Difference between revisions of "Tympanic cavity"

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name the three main parts of the ear and outline the related osteology of the temporal bone; 2. state the location of the tympanic cavity, what forms its boundaries and how it is connected to the mastoid process and pharynx; 6 3. state the location of the organs of hearing and balance and give their nerve supply; 4. name the ossicles and their associated muscles, state their functions and the effects of motor nerve lesions on those functions; 5. state the course of the facial nerve and its branches through the temporal bone; 6. state the function of the facial nerve branches and predict the effects of lesions of the nerve at different points along its course; 7. give an outline of the tympanic plexus and its main branches.
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== Basics ==
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[[Image:Image1209.gif|thumb|200px|Left temporal bone showing surface markings for the tympanic antrum, transverse sinus, and facial nerve.]]
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The ear consists of three parts:
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#the external ear, comprising the auricle and external auditory meatus
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#the middle ear, or tympanic cavity, which is separated from the external auditory meatus by the tympanic membrane (eardrum). It contains three bones, or ossicles
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#the inner ear, which contains the organs of hearing and balance. Most of these structures are contained within the temporal bone
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== Osteology ==
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[[Image:Image138.gif|thumb|200px|Left temporal bone. Inner surface.]]
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*squamous, mastoid, petrous parts, tympanic plate, external auditory meatus, internal auditory meatus, styloid process
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*'''External auditory meatus'''
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**partly cartilage, partly bone (tympanic plate of temporal bone) and lined by skin
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**It is not straight
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**Therefore, for insertion of an auroscope, the auricle is pulled up and back
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**Its deep part is very sensitive to pain
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**The sensory nerve supply is from auricular branches of the auriculotemporal (V3) and facial nerve (minor).
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== Tympanic cavity ==
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=== Basics ===
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*''aka'' '''The middle ear'''
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*located in the petrous part of the temporal bone
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*communicates with the nasopharynx, via the auditory (eustachian, pharyngo-tympanic) tube
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**The tube is partly within the petrous bone and partly formed by cartilage
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*lined by a respiratory type of mucosa and contains the three small articulating bones (ossicles -malleus, incus and stapes) (also covered by mucosa)
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*The ossicles are responsible for transmitting sound vibrations from the tympanic membrane to the fluid-filled cavity of the inner ear, where the organ of hearing (cochlea) is found.
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=== Walls ===
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*'''Roof''' (''tegmen tympani'') - thin plate of bone separating the tympanic cavity from the cranial cavity
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*'''Floor''' - thin plate of bone separating the tympanic cavity from the internal jugular vein
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*'''Posterior wall''' - has an opening (aditus) leading to a space in the mastoid part of the temporal bone, called the ''mastoid antrum''
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**The antrum leads to the mastoid air cells which occupy the mastoid process
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*'''Anterior wall''' - the inferior part is a thin plate of bone separating the tympanic cavity from the carotid canal
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**The superior part has a bony canal passing forward from it
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**The canal is divided in two by a thin shelf of bone
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**The part below the shelf is the auditory tube, while the part above the shelf is occupied by the tensor tympani muscle
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*'''Lateral wall''' - formed by the [[tympanic membrane]]
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vi) Medial wall (note that this is also the lateral boundary of the inner ear) - the central part consists of a rounded prominence - the promontory, which overlies the cochlea (organ of hearing). Above and behind the promontory is the fenestra vestibuli (oval window), into which the foot plate of the stapes fits. It is here that the vibrations of the stapes are transferred to the fluid-filled cochlea. Below and posterior to the promontory is another opening, connecting to the cochlea. It is the fenestra cochleae (round window), and it is also closed by a membrane, the secondary tympanic membrane. When the stapes pushes on the oval window there is a compensatory bulging of the round window into the tympanic cavity. Above the oval window is a horizontal bulge into the cavity caused by the underlying lateral semicircular canal, which is part of the vestibular system and involved in balance. The facial nerve runs part of its course in a canal (facial canal), part of which is located in the medial wall of the tympanic cavity, above the oval window and below the lateral semi-circular canal.
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 +
 
 +
state the location of the tympanic cavity, what forms its boundaries and how it is connected to the mastoid process and pharynx
 +
 
 +
state the location of the organs of hearing and balance and give their nerve supply
 +
 
 +
name the ossicles and their associated muscles, state their functions and the effects of motor nerve lesions on those functions
 +
 
 +
== Ossicles ==
 +
The ossicles are suspended in the middle ear cavity by small ligaments and they articulate with each other at synovial joints. i) Malleus (= small hammer) - it has long process or handle which attaches to the tympanic membrane, and a head which articulates with the body of the ... ii) Incus (= anvil) - it, too, has a long process which extends inferiorly and articulates with the head of the ... iii) Stapes (= stirrup) - consists of the head, a neck, two limbs and a base (foot) plate which attaches to the medial wall of the cavity.
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i) Tensor tympani - originates in the bony canal immediately above the auditory tube. Its tendon passes into the tympanic cavity and inserts on the handle of the malleus. Since the malleus is attached to the tympanic membrane, contraction of the muscle tenses the tympanic membrane, thus dampening its vibrations and decreasing the volume of sound perceived. The muscle is supplied by a branch of the mandibular division of the trigeminal nerve
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Stapedius - the smallest muscle in the body (for trivia enthusiasts), supplied by a branch of the facial nerve. It originates from the posterior wall of tympanic cavity and its tendon inserts into the neck of the stapes. It acts to dampen the vibration of the stapes on the oval window which, again, would limit the volume of perceived sound. Impaired function of either of the above muscles would lead to hyperacousia - sounds seeming unusually loud.
 +
 
 +
 
 +
state the course of the facial nerve and its branches through the temporal bone
 +
 
 +
state the function of the facial nerve branches and predict the effects of lesions of the nerve at different points along its course
 +
 
 +
give an outline of the tympanic plexus and its main branches
  
 
== Resources ==
 
== Resources ==
 
*[[Media:GrossAnatomyNotesNeuroscienceDrHaase.pdf | Gross anatomy head and neck notes (PDF)]]
 
*[[Media:GrossAnatomyNotesNeuroscienceDrHaase.pdf | Gross anatomy head and neck notes (PDF)]]
 
*[[Media:TympanicCavityDrHaase.pdf | Tympanic cavity diagrams (PDF)]]
 
*[[Media:TympanicCavityDrHaase.pdf | Tympanic cavity diagrams (PDF)]]

Revision as of 15:15, 5 March 2004

Basics

Left temporal bone showing surface markings for the tympanic antrum, transverse sinus, and facial nerve.

The ear consists of three parts:

  1. the external ear, comprising the auricle and external auditory meatus
  2. the middle ear, or tympanic cavity, which is separated from the external auditory meatus by the tympanic membrane (eardrum). It contains three bones, or ossicles
  3. the inner ear, which contains the organs of hearing and balance. Most of these structures are contained within the temporal bone

Osteology

Left temporal bone. Inner surface.
  • squamous, mastoid, petrous parts, tympanic plate, external auditory meatus, internal auditory meatus, styloid process
  • External auditory meatus
    • partly cartilage, partly bone (tympanic plate of temporal bone) and lined by skin
    • It is not straight
    • Therefore, for insertion of an auroscope, the auricle is pulled up and back
    • Its deep part is very sensitive to pain
    • The sensory nerve supply is from auricular branches of the auriculotemporal (V3) and facial nerve (minor).

Tympanic cavity

Basics

  • aka The middle ear
  • located in the petrous part of the temporal bone
  • communicates with the nasopharynx, via the auditory (eustachian, pharyngo-tympanic) tube
    • The tube is partly within the petrous bone and partly formed by cartilage
  • lined by a respiratory type of mucosa and contains the three small articulating bones (ossicles -malleus, incus and stapes) (also covered by mucosa)
  • The ossicles are responsible for transmitting sound vibrations from the tympanic membrane to the fluid-filled cavity of the inner ear, where the organ of hearing (cochlea) is found.

Walls

  • Roof (tegmen tympani) - thin plate of bone separating the tympanic cavity from the cranial cavity
  • Floor - thin plate of bone separating the tympanic cavity from the internal jugular vein
  • Posterior wall - has an opening (aditus) leading to a space in the mastoid part of the temporal bone, called the mastoid antrum
    • The antrum leads to the mastoid air cells which occupy the mastoid process
  • Anterior wall - the inferior part is a thin plate of bone separating the tympanic cavity from the carotid canal
    • The superior part has a bony canal passing forward from it
    • The canal is divided in two by a thin shelf of bone
    • The part below the shelf is the auditory tube, while the part above the shelf is occupied by the tensor tympani muscle
  • Lateral wall - formed by the tympanic membrane

vi) Medial wall (note that this is also the lateral boundary of the inner ear) - the central part consists of a rounded prominence - the promontory, which overlies the cochlea (organ of hearing). Above and behind the promontory is the fenestra vestibuli (oval window), into which the foot plate of the stapes fits. It is here that the vibrations of the stapes are transferred to the fluid-filled cochlea. Below and posterior to the promontory is another opening, connecting to the cochlea. It is the fenestra cochleae (round window), and it is also closed by a membrane, the secondary tympanic membrane. When the stapes pushes on the oval window there is a compensatory bulging of the round window into the tympanic cavity. Above the oval window is a horizontal bulge into the cavity caused by the underlying lateral semicircular canal, which is part of the vestibular system and involved in balance. The facial nerve runs part of its course in a canal (facial canal), part of which is located in the medial wall of the tympanic cavity, above the oval window and below the lateral semi-circular canal.


state the location of the tympanic cavity, what forms its boundaries and how it is connected to the mastoid process and pharynx

state the location of the organs of hearing and balance and give their nerve supply

name the ossicles and their associated muscles, state their functions and the effects of motor nerve lesions on those functions

Ossicles

The ossicles are suspended in the middle ear cavity by small ligaments and they articulate with each other at synovial joints. i) Malleus (= small hammer) - it has long process or handle which attaches to the tympanic membrane, and a head which articulates with the body of the ... ii) Incus (= anvil) - it, too, has a long process which extends inferiorly and articulates with the head of the ... iii) Stapes (= stirrup) - consists of the head, a neck, two limbs and a base (foot) plate which attaches to the medial wall of the cavity.


i) Tensor tympani - originates in the bony canal immediately above the auditory tube. Its tendon passes into the tympanic cavity and inserts on the handle of the malleus. Since the malleus is attached to the tympanic membrane, contraction of the muscle tenses the tympanic membrane, thus dampening its vibrations and decreasing the volume of sound perceived. The muscle is supplied by a branch of the mandibular division of the trigeminal nerve

Stapedius - the smallest muscle in the body (for trivia enthusiasts), supplied by a branch of the facial nerve. It originates from the posterior wall of tympanic cavity and its tendon inserts into the neck of the stapes. It acts to dampen the vibration of the stapes on the oval window which, again, would limit the volume of perceived sound. Impaired function of either of the above muscles would lead to hyperacousia - sounds seeming unusually loud.


state the course of the facial nerve and its branches through the temporal bone

state the function of the facial nerve branches and predict the effects of lesions of the nerve at different points along its course

give an outline of the tympanic plexus and its main branches

Resources