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Hearing Maddie, Emma, Kelly, Meg. Equilibrium sensations – inform us of the position of the head in space by monitoring gravity, linear acceleration,

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Presentation on theme: "Hearing Maddie, Emma, Kelly, Meg. Equilibrium sensations – inform us of the position of the head in space by monitoring gravity, linear acceleration,"— Presentation transcript:

1 Hearing Maddie, Emma, Kelly, Meg

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: 1.External Ear 2.Middle Ear 3.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 Auditory ossicles: 1.Malleus (hammer)-attaches to tympanic membrane 2.Incus (anvil)- attaches malleus to the stapes 3.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 2 nd layer  Perilymph – liquid in between the bony and membranous labyrinths 3 rd 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

12 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 Membranous labyrinth Bony labyrinth

13 Inner Ear Bony labyrinth – subdivided into… 1.Vestibule – consists of the saccule and the utricle (membranous sacs) 2.3 semicircular canals – enclose semicircular ducts Combination of vestibule and semicircular canals is called the vestibular complex 3.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 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 Equilibrium Each hair cell in the vestibule contains a kinocilium (single large cilium)

17 Equilibriu m 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 Equilibriu m 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 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 The Utricle and Saccule

20 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) The Utricle and Saccule

21 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 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 Pathways for Equilibrium Sensations

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

27 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) Hearing

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

29 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 The Cochlear Duct

30 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) The Cochlear Duct

31 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 An Introduction to Sound

32 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 An Introduction to Sound

33 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 An Introduction to Sound

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35 The Hearing Process Sound waves arrive at the tympanic membrane… 1.Enter external acoustic canal and travel to tympanic membrane 2.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

36 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 The Hearing Process

37 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 The Hearing Process

38 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 The Hearing Process

39 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 The Hearing Process

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 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 Auditory pathways

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 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 Auditory sensitivity

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