Auditory and Vestibular Systems: Sensory Perception and Pathways Explored

1. Psychology 210 Lecture 5 Kevin R Smith

2. Today • The Auditory system • The Somatosensory system • The chemical systems

3. Properties of sounds • Sounds are waves • Amplitude: loudness • Frequency: pitch

4. Audible Sound

5. The ear

6. The ear • Outer ear • Pinna • Auditory canal

7. Anatomy of the ear • Middle ear • Tympanic membrane: Ear drum • Oscicles • Malleus (Hammer) • Incus (Anvil) • Stapes (Stirrup) • Oval Window

8. Anatomy of the ear • Inner ear • Semicircular canals • Cochlea • Basilar membrane • Hair cells

9. The basilar membrane • Hair cells translate vibrations from the sound waves into frequencies • Higher pitches are processed closer to the base • Lower pitches are processed closer to the apex • Tonotopic organization

10. The hair cells move Opens Ca channels Leads to the perception of a signal Different hair cells move depending on the frequency of the incoming sound Transduction

11. Hair cells • Hair cell damage • Noise, infections, genetic diseases, aging • Higher frequencies are harder to hear as you age • Regeneration • Can occur in birds and some invertebrates • Generally does not occur in humans

12. The Pathway to the brain • The auditory nerve • Cochlear nucleus • Superior olivary nucleus • The inferior colliculus • Thalamus (medial geniculate nucleus) • Primary auditory cortex

13. In the superior olivary nucleus • Information from the ears is first combined here • May have some role in localization of sounds • Tonotopically organized

14. Organization of the MGN • Similar to the LGN for vision • Different layers have different inputs • Tuning curves become more specific • Tonotopically organized

15. Organization of A1 • Tonotopically organized • Just like the cochlea, superior olivary nucleus, and MGN, different tones are processed in different locations

16. After A1 • Like vision: A2, A3, A4… • Two pathways • Dorsal “where” pathway • Ventral “what” pathway • Researchers try and relate auditory systems to visual systems • Some similarities have been found, but nothing is certain

17. Is the auditory system contralaterally organized? • Somewhat • 80% of incoming information into each auditory cortex is from the contralateral ear and 20% is from the ipsilateral ear • Why the combining of the incoming information from the two ears?

18. Spatial cues • We need information from both ears to locate where a sound is in space • Two main cues • Interaural intensity (level) difference (IID or ILD) • Interaural time difference (ITD) • Also our pinna provides information about how vertical a sound is

19. Interaural Intensity Differences • The ear that is closer to the sound hears a louder sound than the ear that is farther from the sound • The difference in loudness here is a difference in intensity • Our head provides a shadow effect over the far ear • Based upon the difference in intensity, our brain can calculate where the sound was

20. Interaural Time Differences • The ear that is closer to the sound hears the sound earlier than the ear that is farther from the sound • Based upon the difference in time, our brain can calculate where in space the sound was

21. IIDs and ITDs

22. IIDs and ITDs • Only provide information about where a sound is along the horizontal • We use our pinnas to locate where a sound is vertically • Head related transfer functions

23. Changing the shape of the pinna change localization abilities Eventually subjects learn to localize sounds properly Interesting Note

24. The somatosensory system • The Vestibular System • Touch • Temperature • Pain

25. The Vestibular System • Fluid filled cavaties • Semicircular canals • Otoliths • Saccule • Utricle • Found near the ear and auditory structures

26. How the vestibular system works • Fluid filled cavities • Contain hair cells • Sensitive to direction of movement • Either hyperpolarize or depolarize • Provide information about the location in space of the head • Semicircular canals • Provide more information about the rotation of the head

27. How the vestibular system works

28. Pathway to the brain • Auditory nerve • Pons, medulla, cerebellum • Vestibular nuclei • Ventral posterior thalamus • Primary somatosensory cortex and primary motor cortex

29. The vestibular system • Information is highly integrated with information from the visual cortex • Also, projects to the spinal cord for feedback regarding posture

30. Touch • The Sensory inputs • Meissner’s corpuscles • Pacinian corpuscles • Merkel’s disks • Ruffini’s endings • Free nerve distributions • Hair follicle receptors

31. Differences between receptors • Size of receptive field • Small • Meissner’s corpuscles • Merkel’s disks • Large • Pacinian corpuscles • Ruffini’s endings

32. Differences between receptors • Rate of adaptation • Fast • Meissner’s corpuscles • Pacinian corpuscles • Slow • Merkel’s disks • Ruffini’s endings

33. Differences between receptors • Location • Shallow in the skin • Meissner’s corpuscles • Merkel’s disks • Deep in the skin (digestive tracts, joints) • Pacinian corpuscles • Ruffini’s endings

34. Differences between receptors • Type of information processed • Pressure • Meissner’s corpuscles • Merkel’s disks • Pressure and vibrations • Pacinian corpuscles • Stretch • Ruffini’s endings • Pain and temperature • Free nerve endings

35. Meissner’s Corpuscles

36. Pacinian corpuscles

37. Pathway to the brain • Spinal cord • Medial lemniscus • Ventral posterior nucleus of the thalamus • S1

39. Organization of S1 • Somatotopically organized • Cortical magnification • The amount of cortex devoted to your hand is more than the amount of cortex devoted to your torso, even though your torso is larger • Why?

40. Somatotopy • Your hand is much more sensitive to touch than your back • Same with face, mouth, eyes, etc…

41. Homunculus

42. Other types of receptors • Free Nerve Ending Receptors • Thermoreceptors • Respond to warmth or cold • Nociceptors • Respond to mechanical pain, extreme heat, or both

43. The chemical senses • Senses that use chemical receptors • Olfaction: Smell • Olfactory epithelium detects molecules in the air • Taste • Saliva dissolves food into molecules

44. Smelling….. • 1000 different smell receptors • Each receptor detects a broad range of smells • Based upon the combination of activity from the receptors, our brain constructs the smell

45. The olfactory system • The nose • Olfactory epithelium • Olfactory receptor cells synapse onto olfactory nerves within the olfactory bulb

46. The olfactory system • Pathway to the brain • Olfactory bulb axons form the olfactory tract • Olfactory cortex • Thalamus: Medial dorsal nucleus • Projects to all over the brain • Various frontal areas

48. Taste • The tongue • Four different taste buds • Sweet, sour, salty, bitter • Umami: savory • Possibly a fifth type of taste bud • Papilla • Bumps on the tongue • Each contains up to 100 taste buds

49. The Tongue

50. Pathway to the brain • Tongue: taste fibers – cranial nerves –Thalamus: ventral posterior medial nucleus – parietal lobe