Anatomy of ear

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EAR
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Introduction

• Ears are the paired organs , one on the each side
  of head .
• Ears is organs of hearing and is also involved in
  balance or maintaining the equilibrium.
• It is supplied by the 8th cranial nerve.
• Centre of hearing in the temporal lobe of the
  brain .

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Structure of the ear
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Outer ear
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Outer ear consist of

• (1) Auricle (pinna)
• (2) External acoustic meatus
• (auditory canal)

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(1) AURICLE
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Auricle continue

• It is visible part of the ear.
• Lobule(ear lobe) is the soft pliable part at the
  lower.
• Composed of fibrous and adipose tissue , Rich
  blood supply.

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(2) EXTERNAL ACOUSTIC MEATUS

• Slightly S shaped tube.
• 2.5 cm long.
• Outer 1/3 is cartilaginous.
• Inner 2/3 is bony.

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• Lateral 3rd is lined with skin Containing
• hair follicles
• ceruminous glands (produce a
  waxy exudate called cerumen (wax))
• Middle 2/3 is lined with very thin skin

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Nerve supply

• (1) auricular branch of auriculotemporal nerve.
• (2) facial nerve.
• (3) auricular branch of vagus.

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TYMTYMMANPANIC MEMBTYMANIC RANE

• ..

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• It forms partition between the external ear and
  middle ear.
• Tympanic membrane is oval in shape.

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Layers of the tympanic membrane
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Function of tympanic layer

• Transmission of vibration

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Nerve supply

• External surface -
• auriculo-temporal nerve
• auricular branch of vagus .
• Internal surface-
• tympanic branch of
  glossopharyngeal nerve

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Features of middle ear

• Also called tympanic cavity or tympanum.
• Irregular shaped air filled cavity.

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Shape and size

• Shape cube like shape.
• Its lateral and medial walls are large , but
  others walls are narrow,
• Verticle and anterio-posterior diameters is about
  15 mm.

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Parts of the middle ear

• Tympanic cavity.
• Epitympanic recess.

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Communications

• Anteriorly with nasopharynx.
• Posteriorly with mastoid antrum or mastoid air
  cells.

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Middle ear contains..

• Three small bones.
• Ligaments of ear bones.
• Two muscles tensor tympani
• - stapedius
• Vessels of middle ear
• Nerves chordatympani
• -tympanic plexus

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Boundaries of the middle ear

1. Roof / tegmental wall
2. Floor / jugular wall
3. Anterior / carotid wall
4. Posterior / mastoid wall
5. Lateral / membranous wall
6. Medial / labyrinthine wall

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Ear ossicles
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Malleus

• Lateral hammer shaped bone.
• Handle is in contact with the tympanic membrane.
• Head forms a movable joint with the incus.

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Incus

• Anvil - shaped bone.
• Its body articulates with the malleus.
• The long process with the stapes.

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Stapes

• Medial Stirrup shaped bone.
• Smallest bone.
• Head articulates with the incus.
• Foot plate fits into oval window.

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Muscles of the middle ear

• (1) Tensor tympani muscle
• (2) Stapedius muscle

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Tensor tympani

• Arise from the cartilaginous part of the auditory
  tube and from the base of the skull
• Nerve supply -
• mandibular nerve

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Stapedius

• Lies on a bony canal, on the posterior part of
  middle ear.
• Nerve supply-
• a branch of facial nerve

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Function of these muscles

• Damp down the intensity of high pitched sound.

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Auditory tube / pharyngotympanic tube /
eustachian tube

• About 4cm long.
• Connects middle ear cavity with the nasopharynx

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Mastoid or tympanic antrum

• Features --
• It is small, circular ,air filled space situated
  in the posterior part of the temporal bone.
• Size like small pea
• Diameter 1cm.

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Mastoid cells

• These cells are a series of intercommunicating
  space of variable size present within the mastoid
  process.
• They are large and irregular and contains air.
• Communicates with middle ear cavity via mastoid
  antrum.

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Internal ear
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• The Internal ear contains vestibulocochlear
  organ, which is concerned with the reception of
  sound and maintenance of balance.

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Internal ear part

1. Bony labyrinth
2. Membranous labyrinth

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Structure of bony labyrinth and membranous
labyrinth
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Bony labyrinth

• It is cavity with the temporal bone.
• Larger than and encloses, the membranous
  labyrinth of same shape that fits into it, like a
  tube with in a tube.

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It is consist of

• The vestibule
• The cochlea
• Three semi-circular canals

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The vestibule

• Extended part nearest the middle ear.
• The oval window and round window is located in
  its lateral part.

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The cochlea
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• This resembles a snail shell.
• It has broad base where it is continuous with the
  vestibule and a narrow apex.

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The semi-circular canals

• Three tubes .
• they are continuous with the vestibule.

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Membranous labyrinth

• This is a network of delicate tubes filled with
  endolymph .
• It comprises
• The vestibule containing utricle and saccule.
• The cochlea
• Three semi-circular canals

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The cochlea

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• A cross section of cochlea contains three
  compartments
• The scala vestibuli
• The scala media or cochlear duct
• The scala tympani

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Organ of corti

• Structure in the cochlea of inner ear.
• Produce nerve impulses , in response to sound
  vibrations.

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Functions of organ of corti

1. Auditory transduction.
2. Cochlear amplification.

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Hair cells

• These are the sensory cells in the organ of corti
  topped with hair like structures called
  streocilia.

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Physiology / mechanism of hearing
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