Anatomy of the ear

2. ANATOMY AND PHYSIOLOGY OF
THE EAR
• An ear is the organ that enables hearing and (in mammals) body balance using the
vestibular system. In mammals the ear is usually described as having three parts: the
outer ear, the middle ear and the inner ear.
• The outer ear consists of the pinna and the ear canal. Since the outer ear is the only
visible portion of the ear in most animals, the word "ear" often refers to the external
part alone.
• External Ear It consists of :
Pinna and External auditory meatus
Pinna
It is made up of fibro elastic cartilage covered by skin and connected to the surrounding
parts by ligaments and muscles.
• Various landmarks on the pinna are helix, antihelix, lobule, tragus, concha, scaphoid
fossa and triangular fossa . Pinna has two surfaces i.e. medial or cranial surface and a
lateral surface .

5. Sensory nerve supply And
external acoustic meatus
lateral surface:
•Upper two- third is supplied by Auriculotemporal nerve (branch of fifth nerve).
• Lower one-third by Greater Auricular nerve (C2, C3)
Medial or Cranial surface of the pinna:
• Lower two-third is supplied by Greater Auricular nerve.
External acoustic meatus
External Acoustic Meatus: At birth only cartilaginous meatus is present because
the bony part develops from tympanic ring which is incompletely formed at that
time i.e. bony part of meatus is absent in newborn. Its length is 24 mm, outer one-
third (8 mm) being cartilaginous and inner two-thirds (16 mm) bony.
The canal forms a mild S-shaped curve directed medially, upwards and forwards
and then medially, backward and downward.

6. External meatus cont'd
• The canal has two constrictions in the EAC.
The external acoustic meatus does not have a straight
path, and instead travels in an S-shaped curve as follows:
Initially it travels in a superoanterior direction.
•In then turns slightly to move superoposteriorly.
•It ends by running in an inferoanterior direction
• Nerve supply of Meatus
• • Anterior and superior walls comes through
Auriculotemporal branch of Mandibular nerve,
• • Posterior and inferior walls are supplied byAuricular
branch of Vagus (Arnold’s nerve).

7. THE MIDDLE EAR
• The middle ear is an air-filled pressurized space within the
petrous portion of the temporal bone, extending from the
tympanic membrane (eardrum) to the lateral wall of the inner
ear. It is lined by mucous membrane and communicates with
the nasopharynx anteriorly via the pharyngotympanic
(Eustachian) tube and the mastoid antrum and air cells
posteriorly.
• Structurally, the middle ear is made up of two parts: the
tympanic cavity and epitympanic recess. The tympanic cavity is
directly medial to the tympanic membrane, whereas the
epitympanic recess is the space superior to the membrane.

9. THE MIDDLE CONTD
TEMPANIC MEMBRANE
• Tympanic membrane
• The tympanic membrane is an oval structure that is
situated at an angle relative to the external acoustic
meatus
• It is among the first to begin vibrating once it is struck
by the sound waves collected by the external auditory
meatus. This thin, fibrous structure has an external
surface that is exposed to the external environment
and lined by stratified squamous epithelium, and an
inner surface (facing the tympanic cavity) that is lined
by low columnar epithelium.

10. The middle ear condt
• Auditory ossicles
•
• The auditory ossicles are a chain of three small bones
located in the middle ear. From lateral to medial, these
are called the malleus (hammer), incus (anvil), and the
stapes (stirrup). Although they are the three smallest
bones in the human body, they are extremely
important components of the auditory pathway.
Through synovial articulations, these bones are able to
transmit mechanical energy from the tympanic
membrane to the oval window of the internal ear

11. The middle ear cont'd
Malleus
• The malleus is the largest, and most lateral of the bony chain. It is a club-
shaped structure whose head rests in the epitympanic recess and
articulates with the incus. The constricted region below the head forms the
neck, inferior to which are the anterior and lateral processes of the malleus.
The malleus extends below these processes as the handle of the malleus
which is connected to the medial surface of the tympanic membrane.
• Three ligaments secure the malleus to the walls of the tympanic cavity.
These are the anterior, superior and lateral ligaments of the malleus. The
anterior ligament of the malleus connects the neck of the malleus, just
above the anterior process, to the anterior wall of the tympanic cavity. The
superior ligament attaches on one end to the head of the malleus and on
the other end to the roof of the epitympanic recess. The head of the
malleus is equally connected to the tympanic membrane via the lateral
ligament

13. The incus and stape
INCUS
The incus is the anvil-shaped central ossicle which connects the malleus to the stapes. It
has two limbs and a cuboidal body. The body of the incus sits in the epitympanic recess,
where it articulates with the head of the malleus. Its long limb extends into the
tympanic cavity alongside the handle of the malleus and articulates with the stapes.
The short limb of the incus extends posteriorly and is connected to the upper posterior
wall of the tympanic cavity by a ligament
STAPES
The stapes is the smallest and most medial in the chain of ossicles. The head of stapes
articulates with the long process of the incus laterally. The head is supported by a
constricted narrow neck, from which two processes or crura, namely the anterior crus
and posterior crus diverge. The crura are connected to an oval plate which forms the
base or footplate of the stapes and sits over the oval window (fenestra vestibuli). The
articulation between the footplate of the stapes and the oval window plays an essential
role in the transmission of sound vibrations in the middle ear to the fluid in the
vestibule of the inner ear.

14. Middle ear muscle
• The stapedius muscle originates from the internal
concavity of a small projection on the mastoid wall
called the pyramidal eminence (pyramid).
• The tensor tympani muscle originates from the
cartilaginous portion of the auditory tube, the
greater wing of the sphenoid bone, and the petrous
part of the temporal bone.

15. Blood supply and venous drainage
Blood supply
The blood supply from division of the external carotid artery, which is
complemented by branches of the internal carotid artery.
• The deep auricular artery (from the maxillary artery
• The anterior tympanic artery
Venous drainage
The tympanic veins drain deoxygenated blood to the superior petrosal sinus
and the pterygoid venous plexus.
Innervation
The auriculotemporal nerve (branch of CN V3) and the vagus nerve

16. • INTERNAL EAR
•
• • It consists of a bony labyrinth contained with in the petrous temporal bone along with the
membranous labyrinth. It serves the most important function of hearing and equilibrium.
•
• Bony Labyrinth
• • It consists of: -Vestibule, Semicircular canals, Cochlea.
VESTIBULE:
ovoid in shape measuring 5 mm × 3 mm & forms the central part of bony labyrinth.
•
• • It has a spherical recess containing Saccule, a Cochlear recess for cochlear duct and an
elliptical recess for Utricle. • Opening of vestibular aqueduct lies below elliptical recess.
• Posterior part of vestibule has 5 openings of 3 semicircular canals.
• Lateral wall has the fenestra vestibuli or oval window. Its medial wall is related to internal
acoustic meatu

17. The internal ear
• It is shaped like a conical snail shell, measures 35 mm (long) × 5
mm (base to apex) and 9 mm across its base. Cochlea has a
central conical axis called modiolus with a spiral canal of 2.5 to
2.75 turns around it.
• Apex of cochlea points towards anterosuperior part of medial wall
of middle ear cavity and the base is towards the fundus of internal
acoustic meatus.
Branches from the cochlear portion of the vestibulocochlear (VIII)
nerve are found at the base of the modiolus.
The presence of the cochlear duct creates two perilymph-filled
chambers above and below:
Scala vestibuli: Located superiorly to the cochlear duct. As its name
suggests, it is continuous with the vestibule.

18. The internal cont'd
• Scala tympani: Located inferiorly to the cochlear duct.
It terminates at the round window.
• Semi-circular Canals
•
• There are three semi-circular canals: anterior, lateral
and posterior. They contain the semi-circular ducts,
which are responsible for balance (along with the
utricle and saccule).
•
• The canals are situated superoposterior to the
vestibule, at right angles to each other. They have a
swelling at one end, known as the ampulla.

20. Membranous Labyrinth
• Membranous Labyrinth
• It lies within the osseous labyrinth and is filled with enendolymphaticl fluid.
Vestibulocochlear nerve fibres are distributed in the walls of membranous labyrinth.
The membranous labyrinth is separated from the bony labyrinth by perilymphatic fluid.
• It has the following parts:• a. Utricle b. Saccule
• c. Semicircular ducts.
Structure of utricle, saccule and semicircular ducts
Each has three layers.
i) External layer is fibrous and vascular,
ii) Middle layer is vascular connective tissue and
iii) Internal layer is simple epithelium varying from squamous to cuboidal with a
basement membrane having light and dark cells

21. Membranous Labyrinth cont'd
• Saccule and Utricle
•
• The saccule and utricle are two membranous sacs located in the vestibule. They are
organs of balance which detect movement or acceleration of the head in the vertical
and horizontal planes, respectively.
•
• The utricle is the larger of the two, receiving the three semi-circular ducts. The
saccule is globular in shape and receives the cochlear duct.
•
• Endolymph drains from the saccule and utricle into the endolymphatic duct. The duct
travels through the vestibular aqueduct to the posterior aspect of the petrous part of
the temporal bone. Here, the duct expands to a sac where endolymph can be
secreted and absorbed.
• Semi-circular Ducts
•
• The semi-circular ducts are located within the semi-circular canals, and share their
orientation. Upon movement of the head, the flow of endolymph within the ducts
changes speed and/or direction.

22. Cont'd
• Sensory receptors in the ampullae of the semi-circular canals detect this change, and send
signals to the brain, allowing for the processing of balance.
• Vasculature
• The bony labyrinth and membranous labyrinth have different arterial supplies. The bony
labyrinth receives its blood supply from three arteries, which also supply the surrounding
temporal bone:
•
• Anterior tympanic branch (from maxillary artery).
• Petrosal branch (from middle meningeal artery).
• Stylomastoid branch (from posterior auricular artery).
•
• The membranous labyrinth is supplied by the labyrinthine artery, a branch of the inferior
cerebellar artery (or, occasionally, the basilar artery). It divides into three branches:
•
• Cochlear branch – supplies the cochlear duct.
• Vestibular branches (x2) – supply the vestibular apparatus.
• Innervation
• Vestibule nerve and cochlear nerve

23. Reference
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Basis Of Disease. 9th ed. Philadelphia, PA: Saunders Elsevier,
2015. Print.
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• •'Notes & Querries': Scientific American 50.14 (1884): 218. Web.
30 May 2015.
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Edinburgh: Churchill Livingstone/Elsevier, 2011. Print.
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Ballenger's Otorhinolaryngology. 16th ed. Hamilton, Ont.: BC
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