Difference between revisions of "Tympanic cavity"

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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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*'''Medial wall''' - also the lateral boundary of the inner ear
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**the central part consists of a rounded prominence (the [http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=promontory promontory])
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**Above and behind the [http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=promontory promontory] is the [http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=fenestra+vestibuli fenestra vestibuli], into which the foot plate of the stapes fits
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**It is at the [http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=fenestra+vestibuli fenestra vestibuli] that the vibrations of the stapes are transferred to the fluid-filled cochlea
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**Below and posterior to the [[http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=promontory promontory] promontory] is another opening, connecting to the cochlea
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**It is the [http://cancerweb.ncl.ac.uk/cgi-bin/omd?query=fenestra+cochleae fenestra cochleae]
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**When the stapes pushes on the oval window there is a compensatory bulging of the round window into the tympanic cavity
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**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
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**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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== Ossicles ==
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[[Image:Image919.gif|thumb|200px|Chain of ossicles and their ligaments]]
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The ossicles are suspended in the middle ear cavity by small ligaments and they articulate with each other at synovial joints
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=== Malleus ===
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*means ''small hammer''
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*See [[:Image:Image916.gif]]
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*it has a long process (handle) which attaches to the tympanic membrane, and a head which articulates with the body of the [[#Incus |incus]]
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=== Incus ===
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*means ''anvil''
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*See [[:Image:Image917.gif]]
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*has a long process which extends inferiorly and articulates with the head of the [[#Stapes |stapes]]
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=== Stapes ===
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*means ''stirrup''
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*See [[:Image:Image918.gif]]
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*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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== Muscles ==
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[[Image:Image915.gif|thumb|200px|Auditory tube]]
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=== Tensor tympani ===
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*originates in the bony canal immediately above the auditory tube
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*Its tendon passes into the tympanic cavity and inserts on the handle of the malleus
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*Since the malleus is attached to the tympanic membrane, contraction of the muscle tenses the tympanic membrane
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*This dampens its vibrations and decreases the volume of sound perceived
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*The muscle is supplied by a branch of the mandibular division of the trigeminal nerve
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=== Stapedius ===
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*the smallest muscle in the body (for trivia enthusiasts)
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*supplied by a branch of the facial nerve
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*Originates from the posterior wall of tympanic cavity
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*its tendon inserts into the neck of the [[#Stapes |stapes]]
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*Acts to dampen the vibration of the stapes on the oval window
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*This would also limit the volume of perceived sound
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*Impaired function of either of the above muscles would lead to hyperacousia
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== Innervation ==
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[[Image:Image789.gif|thumb|200px|The course and connections of the facial nerve in the temporal bone.]]
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=== Facial nerve ===
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==== Basics ====
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*Enters the internal auditory meatus, along with the vestibulo-cochlear nerve and labyrinthine artery
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*Here, the vestibulo-cochlear nerve divides into its vestibular (balance) and cochlear (hearing) branches which enter the respective organs in the inner ear
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*The facial nerve enters its own canal (facial canal) and passes to the medial wall of the tympanic cavity, where it has a swelling (the geniculate ganglion) which contains the cell bodies of sensory neurons
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*At the ganglion, the facial nerve turns posteriorly in the facial canal and passes along the medial wall of the tympanic cavity
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*then, it passes inferiorly in the posterior wall
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*Its terminal branch exits through the stylo-mastoid foramen (between the styloid and mastoid processes)
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==== Greater petrosal nerve ====
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*arises at the geniculate ganglion
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*carries preganglionic parasympathetic fibres
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**pass through the ganglion (they do not synapse here) to the 8 spheno(pterygo)palatine ganglion
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*The postganglionic fibres leaving the ganglion are secreto-motor to the lacrimal gland and glands of the nasal cavity, nasopharynx and palate
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*May also carry taste fibres to the soft palate.
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==== Nerve to stapedius ====
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*leaves the facial nerve in the posterior wall of the tympanic cavity
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*supplies the stapedius muscle
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==== Chorda tympani ====
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*contains taste and preganglionic parasympathetic fibres
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*Leaves the facial nerve just above the stylomastoid foramen and passes forward, into the tympanic cavity, and across the tympanic membrane, to which it is attached
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*It then leaves the cavity through the petro-tympanic fissure, and enters the [[infratemporal region#Infratemporal fossa |infratemporal fossa]], where it joins the lingual nerve (branch of the mandibular nerve)
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*The lingual nerve carries the taste fibres of the chorda tympani to the anterior two-thirds of the tongue and the parasympathetic fibres to the submandibular ganglion
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==== Terminal motor branch ====
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*leaves the stylomastoid foramen to supply the stylohyoid, posterior belly of digastric and muscles of facial expression
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*The small sensory branch that supplies the external auditory meatus and tympanic membrane also leaves the facial nerve in the region of the stylomastoid foramen
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=== Tympanic plexus ===
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* A nerve plexus overlying the promontory
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*Derived from:
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*#the tympanic branch of the glossopharyngeal nerve
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*#sympathetic fibres from the internal carotid plexus
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*#lesser petrosal nerve (parasympathetic branch) - involved in the secretomotor pathway to the parotid gland.
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*Has sensory branches to the mucosa of the tympanic cavity
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== 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)]]
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[[Category:Head]] [[Category:Gross anatomy]]

Latest revision as of 15:09, 10 October 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
  • Medial wall - also the lateral boundary of the inner ear
    • the central part consists of a rounded prominence (the promontory)
    • Above and behind the promontory is the fenestra vestibuli, into which the foot plate of the stapes fits
    • It is at the fenestra vestibuli that the vibrations of the stapes are transferred to the fluid-filled cochlea
    • Below and posterior to the [promontory promontory] is another opening, connecting to the cochlea
    • It is the fenestra cochleae
    • 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.

Ossicles

Chain of ossicles and their ligaments

The ossicles are suspended in the middle ear cavity by small ligaments and they articulate with each other at synovial joints

Malleus

  • means small hammer
  • See Image:Image916.gif
  • it has a long process (handle) which attaches to the tympanic membrane, and a head which articulates with the body of the incus

Incus

  • means anvil
  • See Image:Image917.gif
  • has a long process which extends inferiorly and articulates with the head of the stapes

Stapes

  • means stirrup
  • See Image:Image918.gif
  • consists of the head, a neck, two limbs and a base (foot) plate which attaches to the medial wall of the cavity.

Muscles

Auditory tube

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
  • This dampens its vibrations and decreases 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
  • Originates from the posterior wall of tympanic cavity
  • its tendon inserts into the neck of the stapes
  • Acts to dampen the vibration of the stapes on the oval window
  • This would also limit the volume of perceived sound
  • Impaired function of either of the above muscles would lead to hyperacousia

Innervation

The course and connections of the facial nerve in the temporal bone.

Facial nerve

Basics

  • Enters the internal auditory meatus, along with the vestibulo-cochlear nerve and labyrinthine artery
  • Here, the vestibulo-cochlear nerve divides into its vestibular (balance) and cochlear (hearing) branches which enter the respective organs in the inner ear
  • The facial nerve enters its own canal (facial canal) and passes to the medial wall of the tympanic cavity, where it has a swelling (the geniculate ganglion) which contains the cell bodies of sensory neurons
  • At the ganglion, the facial nerve turns posteriorly in the facial canal and passes along the medial wall of the tympanic cavity
  • then, it passes inferiorly in the posterior wall
  • Its terminal branch exits through the stylo-mastoid foramen (between the styloid and mastoid processes)

Greater petrosal nerve

  • arises at the geniculate ganglion
  • carries preganglionic parasympathetic fibres
    • pass through the ganglion (they do not synapse here) to the 8 spheno(pterygo)palatine ganglion
  • The postganglionic fibres leaving the ganglion are secreto-motor to the lacrimal gland and glands of the nasal cavity, nasopharynx and palate
  • May also carry taste fibres to the soft palate.

Nerve to stapedius

  • leaves the facial nerve in the posterior wall of the tympanic cavity
  • supplies the stapedius muscle

Chorda tympani

  • contains taste and preganglionic parasympathetic fibres
  • Leaves the facial nerve just above the stylomastoid foramen and passes forward, into the tympanic cavity, and across the tympanic membrane, to which it is attached
  • It then leaves the cavity through the petro-tympanic fissure, and enters the infratemporal fossa, where it joins the lingual nerve (branch of the mandibular nerve)
  • The lingual nerve carries the taste fibres of the chorda tympani to the anterior two-thirds of the tongue and the parasympathetic fibres to the submandibular ganglion

Terminal motor branch

  • leaves the stylomastoid foramen to supply the stylohyoid, posterior belly of digastric and muscles of facial expression
  • The small sensory branch that supplies the external auditory meatus and tympanic membrane also leaves the facial nerve in the region of the stylomastoid foramen

Tympanic plexus

  • A nerve plexus overlying the promontory
  • Derived from:
    1. the tympanic branch of the glossopharyngeal nerve
    2. sympathetic fibres from the internal carotid plexus
    3. lesser petrosal nerve (parasympathetic branch) - involved in the secretomotor pathway to the parotid gland.
  • Has sensory branches to the mucosa of the tympanic cavity

Resources