Download Middle ear cavity and its contents

Middle ear cavity and its
contents
Middle ear cavity (Tympanic cavity)
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Middle ear or tympanic cavity is an irregular, laterally
compressed space within the temporal bone.
It is filled with air, which is conveyed to it from the nasal part of
the pharynx through the auditory tube.
Parts of middle ear cavity
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The tympanic cavity consists of two parts:
Tympanic cavity proper, opposite the tympanic membrane,
Attic or epitympanic recess, above the level of the membrane
– contains the upper half of the malleus and the greater part of the
incus
Contents of middle ear cavity
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Contents:
Ossicles – malleus, incus, stapes
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Muscles – tensor tympani, stepedius
Vessels and nerves – chorda tympani and tympanic plexus of ear.
Functions of middle ear cavity
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Properties: Narrow, oblique, slit like, air containing cavity in the
petrous part of temporal bone.
Function: transmit the vibrations of tympanic membrane to the
perilymph of internal ear.
Boundaries of middle ear
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Roof (Tegmental wall) – By thin plate of bone i.e. tegmen
tympani
Floor (jugular wall) – Thin jugular fossa
Anterior (carotid wall) – Thin plate of bone which separates
the tympanic cavity from I.C.A.
Posterior (Mastoid wall) – Aditus of mastoid antrum.
Lateral (membranous wall) – Tympanic membrane
Medial wall is formed by internal ear. Tympanic membrane moves medially
Medial wall of tympanic cavity
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Has following features:
Fenestrae vestibuli (oval window)
– opening leading from the tympanic cavity into
the vestibule of the internal ear
– Covered by stapes
Fenestrae cochleæ (round window)
– leads into the cochlea of the internal ear.
– Closed by the secondary tympanic
membrane.
Promontory
– Rounded hollow prominence, formed by the projection outward
of the first turn of the cochlea.
Prominence of the facial canal.
– Indicates the position of the bony canal in which the facial nerve
is contained
Tympanic Membrane
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Thin, semitransparent membrane, nearly oval in form.
Separates the tympanic cavity from the bottom of the
external acoustic meatus
The greater part of its circumference is thickened, and
forms a fibrocartilaginous ring which is fixed in the
tympanic sulcus at the inner end of the meatus.
Anterior and posterior malleolar folds
Pars flaccida
 small, somewhat triangular part of the membrane
situated above these folds is lax and thin
The manubrium of the malleus is firmly attached to the medial surface of the
membrane as far as its center.
Most depressed part on the lateral surface is named the umbo.
Ossicles – Malleus
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The malleus or hammer is a hammer-shaped bone
Connected with the incus and is attached to the inner
surface of the tympanic membrane
It transmits the sound vibrations from the eardrum to
the incus.
Ossicles – Incus
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The incus or anvil is the anvil-shaped small bone
It connects the malleus to the stapes
The incus transmits sound vibrations from the malleus to the
stapes.
Ossicles – Stapes
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The stapes or stirrup is the stirrup-shaped small
bone.
Attached to the incus laterally and to the fenestra
ovalis, the "oval window", medially.
The oval window is adjacent to the vestibule of the
inner ear.
The stapes is the smallest and lightest bone in the
human body.
The stapes transmits the sound vibrations from the
incus to the membrane of the inner ear inside the
fenestra ovalis
Stapedius
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The stapedius is the smallest skeletal muscle in the human
body. At just over one millimeter in length, its purpose is to
stabilize the smallest bone in the body, the stapes.
The stapedius emerges from a pinpoint foramen in the apex of
the pyramidal eminence (a hollow, cone-shaped prominence in
the posterior wall of the tympanic cavity), and inserts into the
neck of the stapes.
Innervated by the nerve to stapedius, a branch of cranial nerve
VII, the facial nerve.
Tensor tympani
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Tensor tympani, the larger of the two muscles of the tympanic
cavity, is contained in the bony canal above the osseous portion
of the auditory tube.
Its role is to dampen sounds, such as those produced from
chewing.
Origin and insertion
– It arises from the cartilaginous portion of the auditory
tube and the adjoining part of the great wing of the
sphenoid
– Inserted into the handle (manubrium) of the malleus,
near its root.
Auditory tube
 Is the channel through which the tympanic cavity communicates
with the nasal part of the pharynx.
 35 mm long (in adults).
 Extends from the anterior wall of the middle ear to the lateral
wall of the nasopharynx.
 Has two parts
– Osseous part
– Cartilagenous part
Mastoid or posterior wall
 Aditus to mastoid antrum
– large aperture, leading backward from the epitympanic recess
into the tympanic or mastoid antrum.
– The antrum communicates behind and below with the
mastoid air cells
 Pyramidal eminence
 Fossa incudis
Arteries of middle ear
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Anterior tympanic branch (maxillary artery)
Superior tympani (middle meningeal artery) and petrosal branch
Posterior tympani (posterior auricular artery)
Inferior tympanic (ascending Ph artery)
Tympanic branch from artery of pterygoid canal. Coticotympanic
from I.C artery
Nerves of middle ear cavity
– Tympanic branch of glossopharyngeal nerve (tympanic
plexus)
– Superior and inferior corticotympanic nerves from
the sympathetic plexus around internal carotid
artery.
Veins and lymph nodes of middle ear cavity
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Pterygoid plexus of veins which drain into superior
petrosal sinus.
Lymph nodes
– Periauricular and retro pharyngeal nodes.
How does the sound travels?
 Hande of malleus and head of incus moves lateral. The long
process of incus moves medially with stapes.
 The base of stapes pushed medially in the fenestra vestibuli and
motion is communicated to perilymph in scala vestibuli.
Otitis media
 Inflammation of the Middle Ear