What is the blood supply of the outer ear?
a.Posterior auricular a. and v.
b.Superficial temporal a. and v.
What is the innervation to the outer ear?
a.Great auricular (C2,C3) and lesser occipital (C2,C3) nn
b.Auriculotemporal nerve (V3), facial n., vagus n.
What part of the EAM is bony?
What is the blood supply to the EAM?
1.Lateral 1/3 is cartilaginous; medial 2/3 is bony
a.Posterior auricular a. and v.
b.Superficial temporal a. and v.
c.Deep auricular a
What is the innervation to the EAM?
What is an important point to remember about the EAM in peds?
auriculotemporal and vagus
The cartilage part of EAM isnt fully formed so you must be careful or use a different otoscope tip
What is the function of the TM?
convert sound waves into vibrations of middle ear ossicles
The TM is concave from its external view, what causes this?
The TM has a Pars flaccida and pars tensa, which one vibrates for hearing?
Pars tensa- inferior thick walled portion that vibrates.
What is the blood supply to the TM external and internal surfaces?
Deep auricular branch of maxillary for external
Anterior tympanic branch of maxillary for internal
What innervates the external surface of TM?
Auriculotemporal nerve V3 and Vagus
Mesenchyme of the 1st and 2nd pharyngeal arches forms what?
auricular hillocks will later fuse to form the definitive auricle.
What are pits and appendiges on the ears associated with?
Now some embryology, the first pharyngeal cleft forms something what is it?
Persistence of the meatal plug can cause deafness, when does it degenerate?
by 7th month
The TM has three layers and external epithelium, middle connective tissue and internal epithelium, what are they derived from?
External- ectoderm of 1st pharyngeal cleft.
Middle- mesoderm of 1st arch
Internal endoderm of 1st pouch
What is the function of the middle ear?
1. Transfer of sound waves from gas to liquid medium(from external to internal ear).
2.Amplification of sound waves via vibration of bony ossicles.
3. Pretective response to loud sounds (via tnesor typani and stapedius mm)
What part of the tympanic cavity does the tegmen tympani form?
What is the floor of the tympanic cavity?
Temporal bone separating middle ear from internal jugular.
The TM is the lateral wall of the cavity, what is the medial wall?
This medial wall has a promontory, what forms this?
Bony wall separating middle from inner ear.
What is the function of the oval window that sits in the medial wall?
1. Opens to vestibule of internal ear.
2. Contacted by the stapes; transmits motion of stapes to fluid of internal ear.
1. Opens to scala tympani; covered with a thin membrane (round window membrane)
2. Acts as a pressure release valve for the fluids of the internal ear.
We already learned that the temporal bone formed the floor of the tympanic cavity, what other wall does it form?
Within the posterior wall there is an an opening called aditus ad antrum, what is its significance?
It is the entrance to the mastoid antrum,
a.Mastoiditis. Middle ear infections can sometimes spread to the mastoid air cells. Infections can then spread superiorly into the middle cranial fossa.
These infections are very hard to treat and CAN SPREAD TO MENINGES
Floor and posterior wall are temporal bone but wait there is another wall that is too, what is it? What does it seperate the middle ear from?
Anterior wall- separating middle ear from carotid canal. Receives opening for pharyngotympanic tube (auditory tube) and semi-canal (passage of tensor tympani).
What does the auditory tube connect?
What is its makeup (1/3 and 2/3 hint)
1.Cartilaginous and membranous tube connecting middle ear and nasopharynx.
2.Function – balances pressure on external and internal sides of tympanic membrane.
3.Posterolateral third is bony; anteromedial 2/3 is cartilaginous.
What muscle can open the auditory tube?
Bonus points what is its innervation?
1.Tensor veli palatini muscle can open the membranous tube (CN V3 innervation)
I have confidence that you know the 3 auditory ossicles so tell me what the malleus contacts and its function?
a.Contacts tympanic membrane; creates umbo.
b.Vibrates in response to movement of the tympanic membrane.
The base of the stapes contacts what structure?
What is its function?
a.contacts oval window.
b.Vibration of stapes induces motion of the fluid within the cochlear duct.
If someone can name the muscles of the inner ear and their innervation I will give them a cookie, (first try only though, be honest)
Stapedius, Facial nerve SVE
Tensor Tympani V2 SVE
While you eat the cookie you won your chewing sounds like a freight train in your head, what happened?
1.Paralysis of middle ear muscles can cause hyperacusis (excessive hearing acuteness) due to loss of dampening.
There are 5 arteries that supply the middle ear but only one venous drainage, take a stab? Hint put tympanic in the name.
1.Inferior tympanic a (from ascending pharyngeal a)
2.Anterior tympanic a (from maxillary a)
3.Posterior tympanic a (from stylomastoid a.)
4.Superior tympanic (from middle meningeal a.)
5.Artery of pterygoid canal (tubal branches to pharyngotympanic tube).
6.Venous drainage to ptergyoid plexus
CN IX provides GVA and GVE-P to the middle ear and beyond, what is that pathway?
Spend some time on this making sure you have it, Dr Funk loves the nerve pathways.
a.Tympanic branch (GVA; GVE-P) – enters middle ear via tympanic canaliculus; forms tympanic plexus on promontory of tympanic cavity.
b.The tympanic plexus provides sensory (GVA) and GVE-P innervation for the middle ear and pharyngotympanic tube.
c.Lesser petrosal nerve reforms from tympanic plexus and exits middle ear via the hiatus for the lesser petrosal nerve (GVE-P).
Damage to the middle ear could have an effect on what gland
RECALL – Lesser petrosal is the source of parasympathetic innervation to the parotid gland.
CN VII supplies SVE to what muscle in the ear and gives off chorda tympani in the process.
What is its course? This is a thinker, remember your foramen and what portions of the nerve exit where.
a.Supplies motor innervation to stapedius (SVE)
b.Enters internal acoustic meatus, courses along roof of inner ear toward middle ear.
c.Within middle ear, CN VII travels within the facial canal on posterior wall.
d.Chorda tympani is given off right before CN VII exits the middle ear at the stylomastoid foramen; chorda tympani passes between the incus and malleus and then exits the middle ear via the petrotympanic fissure. RECALL – this is the source of SVA to the anterior 2/3rds of the tongue and the source of GVE-P to the submandibular and sublingual glands.
How can the middle ear often become inflammed? (Ottis Media)
often due to spread of infection from pharynx via pharyngotympanic tube.
Ear infections can cause dry mouth, why?
pathways to salivary glands go through middle ear
More embryology, the tympanic cavity and auditory tube are kind pouches right, so they come from a pouch DUH, which one?
TEST ALERT, TEST ALERT
What structure do the stapes and stapedius m come from?
Where do the malleus, incus and tensor tympani come from?
Ok brainstorm, what is tensor tympani innervation and you have the answer.
Congential fixation of the stapes can cause what?
What, I can't hear you, what, deafness.
What bone is the internal ear within?
A.Housed within the petrous portion of the temporal bone, the internal ear contains the vestibulocochlear organ involved in balance and hearing.
What is the inner ear bony passages filled with?
Osseous spiral lamina anchors what to modiolus?
What are the membranous ducts filled with/
What does the vestibgular portion of CN VIII innervate?
semicircular ducts, utricle, and saccule to carry proprioceptive information (movements of the head) to the brain.
cochlear duct to carry information about sound to the brainstem.
How is sound produced? Start from external ear.
1. Airways travel down external acoustic meatus causing vibration of tympanic membrane.
2. Motion of the tympanic membrane causes vibration of the three middle ear ossicles.
3. Footplate of stapes contacts oval window and causes movement of the fluid in the inner ear.
4. Movement of fluid in the cochlear duct causes bending of the hair cells imbedded within the spiral organ.
5. Bending of these hair cells initiates signaling events which ultimately lead to propagation of a nerve impulse along the cochlear portion of CN VIII.
The inner ear actually forms in the neck, thats right more embryo
What does the Membranous labyrinth develop from?
1. Membranous labyrinth develops from otic placode (ectoderm)→ otic pit → otic vesicle
2. Bony labyrinth (vestibule, semicircular canals, cochlea) from surrounding mesenchyme.