Exam 1 Week 2: ppt 5 Generator/Receptor Potentials Flashcards
What is a Receptor (generator) potential?
A change in the membrane potential of a sensory receptor in response to the application of its adequate stimulus. Generator potentials may be depolarizing or hyperpolarizing and may be produced directly by stimulus-gated ion channels or indirectly by G-protein coupled processes, depending on the receptor type.
What does a receptor (generator) potential do?
Receptor (Generator) Potentials Transduces environmental energy into an electrical change that encodes the relevant information about the environmental stimulus. Each receptor has Receptor specificity: Transduction between specific forms of energy to electrical potentials.
what type of receptors are the most common?
The most common receptors are mechanoreceptors which convert Mechanical to electrical These include receptors for touch, pain, balance, auditory and baroreceptors.
What are four types of receptors (based on what type of environmental energy they transduce into electrical energy)?
- Mechanical to electrical (touch, pain, balance, baroreceptors)
- Chemical to electrical (respiratory chemoreceptors & perhaps some pain reception)
- Thermal to electrical (cold/heat receptors)
- Electromagnetic to electrical (vision)
- Nociceptor – intense of any of mechanical, chemical or polymodal to electrical
What type of ion channels are involved in receptor potential generation?
Modality-gated ion channels
They are membrane spanning channels that connect the extracellular domain with the inside of the cell
What are mechanoreceptors?
Mechanoreceptors are receptors at the end of sensory nerve axons.
They may have specialized structures or none associated with the ending but all involve the physical deformation of ending
Activation of the receptor produces a _____________which occurs as a result of _____________.
Activation of the receptor produces a **depolarizing generator (receptor) potential ** which occurs as a result of increased ionic Na+ permeability
Are generator potentials graded or All or None?
graded
Using mechanoreceptors as an example:
The larger the mechanical deformation the greater the the opening of the channels and the greater the amount of Na+ that enters the ending. So the larger the mechanical deformation the greater the depolarization
where are generator potentials usually restricted to?
the “receptor” region of the nerve ending
are generator potentials propigated or do they decay as you get further away from the generation site?
Generator potentials are restricted to the “receptor” region of the nerve ending – nonpropagated and they Decay in amplitude as it spreads away from generation site
what is stimulus coding?
Any sensed characteristics of a stimulus must be coded, such as:
Modality of stimulus
Intensity or strength of stimulus
Duration & pattern of stimulus
what is modality coding?
Modality Coding – that is what sensation is being sensed is due at least in part to the Variety of sensory receptors & each type of receptor is most sensitive to a single kind of stimulus energy – a phenomenon which is sometimes called the Doctrine of Specific Nerve Energies
Receptors are connected to specific CNS pathways. These pathways in turn are responsible for activating specific brain regions and producing specific perceived sensations. This is sometimes called the Law of Labeled lines.
(Now if these pathways go to several different brain regions rather than just the one – the input may result in several different types of sensation so touch may give rise not just to the sense of touch but a person may see colors or hear sounds when they touch something – this would be a condition known as synesthesia. Although somewhat rare, a relatively common form of synesthsia seen in musicians is seeing colors when a tone is played. Gives a whole new meaning to the phrase “singing the blues”)
what is the
Doctrine of Specific Nerve Energies?
a phenomonon where there is a variety of sensory receptors and each receptor time is most sensitive to a single kind of stimulus energy.
what is the
Law of Labeled lines?
part of modality coding of sensors
Receptors are connected to specific CNS pathways, activating specific brain regions and producing specific perceived sensations
The Doctrine of Specific Nerve Energies
and
The Law of Labeled Lines
are both part of what?
Modality coding
(a type of modality coding)
Modality Coding – that is what sensation is being sensed is due at least in part to the Variety of sensory receptors & each type of receptor is most sensitive to a single kind of stimulus energy – a phenomenon which is sometimes called the Doctrine of Specific Nerve Energies. Receptors are connected to specific CNS pathways. These pathways in turn are responsible for activating specific brain regions and producing specific perceived sensations. This is sometimes called the Law of Labeled lines. Now if these pathways go to several different brain regions rather than just the one – the input may result in several different types of sensation so touch may give rise not just to the sense of touch but a person may see colors or hear sounds when they touch something – this would be a condition known as synesthesia. Although somewhat rare, a relatively common form of synesthsia seen in musicians is seeing colors when a tone is played. Gives a whole new meaning to the phrase “singing the blues”
what is
Intensity coding?
Generator potentials cannot be transmitted more than a few hundred microns so the signal must be converted to action potentials for conduction over distances. This Conversion occurs in the spike-generating region right next to the site where the generator potentials are produced.
(In the spike generating region the amplitude modulated generator potential has its signal converted to frequency modulated action potentials (action potentials are all or none and cannot vary in amplitude. So we have what some refer to as an AM to FM conversion.)
Intensity Coding:
Action potential (spike) frequency is ________ related to the magnitude of the stimulus.
linearly
Explain adaption in regards to receptors, generator potential, and action potential.
receptors have what is called Adaptation. With a sustained applied stimulus to the receptor there is a Decrease in the generator potential and a decrease in action potential firing rate even though the stimulus is sustained at a constant level
What are the two categories of receptors in regards to adaptation to a constant stimulus? Describe them
- Fast adapting receptors – Receptor Potential falls rapidly to 0 with a maintained stimulus but Receptor potential reoccurs when the stimulus is released
- Slowly adapting receptors – maintain a Graded Potential response throughout the duration of the stimulus
How is the slow and fast adapting receptors reflected in action potential behavior?
- In rapidly adapting receptors (the top image), both the beginning and ending of a stimulus is marked by a burst of action potentials with no activity between those points reflecting the receptor potentials seen at the beginning and end of the applied stimulus.
- In slowly adapting receptors (the lower recording), there is a decline in action potential frequency during the maintained stimulus reflection the decline in the receptor potential. And there is a cessation of action potential activity or a precipitous decline in that activity signals the end of the stimulus just as there is an end to the receptor potential at that point.
