototropism) or closing of leaves in response to touch (thigmotropism).

14. What is receptor potentiation, and how does it affect sensory perception?

Receptor potentiation is an increase in receptor sensitivity or responsiveness due to repeated or prolonged stimulation. This can lead to heightened sensory perception. For example, in the olfactory system, repeated exposure to an odor can increase the sensitivity of the receptors to that specific odor, allowing for detection at lower concentrations. This process can be important for adapting to and recognizing important stimuli in our environment.

15. How do receptors in the tongue and nose work together to create the sensation of flavor?

Flavor perception is a combination of taste (gustation) and smell (olfaction):

16. What is the role of receptors in the immune system?

Receptors play a crucial role in the immune system by helping immune cells recognize and respond to potential threats. For example:

17. How do magnetoreceptors work in animals that can sense the Earth's magnetic field?

While not present in humans, some animals have magnetoreceptors that can detect the Earth's magnetic field. These may work through iron-containing crystals in cells that align with the magnetic field or through light-sensitive molecules whose chemical reactions are influenced by the magnetic field. This ability helps in navigation and migration.

18. What is the difference between ionotropic and metabotropic receptors?

Ionotropic receptors are ligand-gated ion channels that open directly in response to a specific molecule binding to them, allowing ions to flow and quickly change the cell's membrane potential. Metabotropic receptors, when activated, trigger a cascade of intracellular signaling molecules, which can lead to various cellular responses, including the opening or closing of ion channels. Metabotropic receptors typically have slower but longer-lasting effects.

19. How do receptors contribute to our sense of balance and spatial orientation?

Balance and spatial orientation rely on input from multiple receptor types:

20. How do receptors contribute to the sense of pain?

Pain sensation involves several types of receptors:

21. What is the role of receptors in reflexes?

Receptors play a crucial role in reflexes by detecting the initial stimulus that triggers the reflex action. For example, stretch receptors in muscles detect sudden stretching, initiating the knee-jerk reflex. The rapid response of these receptors allows for quick, automatic reactions without conscious thought.

22. How do proprioceptors help maintain balance and posture?

Proprioceptors are sensors in muscles, tendons, and joints that provide information about body position and movement. They send this information to the brain and spinal cord, allowing for continuous adjustments to maintain balance and proper posture.

23. What is the role of baroreceptors in blood pressure regulation?

Baroreceptors are pressure sensors located in blood vessels, particularly in the carotid sinus and aortic arch. They detect changes in blood pressure and send signals to the brain, which then adjusts heart rate and blood vessel dilation to maintain proper blood pressure.

24. How do nociceptors detect pain?

Nociceptors are specialized sensory neurons that detect potentially harmful stimuli such as extreme temperatures, intense pressure, or certain chemicals. When activated, they send pain signals to the brain, alerting the body to potential damage.

25. How do receptors in the carotid body help regulate breathing?

The carotid body contains chemoreceptors that detect changes in blood oxygen, carbon dioxide, and pH levels. When these levels become imbalanced (e.g., low oxygen or high CO2), the receptors signal the brain to increase the rate and depth of breathing, helping to maintain proper blood gas levels.

26. What is the function of cold and heat receptors in the skin?

Cold and heat receptors in the skin help regulate body temperature and protect us from extreme temperatures. Cold receptors are activated by temperatures below about 25°C, while heat receptors respond to temperatures above about 43°C. This information is used by the brain to initiate appropriate responses, such as shivering or sweating.

27. What is the role of mechanoreceptors in the inner ear for hearing?

Mechanoreceptors in the inner ear, specifically the hair cells in the cochlea, are crucial for hearing. Sound waves cause the basilar membrane in the cochlea to vibrate, which in turn moves the hair cells. This movement causes ion channels in the hair cells to open, generating electrical signals that are sent to the brain and interpreted as sound.

28. How do osmoreceptors help regulate body fluid balance?

Osmoreceptors in the hypothalamus detect changes in blood osmolarity (concentration of dissolved particles). When activated by increased osmolarity, they trigger thirst and the release of antidiuretic hormone (ADH) to help the body retain water and maintain fluid balance.

29. How do receptors in the cardiovascular system help maintain homeostasis?

The cardiovascular system contains several types of receptors that help maintain homeostasis:

30. How do receptors in the hypothalamus help regulate body temperature?

The hypothalamus contains thermoreceptors that monitor the temperature of blood flowing through it. When these receptors detect a deviation from the set point temperature, they trigger responses to either increase or decrease body temperature. For example, if the blood is too warm, the hypothalamus may initiate sweating and vasodilation. If it's too cold, it may trigger shivering and vasoconstriction.

31. What is the role of receptors in circadian rhythms?

Receptors play a crucial role in circadian rhythms, particularly photoreceptors in the eyes. Specialized retinal ganglion cells containing the photopigment melanopsin detect light levels an

32. How do receptors contribute to our ability to sense the world around us?

Receptors allow us to sense the world by detecting various stimuli such as light, sound, temperature, pressure, and chemicals. They convert these stimuli into electrical signals that our brain can interpret, enabling us to perceive and interact with our environment.

33. What are the five main types of stimuli that receptors can detect?

The five main types of stimuli that receptors can detect are:

34. How do mechanoreceptors work?

Mechanoreceptors detect mechanical pressure or distortion. When pressure is applied to these receptors, it causes ion channels to open, leading to a change in the cell's membrane potential. This change can trigger an action potential if the stimulus is strong enough.

35. What is the difference between exteroceptors and interoceptors?

Exteroceptors detect stimuli from the external environment, such as touch, light, or sound. Interoceptors, on the other hand, detect stimuli from within the body, such as blood pressure, pH levels, or the stretch of internal organs.

36. How do thermoreceptors detect temperature changes?

Thermoreceptors contain temperature-sensitive ion channels that open or close in response to temperature changes. When activated, these channels allow ions to flow, changing the receptor's membrane potential and potentially triggering an action potential.

37. How do receptors differ from regular cells in the body?

Receptors are specialized cells designed to detect specific stimuli, while regular cells perform other functions. Receptors have unique protein structures that allow them to respond to particular types of stimuli and convert them into electrical signals.

38. What is the main function of receptors in the nervous system?

The main function of receptors is to detect changes in the internal or external environment and convert these stimuli into electrical signals that can be interpreted by the nervous system. This process is called transduction.

39. What is the difference between a receptor and an effector in the nervous system?

A receptor detects stimuli and converts them into electrical signals, while an effector is a structure (like a muscle or gland) that carries out a response based on signals from the nervous system. Receptors input information, while effectors output responses.

40. What is the difference between tonic and phasic receptors?

Tonic receptors adapt slowly to a stimulus and continue to send signals as long as the stimulus is present. Phasic receptors adapt quickly and mainly respond to changes in stimuli, sending signals only when the stimulus intensity changes.

41. What is receptor adaptation, and why is it important?

Receptor adaptation is the decrease in receptor response to a constant stimulus over time. It's important because it allows us to focus on new or changing stimuli in our environment while filtering out constant, unchanging stimuli.

42. What is the difference between a primary and secondary receptor cell?

Primary receptor cells are specialized neurons that directly generate action potentials in response to stimuli. Secondary receptor cells are not neurons themselves but stimulate adjacent nerve fibers when activated. For example, hair cells in the ear are secondary receptors, while olfactory neurons are primary receptors.

43. What is the difference between fast-adapting and slow-adapting receptors?

Fast-adapting receptors quickly stop responding to a constant stimulus, making them sensitive to changes. Slow-adapting receptors continue to respond to a constant stimulus over time. This difference allows the nervous system to detect both rapid changes and sustained stimuli.

44. How do receptors in the skin help us distinguish between different textures?

The skin contains various types of mechanoreceptors that respond to different aspects of touch. Meissner's corpuscles detect light touch and texture changes, Merkel's disks sense pressure and texture, and Pacinian corpuscles respond to vibration. The combined input from these receptors allows us to distinguish different textures.

45. How do pheromone receptors work in animals?

Pheromone receptors are specialized chemoreceptors found in many animals but not in humans. They detect specific chemical signals (pheromones) released by other members of the same species. In mammals, these receptors are often located in the vomeronasal organ in the nasal cavity. When pheromones bind to these receptors, they trigger signals that can influence behavior, such as mating or aggression.

46. What is the function of pacinian corpuscles in the skin?

Pacinian corpuscles are rapidly adapting mechanoreceptors found deep in the skin and some internal organs. They are particularly sensitive to vibration and pressure changes. Their onion-like structure allows them to detect the onset and offset of pressure stimuli, making them important for sensing texture and vibrations, such as those produced by tools or musical instruments.

47. What is the role of photoreceptors in vision?

Photoreceptors in the retina of the eye detect light and convert it into electrical signals. There are two types: rods (for low-light vision) and cones (for color vision and detail). These cells initiate the visual processing pathway that allows us to see.

48. What is the role of hair cells in hearing and balance?

Hair cells are specialized mechanoreceptors found in the inner ear. In the cochlea, they detect sound vibrations and convert them into electrical signals for hearing. In the vestibular system, they detect head movements and position, contributing to our sense of balance.

49. How do receptors in the retina adapt to different light levels?

The retina contains two types of photoreceptors: rods (for low light) and cones (for bright light and color). In low light, rods become more sensitive. In bright light, cones take over, and a pigment in rods bleaches, reducing their sensitivity. This allows adaptation to a wide range of light intensities.

50. How do receptors in the retina contribute to color vision?

Color vision is primarily mediated by cone photoreceptors in the retina. There are three types of cones, each sensitive to different wavelengths of light: