Sense Organs II: The Ear

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Lecture 16

• Sense Organs II The Ear

2
Basic Parts of the Ear
Fig. 19.20

• External ear Hearing terminates at eardrum
• Middle ear Hearing contains auditory ossicles
• Inner ear Hearing and balance interconnecting
  fluid-filled tunnels and chambers

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External Ear

• Auricle or pinna elastic cartilage
• External auditory canal
• Tympanic membrane

External ear
Inner ear
Middle ear
Auricle (pinna)
External auditory canal
Tympanic membrane
Elastic cartilage
Fig. 19.20
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Middle Ear

• Auditory or eustachian tube
• Opens into pharynx, equalizes pressure
• Ossicles malleus, incus, stapes transmit
  vibrations
• Oval window

Fig. 19.21
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Inner Ear

• Labyrinth
• Bony
• Cochlea Hearing
• Vestibule Balance
• Semicircular canals Balance
• Membranous

• Lymphs
• Endolymph
• In membranous labyrinth
• Perilymph
• Space between membranous and bony labyrinth

Fig. 19.22
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Structure of Cochlea

• Membranous labyrinth of cochlea
• Scala vestibuli (perilymph)
• Scala tympani (perilymph)
• Cochlear duct (endolymph)

Fig. 19.27
Fig. 19.27
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Structure of Cochlea

• Spiral organ (organ of Corti)
• Hair cells
• Stereocilia (microvilli)
• Tectorial membrane
• Cochlear nerve

Fig. 19.27
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Effect of Sound Waves on Cochlear Structures
Fig. 19.28
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Balance

• Two structural and functional components of
  balance in inner ear
• Stationary Position and Linear Movement of Head
• Evaluates position of head relative to gravity
• Detects linear acceleration and deceleration
• Utricle and saccule
• Maculae Consist of hair cells embedded in
  statoconic membrane containing otoliths

Fig. 19.23
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Vestibule in Maintaining Balance
Fig. 19.24
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Balance

• Rotational Movements of Head
• Evaluates movements of head (i.e. angular
  acceleration)
• 3 semicircular canals
• Ampulla
• Crista ampullaris
• Hair cells
• Cupula

Fig. 19.25
Vestibular nerve Cochlear nerve
Vestibulocochlear nerve (VIII)
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Crista Ampullaris and Balance
Fig. 19.26
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Review Question

• A person driving a car along a straight street
  suddenly sees an animal dart in front of the car.
  He slams on the brakes and manages to stop in
  time. The sensation of rapid deceleration is
  generated by the
• Bending of the microvilli of the spiral organ
• Movement of perilymph fluid in the vestibule
• Movement of the gelatinous covering over the
  maculae
• Movement of endolymph fluid in the semicircular
  canals
• Movement of the cupula

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Points to Remember

• Inner ear functions for hearing and balance.
• Sound waves enter the external auditory canal,
  impact tympanic membrane, vibrate middle ear
  ossicles, strike oval window, create waves in
  perilymph of scala vestibuli, increase pressure
  in endolymph in cochlear duct, membrane
  supporting hair cells vibrates, hair cells
  stimulated, vibrations transferred to perilymph
  of scala tympani, travel to round window and
  dampened.

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Points to Remember

• Static balance is orientation of body relative to
  pull of gravity - maculae of utricle and saccule
  (static labyrinth) are sense organs of static
  balance.
• Kinetic balance is maintenance of body position
  in response to movement - crista ampullaris in
  semicircular canals (kinetic labyrinth) are sense
  organs of kinetic balance.

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Questions?