Ear and Temporal Bone- Gilland

Question 1

Temporal bone consists of:

Answer 1

squamous

petrous

Question 2

Difference between EAM and IAM

Answer 2

The internal auditory meatus (also meatus acusticus internus, internal acoustic meatus, internal auditory canal, or internal acoustic canal) is a canal within the petrous part of the temporal bone of the skull between the posterior cranial fossa and the inner ear.

The ear canal (external acoustic meatus, external auditory meatus, EAM; Latin: meatus acusticus externus) is a tube running from the outer ear to the middle ear.

Question 3

Petrous Temporal Bone

Answer 3

• Intracranial surfaces are covered by dura of middle and posterior cranial fossae
• surrounded by Dural Venous Sinuses:

Cavernous Sinus
Superior Petrosal Sinus
Inferior Petrosal Sinus
Sigmoid Sinus

Question 4

Petrous part of the Temporal Bone

Answer 4

• means stony or hard and is very densely mineralized much more than most bones because it has the inner ear inside of it
• the part that contains the middle ear cavity, the inner ear cavity, and passing through it are internal carotid artery, right next to it leaving the skull would be the internal jugular vein and the CN VII, IX, X (either go through the bone or send branches into the bone to provide critical innervation)
• has internal auditory meatus in the middle
• is completely covered by dura on its upper surface

Question 5

External Ear

Pinna (= auricle, = external ear)

Answer 5

• the end of the ear canal is the tympanic membrane
• made up of elastic cartilage covered by thin skin
• funnels sound waves into canal
• asymmetric path assists vertical localization of sound sources
• helix; antihelix (deep to the helix); tragus (funny little piece in front of the ear); concha (shell in the antihelix); lobule (lower part of the ear) makes up the great outer curvature of the ear
• auricular muscles which are part of the muscles of facial expression ??and innervated by facial nerve; there is no significant functional aspect of these muscles

Question 6

Middle Ear

Answer 6

-when you cross through the tympanic membrane you enter into the middle ear which is very long because the pharyngotympanic tube which opens in the pharynx is an extension of the middle ear cavity

-contains the ear ossicles
that when infected gives you intense pain:
-malleus (hammer): has manubrium which was attached to TM; neck is where the chorda tympani passes across, head has an articular facet which will articulate with the articular facet of the incus; anterior process
-incus (anvil)
-stapes (stirrup)

Question 7

Inner Ear

Answer 7

-seed of your vestibular and auditory organs

Question 8

General view of temporal

Answer 8

squamous portion:

• thin lamina extends off the petrous part which is the squamous part of the temporal bone which is flat
• the big plate on the side of the head is the squamous portion

petrous portion:
-endochondral bone with many centers of ossification and adding to it are membrane bones of the calvaria and it fuses together to give you one bone

Question 9

Mastoid process is part of the temporal bone.

Answer 9

-full of mastoid air cells which are pneumatic spaces lined with respiratory type epithelium

same that we will see in the frontal, sphenoid and maxillary sinuses

Question 10

EAM= external auditory meatus

Answer 10

• is the ear canal
• behind the mandibular fossa
• lateral part of the canal, its walls are cartilaginous (lateral 1/3rd)
• as you go farther in it is surrounded by the temporal bone (medial 2/3rd)
• skin lining it has ceruminous glands and sebaceous glands which produce ear wax (cerumen) (mostly in the outer 2/3rd of the canal)
• the ear canal does not go straight in, the ear canal is directed forward and downward

otoscopy requires elevation of pinna and downward, forward look to see tympanic membrane

Question 11

zygomatic process

Answer 11

bony prolongation forward from the temporal bone

Question 12

Styloid process

Answer 12

is a process of the temporal bone (lateral view)

-tip of the mastoid process is right behind the styloid process with the stylomastoid foramen right in between the two

Question 13

medial side of the temporal bone

Answer 13

• comes to a point in the front and then from that point backwards there is a ridge which is the line of attachment of the tentorium cerebelli
• exactly where the tentorium cerebelli attaches to the petrous bone that line there is a tiny venous sinus which is the superior petrosal sinus

Question 14

IAM= internal auditory meatus

Answer 14

where CN VII and VIII along with labyrinthine artery (an internal auditory branch of the basilar artery) goes into the temporal bone

Question 15

Why are infections of the mastoid air cells so common? Mastoiditis

Answer 15

• a sinus infection in your temporal bone
• the sinuses all open up somewhere into the nasopharynx
• the air cells, the air in here is exchanged with ambient air by a trip through the middle ear cavity and pharyngotympanic tube
• The mastoid cells are a long way from getting fresh air from your nasopharynx.

Question 16

Petrous temporal bone is surrounded by what dural venous sinuses?

Answer 16

• petrous bone is bounded by the superior petrosal sinus
• cavernous sinus in front of the tip of the temporal bone
• sigmoid sinus swings its way behind the petrous bone on its was to the jugular foramen
• inferior petrosal sinus connects between the cavernous sinus and sigmoid sinus
• inferior petrosal sinus is inferior of the temporal bone ; connects btw the cavernous sinus and jugular foramen; it is the alternative way to get blood from cavernous sinus into internal jugular vein to get out of that region

Question 17

Ear-embryologically

Answer 17

• ear develops from elements of multiple pharyngeal arches
• because of that we will have multiple sensory nerves innervating the skin of these structures
• ear: external ear, EAM, IAM, middle ear cavity

Question 18

Sensory innervation of the pinna, ear canal, and tympanic

Answer 18

-skin of the external ear
skin lining the ear canal and all the in to the outer surface of the tympanic membrane
-all of those if you think of them as a unit there are sensory branches of trigeminal, facial, glossopharyngeal, and cervical nerve 2 innervating them

Sensory innervation of the pinna, ear canal and tympanic cavity is supplied by branches of CN V3=mandibular nerve (auriculotemporal nerve: pathway for fibers from otic ganglion to get to the parotid gland; innervates the auriculotemporal region of the ear), IX, X (at the area of the concha and tragus we have a little patch of vagus with smaller contributions from CN VII), and C2 (greater auricular and lesser occipital nerve which is C2-C3).

-so CN V, VII, IX, C2 all give innervation to the skin overlying the ear

The complex sensory innervation results from derivation of the pinna, canal and tympanic cavity from multiple branchial arches.

Question 19

Most of the skin in the upper half of the auditory canal plus the upper half of the outer surface by the tympanic membrane is innervated by what nerve?

Answer 19

V3 (auriculotemporal nerve)

Question 20

The floor or the ear the canal including the lower half of the lateral surface of the tympanic membrane is innervated by what nerve?

Answer 20

auricular branch of the vagus nerve with a little patch of sensation from the facial nerve

Question 21

All of the areas in the mucosa lining of the middle ear including the air cells in the mastoid are innervated by what nerve?

Answer 21

branches of CN IX

Question 22

Somatosensory sensations

Answer 22

touch, temperature, and pain

Question 23

Referred otalgia

Answer 23

pain of the ear= otalgia

all kinds of different structures in your head and neck where problems with them can result with pt coming in complaining of earache

-infection of the middle ear cavity or external cavity= proper otalgia

-TMJ pain, lesion in your infratemporal fossa, problems with your maxilla (upper teeth), infections in the mouth and pharynx (tonsil infection), various trigeminal neuralgias affecting the maxillary region; larynx and thyroid
all of these can be areas where problems will refer pain in your brain to make you think that you have an earache

• all those places where the lesion is NOT in your ear canal or middle ear and yet you come in complaining of earache is REFERRED OTALGIA
• The multiple sources of sensory innervation to the external and middle ear (V3, VII, IX, X, C2-3) complicate precise diagnosis of referred otalgia.

Question 24

What is the common terminus for the nerve pathway innervating the skin of the ear (V3, VII, IX, X, C2-3)?

Answer 24

Trigeminal Spinal Tract Nucleus (pain and temp)

-so the referral of pain is occurring through interneurons of that trigeminal spinal nucleus feeding information that gets interpreted somewhat incorrectly

Question 25

Otoscopic view of the tympanic membrane (anterior of the patient is to the right the patient in this slide)

Answer 25

-a 3 layered membrane
outside of it is the air of the room:

• outer layer is of thin meatal lining innervated by V3, X (auricular branch)
• internal, mucosal lining of tympanic cavity innervated by sensory branches of CN IX)
• intermediate (connective tissue layer in between external and internal layer), fibrous layer

drum-like sheath is attached around the tympanic membrane margins to a fibrocartilage ring, and centrally to malleus (hammer)

• inside of it is the middle ear cavity AKA the tympanic cavity
• tip of malleus is the umbo where the tympanic membrane is firmly attached along the line of tympanic membrane

tympanic membrane is attached around most of its perimeter to that fibrocartilaginous ring which is really tight the tense part of the membrane (5/6th tense part of TM)

superiorly and posteriorly TM is not tightly attached = flaccid part of the tympanic membrane (1/6th flaccid part of TM)

important structures behind the TM that you don’t want to mess with: when draining middle ear infection you have to poke a hole into TM to drain the pus= this is why this is important

The posterior inferior quadrant (quadrant 3) is the ONLY SAFE zone for perforation. If not you could damage chorda tympani, ear ossicles, small BVs

The TM heals itself very well.

Question 26

Normal Otoscopic view of TM AKA eardrum

Answer 26

• annulus fibrosis
• where you can’t see the ring is the flaccid part
• long process of the incus
• umbo which is the end of the malleus handle and the center of the drum
• light reflex: cone of light anteroinferiorly
• lateral process of the malleus
• attic also known as pars flaccida
• handle of the malleus

Question 27

Pathological view of the TM

Answer 27

In otitis externa (infection of the external ear canal), an infective/inflammatory condition, the canal may be so swollen that a view into the ear is impossible.

In otitis media (middle ear infection), the tympanum typically bulges outward.

Chronic negative middle ear pressure leads to inward retraction of the tympanic membrane, as shown in an extreme case here, where it contacts the medial wall of the middle ear

Question 28

Middle Ear Ossicles

Answer 28

contains the ear ossicles
that when infected gives you intense pain:
-malleus (hammer): has manubrium which was attached to TM; neck is where the chorda tympani passes across, head has an articular facet which will articulate with the articular facet of the incus; anterior process
-incus (anvil): facet covered with hyaline cartilage; body articulates with the malleus; process sticking down incudostapedial joint
forms a joint with the stapes which is the
-stapes (stirrup)

There are proper synovial joints:

• Incudomalleolar joint
• Incudostapedial joint

The point of the beautiful mechanical system here is to take the inward and outward movements of the TM due to sound waves impinging on it transfer that through the Incudomalleolar joint to the incus and Incudostapedial joint to the stapes such that now the foot plate of the stapes moves in and out of the oval window

there’s a certain mechanical advantage because the surface area of TM is a few times bigger of the foot plate of the stapes allowing for amplification of the moton

tendons of muscle attached to middle ear ossicles damp or slow down vibrations and are part of the reflex related to loud sounds (allowing for hair cells not to get damaged):

• tensor tympani innervated by trigeminal nerve
• stapedius muscle innervated by the facial nerve

Question 29

Tympanic Cavity

Answer 29

=middle ear cavity

• is analogous to a 6 sided room which is elongated front to back but narrow left to right
• on the lateral side is Tc
• on the medial side is the inner ear (labyrinthine wall due to the vestibular system in the inner ear) specifically the oval window
• roof is the tegmental wall
• floor is the jugular wall due to the jugular foramen and sinus sit right underneath it
• all of this room is lined with mucosa that are continuous with those that line respiratory surfaces such as the pharynx and mastoid air cells
• back wall of TC is the mastoid wall due to mastoid air cells whose opening is through the TC
• anterior wall is the carotid wall due to carotid canal that comes vertically underneath the petrous temporal bone and turn forward then upwards
• lateral wall has the chorda tympani for salivary glands and taste run at the neck of the malleus (why we stay away from the upper quadrants of TM); promontory surface that bulges inward as the base of the cochlea; CN VII enters at the temporal bone at the IAM and arches behind structures and run in the back wall and emerges down leaving the temporal bone at the stylohyoid foramen AKA facial canal; somewhere along this pathway is where chorda tympani is given off as well a branch to the stapedius muscle; tympanic branch of CN IX that fans out all throughout the inside of the middle ear called the tympanic plexus whose somatosensory fibers that is richly endowed with pain fibers (this is why otitis media is PAINFUL); some of the branches of the tympanic plexus are not somatosensory but preganglionic PS fibers which reform a nerve that exits the temporal bone called the lesser petrosal nerve to the otic ganglion

Question 30

How do you get air into and out of the tympanic cavity?

Answer 30

-through the pharyngotympanic tube

• right above the tube and parallel is the tensor tympani muscle: a trigeminal muscle that runs in that tube and sends its tendon which attaches to the malleus
• as the facial nerve does down through the facial canal a branch comes back off of it and runs up over the malleus called the chorda tympani nerve (medial view of the TC)

Question 31

Grinding away the lateral wall to get to the medial wall of the tympanic cavity

Answer 31

• parameter eminence where the stapedius tendon goes through to get to the stapes
• mastoid air cells are immediately behind the part of the middle ear cavity that contains the ossicles
• if we grind deeper we can see the facial canal where it begins at the IAM runs posteriorly then turn inferiorly and opens up at the stylomastoid foramen

Question 32

What two canals do we have through the petrous temporal bone?

Answer 32

facial canal:

carotid canal: right in front of it is the cavernous sinus

-internal carotid artery leaves the temporal bone and goes right into the cavernous sinus through the carotid canal

Question 33

Pharyngotympanic Tube and cartilage

Answer 33

• floor is a cartilaginous tube
• the roof is from the bony parts of skull above it
• it runs a long way forward and opening into the nasopharynx surrounded by torus tubarius
• the tube is usually closed; muscles originating on it open the tube allowing equalization of pressure in tympanic cavity
• the purpose of the tube is because we don’t want to have air trapped inside the middle ear cavity and the mastoid air cells and so on occasion the tube opens up allowing air to be exchanged between the air in your mouth and pharynx and air in the middle ear cavity
• the way it opens is through muscles that elevate and tense your soft palate: levator veli palatini (X) and tensor veli palatini (V)
• when you make a yawning motion with them they tug on the bottom of the the pharyngotympanic tube (the cartilaginous part)

when you fly in airplane air pressure goes down you feel pressure in your middle ear because you haven’t equalized yet and all of sudden the tube will open and you equalize allowing some of the high pressure air to come out of that tube

Question 34

What are the nerves on directly top of the surface of the internal carotid artery?

Answer 34

sympathetics; internal carotid plexus with fibers coming from the superior cervical ganglion

Question 35

The facial nerve passing through the temporal bone will give rise to what three major branches whose functions are what?

Answer 35

greater petrosal nerve
nerve to stapedius
chorda tympani

the moment the facial nerve goes through the temporal bone it makes a sharp turn which is the geniculate ganglion (sensory ganglion of the facial nerve)

coming forward off that there is the greater petrosal nerve which will go to the pterygopalatine fossa for sensory and PS innervation to pterygopalatine ganglion to lacrimal gland and small mucous glands of palate and nasopharynx

right under when it leaves the bone is the internal carotid

so it picks up the deep petrosal from the carotid plexus

then we follow the facial nerve into the facial canal which will send a little branch to the stapedius muscle for that loud sound reflex

but before it passes out it gives off the chorda tympani nerve which joins lingual branch of V3 to give taste to the anterior 2/3 of the tongue and PS innervation to the submandibular/sublingual ganglion

the nerve then emerges from the stylomastoid foramen mainly motor to muscles of facial expression, stylohyoid and posterior digastric

Question 36

The petrous temporal bone contains the bony and membranous labyrinths.

Answer 36

contains the bony and membranous labyrinths

is just a complicated passage
the membranous labyrinths is the sensory structure of the inner containing the cochlea and auditory organs, vestibular organs of the semicircular canals

even though much of the petrous bone is well ossified a thin layer around the membranous labyrinth is exceptionally densely ossified called the otic capsule (which is the embryonic name of the structure that builds this whole region)

but this adult otic capsule is a very firm dense bone that forms right around the membranous labyrinth

inner ear has cochlea and auditory organs, vestibular organs of the semicircular canals

Question 37

How is the bony labyrinth revealed?

Answer 37

by carving away surrounding bone matrix of the temporal bone

The membranous labyrinth helps to develop the otic capsule. So the temporal bone is very well protected.

Question 38

Petrous bone is an anatomical HOTSPOT!!!

Answer 38

• Highly pneumatized with long mucosal passages leading to nasopharynx: you have a lot mastoid air cells which is a constant problem for people; these passages of mucosa leading to an opening in the nasopharynx is a very long path through the whole middle ear cavity and down out through the pharyngotympanic tube
• Covered with dura and dural venous sinuses: which are great things when things are going well but can become seriously detrimental when you have infections of them
• Penetrated by internal carotid artery and carotid plexus: you have potential for PS problems if you have an infection that starts getting into the connective tissue covering of the internal carotid artery and you will start giving yourself a partial Horner’s syndrome
• Adjacent to jugular fossa:
  jugular fossa is right under medial to the temporal bone, infection there is unfortunately very common too
• Transited and supplied by CN VII, IX and X: branches of CN VII, IX, and X going into or through the temporal bone
• Immediately behind TMJ: the whole system is IMMEDIATELY behind the TMJ, so problems with the TMJ (swelling) pressing on sensory branches to your ear
• Contains delicate bony mechanical conduction system for auditory input: mechanical conduction of ear ossicles which are proper synovial joints means you can get osteoarthritis of your ear ossicles (one of the general reason for hearing loss in the elderly)
• Contains the mechanosensory organs for audition and vestibular function and balance

SO ENT has a lot to work with in this area!!!