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Physiology · Structural and functional organization of analyzers

Classification and mechanisms of receptor action

Sensory receptors are specialized structures that perceive stimuli and convert them into nerve impulses. They differ by the nature of the adequate stimulus, location, and signal transmission mechanism, ensuring the connection of the body with the external and internal environment.

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TransductionThe process of converting a stimulus into an adequate receptor response
Receptive fieldA group of receptors connected to the branches of a single nerve fiber
AdaptationReceptors can be rapidly adapting, slowly adapting, or non-adapting
2 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Principles of receptor classification

Sensory receptors can be divided into groups according to several key criteria:

  • By type of adequate stimulus: mechanoreceptors, photoreceptors, thermoreceptors, chemoreceptors, nociceptors.
  • By number of perceived stimuli: monomodal (one type of stimulus), bimodal, trimodal, and polymodal.
  • By localization: exteroreceptors (sense organs, contact with the external environment), interoreceptors (internal organs), and proprioceptors (musculoskeletal system).
  • By excitation threshold: low-threshold and high-threshold.
  • By adaptation rate: rapidly adapting (e.g., Pacinian corpuscles), slowly adapting (proprioceptors), and non-adapting (vestibular).

Mechanisms of action: primary sensory receptors

In primary sensory receptors (e.g., Pacinian corpuscle), the signal perception process occurs directly. The stimulus acts directly on the membrane of the nerve ending.

This leads to an increase in membrane permeability, primarily for sodium ions ($Na^+$). As a result of the local ionic shift, a receptor potential is generated. This potential causes rapid structural changes in the tubulin protein in electrogenic zones, which alters membrane permeability and triggers the generation of an action potential (AP). The AP then propagates along the nerve fiber to the central nervous system.

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Mechanisms of action: secondary sensory receptors

Unlike primary receptors, secondary sensory receptors (e.g., hair cells of the organ of Corti) have a specialized intermediary cell.

The signal transmission process here is more complex:

  1. The stimulus acts on the membrane of the specialized receptor cell.
  2. Ionic permeability changes, and a receptor potential arises inside this cell.
  3. The excited cell releases a chemical messenger — a neurotransmitter.
  4. The neurotransmitter acts on the postsynaptic membrane of the afferent sensory fiber.
  5. A generator (postsynaptic) potential arises in the nerve fiber.
  6. Based on the generator potential (involving changes in the tubulin protein), an action potential is formed and sent to the CNS.

Briefly: answers to topical questions

What specific structures and organs belong to proprioceptors?

Proprioceptors include receptors of the musculoskeletal system, specifically muscle and joint receptors.

In spinal reflex arcs, the following receptor structures are distinguished:

  • Muscle spindle — responds to muscle stretch.
  • Golgi tendon organ — located in series with muscle fibers and responds to strong muscle tension, for example, during active contraction or extreme stretch.

Class and exam questions

What is the main difference between primary and secondary sensory receptors?

In primary sensory receptors, the stimulus acts directly on the nerve ending, where the action potential arises. In secondary receptors, there is an additional link — a specialized receptor cell that perceives the stimulus and transmits the signal to the nerve fiber using a neurotransmitter.

What is a receptor potential?

This is a local change in membrane potential at the site of stimulus action. In primary receptors, it arises directly in the nerve ending, and in secondary receptors, in a specialized receptor cell.

What is the role of tubulin in nerve impulse generation?

Changes in the structure of the tubulin protein affect the state of membrane receptors associated with it, which alters the excitability of the sensory neuron membrane and leads to the generation of an action potential.

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What else to study on this topic

  • Detailed mechanism of transduction in different receptor types
  • Properties of the receptive field and spatial summation
  • Molecular basis of mechanoreceptor function (Pacinian corpuscles)
  • The role of neurotransmitters in secondary sensory receptors
  • Interaction of tubulin with ion channels

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Other topics in the section «Structural and functional organization of analyzers»

Structural and functional organization of analyzersAfferentation: situational, triggering, and feedbackStructure of the analyzer according to I.P. PavlovProperties of receptorsConductive and central divisions of analyzersThresholds and laws of perception
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