Hearing - Middle Ear Development: Difference between revisions
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==Some Recent Findings== | ==Some Recent Findings== | ||
==Ossicles== | |||
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. Meckel’s cartilage first appears histologically at 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. | |||
==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. | |||
==Tympanic Cavity== | ==Tympanic Cavity== | ||
Revision as of 22:23, 14 April 2011
Introduction
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.
Some Recent Findings
Ossicles
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. Meckel’s cartilage first appears histologically at 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.
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.
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 auditory tube(eustachian tube, pharyngotympanic tube)
Ossicles
- develop from first and second pharyngeal arches
- tympanic cavity enlarges to incorporate
- coats with epithelia
- first arch mesoderm
- tensor tympani muscle
- malleus and incus
- second arch mesoderm
- stapedius muscle and stapes
Middle Ear Genes - gooscoid, RARs, Prx1, Otx2, Hoxa1, Hoxb1, endothelian related molecules
Additional Images
References
Reviews
Articles
Search PubMed
May 2010 "Middle Ear Development" All (2368) Review (226) Free Full Text (272)
Search Pubmed: Middle Ear Development | Ossicle Development | Malleus Development | Incus Development | Stapes Development
External Links
- Neuroscience Neuroscience - The Middle Ear
Glossary Links
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Cite this page: Hill, M.A. (2024, May 18) Embryology Hearing - Middle Ear Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Hearing_-_Middle_Ear_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
