Sensory Receptors: Classification and Functions in Perception

1. Classification based on type of information detected by specialized sensory receptors each of which has an adequate stimulus type. • Details not on the exam

2. The Variety of Eyes

3. Do You Hear What I Hear?Evolutionary influence on auditory perception. • Details not on the exam

4. Sensory Receptor Organs Detect Energy or Substances • Sensory receptor organs are organs specialized to detect a certain stimulus. • The doctrine of specific nerve energies says: • Receptors and neural channels for different senses are independent. • Receptor cells within the organ convert the stimulus into an electrical signal a “transduction” process. • Receptor organs are very diverse because they specialize in detecting different types of stimuli in the environment. • An adequate stimulus is the type of stimulus to which a sensory organ is particularly adapted. • photic (light) energy for the eye • mechanical energy for touch

5. For Example: Receptors in Skin are TransducersThey can change mechanical energy into action potentials.

6. The Structure and Function of the Pacinian Corpuscle as an example of transduction of mechanical energy into action potentials

7. Different types of sensory information come in on different pathways, the so called “Labeled Lines” concept illustrated here in the touch system. As shown in Fig. 8.8 it also explains the distinction between auditory, visual, touch, odor and taste.

8. Sensory information is processed through several levels of Sensory Circuits

9. Intensity Coding correlated to amount “intensity” of stimulus detected by the receptors measured by frequency of action potentials. Range fractionation takes place when different cells have different thresholds for firing, over a range of stimulus intensities.

10. Sensory Adaptation occurs even with constant stimulation so frequency of action potentials decreases after an initial high frequency at the onset of the stimulus.

11. Sensory Information Processing Is Selective and AnalyticalThe receptive field is the space in which a stimulus will alter a neuron’s firing rate. The procedures illustrated here are used to record from somatosensory neurons of the cerebral cortex. Changes in the position of the stimulus affect the rate of action potentials. Neuron A responds to touch on a region of the forepaw; neuron B, only a few centimeters away in the somatosensory cortex, responds to stimulation of the tail. The receptive fields of these neurons include an excitatory center and an inhibitory surround, but other neurons have receptive fields with the reverse organization: inhibitory centers and excitatory surrounds.

12. Representation of the Body Surface in Somatosensory Cortex (A) The locations of primary (S1) somatosensory cortex on the lateral surface of the parietal cortex. Secondary somatosensory cortex (S2) is much smaller than S1. (B) The order and size of cortical representations of different regions of skin. Note that information from the various parts of the hand and fingers takes up much more room than does information from the shoulder. (C) The homunculus (literally, “little man”) depicts the body surface with each area drawn in proportion to the size of its representation in the primary somatosensory cortex.

13. The Chemical Senses: Taste and Olfaction • The Human Tongue Discriminates at least Five Basic Tastes • salty, sour, sweet, bitter, umami • Taste receptor cells are located within taste buds on papillae on the tongue. • Taste cells extend cilia into the taste pore to contact tastants. • Chemicals in the Air Elicit Odor Sensations • Flavor is the perception of taste and smell together.

14. A Taste Bud and Taste Receptor Cells

15. Salty and Sour Transduction ***************************************************************************** And Maybe TRPV1 May require PKD2L1 ion channel

16. Sweet and Bitter Transduction ********************************************************************* T2R 30 different types gusducin T1R2 + T1R3

17. Is Oleogustus the sixth taste ? • Criteria for “primary tastes,” including that the sensation: • 1) has ecological consequence • 2) is elicited by a distinctive class of chemicals • 3) stems from activation of specialized receptors • 4) is detected through gustatory nerves and is processed in taste centers • 5) has a quality nonoverlapping with other primary qualities • 6) evokes a behavioral and/or physiological response • Oleogustus “fat taste” is triggered by nonesterified fatty acids (NEFA) • medium and long-chain NEFA • oleic acid, linoleic acid or 9-decenoic acid • have a taste sensation that is distinct from other basic tastes • Oleogustus: The Unique Taste of Fat. Cordelia A. Running, Bruce A. Craig, and Richard D. Mattes. Chemical Senses, 2015, 1–10.

18. Anatomy and Main Pathways of the Human Gustatory System • Details not on the exam

19. Chemicals in the Air Elicit Odor Sensations The sense of smell starts with receptor neurons in the nose-within the olfactory epithelium. Three types of cells in the epithelium: • Receptor neurons • supporting cells • basal cells From the receptor cell an apical dendrite extends to the mucosal surface. Cilia emerge from the dendritic knob. An axon extends from the other end of the receptor cell to the olfactory bulb.

20. Anatomy and Main Pathways of the Human Olfactory System

21. Chemicals in the Air Elicit Odor Sensations • A large number of different odor receptors • Mice have about 1000 different types of receptor proteins • divided into four different subfamilies of about 250 receptors each • Each subfamily of receptors is synthesized in a separate band of the epithelium. See figure 9.27 • humans have approximately 400 different receptor proteins • Each type of olfactory receptor can bind a range of odor molecules • a single odorant molecule may bind to a number of olfactory receptors

22. Steps in Olfactory Sensory Transduction many different types Golf