Ear Development Flashcards
What is the critical development period of the ear?
Weeks 4-8
What are the components of the external ear?
Auricle (Pinna)
External Acoustic Meatus
External layer of Tympanic Membrane
What are the components of the middle ear?
Three Ossicles (Incus, Malleus, Stapes)
Internal layer of Tympanic Membrane
Middle ear cavity
What are the components of the inner ear?
Vestibulocochlear organ
The component of the outer ear is developed from the 1st and 2nd pharyngeal arches.
Auricle
The Auricle is developed from ________ _______ which are from NCC and are swellings covered with Surface Ectoderm.
Auricular Hillocks
What innervates the external ear?
Great Auricular N.
Auriculotemporal N. (CN V3) – from 1st arch
CN VII – from 2nd arch
Auricular branches (CN X)
When skin tags or formed by the ear, this could be the result of what?
– The Auricular Hillocks did not migrate properly IF there is NCC (cartilage) within the skin tags.
– The Surface Ectoderm did not migrate properly
How is Anotia (no ear) caused?
Abnormal migration of NCC, no Auricular Hillocks were formed.
How is Microtia (small ear) caused?
Abnormal migration of NCC (abnormal migration of Auricular Hillocks).
The External Auditory Meatus is formed by what pharyngeal component?
1st Pharyngeal Cleft (Groove)
The 1st Pharyngeal Cleft (Groove) will meet up with the 1st Pharyngeal Pouch, and this will induce the formation of the…
Meatal plug – This closes off the opening until later stages when the cells undergo apoptosis and create the actual External Auditory Meatus.
The Tubotympanic Recess, which meets up with the 1st Pharyngeal Cleft to make the meatus, is derived from what pharyngeal component?
1st Pharyngeal Pouch
***Becomes Tympanic Cavity
The inner ear is developed from what embryological layer?
Surface ectoderm
In the formation of the inner ear, a new genetic program starts that initiates the thickening of the Surface Ectoderm which forms the _______ _______. This will invaginate and form the _______ _______, which will eventually round up and form the ________ ________.
Otic Placode
Otic Pit
Otic Vesicle
The inner ear is developed during what week?
4th week
The Otic Placode, Otic Pit, and Otic Vesicle (all inner ear) form the primordium of…
Membranous Labyrinth
T/F. As the mandibular prominence grows together medially, the ears will rise up to their appropriate spot on the head.
True
The Membranous Labyrinth (from Surface Ectoderm) is divided into a ventral and dorsal side. What develops from the dorsal side?
Utricle
Endolymphatic Duct and Sac
Semicircular Ducts and Ampullae
Macula of Utricle
The Membranous Labyrinth (from Surface Ectoderm) is divided into a ventral and dorsal side. What develops from the ventral side?
Saccule Cochlear Duct Ductus reunions Macula of Saccule Organ of Corti
Where are hair cells located in the inner ear?
Ampullae
Macula of Utricle and Saccule
Organ of Corti
Hair cells are derived from what embryological layer?
Surface Ectoderm
***Remember, they’re in the inner ear and it is surface ectoderm!
What do the hair cells in the Ampullae detect?
Rotational acceleration
What do the hair cells in the Macula of the Utricle and Saccule detect?
Gravity and linear acceleration
What do the hair cells in the Organ of Corti detect?
Sound vibration
T/F. Hair cells are easily regenerated, so if damaged they can grow back quickly.
False. When hair cells are damaged they don’t come back.
There is a Perilymphatic Duct that opens into the Subarachnoid Space. This duct can be reached from the middle ear’s Tympanic Cavity, why can this be bad?
If you get a chronic middle ear infection, which is in the Tympanic Cavity, then the infection can get into the Perilymph and reach the Perilymphatic Duct where it can drain into the Subarachnoid Space. This can cause Meningitis!
The Membranous Labyrinth has (CANALS/DUCTS) and contains hair cells. It has (PERILYMPH/ENDOLYMPH) inside of it.
Ducts
Endolymph
The Bony Labyrinth has (CANALS/DUCTS) and is separated from the Membranous Labyrinth via (PERILYMPH/ENDOLYMPH).
Canals
Perilymph
The inner ear is innervated by which cranial nerve?
CN VIII (Vestibulocochlear)
CN VIII (Vestibulocochlear) is derived from which embryological layer?
Surface Ectoderm
CN VIII (Vestibulocochlear) is derived from the Otic Placode (surface ectoderm). The ganglion that form the nerve are…
Vestibular Ganglion
Spiral (Cochlear) Ganglion
This substance is similar in content to the CSF, has high Na+, low K+ and protein.
Perilymph
This substance is similar in content to the intracellular fluid, has high K+ and protein and low Na+.
Endolymph
This endolymph is produced by the…
Stria vascularis
This is what stores endolymph.
Endolymphatic sac
This is formed by a condensation of mesenchyme (mostly mesoderm), and there are vacuoles that form within it.
Bony Labyrinth
The vacuoles in the bony labyrinth give rise to what?
Perilymphatic space (Semicircular ducts)
Scala Vestibuli
Scala Tympani
This is part of the cochlear duct and is made of surface ectoderm. It is surrounded by mesenchyme and the bony labyrinth. Contains endolymph.
Sclera Media
These two components of the bony labyrinth hold perilymph.
Scala Vestibuli
Scala Tympani
There are ligaments made from mesenchyme that stabilize the Organ of Corti. This component is located within these ligaments.
Stria Vascularis
***This produces endolymph!
Where is the bony labyrinth being formed?
Petrous part of Temporal bone
The middle ear part of the External Auditory Meatus is made what embryological layer and what pharyngeal component?
Surface Ectoderm
1st Pharyngeal Cleft (Groove)
In the middle ear, the Tubotympanic Recess is formed from what embryological layer and what pharyngeal component?
Endodermal epithelium
1st Pharyngeal Pouch
In the middle ear, the Tympanic Membrane is formed from what embryological layer and what pharyngeal component?
Surface Ectoderm, Mesoderm, and Endoderm
1st Pharyngeal Membrane
In the middle ear, the Malleus, Incus, and Stapes are formed from what embryological layer and what pharyngeal component?
Malleus and Incus – NCC and 1st Pharyngeal Arch
Stapes – NCC and 2nd Pharyngeal Arch
The ossicles in the middle ear (Malleus, Incus, and Stapes) are covered with what?
Endodermal epithelium
This muscle of the ear is derived from mesoderm and inserts on the handle of the Malleus. It prevents damage from loud sounds.
Tensor Tympani
What embryological layer and pharyngeal component is the Tensor Tympani derived from?
Mesoderm
1st Pharyngeal Arch
What innervates the Tensor Tympani?
CN V
***Remember, Tensor Tympani is from 1st pharyngeal arch and so is CN V
This muscle is derived from mesoderm and inserts on the neck of the Stapes. It pulls the Stapes posteriorly and tilts its base in the oval window. Prevents damage from loud sound.
Stapedius
What embryological layer and pharyngeal component is the Stapedius derived from?
Mesoderm
2nd Pharyngeal Arch
What innervates the Stapedius?
CN VII
***Remember, Stapedius is from 2nd pharyngeal arch and so is CN VII
This can occur because the inner forms independently from the middle and external ears. It is most often from genetic factors such as:
- Maldevelopment of sound-conduction apparatus of middle and external ears
- Neurosensory sensory structures of inner ear
- Infections
Congenital Deafness
What are some of the infections that can cause congenital deafness?
- Rubella
- Cytomegalovirus
- Toxoplasmosis
- Syphilis (Treponema pallidum)
- Zeka
What are the maldevelopments of the sound-conduction apparatus of the middle and external ear that can cause congenital deafness?
- First arch syndrome
- Abnormalities of Malleus and Incus (1st arch – NCC)
- Congenital fixation of the Stapes (2nd arch – NCC)
Contracting this infection during the 7-8th week of development can cause defects of the spiral organ and deafness.
Rubella
This is the leading cause of congenital sensorineural hearing loss.
Cytomegalovirus
***Form of herpes virus
