The nervous system: the ear

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The nervous system the ear

• Emily Torres
• Ariana Soto
• Per 5

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Sense of Hearing

• The Ear enables us to be able to
• - hear sound waves
• - have sense of equilibrium
• The Ear is composed of the
• - Outer (External) Ear
• - Middle Ear
• - Inner (Internal) Ear

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Outer (External) Ear

• The Outer Ear consists of these structures
• - Auricle (Pinna)
• - External Auditory Canal
• - Tympanic membrane
• The opening before the temporal bone, there are
  hairs that guard the canal and skin that contains
  ceruminous glands.
• - Ceruminous glands secrete cerumen (wax)
• - wax helps keep foreign particles out

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Middle Ear

• The middle ear consists of these structures
• - tympanic membrane
• - auditory ossicles
• i. Malleus
• ii. Incus
• iii. Stapes
• - oval window
• - tensor tympani
• - stapedius

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Malleus, incus, stapes

• These three bones connect the tympanic membrane
  and inner (internal) ear by tiny ligaments
• Malleus
• - vibrates at the same time as tympanic
  membrane, then causing the incus to vibrate
• Incus
• - vibrates and sends the vibrations on to the
  stapes
• Stapes
• - vibrates and sends a fluid into the inner ear
  through the oval window

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Tensor tympani stapedius

• Tensor tympani
• - connected to the wall of the auditory tube
• - pulls malleus inward when contracted
• Stapedius
• - pulls the stapes outward
• These involuntary actions are part of the
  effectors in the tympanic reflex

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Tympanic reflex

• Occurs in about 1/10th of a second after a loud
  sound in order to protect the hearing receptors
  from possible damage from a loud external noise
• - also occurs when a person is simply talking or
  singing

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Auditory tube Ear pressure adjustment

• Connects each middle ear to the nasopharynx
• Helps provide equal air pressure on each side of
  the tympanic membrane

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Ear Infections

• Infection of the middle ear
• Most common ear infection is otitis media and is
  usually a result from
• - common cold
• - flu
• - allergies
• - sinus infection

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Inner (Internal) ear

• Structures include
• Cochlea
• Semicircular canals
• Vestibule

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cochlea

• Fluid filled snail-like structure that contains
  the receptor organ for hearing
• ?Spiral organ of Corti
• Divided into 3 chambers
• Contains hair cells
• 2 types of fluid
• Perilymph
• Endolymph

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Cochlea Chambers

• Scala Vestibuli-
• Perilymph (provides cushioning support, similar
  to interstitial fluid)
• Scala Media-
• Endolymph
• Organ of Corti
• Scala Tympani-
• Perilymph (provides cushioning support, similar
  to interstitial fluid)

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Organ of corti

• Found on basilar membrane in the scala media
  chamber
• Sensory organ of hearing
• Sound sensitive hair cells
• Pressure change causes hair cells to bend and
  stimulate a nerve signal which is carried to the
  brain
• This is how sound can be recognized

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Semicircular Canal

• Bodys balance organ
• 3 canals (superior, horizontal, and posterior)
  filled with endolymph that are each responsible
  for detecting motion on a different plane
• Sense head rotations/movement

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Vestibule

• Senses movement
• Holds 2 sacs of fluid
• ? the ultricle the saccule
• Hair cells
• Macula
• Known as gravity receptors

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Equilibrium

• State of balance
• Condition in which contending forces are equal
• 2 types
• Static
• Dynamic

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Static equilibrium

• Occurs when the body is motionless or moving in a
  straight line
• Maintains stability and posture
• Entrance of inner ear is the Vestibule
• Vestibule contains 2 sacs of fluid (Ultricle
  Saccule)
• The maculae of the ultricle and saccule are the
  gravity receptors that respond to linear
  acceleration, deceleration, and position in space
• Otoliths are calcium carbonate particles found in
  the fluid
• When your head moves, the otoliths bursh against
  the hair cells that line the utricle saccule
• Sends message to brain

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Static equilibrium diagram
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Dynamic equilibrium

• Occurs when the body is moving in a rotational or
  angular direction (spinning)
• Detects motion
• Sense of balance is interpreted in the
  Semicircular Canals
• Ampullae, the organs of dynamic equilibrium, are
  located at the base of each semicircular canal
• A gelatinous cupula is found in the ampullae
• Hair cells found on the cupula respond to
  movement
• When head rotates, endolymph moves and flows into
  the ampulla and causes the cupula to bend which
  triggers the hair cells to send messages to the
  brain

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Dynamic equilibrium diagram
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Sound collection pathway through the ear canal

• The Auricle (Pinna)
• - collects sound waves in the air, then sends
  them into the auditory canal
• The Auditory Canal
• - once sound waves enter here and pass to the end
  of the canal, they alter pressure on the tympanic
  membrane
• The Tympanic Membrane
• - moves back and forth due to sound waves, which
  then makes the vibrations

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Malleus, incus, stapes (ossicles)

• These three bones connect the tympanic membrane
  and inner (internal) ear by tiny ligaments
• Malleus
• - vibrates at the same time as tympanic
  membrane, then causing the incus to vibrate
• Incus
• - vibrates and sends the vibrations on to the
  stapes
• Stapes
• - vibrates and sends fluid into the inner ear
  through the oval window

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(Continued)

• The Oval Window
• - is an opening that transmits pressure waves of
  sound into the cochlea
• The Round Window
• -waves move to the round window and it releases
  pressure caused by the vibrations of the stapes
  in the oval window
• The Cochlea
• - sound waves make fluid in cochlea move and
  trigger the hair cells to move as well. The hair
  cells located on the organ of corti separate the
  sound waves according to their frequencies

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(Continued)

• The Auditory Nerve
• - hair cells cause an electrical signal to travel
  through the auditory nerve and to your brain
• The Brain
• - the brain responds to these separate
  frequencies and makes a complete sound from them

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  Localization - Boundless Open Textbook." Boundless
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  Apr. 2015.
• "Hearing and the Cochlea - Anatomy Video
  MedlinePlus Medical Encyclopedia." U.S National
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  Medicine, n.d. Web. 30 Apr. 2015.
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  30 Apr. 2015.
• "The Cochlea - HowStuffWorks." HowStuffWorks.
  N.p., n.d. Web. 30 Apr. 2015.
• "Middle Ear." Middle Ear Anatomy, Function
  Diagram. N.p., n.d. Web. 30 Apr. 2015.
• "Ear Infection Facts Causes, Acute Infections,
  Chronic Infections, and More."WebMD. WebMD, n.d.
  Web. 30 Apr. 2015.
• "Pharyngotympanic Tube." Eustachian Tube
  Function, Anatomy Diagram. N.p., n.d. Web. 30
  Apr. 2015.
• "See Pictures of Ear Infection Causes, Symptoms
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• "Anatomy of the Ear." Anatomy of the Ear. N.p.,
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