1. Today –Sensory receptors General properties –Skin receptors

2. Sensory receptors Vision Taste Smell Hearing Touch Internal –Proprioception - limb position and movement –Baroreceptors - blood pressure –Osmoreceptors - osmolarity –Chemoreceptors – chemical concentration Chemical Mechanical Light

3. Sensory receptors General Properties: 1.Specialized structures to receive sensory information 2.Amplification and Transduction of sensory stimuli to electrical activity 3.Coding of information by the number and frequency of APs

4. Types of Sensory Neurons Sensory receptor Spike Initiating Zone Action Potentials

5. Chemical synapse Action Potentials Sensory receptor Spike Initiating Zone

6. Stimulus reaches receptor cells Activation of receptors Protein interactions & Second messengers Ion channels open or close Generates a receptor current Changes in Vm Spread to spike initiating zone Changes in the amount of neurotransmitter release Influence number and frequency of APs in sensory neuron Sensory Energy Electrical Energy Graded Events All or none APs Sensory Reception Cascade

7. Common Physiological Properties Dynamic Range –The range of stimulus intensity the sensory system can respond to Adaptation 1.Phasic receptors Fire APs for only one part of stimulus 2.Tonic receptors Fire APs for duration of stimulus

8. Dynamic Range Frequency of APs (Hz) Log Stimulus Intensity 110100100010,000 Sensory receptor responds in this range Upper limit set by refractory period Threshold for detection Sensory receptor can’t respond further

9. How to overcome limited range? For each type of receptor, there are individual receptors specialized to respond to specific parts of the range Log Stimulus Intensity 110100100010,000 Range of the whole sensory system Frequency of APs (Hz) Range of individual receptors

10. Receptors of the skin Pacinian CorpuscleDeep touch Meissner’s CorpuscleLight touch Ruffini’s Corpusclestretching Free nerve endingspain & temperature

11. Pain –Nociceptors –respond to painful stimulus –Carried by non-myelinated C fiber sensory neurons –Painful heat, acids, mechanical damage all activate non-specific cation channels

12. Na + Ca ++ Painful heat Acids Mechanical damage Substances released from Damaged cells: ATP Bradykinin Substance P Pain Free nerve ending

13. Receptors of the Skin Tactile sensory input –Respond to pressure and movement of skin –Specialized receptors that respond to particular types of inputs Pacinian – heavy pressure, rapid vibration (300Hz) Meissner’s – light pressure, slow vibration (50 Hz) Use mechanically gated ion channels

14. Pacinian Corpuscle Mechanical Stimulus Fluid filled layers Extracellular recording Nerve axon Saline bath

15. Mechanical stimulus Opens ion channels Receptor currents flow passively within axon If receptor potential is large enough APs produced axon myelin First Node Of Ranvier

16. Pacinian Corpuscle Example of a rapidly adapting receptor –Only gives an ‘on’ and an ‘off’ response –Epithelial layers filter out steady pressure but transfer rapid changes in pressure

17. Receptive Field The region of the skin in which a stimulus evokes a response in a single sensory neuron Discrimination depends on the density of receptors Fingers 1-4 mm Thigh 45 mm

18. skin Sensory neuron dendrites Sensory neuron dendrites AP generated in one neuron AP generated in two different neurons

19. Good Luck!