Hearing - Middle Ear Development
|Embryology - 26 Sep 2017 Expand to Translate|
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- 1 Introduction
- 2 Some Recent Findings
- 3 Middle Ear Origins
- 4 Week 8
- 5 Ossicles
- 6 Malleus
- 7 Incus
- 8 Stapes
- 9 Tympanic Membrane
- 10 Middle Ear Muscles
- 11 Tympanic Cavity
- 12 Adult Middle Ear
- 13 Other Species
- 14 Additional Images
- 15 References
- 16 External Links
- 17 Glossary Links
The embryology of the middle ear requires many separate components from different embryonic origins. The tympanic membrane separates the outer ear from the middle ear and is formed initially from the first pharyngeal arch membrane. The middle ear bones (ossicles) are derived from separate origins in the first and second arch mesenchyme. The space in which these bones sit (tympanic cavity) is derived from the first pharyngeal pouch and is connected directly to the oral cavity by a hollow tube (auditory tube). In addition there are two muscles (tensor tympani and stapedius) formed from arch mesenchyme. (More? Pharyngeal Arches, Bone Development, Muscle Development).
Note that in other species, such as the guinea pig, the malleus and incus are normally found as a single complex.
Some Recent Findings
|More recent papers|
This table shows an automated computer PubMed search using the listed sub-heading term.
References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.
Oh Joon Kwon, Jae Moon Sung, Hwi Kyeong Jung, Chang Woo Kim Postoperative Mastoid Aeration Following Canal Wall Up Mastoidectomy according to Preoperative Middle Ear Disease: Analysis of Temporal Bone Computed Tomography Scans. J Audiol Otol: 2017, 21(3);140-145 PubMed 28942628
Neal Anthwal, Abigail S Tucker Q&A: Morphological insights into evolution. BMC Biol.: 2017, 15(1);83 PubMed 28915884
Neal Anthwal, Daniel J Urban, Zhe-Xi Luo, Karen E Sears, Abigail S Tucker Meckel's cartilage breakdown offers clues to mammalian middle ear evolution. Nat Ecol Evol: 2017, 1(4);93 PubMed 28812679
Toshiko Furutera, Masaki Takechi, Taro Kitazawa, Junko Takei, Takahiko Yamada, Tri Vu Hoang, Filippo M Rijli, Hiroki Kurihara, Shigeru Kuratani, Sachiko Iseki Differing contributions of the first and second pharyngeal arches to tympanic membrane formation in the mouse and chick. Development: 2017; PubMed 28807901
Ana Sánchez-Del-Rey, José Maria Sánchez-Fernández, Arantza Ibargutxi, Agustin Martinez-Ibargüen, Francisco Santaolalla A comparative morphologic and morphometric study about geniculate ganglion development in man and in rat. Acta Otolaryngol.: 2016;1-9 PubMed 27910733
Jose Francisco Rodríguez-Vázquez, Yohei Honkura, Yukio Katori, Gen Murakami, Hiroshi Abe Fetal development of the pulley for muscle insertion tendons: A review and new findings related to the tensor tympani tendon. Ann. Anat.: 2016; PubMed 27693602
José Francisco Rodríguez-Vázquez, Koji Sakiyama, Hiroshi Abe, Osamu Amano, Gen Murakami Fetal tendinous connection between the tensor tympani and tensor veli palatini muscles: A single digastric muscle acting for morphogenesis of the cranial base. Anat Rec (Hoboken): 2016; PubMed 26744237
A Blanke, H Aupperle, J Seeger, C Kubick, G F Schusser Histological Study of the External, Middle and Inner Ear of Horses. Anat Histol Embryol: 2014; PubMed 25283481
Middle Ear Origins
- neural crest from the first and second pharyngeal arches forms the cartilage origin of the middle ear bones (ossicles).
- first arch cartilage - (Meckel's) malleus and incus
- second arch cartilage - (Reichart's) stapes
- first pharyngeal pouch endoderm forms the auditory tube that enlarges to incorporate the tympanic cavity surrounding the ossicles.
- endoderm forms the lining epithelium and glands.
- mesoderm from the first and second arch forms the middle ear muscles
- first arch - tensor tympani muscle
- second arch - stapedius muscle
Middle Ear Genes - gooscoid, RARs, Prx1, Otx2, Hoxa1, Hoxb1, endothelian related molecules
Middle ear structure visible are the primordial maleus, the developing tensor tympani muscle, the developing auditory tube (tubo tympanic recess) extending from the oral cavity towards the middle ear region. Note the ossicle is still embedded, and surrounded by, the mesenchyme of the head.
Middle ear development begins closely associated with head formation and involves both the foregut tube (pharynx) and the pharyngeal arches. Pharyngeal arches form the main anatomical structures of the head and neck, including all components of the middle and outer ear.
The three middle ear bones or auditory ossicles (malleus, incus, stapes) are formed from the cartilage template found within pharyngeal arch 1 and 2. These bones are commonly named the hammer (malleus), anvil (incus) and stirrup (stapes), and the cartilage bands are historically named after two German anatomists and are called Meckel’s cartilage (first pharyngeal arch; named after Johann Friedrich Meckel, 1781–1833) and Reichert’s cartilage (second pharyngeal arch; named after Karl Bogislaus Reichert, 1811–1883). There are several theories as to how each arch cartilage contributes individual components of the middle ear ossicles. For example, a recent study suggests a mesenchymal origin for the stapes rather than directly from Reichert's cartilage. Meckel’s cartilage first appears histologically at Carnegie stage 16 and Reichert’s cartilage slightly later.
The early stages of auditory ossicle development all occur within the solid mesenchyme of the pharyngeal arches until the eighth month of development, then within a fluid-filled space for the final month, and finally only postnatal in the neonate in the air-filled tympanic cavity. This transition in auditory ossicle environment means that the middle ear does not function correctly until after birth, and any prenatal conduction to the cochlea must be mediated through bone conduction.
During development of the tympanic cavity, the auditory ossicles are held in their correct anatomic positions by supporting ligaments. Arch cartilages ossify by the process of endochondral ossification, where a pre-existing cartilage template is first formed and later replaced by bone. Endochondral ossification is the main process of bone formation throughout the entire skeleton, except for the cranial vault and the clavicle that ossify by a process of intramembranous ossification.
Initially, the malleus and incus form as a single structure, and it is only later that they separate to form two separate bones. Ossification continues through the entire fetal period, and the newly formed bones also have a transient bone marrow cavity. The marrow cavity is still present at birth, in both the malleus and the incus, and with continued ossification is lost during the first two years after birth. Postnatally, first the malleus and then the incus lose their marrow spaces.
Malleus (left) A. From behind. B. From within.
This ossicle was named from its resemblance to a hammer.
The structure of the adult bone can be divided into a head, neck, and three processes (manubrium, anterior and lateral processes). In the fetus, of the three processes the anterior process is the longest and is in direct continuity with Meckel's cartilage.
The newborn and infant malleus head normally contains bone marrow, that is eventually replaced by bone.
Malleus Development (timing from )
|Head (capitulum mallei)||large upper extremity of the bone, oval in shape||articulates posteriorly with the incus, being free in the rest of its extent||facet for articulation with the incus is constricted near the middle (consists of an upper larger and lower smaller part nearly a right angle with each other) opposite the constriction (lower margin of the facet projects in the form of a process, cog-tooth or malleus spur)|
|Neck (collum mallei)||narrow contracted part, just beneath the head||below it is a prominence||various processes are attached to the prominence|
|Handle (manubrium mallei)||connected by its lateral margin with the tympanic membrane||directed downward, medialward, and backward||decreases in size toward its free end, which is curved slightly forward, and flattened transversely. Medial side, near its upper end, is a slight projection, into which the tendon of the tensor tympani is inserted|
|Anterior Process (processus anterior (Folii), processus gracilis)||delicate spicule from the eminence below the neck||directed forward to the petrotympanic fissure||to which it is connected by ligamentous fibers|
|Lateral Process (processus lateralis, processus brevis)||a slight conical projection from the root of the manubrium||directed laterally, and is attached to the upper part of the tympanic membrane||attached by means of the anterior and posterior malleolar folds, to the extremities of the notch of Rivinus.|
|(some text modified from Gray's Anatomy)|
Incus (left) A. From within. B. From the front
| Originally named from resemblance to an anvil, onsists of a body and two crura.
The two crura diverge from one another nearly at right angles.
Gray suggested the incus has more like a "premolar tooth" appearance, with two roots, which differ in length, and are widely separated from each other.
Incus ossification is initiated in the fetal period.
Incus Development (timing from )
The newborn and infant incus body normally contains bone marrow, that is eventually replaced by bone.
|Body (corpus incudis)||somewhat cubical but compressed transversely||anterior surface is a deeply concavo-convex facet||facet articulates with the head of the malleus|
|Short Crus (crus breve, short process)||somewhat conical in shape||projects almost horizontally backward||attached to the fossa incudis, in the lower and back part of the epitympanic recess|
|Long Crus (crus longum, long process)||descends nearly vertically behind and parallel to the manubrium of the malleus||bending medialward, ends in a rounded projection, the lenticular process||lenticular process is tipped with cartilage, and articulates with the head of the stapes|
A. Left stapes. B. Base of stapes, medial surface.
Originally named by its resemblance to a stirrup and structurally consists of a head, neck, two crura, and a base.
Stapes Development (timing from )
|Head (capitulum stapedis)||presents a depression, which is covered by cartilage||articulates with the lenticular process of the incus|
|Neck||constricted part of the bone, succeeding the head||gives insertion to the tendon of the Stapedius muscle|
|Two crura (crus anterius and crus posterius)||diverge from the neck , connected at their ends by a flattened oval plate||anterior is shorter and less curved than the posterior|
|Base (basis stapedis)||forms the foot-plate of the stirrup||fixed to the margin of the fenestra vestibuli by a ring of ligamentous fibers|
The tympanic membrane (membrana tympani) or "ear drum", separates the external acoustic meatus from the tympanic cavity. In the adult, this thin membrane is nearly oval in shape about 9 to 10 mm in diameter. The circumference is slightly thickened to form a fibrocartilaginous ring that is attached to the tympanic sulcus at the inner end of the meatus. The malleus manubrium is attached to the medial surface of the membrane and is the mechanism for transmitting vibration of the tympanic membrane to the other middle ear ossicles. See also recent review.
Middle Ear Muscles
The middle ear also contains the two smallest muscles of the body, the stapedius and tensor tympani muscles, which both differentiate from arch mesenchyme. These muscles form and differentiate in a similar fashion to other developing skeletal muscle. Initially myoblasts proliferate under the influence of growth factors in the region of where the muscle will form. Myoblasts are the embryonic undifferentiated single cells of all skeletal muscles.
- The adult tensor tympani is classed as a mixed muscle containing slow (type 1) and fast (type 2A, and probably 2X) muscle fibers.
- The adult mammalian stapedius muscle contains mainly (77%) fast oxidative glycolytic type muscle fibers and the avian muscle only contains fast fibers.
A recent study of the stapedius region (see table below) and muscle development in 50 human embryos and fetuses between 38 days to 17 weeks post-conception identified 2 origins:
- for the tendon - derives from the internal segment of the interhyale
- for the belly - located in the second pharyngeal arch, medially to the facial nerve and near the interhyale
interhyale - term describing the internal part of the second pharyngeal arch that forms the tendon of the stapedius muscle
|Carnegie Stage||CRL (mm)||Description|
|13||6||Presumptive stapedial area|
|14||7||Appearance of the stapedial anlage|
|16||9||Relationship between the stapedial artery and the stapedial anlage. Appearance of the interhyale|
|17||12||Delimitation of the parts of the stapedial anlage|
|18||16||Chondrogenesis phase. Start of involution of the stapedial artery|
|20||18.5||Delimitation of the ossicular anlages. Cartilaginous phase. Disappearance of the stapedial artery|
|22||26||Delimitation of the interhyale|
|23||28||Anlage of the stapedial muscle tendon|
|Data summarised from Table 1|
The tympanic cavity (cavum tympani) extends from the first pharyngeal pouch to surround the middle ear ossicles. This small air-filled space is connected to the oral cavity by the narrow auditory tube. The adult tympanic cavity anatomy is a single space constricted slightly into an upper (attic) and a lower (atrium) chamber.
The auditory tube or eustachian tube (named after Bartolomeo Eustachi, 1500–1574) (or otopharyngeal or pharyngotympanic tube) develops from the first pharyngeal pouch and is lined with endoderm. This narrow cavity links the pharynx to the middle ear and is continuous with the tympanic cavity. The auditory tube has two main functions: ventilation, to allow the equalization of pressure in the middle ear, and clearance, to allow the middle ear fluid continuously produced by the epithelial lining to drain from the middle ear.
In normal human development, the auditory tube has an almost straight posterolateral to anteromedial pathway. The main growth of the auditory tube occurs in extension and lumen of the cartilaginous portion in the fetal period between weeks 16 to 28.
At birth, and in the young child, the tube is both shorter (8-9 mm) compared to the adult length (17-18 mm), runs almost horizontal and is narrower in diameter. Head growth in the child to adult size results in a longer wider tube that runs at approximately 45 degrees to the horizontal. The auditory tube is also normally closed and is opened by muscles—in the infant this is only a single muscle, the tensor palati muscle. In the adult the auditory tube is now opened by two separate muscles, the tensor palati and levator palati muscles.
he middle ear cavity or tympanic cavity is formed by an expansion of the pharynx. The initial early cavity lining is formed by the pharyngeal endoderm epithelium. The epithelium will then continue to expand, to eventually also line the entire mastoid antrum.
- 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 auditory tube(eustachian tube, pharyngotympanic tube)
Auditory Tube Postnatal Changes
Adult Middle Ear
The adult middle ear, like the inner ear, eventually will lie within the petrous portion of temporal bone. Initially, both the middle and inner ear form within mesenchyme, embryonic connective tissue, forming the otic capsule, and this will also form the base of the skull. The mesenchyme differentiates first to form cartilage, forming a structure known as the chondrocranium. This initial cartilage is gradually replaced by bone forming at a number of sites within the cartilage, ossification centers. The initial bone that is formed also contains marrow spaces that disappear with ongoing ossification (Yokoyama et al., 1999). Between the weeks 16 to 24, centers of ossification appear in the remaining cartilage of the otic capsule, and these continue to ossify to eventually form mastoid process of temporal bone.
Avian - the columella is a single ossicle, it has a shaft and footplate inserted into the oval window.
|Historic Disclaimer - information about historic embryology pages|
|Embryology History | Historic Embryology Papers)|
Keith A. Human Embryology and Morphology. (1902) London: Edward Arnold.
Frazer JE. The early formations of the middle ear and eustachian tube - a criticism. (1922) J Anat. 57(1): 18-30. PMID 17103958
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- Yoshitaka Takanashi, Shunichi Shibata, Yukio Katori, Gen Murakami, Shinichi Abe, Jose Francisco Rodríguez-Vázquez, Tetsuaki Kawase Fetal development of the elastic-fiber-mediated enthesis in the human middle ear. Ann. Anat.: 2013, 195(5);441-8 PubMed 23706648
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Masaki Takechi, Taro Kitazawa, Tatsuya Hirasawa, Tamami Hirai, Sachiko Iseki, Hiroki Kurihara, Shigeru Kuratani Developmental mechanisms of the tympanic membrane in mammals and non-mammalian amniotes. Congenit Anom (Kyoto): 2016, 56(1);12-7 PubMed 26754466
Susan Caroline Chapman Can you hear me now? Understanding vertebrate middle ear development. Front Biosci (Landmark Ed): 2011, 16;1675-92 PubMed 21196256
| PMC3065862 Masaki Takechi, Shigeru Kuratani History of studies on mammalian middle ear evolution: a comparative morphological and developmental biology perspective. J. Exp. Zool. B Mol. Dev. Evol.: 2010, 314(6);417-33 PubMed 20700887
Alison S Laufer, Joshua P Metlay, Janneane F Gent, Kristopher P Fennie, Yong Kong, Melinda M Pettigrew Microbial communities of the upper respiratory tract and otitis media in children. MBio: 2011, 2(1);e00245-10 PubMed 21285435
J F Rodríguez-Vázquez Development of the stapes and associated structures in human embryos. J. Anat.: 2005, 207(2);165-73 PubMed 16050903
May 2010 "Middle Ear Development" All (2368) Review (226) Free Full Text (272)
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