Receptor potential

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

Labeled line principle Receptor Stimulation Impulse Nerve Brain Touch Pain Temp

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.

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

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

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

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

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

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.

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.

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

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

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

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

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