1. Hearing Maddie, Emma, Kelly, Meg Underlined words… guided notes FITB
Bold… vocab

2. Equilibrium sensations – inform us of the position of the head in space by monitoring gravity, linear acceleration, and rotation
Hearing – enables us to detect and interpret sound waves
Hair cells – the receptor mechanism for both equilibrium and hearing (respond to different stimuli and thus provide input)

3. Ear is divided into 3 regions:
External Ear
Middle Ear
Inner Ear

4. External Ear
Visible portion of the ear
Collects and directs sound waves toward the middle ear
Auricle- protects the opening of the canal and provides directional sensitivity
Auricle- blocks sounds from behind while sounds from the front are channeled into the external acoustic canal

5. External Acoustic Canal- passageway that ends at the tympanic membrane (ear drum) Tympanic membrane- separates external ear from middle ear Ceruminous glands- glands along the external acoustic canal that secrete a waxy material, cerumen, to block out foreign objects and increase sensitivity

6. Middle Ear aka tympanic cavity
Communicates with the nasopharynx through the auditory tube
With the mastoid air cells through small connections

7. Auditory tube- equalizes the pressures on either side of the tympanic membrane (ear drum)
Otitis media- a middle ear infection caused by invasion of microorganisms

8. Middle Ear- contains three tiny ear bones called auditory ossicles
Malleus (hammer)-attaches to tympanic membrane
Incus (anvil)- attaches malleus to the stapes
Stapes –inner ossicle, bound to the oval window which surrounds the inner ear

9. Auditory ossicles-
Act as levers that conduct vibrations to the inner ear
Produces rocking motion

10. Tensor tympani muscle – contracts and pulls malleus medially and stiffens the tympanic membrane and reduces movement for loud sounds Stapedius muscle – pulls the stapes, reducing their movement at the oval window

11. Inner Ear
4 layers
Outer layer  Bony Labyrinth – made up of dense bone
2nd layer  Perilymph – liquid in between the bony and membranous labyrinths
3rd layer  Membranous labyrinth – delicate, interconnected network of fluid filled tubes (receptors of the inner ear are found within these tubes)
Inner layer  Endolymph – a fluid with electrolyte concentrations
Cross section pic pg 575

12. Diagram from 575 goes here KEY Lateral Semicircular canal
Cristae within
ampullae
Maculae
Endolymphatic sac
Cochlea
Vestibular duct
Cochlear duct
Organ of
Corti
Tympanic
duct
Posterior
(a)
(b)
Anterior
Semicircular
ducts
Vestibule
Saccule
Utricle
Endolymph
Perilymph
Membranous
labyrinth
Bony labyrinth
Diagram from 575 goes here

13. Inner Ear Bony labyrinth – subdivided into…
Vestibule – consists of the saccule and the utricle (membranous sacs)
3 semicircular canals – enclose semicircular ducts
Combination of vestibule and semicircular canals is called the vestibular complex
Cochlea – spiral shaped bony chamber that contains the cochlear duct

14. Inner Ear
Bony labyrinth consists of dense bone everywhere except the round window and oval window

15. Equilibrium
Equilibrium sensations provided by receptors of the vestibular complex

16. Equilibrium
Semicircular Ducts (Anterior, Posterior, Lateral semicircular)
Sensory receptors in the semicircular ducts respond to rotation movements of the head
Each semicircular duct contains an ampulla (expanded region that contains the receptors)
Crista – region in the wall of the ampulla that contains the receptors
Bound to cupula
Each hair cell in the vestibule contains a kinocilium (single large cilium)

17. Equilibrium
Hair cells (receptors) are active during a movement, quiet when the body is motionless
Free surface of each hair cell supports long stereocilia (resemble microvilli)
Hair cells provide information about the direction and strength of mechanical stimuli
Stimuli involved varies by hair cell’s location
Gravity or acceleration in the vestibule
Rotation in the semicircular canals
Sound in the cochlea

18. Equilibrium
Movement of receptors controlled by three rotational planes
Horizontal rotation (ex. Shaking your head no) stimulates the hair cells of the lateral semicircular duct
Vertical movement (ex. Nodding “yes”) excites the anterior duct
Tilting your head from side to side activates receptors in the posterior duct

19. The Utricle and Saccule
Function – provide equilibrium sensations
Utricle and Saccule are connected by a slender passageway that is continuous with the narrow endolymphatic duct, which ends in the endolymphatic sac

20. The Utricle and Saccule
Hair cells of utricle and saccule are clustered in oval structures called maculae
Hair cell processes are embedded in a gelatinous mass (contains densely packed calcium carbonate crystals known as statoconia)
Otolith  Whole complex (gelatinous matrix + statoconia)

21. 1 2 (a) (b) Structure of a macula (c) Gelatinous material Statoconia
Nerve fibers
Otolith
Gravity
Receptor
output increases
“Otolith
moves
downhill,”
distorting
hair cell
processes
(b) Structure of a macula
STEP 1 2
Head in the anatomical position
Head tilted posteriorly
(a)
(c)

22. Macula of Saccule
When your head is in the normal, upright position, the statoconia sit atop the macula (their weight pushes the hair cell processes down rather than one side or another)
When your head is tilted, the pull of gravity on the statoconia shifts them to the side, distorting the hair cell processes (alerts the central nervous system that the head is no longer level)

23. Macula of Saccule
Under normal circumstances, body can distinguish between sensations of tilting and linear acceleration through visual information (amusement park rides confuse your sense of equilibrium because of the change in position and acceleration with restricted/misleading visual information)

24. Pathways for Equilibrium Sensations
Sensory fibers contained within the vestibular nuclei  4 functions of the 2 vestibular nuclei
Integrating sensory information about balance and equilibrium that arrives from both sides of the head
Send information to cerebral cortex and cerebellum of brain

25. Pathways for Equilibrium Sensations
Reflexive motor commands issued by vestibular nuclei are distributed to motor nuclei for cranial nerves involved with eye, head, and neck movements
Automatic movements of eye that occur in response to sensations of motion
directed by the superior colliculi of the mesencephalon (in an attempt to keep your gaze focused on a specific point, despite changes in body position and orientation)
Nystagmus  condition in which people have trouble controlling their eye movements

26. To ipsilateral superior colliculus and relay to cerebral cortex
Vestibular
ganglion
Vestibule
Semicircular
canals
Cochlear
branch XI VI IV
III
Red nucleus
To ipsilateral superior colliculus
and relay to cerebral cortex
nucleus To
cerebellum
Vestibulospinal
tracts
Vestibulocochlear
nerve (VIII)

27. Hearing
Receptors responsible for hearing are hair cells in the cochlear duct
Auditory ossicles convert pressure fluctuation in the air into fluctuation in the perilymph of the cochlea (outside pressure to inside pressure)

28. Hearing
Frequency of sound determined from which part of cochlear duct is stimulated
Volume is determined from how many hair cells are stimulated

29. The Cochlear Duct
Cochlear duct is between perilymph ducts: vestibular duct and tympanic duct
Outer surfaces encased by bony labyrinth everywhere except bases of ducts
Ducts are connected and actually form one long duct

30. The Cochlear Duct
Hairs are located in the organ of Corti in longitudinal rows
When the basilar membrane (which the hairs are located on) bounces, the hair cells are distorted by pressing against the upper membrane (tectorial membrane)

31. An Introduction to Sound
Hearing is perception of sound
Sine waves: S-shaped curves created by high and low pressure, travel in cycles
Travel at about 768 mph: speed of sound

32. An Introduction to Sound
Wavelength inversely related to frequency (number of waves that pass through reference point for certain amount of time)
Pitch=sensory response to frequency
Amplitude=intensity of sound, energy content
Cycles per second=hertz, Hz
Sound energy reported in decibels

33. An Introduction to Sound
With the right combination of frequency and amplitude, object will vibrate at same frequency as sound: called resonance
To hear sound, tympanic membrane must vibrate in resonance with sound waves

35. The Hearing Process
Sound waves arrive at the tympanic membrane…
Enter external acoustic canal and travel to tympanic membrane
Movement of the tympanic membrane causes displacement of the auditory ossicles
a) Tympanic membrane is the surface for sound collection
b) Resonate with frequencies ~20-20,000 Hz
c) When tympanic membrane vibrates, inner ossicles also vibrate= amplify the sound
Include diagram from book

36. The Hearing Process
3. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct
a) Because liquid is incompressible, pressure can only be relieved at the round window
b) Stapes vibrate and creates pressure waves in the perilymph

37. The Hearing Process
4. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct
a) Pressure waves travel around perilymph and reach round window
b) As they do this, they disrupt the basilar membrane
c) High frequencies vibrate the basilar membrane near oval window
d) Lower the frequency, longer wavelength and further from oval window is the maximum distortion
e) Frequency translated to position along basilar membrane
f) Amount of movement depends on force of sound

38. The Hearing Process
5. Vibration of the basilar membrane causes vibration of hair cells against the tectorial membrane
a) Vibration of basilar membrane moves hair cells against tectorial membrane
b) Ion channels open, depolarizes hair cells
c) Leads to release of neurotransmitters/ stimulates sensory organs
d) Hairs are stimulated in rows
e) Number of cells responding indicates intensity of sound

39. The Hearing Process
Region and intensity of stimulated area is relayed to the CNS over the Cochlear branch of the vestibulocochlear nerve
a) Cell bodies of sensory neurons located in spiral ganglion
b) Vestibulocochlear nerve is responsible for transmitting sound and equilibrium to the brain for further distribution

40. Auditory pathways Vestibulocochlear nerve formed by neurons
Info then goes to opposite side of brain to processing center which coordinates reflexes such as turning your head from a loud noise
Auditory cortex in temporal lobe maps out the organ of Corti

41. Auditory pathways
Frequency to position of basilar membrane is projected onto auditory cortex
Creates sensation of pitch
Damaged auditory cortex-responds to sound, but cannot interpret sounds or find patterns

42. Auditory sensitivity
Difficult to assess the absolute sensitivity of the system
We could, in theory hear air molecules, but full potential is never reached because of our own body and other peripheral sounds
We adapt to environment which affects hearing i.e. Relaxing in a quiet room

43. Auditory sensitivity Young children have the greatest hearing range
Declines with age due to damage or other accumulated injuries
Tympanic membrane is less flexible, articulations between ossicles stiffen and round window may begin to ossify
Result: older individuals exhibit hearing loss