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 speed: 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 excitability and triggers the generation of an action potential (AP). The AP then propagates along the nerve fiber into the central nervous system.
Mechanisms of action: secondary sensory receptors
Unlike primary ones, secondary sensory receptors (e.g., hair cells of the organ of Corti) have a specialized mediator cell.
The signal transmission process here is more complex:
- The stimulus acts on the membrane of the specialized receptor cell.
- Ionic permeability changes, and a receptor potential arises inside this cell.
- The excited cell releases a chemical messenger — a mediator.
- The mediator acts on the postsynaptic membrane of the afferent sensory fiber.
- A generator (postsynaptic) potential arises in the nerve fiber.
- Based on the generator potential (involving changes in the tubulin protein), an action potential is formed, which is sent to the CNS.
Kurz gefasst: Antworten auf Fragen zum Thema
Which specific structures and organs belong to proprioceptors?
Proprioceptors include receptors of the musculoskeletal system, in particular muscle and joint receptors.
The following receptor structures are distinguished in spinal reflex arcs:
- Muscle spindle — responds to muscle stretch.
- Golgi tendon organ — located in series with muscle fibers and responds to high muscle tension, for example during active contraction or extreme stretch.
Fragen aus Vorlesungen und Prüfungen
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 via a mediator.
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, while in secondary receptors, it arises in a specialized receptor cell.
What is the role of tubulin in the generation of a nerve impulse?
Changes in the structure of the tubulin protein affect the state of membrane receptors associated with it, which alters the membrane excitability of the sensory neuron and leads to the generation of an action potential.
Was es zum Thema noch zu wiederholen gibt
- 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 mediators in secondary sensory receptors
- The relationship of tubulin with ion channels
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