Sensory Systems

1. Sensory Systems Inputs to the Nervous System

2. Oh, I forgot to mention… • a postsynaptic membrane integrates synaptic inputs • a nerve impulse (action potential) is all-or-none • membrane depolarization must reach a threshold • firing of an action potential depends on the sum of all incoming information • hyperpolarizing neurotransmitters cause an inhibitory post-synaptic potential (IPSP) • an axon hillock receives EPSP/IPSP from all dendrites and the cell body

3. >post-synaptic signal integration >many post-synaptic potentials influence the firing of an action potentialFigure 44.15 spatial summation temporal summation

4. Sensory Systems • sensory cells respond to stimuli • perceive stimuli through membrane proteins • detect stimuli • alter membrane ion permeability • transduce stimuli into action potentials • directly (modified neurons) • indirectly (cells associated with neurons) • encode the intensity of the stimulus by the action potential frequency

5. membrane proteins in sensorsFigure 45.1

6. Sensory cell stimulation neuronal sensor of muscle stretching Figure 45.2

7. Sensory Systems • sensory organs • sensor cells combine with other cells to enhance • collection • filtering • amplification

8. Sensory Systems • sensory transduction • a sensory cell receptor protein is activated • the receptor opens or closes ion channels • direct or indirect • changed potential = receptor potential • a generator potential fires an action potential in a sensory neuron • or, the receptor potential causes release of neurotransmitterin a non-neuronal cell

9. alternate signal generation pathsin differenttypes of sensorycells

10. Sensory Systems • sensation depends on the CNS • different sensors/different parts of the CNS • visual, auditory, olfactory • specific pathways transmit sensory signals • homeostatic sensors produce internal signals • signals are received and processed by CNS • signals don’t produce conscious sensation

11. Sensory Systems • receptor adaptation to repeated stimulation • allows animal to ignore background data • remains responsive to changes or new data • adaptation rates/capacities vary in different receptors

12. female silkworm moth, Bombyx sp. male silkworm moth, Bombyx sp.Figure 45.3

13. Sensory Systems • Chemoreceptors - specific molecular stimuli • pheromonal signals in arthropod sexual attraction • female moths release a species-specific pheromone • male moths perceive the signal through chemosensory antennae hairs • male moths fly up the concentration gradient of pheromone

14. Sensory Systems • Chemoreceptors - specific molecular stimuli • olfaction - the sense of smell • neuronal sensors in the nasal cavity • dendrites extend receptors into the mucus layer of nasal epithelium • axons extend to the olfactory bulb above the nasal cavity

15. LocationFigure 45.4

16. OrganizationFigure 45.4

17. Sensory Systems • Chemoreceptors - specific molecular stimuli • olfaction - sense of smell • odorant binds the matching receptor • a the receptor activates a G protein • the G protein activates adenylyl cyclase • cAMP opens gated Na+ channels • depolarization causes an action potential • intensity number of action potentials

18. Taste Pore of taste budFigure 45.5

19. taste sensors and associated sensory neuronsFigure 45.5

20. Sensory Systems • Chemoreceptors - specific molecular stimuli • gustation - sense of taste • sensors are clustered in “taste buds” • taste buds are in the tongue epithelium • taste pores expose sensory microvilli to the mouth’s contents • sensory cells form synapses with associated sensory neurons • sensory neuron fires an action potential

21. Sensory Systems • Mechanoreceptors - membrane distortion • conscious sensations • touch, tickle, pressure • hearing • homeostatic monitoring • stretch in muscle, tendon, ligament • stretch in blood vessel • hair movement

22. Sensory Systems • Mechanoreceptors - membrane distortion • membrane distortion opens channels • the membrane potential changes • the membrane fires an action potential • stimulus strength determines the rate of action potentials

23. some skin mechanoreceptorsFigure 45.6 fast slow slow fast

24. Sensory Systems • Mechanoreceptors • muscle spindles • detect muscle stretching • associated neurons fire action potentials • motor neurons stimulate contraction • Golgi tendon organs • monitor force of muscle contraction • associated neurons fire action potentials • inhibit motor neuron; relax muscle

25. stretch sensors participate in muscle contraction, relaxationFigure 45.7

26. Sensory Systems • Mechanoreceptors • hair cells • microvilli project from the cell body • displacement of hair produces receptor potential • depolarization to threshold releases neurotransmitter • sensory neuron fires action potentials

27. lateral line system of fishFigure 45.8

28. semicircular canal systemFigure 45.9

29. Sensory Systems • vertebrate equilibrium organs • semicircular canals • right angles to each other • contain cupules • register direction of head movement • vestibule • otoliths positioned on gelatinous matrix • body movement displaces microvilli

30. otoliths in the vestibular apparatusFigure 45.9

31. pressure waves to vibrations to pressure wavesFigure 45.10

32. cochlear canalsFigure 45.10

33. Sensory Systems • auditory system - hearing • transduces pressure waves into action potentials • tympanic membrane vibrates • ossicles amplify vibration to oval window • oval window makes waves in cochlear canal • waves displace basilar membrane • hairs are displaced in organ of Corti • auditory nerve fires action potentials

34. source of pitchin the auditory systemFigure 45.11

35. retinal isomerizationFigure 45.12

36. a rod cell: a modified neuron, sensitive to lightFigure 45.13 location of rhodopsin

37. light absorption causes membrane hyperpolarizationFigure 45.13

38. Sensory Systems • photosensitivity and sight • rhodopsin receptors • opsin + 11-cis-retinal • in membrane of photoreceptor cell • isomerized by light absorption to all-trans-retinal • causes opsin conformational change • excited rhodopsin hyperpolarizes cell • neurotransmitter release decreases

39. pathway of hyperpolarization in a rod cellFigure 45.14

40. Sensory Systems • photosensitivity and sight • flatworms detect differences in light intensity using rhodopsin • arthropods use clusters of ommatidia in their compound eyes • retinula cells in the ommatidia contain rhodopsin

41. components of a compound eyeFigure 45.15

42. Figure 45.18Rods & Cones Absorb Different Wavelengths of Light

43. Sensory Systems • vertebrate eye • the retina is the site of • light absorption • signal processing • the retina contains • rods - light perception • cones - color perception • the fovea contains highest density of receptors • the blind spot lacks receptors

44. Human EyeFigure 45.16

45. focusing the mammalian eyeFigure 45.17

46. retinal structure in the human eyeFigure 45.20

47. Sensory Systems • vertebrate eye • receptors are deep in the retina • receptors synapse with • bipolar cells • horizontal cells • bipolar cells synapse with • ganglion cells • amacrine cells • ganglion cell axons form the optic nerve

48. measure ganglion signalsFigure 45.21

49. Sensory Systems • vertebrate eye • 100,000,000 receptors • 1,000,000 ganglion cells • a ganglion cell receives and processes information from its receptive field of receptors • receptive fields include center & surround • receptive fields are on-center or off-center

50. ganglion signals in response to lightFigure 45.21