The Nature of Sound

1. Sound- any audible vibration of molecules;they can be transmitted through liquids, solids and gases, but not sound will not travel in a vacuum.. Soundwaves are energy waves that are Sine waves ( have a crest and a trough) One wavelength is from peak of crest to the peak of another crest. The Nature of Sound

2. Pitch- is whether a sound is “high” or “low” and is based on the frequency of wavelength. Frequency is inversely proportionate to size of wavelength. Frequency is a function of frequency or directly proportionate to frequency. Q: Which figure on left, top or bottom, would have the have the higher sounding pitch? All about Pitch

3. Properties of Sound • Ear detects pressure waves • Amplitude of waves corresponds to perceived loudness • Frequency of waves (number per second) corresponds to perceived pitch

4. Pitch and Loudness • Pitch - frequency vibrates specific parts of ear • hearing range is 20 (low pitch) - 20,000 Hz (cycles/sec) • speech is 1500-4000 where hearing is most sensitive • Loudness – amplitude; intensity of sound energy

5. Fooled The Teacher Again • Beyond a certain age around 17 or so, most people cannot hear sounds higher than 13 KHz (13,000 Hz). There is a set of frequencies (around 15 kHz) an astute teen set his cell phone ringer to so his teacher would hear it.

6. Classification of Receptors • By modality: • chemo-, thermo-, mechano-, photo- receptors and nociceptors • By origin of stimuli • interoceptors - detect internal stimuli • proprioceptors - sense body position and movements • exteroceptors - detect external stimuli • By distribution • general senses - widely distributed • special senses - limited to head

7. Balance and Equilibrium • In humans, organs of equilibrium are located in the inner ear • Vestibular apparatus

8. The Ear • Houses two senses • Hearing • Equilibrium (balance) • Receptors are mechanoreceptors

9. Mechanoreceptor is a Sensory Receptor WHICH IS… • Sensory Receptors- Take sensory information from the environment ; it is transduced into nerve impulses in the CNS. • The Ear is an organ that contains mechanoreceptors, receptors that can detect sound waves and the transducer. • Transduced sound waves (pressure waves) can be interpreted ONLY by AUDITORY CORTEX.

10. Specialized Areas of the Cerebrum Figure 7.13c

11. Anatomy of Human Ear oval window (behind stirrup) MIDDLE EAR BONES: stirrup auditory nerve anvil hammer auditory canal round window EARDRUM COCHLEA

12. Anatomy of the Ear • The ear is divided into three areas • Outer (external) ear • Middle ear • Inner ear Figure 8.12

13. The External Ear • Involved in hearing only • Structures of the external ear • Pinna (auricle) • External auditory canal Figure 8.12

14. Sound Reception • Sound waves make the eardrum vibrate • Vibrations are transmitted to the bones of the middle ear • The stirrup transmits force to the oval window of the fluid-filled cochlea

15. The Middle Ear or Tympanic Cavity • Two tubes are associated with the ear • The opening from the auditory canal is covered by the tympanic membrane • The auditory tube connecting the middle ear with the throat (Eustachian Tube)(Yoo station) • Allows for equalizing pressure during yawning or swallowing • This tube is otherwise collapsed

16. Inner Ear or Bony Labyrinth • Includes sense organs for hearing and balance • Filled with perilymph Figure 8.12

17. Bones of the Tympanic Cavity • Three bones span the cavity • Malleus (hammer) • Incus (anvil) • Stapes (stirrip) Figure 8.12

18. Inner Ear or Bony Labyrinth • A maze of bony chambers within the temporal bone • Cochlea • Vestibule • Semicircular canals Figure 8.12

19. Sound Reception • Movement of oval window causes waves in the fluid inside cochlea ducts

20. Sound Reception • Fluid movement is sensed by the organ of Corti • Hair cells are bent against overlying tectorial membrane and fire

23. Physiology of Hearing - Middle Ear • Tympanic membrane • has 18 times area of oval window • ossicles transmit enough force/unit area at oval window to vibrate endolymph in scala vestibuli • (Endolymph differs from perilymph; very conc. In K+ ions.) • Tympanic reflex – muscle contraction

24. Cochlear Hair Cells • Stereocilia of OHCs • bathed in high K+ • creating electrochemical gradient • tips embedded in tectorial membrane • bend in response to movement of basilar membrane • pulls on tip links and opens ion channels • K+ flows in – depolarization causes release of neurotransmitter • stimulates sensory dendrites at base

25. Stimulation of Cochlear Hair Cells • Vibration of ossicles causes vibration of basilar membrane under hair cells • as often as 20,000 times/second

26. Sensory Coding • Vigorous vibrations excite more inner hair cells over a larger area • triggers higher frequency of action potentials • brain interprets this as louder sound • Pitch depends on which part of basilar membrane vibrates • at basal end, membrane narrow and stiff • brain interprets signals as high-pitched • at distal end, 5 times wider and more flexible • brain interprets signals as low-pitched

27. Stapes pushes down on perilymph of scala vestibuli Perilymph pushes vestibular membrane down. VM pushes on endolymph of coclear duct BM goes down and up. Secondary tympanic membrane goes out an in Vestibular membrane separates perilymph of scala vestibuli from endolymph of coclear duct. When hair cells embedded in tectorial membrane vibrate in basilar membrane, this bends stereocilia Potassium Channels are opened; This depolarizes cells Action Potential Generated and Neurotransmitters are released. Message is sent to Cochlear Nerve Here’s How We Hear

28. Anatomy of Cochlea • Scala media (cochlear duct) • separated from • scala vestibuli by vestibular membrane • scala tympani by basilar membrane • Spiral organ (organ of corti)

29. Spiral Organ • Stereocilia of hair cells attach to gelatinous tectorial membrane • Inner hair cells • hearing • Outer hair cells • adjust cochlear responses to different frequencies • increase precision

30. Sound Reception • Sound waves make the eardrum vibrate • Vibrations are transmitted to the bones of the middle ear • The stirrup transmits force to the oval window of the fluid-filled cochlea

31. Sound Reception • Movement of oval window causes waves in the fluid inside cochlea ducts

33. Sound Reception • Fluid movement is sensed by the organ of Corti • Hair cells are bent against overlying tectorial membrane and fire

34. Cochlear Hair Cells • Stereocilia of OHCs • bathed in high K+ • creating electrochemical gradient • tips embedded in tectorial membrane • bend in response to movement of basilar membrane • pulls on tip links and opens ion channels • K+ flows in – depolarization causes release of neurotransmitter • stimulates sensory dendrites at base • The tip link is a protein that connects the tip of a steriocilia to an adjacent potassium channel.

35. Leading to Interpretation • The nerve impulse that have generated at the sensory hairs of spiral organ, form the Cochlear nerve which leads away from the cochlear. • This nerve joins the vestibular nerve and together they form the vestibulocochlear nerve or cranial nerve VIII. • The pathway of the neurons here end up in AUDITORY CORTEX. (see next slide) where we can interpret the sounds.

36. Cochlear branch of CN VIII • To inferior colliculus of opposite side of midbrain • To cochlear nucleus of medulla • To thalamus • To auditory cortex

37. What is a “tip-link?” • This is a protein filament that extends from one ion channel of one sterocilium to the sidewall of the steriocilium next to it.

38. Potassium Gates (Which are Mechanical Gates)

39. Sensory Coding • Vigorous vibrations excite more inner hair cells over a larger area • triggers higher frequency of action potentials • brain interprets this as louder sound IF THIS IS TRUE THEN….softer vibrations would excite……_______ and be interpreted by the brain as___________??? • Pitch depends on which part of basilar membrane vibrates • at basal end, membrane narrow and stiff • brain interprets signals as high-pitched • at distal end, 5 times wider and more flexible • brain interprets signals as low-pitched

40. Cochlear Tuning • Increases ability of cochlea to receive some sound frequencies • Outer hair cells contract reducing basilar membranes freedom to vibrate • fewer signals from that area allows brain to distinguish between more and less active areas of cochlea • Pons has inhibitory fibers that synapse near the base of IHCs • increases contrast between regions of cochlea

41. The Reason Ears Were Invented • The original function in evolution? ….Equilibrium, coordination and balance. • The VESTIBULAR APPARATUS : This is where we find Equilibrium Receptors. • Like the hearing “apparatus” in the cochlea the VA has HAIRS too. The hairs work a little differently but the result is the same we get TRANSDUCTION: this time we will transduce motion into nerve impulses. BUT THIS IS THE NEXT LECTURE’s TOPIC…..LATER!

42. The Reason For MY Ears…WHAT DID YOU SAY? • NOT ORIGINALLY for HEARING!! The hairs work a little differently but the result is the same we get TRANSDUCTION: this time we will transduce motion into nerve impulses. BUT THIS IS THE NEXT LECTURE’s TOPIC…..LATER!