Advertisements help pay for this website. Thank you for
nasal cavity | Main Anatomy
Index | The oral cavity
Last updated 30 March 2006
- The ear contains the vestibulocochlear
organ and consists of three main parts:
external, middle, and internal.
- It has two functions, balance and
- The tympanic membrane
(eardrum) separates the external ear from the middle ear.
- The auditory tube joins the
middle ear or tympanic cavity to the nasopharynx.
- The auricle (L. auris, ear) is the visible,
shell-like part of the external ear.
- It consists of a single elastic cartilage that is covered
on both surfaces with thin, hairy skin.
- The external ear contains hairs, sweat glands, and
- The cartilage is irregularly ridged and hollowed, which
gives the auricle its shell-like form.
- It also shapes the orifice of the external acoustic meatus.
Lobule (p. 763)
- The great auricular nerve supplies the superior surface
and the lateral surface inferior to the external acoustic
meatus with nerve fibres from C2.
- The auriculotemporal nerve supplies the skin of the
auricle superior to the external acoustic meatus.
External Acoustic Meatus (pp. 763, 765)
- This passage extends from the concha
(L. shell) of the auricle to the tympanic membrane (L. tympanum,
tambourine). It is about 2.5 cm long in adults.
- The lateral 1/3 of the S-shaped
canal is cartilaginous, whereas its medial 2/3
- The lateral third of the meatus is lined with the skin of
the auricle and contains hair
glands, and ceruminous
- The latter glands produce cerumen
(L. cera, wax).
- The medial two-thirds of the meatus is lined with very
thin skin that is continuous with the external layer of
the tympanic membrane.
- The lateral end of the meatus is the widest part. It has
the diameter about that of a pencil.
- The meatus becomes narrow at its medial end, about 4 mm
from the tympanic membrane.
- The constricted bony part is called the isthmus.
- Innervation of the external acoustic meatus is derived
from three cranial nerves:
- The auricular branch of
nerve (derived from the mandibular, CN V3).
- The facial
nerve (CN VII) by the branches from the tympanic
- The auricular branch of
the vagus nerve
Tympanic Membrane (p. 765)
- This is a thin, semi-transparent, oval membrane at the
medial end of the external acoustic meatus.
- It forms a partition between the external and middle
- The tympanic membrane is a thin fibrous membrane, that is
covered with very thin skin
externally and mucous
- The tympanic membrane shows a concavity toward the meatus
with a central depression, the umbo,
which is formed by the end of the handle
of the malleus.
- From the umbo, a bright area referred to as the cone of light, radiates anteroinferiorly.
- The external surface of the tympanic membrane is supplied
by the auriculotemporal
- Some innervation is supplied by a small auricular branch of the vagus nerve (CN X);
this nerve may also contain some glossopharyngeal and
facial nerve fibres.
Click here for a
schematic of the tympanic cavity or middle ear.
- This part of the ear is in a narrow
cavity in the petrous part of the temporal bone.
- It contains air, three auditory
ossicles, a nerve and two small
- The middle ear is separated from the external acoustic
meatus by the tympanic membrane.
- This cavity includes the tympanic
cavity proper, the space directly internal to
the tympanic membrane, and the epitympanic
recess, the space superior to it.
- The middle ear is connected anteriorly with the
nasopharynx by the auditory tube.
- Posterosuperiorly, the tympanic cavity connects with the mastoid cells through the aditus ad antrum (mastoid
- The tympanic cavity is lined with mucous membrane that is
continuous with the mucous membrane of the auditory tube,
mastoid cells, and aditus ad antrum.
of the Tympanic Cavity or Middle Ear (p. 769)
- This cavity contains the auditory
ossicles (malleus, incus and stapes);
the stapedius and tensor tympani muscles; the chorda tympani nerve (a branch
of the facial nerve, CN VII); and the tympanic plexus of
Walls of the Tympanic Cavity or
Middle Ear (pp. 769, 771-2)
- This cavity is shaped like a narrow six-sided box that
has convex medial and lateral walls.
- It has the shape of the biconcave lens in cross-section
(like a red blood cell).
Roof or Tegmental Wall (p. 769)
- This is formed by a thin plate of bone, called the tegmen tympani (L. tegmen,
- It separates the tympanic cavity from the dura on the
floor of middle cranial fossa.
- The tegmen tympani also covers the aditus ad antrum.
Floor or Jugular Wall (p. 769)
- This wall is thicker than the roof.
- It separates the tympanic cavity from the superior bulb
of the internal
jugular vein. The internal jugular vein and the internal
carotid artery diverge at the floor of the tympanic
- The tympanic nerve, a
branch of the glossopharyngeal
nerve (CN IX), passes through an aperture in the
floor of the tympanic cavity and its branches form the tympanic plexus.
Lateral or Membranous Wall (p. 769)
- This is formed almost entirely by the tympanic membrane.
- Superiorly it is formed by the lateral bony wall of the epitympanic recess.
- The handle of the malleus is
incorporated in the tympanic membrane, and its
head extends into the epitympanic recess.
Medial or Labyrinthine Wall (pp. 769, 771)
- This separates the middle ear from the membranous
labyrinth (semicircular ducts and cochlear
duct) encased in the bony labyrinth.
- The medial wall of the tympanic cavity exhibits several
- Centrally, opposite the tympanic membrane, there is a
rounded promontory (L.
eminence) formed by the first turn of the cochlea.
- The tympanic plexus of nerves,
lying on the promontory, is formed by fibres of the facial and glossopharyngeal
- The medial wall of the tympanic cavity also has two small
apertures or windows.
- The fenestra vestibuli
(oval window) is closed by the base of the stapes, which is bound to its
margins by an annular ligament.
- Through this window, vibrations of the stapes are
transmitted to the perilymph window within the bony
labyrinth of the inner ear.
- The fenestra cochleae
(round window) is inferior to the fenestra vestibuli.
- This is closed by a second tympanic membrane.
Posterior or Mastoid Wall (p. 771)
- This wall has several openings in it.
- In its superior part is the aditus
ad antrum (mastoid antrum), which leads
posteriorly from the epitympanic recess to the mastoid
- Inferiorly is a pinpoint aperture on the apex of a tiny,
hollow projection of bone, called the pyramidal
- This eminence contains the stapedius
- Its aperture transmits the tendon of the stapedius, which
enters the tympanic cavity and inserts
into the stapes.
- Lateral to the pyramid, there is an aperture through
which the chorda tympani nerve,
a branch of the facial
nerve (CN VII), enters the tympanic cavity.
Anterior Wall or Carotid Wall (pp. 771-2)
- This wall is a narrow as the medial and lateral walls
- There are two openings in the anterior wall.
- The superior opening communicates with a canal occupied
by the tensor tympani muscle.
- Its tendon inserts into the handle
of the malleus and keeps the tympanic membrane
- Inferiorly, the tympanic cavity communicates with the nasopharynx through the auditory tube.
Auditory Tube (p. 772)
- This is a funnel-shaped tube connecting the nasopharynx to the tympanic cavity.
- Its wide end is towards the nasopharynx, where it opens
posterior to the inferior meatus
of the nasal cavity.
- The auditory tube is 3.5 to 4 cm long; its posterior 1/3
is bony and the other 2/3 is cartilaginous.
- It bony part lies in a groove on the inferior aspect of
the base of the skull, between the petrous
part of the temporal
bone and the greater wing
of the sphenoid bone.
- The function of the auditory tube is to equalise pressure of the middle ear with
Auditory Ossicles (p. 772)
The Malleus (p. 772)
- Its superior part, the head,
lies in the epitympanic recess.
- The head articulates with the incus.
- The neck, lies against
the flaccid part of the tympanic
- The chorda tympani nerve
crosses the medial surface of the neck of the malleus.
- The handle of the malleus
(L. hammer) is embedded in the tympanic membrane and
moves with it.
- The tendon of the tensor tympani
muscle inserts into the handle.
The Incus (p. 772)
- Its large body lies in
the epitympanic recess
where it articulates with the head
of the malleus.
- The long process of the
incus (L. an anvil) articulates
with the stapes.
- The short process is
connected by a ligament to the posterior wall of
the tympanic cavity.
The Stapes (p. 772)
- The base (footplate) of
the stapes (L. a stirrup), the smallest ossicle, fits
into the fenestra vestibuli
or oval window on the medial wall of
the tympanic cavity.
Functions of the Auditory Ossicles (p. 772)
- The auditory ossicles increase the
force but decrease the amplitude of the
vibrations transmitted from the tympanic membrane.
Muscles Moving the Auditory Ossicles
The Tensor Tympani Muscle (p. 773)
- This muscle is about 2 cm long.
- Origin: superior surface of the cartilaginous part of the
auditory tube, the greater wing of the sphenoid bone, and
the petrous part of the temporal bone.
- Insertion: handle of the malleus.
- Innervation: mandibular nerve (CN V3) through
the nerve to medial pterygoid.
- The tensor tympani muscle pulls the handle of the malleus
medially, tensing the tympanic membrane, and reducing the
amplitude of its oscillations.
- This tends to prevent damage to the internal ear when one
is exposed to load sounds.
Stapedius Muscle (p. 773)
- This tiny muscle is in the pyramidal eminence or the
- Origin: pyramidal eminence on the posterior wall of the
tympanic cavity. Its tendon enters the tympanic cavity by
traversing a pinpoint foramen in the apex of the pyramid.
- Insertion: neck of the stapes.
- Innervation: nerve to the stapedius muscle, which arises
from the facial nerve (CN VII).
- The stapedius muscle pulls the stapes posteriorly and
tilts its base in the fenestra vestibuli or oval window,
thereby tightening the anular ligament and reducing the
- It also prevents excessive movement of the stapes.
- Osseous labyrinth: a
complex system of cavities in the substance of the
- Membranous labyrinth:
filled with endolymph, bathed in perilymph.
- Note (quotation from Anatomy Class
Notes): "The students are not
required to know in detail about the inner ear, apart
from the fact that it is made up of the vestibule
(utricle, saccule, and 3 semicircular canals for
perception of position and movement of the head,
vestibular portion of CN VIII) and the cochlea for
hearing (cochlear portion CN VIII). Only a basic
understanding of the structure of the cochlea and its
role in hearing is required (Refer to Moore p.