2. Receptor potential

3. Learning Objectives of this class
Concept of labeled line principle
Explain the receptor potential with reference to pacinian corpuscle
Describe the mechanism of adaptation of receptors

5. Labeled line principle
Receptor
Stimulation
Impulse
Nerve
Brain
Touch Pain Temp

6. Receptor Potentials All sensory receptors have one feature in common.
Whatever the type of stimulus excites
Change in electrical potential of the receptor.
This change in potential is called a Receptor potential.

7. Mechanisms of Receptor Potentials.
By mechanical deformation
Stretches the receptor membrane
Opens ion channels
By application of a chemical
By change of the temperature of the membrane
Alters the permeability of the membrane
By the effects of electromagnetic radiation, such as light
Allows ions to move
Basic cause of the change in membrane potential is a change in membrane permeability of the receptor

8. Maximum Receptor Potential Amplitude.
The maximum amplitude of most sensory receptor potentials
100 millivolts
Change in voltage when the membrane - maximally permeable to sodium ions.
When the receptor potential rises above the threshold for eliciting action potentials
Action potentials occur
More the receptor potential rises above the threshold level - Greater - action potential frequency

10. Pacinian Corpuscle Central nerve fiber extending through its core.
Surrounding – multiple concentric capsule layers
Compression anywhere on the outside of the corpuscle will
Elongate,
Indent or
Deform the central fiber

11. Central fiber of the pacinian corpuscle
The tip of the central fiber - unmyelinated
The fiber - Myelinated
Deformed by compression
Sodium influx - a local circuit of current flow
Node of Ranvier, typical action potentials transmitted

12. Relation Between Stimulus Intensity and the Receptor Potential.
Very intense stimulation
Progressively less and less additional increase in numbers of action potentials
Allows the receptors to have an extreme range of response,
From very weak
To very intense

14. Adaptation of Receptors
Receptors adapt either partially or completely to any constant stimulus after a period of time.
When a continuous sensory stimulus is applied,
The receptor responds at a high impulse rate at first
Then progressively slower rate until
Finally the rate of action potentials decreases to very few
To ………… none at all.

15. Adaptation of different types of receptors
Some sensory receptors adapt to a far greater extent than others
Mechanoreceptors adapt almost completely
Nonmechanoreceptors
Chemoreceptors
Pain receptors,
never adapt completely.

16. Mechanism of Receptor adaptation
Studied in greatest detail - pacinian corpuscle.
Readjustments - structure of the receptor
Pacinian corpuscle is a viscoelastic structure
Distorting force - transmitted by the viscous component
Elicit a receptor potential.
Within a few 100ths of a second- fluid within the corpuscle redistributes
Electrical type of accommodation
Progressive “inactivation” of the sodium channels

17. Slowly Adapting Receptors
Detect Continuous Stimulus Strength
The “Tonic” Receptors.
Continue to transmit impulses to the brain as long as the stimulus is present/hours.
Keep the brain constantly apprised of the status of the body and its relation to its surroundings.
Golgi tendon apparatuses
Macula in the vestibular apparatus
Baroreceptors and chemoreceptors

18. Rapidly Adapting Receptors -Imp
Detect Change in Stimulus Strength
The Rate / Movement / Phasic Receptors
Cannot be used to transmit a continuous signal
React strongly while a change is actually taking place.
Pacinian
Sudden pressure applied to the tissue excites this receptor for a few milliseconds
Transmits a signal again when the pressure is released….
Importance

19. Learning Objectives were
Concept of labeled line principle
Explain the receptor potential with reference to pacinian corpuscle
Describe the mechanism of adaptation of receptors

20. Thank You