UNSW Embryology

Development of the Organs of Audition and Equilibrium

 Middle Ear

© Dr Mark Hill (2008)

Acknowledgements

Introduction

Hearing Anatomy

Cartilage origins of the middle ear ossicles (bones)

The middle ear ossicles (bones) are derived from 1st and 2nd arch mesenchyme. The space in which these bones sit is derived from the 1st pharyngeal pouch.

Page Links: Introduction | Some Recent Findings | Middle Ear Ossicles | Malleus | Incus | Stapes | Ossicle Joints | Middle Ear Muscles | Development Timing | Development Overview | Abnormalities | stage 13/14 embryo | stage 22 embryo | References | Terms | Glossary

External Link: Embryo Images Unit - Middle Ear

Some Recent Findings

Rodriguez-Vazquez JF. Development of the stapes and associated structures in human embryos. J Anat. 2005 Aug;207(2):165-73.

"The objective of this study was to clarify the development of the stapes in humans and its relationship with the cartilage of the second branchial arch. The study was carried out in 25 human embryos between 6 and 28 mm crown-rump length. The stapes develops at the cranial end of the second branchial arch through an independent anlage of the cartilage of this arch. Between the stapedial anlage and the cranial end of the Reichert's cartilage there is a formation called the interhyale, the internal segment of which gives rise to the tendon of the stapedial muscle. The stapedial anlage is a unique formation with two distinct parts: the superior part that will comprise the base and the inferior part that will be crossed by the stapedial artery during embryonic development and will constitute the limbs and the head of the stapes. According to the results, the otic capsule is not involved in formation of the base of the stapes."

Rowe TM, Rizzi M, Hirose K, Peters GA, Sen GC. A role of the double-stranded RNA-binding protein PACT in mouse ear development and hearing. Proc Natl Acad Sci U S A. 2006 Mar 29; [Epub ahead of print]

".. Pact(-/-) mouse were reduced size and severe microtia. As a result of the congenital abnormality of both outer and middle ears, these mice were hearing impaired. Our study demonstrated an essential role of PACT in mammalian ear development and produced the first animal model for studying human microtia."

Middle Ear Ossicles

 

Malleus

Malleus (Left , from behind and within)
Incus

Incus (Left, from within and front)

Historic images of the middle ear ossicles

Stapes (Left, and base of stapes, medial surface)

Development Timing

Week 3 - otic placode, otic vesicle

Week 5 - cochlear part of otic vesicle elongates (humans 2.5 turns)

Week 9 - Mesenchyme surrounding membranous labrynth (otic capsule) chondrifies

Week 12-16 - Capsule adjacent to membranous labrynth undegoes vacuolization to form a cavity (perilymphatic space) around membranous labrynth and fills with perilymph

Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form petrous portion of temporal bone. Continues to ossify to form mastoid process of temporal bone.

3rd Trimester - Vibration acoustically of maternal abdominal wall induces startle respone in fetus.

(These are Human embryonic timings, not clinical which is based on last menstral period +2 weeks)

3 Sources:

Inner ear - epidermal otic placode at level of hindbrain.

Middle ear - cavity: 1st pharyngeal pouch, ossicles: mesenchyme 1st and 2nd pharyngeal arches.

Outer ear - external auditory meatus: 1st pharyngeal cleft, auricle: 6 hillocks 1st and 2nd pharyngeal arches.

Malleus

Malleus (Left , from behind and within)

Malleus is initially connected to Meckel’s cartilage during the fisrt and second trimester.

Processus anterior mallei

Malleus and incus are fused as a single complex (malleal-incudo) in adult guinea pigs.

(More? Incudomallear Articulation)

Incus

Incus (Left, from within and front)

(More? Incudomallear Articulation)

Stapes

Stapes (Left, and base of stapes, medial surface)

Stapes primordium

Develops at the cranial end of the second pharyngeal arch through an independent portion of arch cartilage.

Two distinct parts:

Interhyale - lies between the stapedial primordium and the cranial end of the Reichert's cartilage (its internal segment of generates the tendon of the stapedial muscle).

(Text modified from: Rodriguez-Vazquez JF. Development of the stapes and associated structures in human embryos. J Anat. 2005 Aug;207(2):165-73.)

Stapes is usually synostotically fixed in the fenestra vestibuli in sea-cows (manatus) and whales.

(More? Incudostapedial Articulation | Stapediovestibular Articulation)

Ossicle Joints

Incudomallear Articulation (diarthrosis and sellar joint characteristics)

week 7 - homogenous interzone

week 8 - a three-layered interzone

week 9 - first cavitation signs

week 10 - presence of an articular cavity

week 20 - presence of a hyaline cartilage covering articular surfaces

Gliding motion in this joint - generates an upward and downward movement of the anvil.

Incudostapedial Articulation (diarthrosis and spheroidal joint characteristics)

week 7 to 12 - homogenous interzone

week 16 - completed cavitation

week 29 - presence of a hyaline cartilage covering articular surfaces

Gliding motion in this joint.

Stapediovestibular Articulation (syndesmosis joint characteristics)

Week 12 - definitive characteristics

Stapes and the inner ear are decoupled.

(Developmental timing data: Whyte JR, Gonzalez L, Cisneros AI, Yus C, Torres A, Sarrat R. Fetal development of the human tympanic ossicular chain articulations. Cells Tissues Organs. 2002;171(4):241-9.)

In developing guinea pigs, malleus and incus joint formation (incudomallear articulation) is initiated but does not proceed to cavitation, leaving a single complex divided by a thin suture.

(Data: Amin S, Tucker AS. Joint formation in the middle ear: lessons from the mouse and guinea pig. Dev Dyn. 2006 May;235(5):1326-33.)

Joint Classifications

Diarthroses - freely movable articulations

Syndesmosis - slightly movable articulations

Sellar joint - (saddle-joint) opposing surfaces are reciprocally concavo-convex

Spheroidal joint - (enarthrosis or ball and socket joint) distal bone is capable of motion around an indefinite number of axes, which have one common centre

Middle Ear Muscles

Tensor tympani muscle

Muscle draws the tympanic membrane medialward increasing its tension.

Nerve supply - branch of the mandibular nerve through the otic ganglion.

Arises from the cartilaginous portion of the auditory tube. In bony canal above the osseous portion of the auditory tube.

Ends in a slender tendon which enters the tympanic cavity, makes a sharp bend around the extremity of the septum.

Inserted into the manubrium of the malleus, near its root.

Stapedius muscle

Muscle pulls the head of the stapes backward, increasing the tension of the fluid within the inner ear.

Nerve supply - branch of the facial nerve.

Arises from the wall of a conical cavity, hollowed out of the interior of the pyramidal eminence;

Tendon emerges from the orifice at the apex of the eminence.

Inserted into the posterior surface of the neck of the stapes.

Stapedius muscle reflex (SMR) - ound-evoked contraction of the stapedius muscle used in the diagnostics of auditory processing disorders.

(Some text modified from Gray's Anatomy)

Developmental Overview

  • middle
  • Middle- tympanic cavity
    • derived from first pharyngeal pouch
    • extends as tubotympanic recess
    • during week 5 recess contacts outer ear canal
  • mesoderm between 2 canals forms tympanic membrane
  • expands to form tympanic recess
  • stalk of recess forms eustacian tube
  • pharyngotympanic tube
  • Middle- Ossicles
  • first arch mesoderm
  • second arch mesoderm
  • Middle Ear Genes

    • Stage 13/14 Embryo

    A2: Otocyst (R). Apex of otocyst (primordium of L endolymphatic sac).

    A3: Otocyst; surrounding mesenchyme = otic capsule. Note proximity of otocyst to wall of rhombencephalon. Superior glossopharyngeal ganglion. Vestibulo-cochlear-facial ganglion complex (R). Trigeminal ganglion (not in image excerpt).

    A4: Indentation in rostral margin of otocyst = primordium of utriculosaccular canal. Note alignment of superior cardinal vein (LS) in relation to the nerve trunks (XS). Trigeminal ganglion (not in image excerpt). Note variation in height of cells of L otocyst wall. Dorsal end of 1st pharyngeal arch and groove (not in image excerpt).

    A5: Facial ganglion (R). "Floor" of L otocyst. Note on R, the former position of the otocyst in relation to the 2nd pharyngeal arch.

    Stage 22 Embryo

    B3: Rhombic lip (developing cerebellum). IVth ventricle. Trigeminal ganglion. Adenohypophysis. Sphenoid cartilage.

    B4: Cochlear duct and temporal cartilage. Semicircular duct (ampulla on L). precartilage of auricle (pinna). malleus (medial, L). Incus (lateral, L).

    B5: Extemal auditory meatus. Auricle. Incus (dorsal). Malleus (ventral). Tubotympanic recess (auditory rube). Tensor tympani m. (L). Utricle. Semicircular ducts. Intemal auditory meatus (R), containing vestibular and spiral ganglia. Endolymphatic sac (L). Note proximity of sac to choroid plexus of 4th ventricle.

    B6: External auditory meatus. Primordium of tympanic membrane (L). Manubrium of malleus(L). Basal turn of cochlea duct (L). Endolymphatic sac (R). Common crus (R). Junction of utricle and saccule (R). Meckel's cartilage. Stapes (R). Auditory tube.

    Stage 22 Embryo (selected)


    Regions of stage 22 embryo head (mouth at top) in selected images of inner ear below

    Abnormalities

    Ossicle Abnormalities

    spindle handle - (from shape of the malleus handle) disconnection between the long process of the incus and the capitulum of the stapes.

    malleus bar - small bony bar connects tip of the malleus handle to posterior wall of the tympanic cavity (malleus fixation).

    dislocated annulus - annulus is dislocated cranially in relation to the middle-ear structures.

    Muscle Abnormalities

    Middle-ear myoclonus -Tinnitus produced by repetitive contraction of the middle ear muscles. Treated by sectioning the tensor tympani and stapedial tendons.

    Syndromes Associated with Middle Ear Abnormalities

    Beckwith–Wiedemann syndrome - malleus and stapedial fixation.

    References

    Molecular Normal Development

    List of recent Ear Development Reviews

    Recent Reviews Abnormal Development

    Hearing Development Terms

    ampulla

    auricle

    - "ear"

    Cranial Nerve VIII

    cristae ampularis

    Equilibrium

    Eustacian tube

    Hillock

    ossicles

    Otic vesicle

    - otocyst

    Pharyngeal arch

    Pharyngeal cleft

    Pharyngeal pouch

    Pharynx

    Placode

    Semicircular canals

    tympanic membrane

    - "eardrum"

    Glossary of Terms

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