Ear Development Flashcards
What makes up the external ear?
Auricle (pinna), external acoustic meatus, and external layer of tympanic membrane
What makes up the middle ear?
3 ossicles, internal layer of tympanic membrane, and middle ear cavity
What makes up the internal ear?
Vestibulocochlear organ
What is the auricle derived from? What embryological layer does this come from?
Derived from PA1 and PA2; comes from neural crest cells
What are auricular hillocks?
Mesenchymal swellings covered with ectoderm
What nerves give innervation to the external ear?
Great auricular, V3 (auriculotemporal branch), VII, and X (auricular branches)
Where is the external auditory meatus derived from? What is posterior to this meatus?
First pharyngeal cleft; meatal plug
Where is the inner ear derived from?
Ectoderm
What week does the otic placode, otic pit, and otic vesicle all develop? What do these form?
4th week; primordium of membranous labyrinth
What makes up the membranous labyrinth?
Utricle (dorsally) and saccule (ventrally)
What are the components of the utricle?
Endolymphatic duct and sac, semicircular ducts and ampullae, a lateral canal, and the macula of the utricle
What are the components of the saccule?
Cochlear duct, ducuts reunions, the macula of the saccule, and the organ of Corti
What are the hair cells of the inner ear and what do they do?
Ampullae: function during acceleration
Macula: function with gravity
Organ of Corti: function in sound vibration
What is the innervation of the inner ear?
VIII; specifically the vestibular ganglion and the spiral (cochlear) ganglion
What is perilymph and the perilymphatic duct? What is the ion content of perilymph and what is it similar to?
Perilymphatic duct is usually patent - a free passage from the subarachnoid space into the inner ear; perilymph may come from filtration of blood in perilymphatic space; it is similar in ion content to CSF (high Na, low K and protein)
What produces endolymph? What is the ion content and what is it similar to?
Stria vascularis appears to produce endolymph while endolymphatic sacs store endolymph; similar in ion content to intracellular fluid (high K and protein, low Na)
What is the bony labyrinth? What are the vacuoles in the bony labyrinth?
It is a condensation of mesenchyme; vacuoles are perilymphatic space (semicircular ducts), scala vestibuli, and scala tympani
What happens to the bony labyrinth?
Ossifies and becomes the petrous part of the temporal bone
In the middle ear, where does the external auditory meatus come from?
1st pharyngeal cleft (ectoderm)
In the middle ear, where does the tubotympanic recess come from?
1st pharyngeal pouch (endoderm)
In the middle ear, where does the tympanic membrane come from?
Derived from ectoderm, mesoderm, and endoderm
In the middle ear, where does the malleus and incus come from? Stapes?
Malleus and Incus: PA1
Stapes: PA2
In the middle ear, what are the ossicles covered with?
Endodermal epithelium
Where does the tensor tympani insert? What is its action? Where is it derived from?
Insertion: into handle of malleus
Action: prevents damage from loud sounds
Derived: PA1 mesoderm
Where does the stapedius insert? What is its action? Where is it derived from?
Insertion: neck of stapes
Action: pulls the stapes posteriorly and tilts its base in the oval window; prevents damage from loud sounds
Derived: PA2 mesoderm
What is congenital deafness? What is it usually caused by?
Occurs when inner ear forms independently from the middle and external ears; usually caused by genetic factors; can be caused by defects in neurosensory sensory structures of the inner ear and other problems
Another cause of congenital deafness is maldevelopment of sound-conduction apparatus of the middle and external ears. Why does this occur?
It is a PA1 syndrome, specifically abnormalities of the malleus and incus or congenital fixation of the stapes
What infections can cause congenital deafness?
Rubella, cytomegalovirus, toxoplasmosis, syphilis, and zika
Explain a rubella infection in terms of congenital deafness
Infection during 7th-8th week can cause defects of the spiral organ and deafness
What is the leading cause of congenital sensorineural hearing loss?
Cytomegalovirus
What ear defects can cytomegalovirus cause?
Sensorineural hearing loss
What ear defects can rubella virus cause?
Sensorineural deafness
What ear defects can toxoplasma gondii cause?
Hearing loss
What ear defects can treponema pallidum cause?
Congenital deafness
