What is receiving potential and generating potential?

The Nervous System is continuously receiving information about the physical-chemical conditions of the environment and its internal organs. This information is collected by sensory receptors and transformed into nerve stimuli, a process known as sensory transduction. The receiving and generating potentials are the membrane potentials that occur at sensory receptors during this process.

sensory receptors

sensory receptors are nervous system cells highly specialized who are capable of react to certain stimuli and generate nerve impulses. The captured information is sent through afferent pathways to different areas of the central nervous system, where it is processed to craft an answer according to perceived conditions

All sensory stimuli are physical phenomena, for example pressure, temperature or light. Depending on the type of stimulus to which they are sensitive, sensory receptors can be:

  • mechanoreceptors: they respond to the mechanical deformation of the cell itself or of the adjacent tissue. For example, touch receptors, sound receptors, and balance or pressure receptors in blood vessels.
  • thermoreceptors: they respond to variations in temperature, for example the thermoreceptors of the skin.
  • nociceptors: respond to potentially harmful stimuli, both physical and chemical. There are thermal, chemical, and mechanical nociceptors.
  • photoreceptors: respond to light stimuli, for example the rods and cones of the eye.
  • Qimoreceptors: they respond to certain conditions and chemical substances, for example the receptors of smell, taste or glomus cells and peripheral chemoreceptors that detect the concentration of oxygen in the blood.

Sensory receptors can also be classified into primary and secondary:

  • primary recipients: are sensory neuron endings, the neurons themselves respond to physical stimuli. For example, the Meissner corpuscles of the skin.
  • secondary receptors: are specialized cells connected to sensory neurons by synapse. For example the hair cells of the ear.

Transduction and receptor/generator potentials

In the process of sensory transduction, the physical-chemical energy of a stimulus is transformed into an action potential, the basic unit of information in the Nervous System, but before the action potential is produced in the neuron and actually occurs a nerve impulse, the receptor membrane depolarizes, generating potentials known as receptor potential and generator potential.

primary recipients

The transduction process in the primary receptors takes place in a specialized area called sensor. The energy of the sensory stimulus induces a change in the permeability of the membrane in this area, causing voltage-dependent ion channels to open or close, either directly or through intracellular messengers (cAMP, cGMP).

With the opening of the ion channels, a flow of positive charges is produced, which if it is towards the interior, it will produce depolarization (mainly of sodium, Na+), and if it is towards the outside, it will produce hyperpolarization (mainly of K+). This change in membrane potential in the sensor is the receptor potential or receptor potential.

The receptor potential generates an electrical current that spreads from the sensor to the membrane of the neuronal axon. The receiving potential reaching the first node of Ranvier (interruptions in the myelin sheath) is known generator potential and if it is strong enough it will generate an action potential and with it a nerve impulse.

secondary receptors

In secondary sensory receptors, the stimulus is transmitted to the nerve fiber through the synapse with a specialized cell that makes intermediate receiver.

For example, hair cells in the ear have membrane projections that react to the movement of endolymph by opening ion channels. Opening of these channels initiates voltage change until voltage-gated channels open and trigger the receptor potential. Unlike the primary receptors, the receptor potential does not transmit the stimulus directly; in secondary receptors receptor potential triggers release of neurotransmitters to the synaptic space, and it is the neurotransmitters that will generate the action potential in the nerve fiber.

A feature common to all types of sensory receptors is that they can spatially and temporally add potential receptors. This makes it possible for the action potential threshold to be reached faster and for repetitive potentials to be produced as long as the stimulus is maintained.

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