Ear

Question 1

What is the Umbo?

Answer 1

Umbo means a knob or projection. The central part of the tympanic membrane where the tip of the handle of the malleus is attached is called the umbo.. The handle (manubrium) of the malleus attaches to the center of the eardrum creating a slight projection at the center – the umbo.

Question 2

The tympanic membrane consists of three layers: outer, middle, and inner. What are each comprised of?

Answer 2

outer (lateral): skin
middle layer: fibrous connective tissue
inner: mucosal layer.

Question 3

What is the pars flaccida? What is the pars tensa?

Answer 3

A small portion of the tympanic membrane (superior aspect) does not contain the fibrous connective tissue – it is therefore very thin and is called the pars flaccida.
The remaining part of the membrane (with all three layers) is the pars tensa.

Realize that the composition of the three layers reflects their development origin from the three different germ layers.

Question 4

What is the sensory innervation of the the tympanic membrane?

Answer 4

the auriculotemporal nerve branch of V3 innervates the external aspect of the tempanic membrane and the tympanic branch of CN IX innervates the internal of the tympanic membrane.

Sound waves collected by the external ear cause the tympanic membrane to vibrate. These vibrations are transmitted to the ossicles of the middle ear.

Question 5

What does the middle ear do? What bone surrounds the middle ear cavity?

Answer 5

The middle ear receives the sound waves transmitted by the tympanic membrane and transmits them to the oval window of the inner ear. The middle ear consists of an irregularly shaped cavity within the temporal bone (middle ear cavity or tympanic cavity) that is lined with a mucous membrane. The contents of the cavity will be discussed in the subsequent slides.

Question 6

Thought Question: Why does yawning or swallowing relieve pressure from the middle ear?

Answer 6

The middle ear cavity communicates with the nasopharynx via the eustachian tube (also called pharyngotympanic or auditory tube). The eustachian tube is normally closed at the pharyngeal end, however swallowing or yawning will open the tube when the pressure in the middle ear cavity needs to equalize with the atmospheric pressure. The epithelium of the eustachian tube contains cilia that function to clear mucous and fluid from the middle ear cavity.

Clinical note: Otitis media (inflammation of the middle ear) can occur if secretions accumulate in the cavity. In children this is most often due to inadequate drainage (the eustachian tube is more horizontal in infants and toddlers) or blockage of the tube opening (e.g. by swollen adenoids). In adults, otitis media is often associated with smoking (tobacco smoke paralyzes cilia).

Question 7

What are the three bones, two muscles, one nerve, and one nerve plexus of the middle ear?

Answer 7

three ossicles (bones of the middle ear - malleus, incus, stapes)
two muscles (tensor tympani and stapedius)
one nerve (chorda tympani branch of VII)
tympanic plexus

Extra: The tympanic plexus is a nerve plexus from the tympanic nerve branch from CN IX. the plexus gives off three nerves:
(1) the lesser petrosal nerve
(2) the Deep branch to join the greater petrosal nerve
(3) branches to the tympanic cavity
The branches of the tympanic cavity provide innervation to the mucosa of the middle ear. The lesser petrosal nerve provides autonomic parasympathetic fibers that eventually innervate the parotid gland.

Question 8

What is the function of the ossicles?

Answer 8

The function of the ossicles is to conduct the sound waves collected by the external ear to the internal ear. Additionally, they amplify the sound waves due to the difference in size between the tympanic membrane and the base of the stapes (energy in the waves is concentrated when it is transmitted to a structure with a smaller surface area).

The three small bones in the tympanic cavity are called ossicles. The malleus is the most lateral bone that is attached to the tympanic membrane via its handle and lateral (short) process. The incus is in the middle of the chain of ossicles, thus it articulates with malleus and stapes. The stapes has an oval-shaped base that is applied to the oval window of the inner ear

Question 9

What is the only structure on the lateral wall?

Answer 9

the tympanic membrane

Question 10

What are the structures on the anterior wall?

Answer 10

opening of the eustachian tube
internal carotid artery (within the carotid canal)
tensor tympani muscle

Question 11

What is the course of the internal carotid artery compared to the eustacian tube?

Answer 11

the artery makes an approximate 90 degree turn while it is anterior to the eustachian tube.

Question 12

What is the origin and insertion of the tensor tympani muscle? What is its function? What is its innervation?

Answer 12

originates from the cartilage of the eustachian tube and the bony canal in which it is located; inserts on the handle of the malleus.
The function of tensor tympani is to tighten the tympanic membrane (thus reducing its oscillations) in response to loud sounds (i.e. a protective function).
Tensor tympani is innervated by CN V3.

Question 13

What is the nerve that travels through the tympanic cavity?

Answer 13

chorda tympani nerve.

Question 14

The chorda tympani travels through a small crack in on the anterior wall of the tympanic cavity called the?

Answer 14

petrotympanic fissure.

Question 15

What is the petrotympanic fissure?

Answer 15

The chorda tympani travels through a small crack in on the anterior wall of the tympanic cavity called the petrotympanic fissure.

Question 16

What are the structures of the medial wall?

Answer 16

promontory - a bulge caused by the basal turn of the cochlea
tympanic plexus – a nerve plexus located on the promontory
oval window – opening between middle ear and the vestibule (sealed by a membrane)
round window – opening between middle ear and the cochlea (sealed by a membrane)
prominence of facial canal – a bump that marks the position of the facial canal, which contains the facial nerve
prominence of lateral semicircular canal – a bump that marks the position of the lateral semicircular canal

Question 17

Of the medial wall what are the following?
promontory
tympanic plexus
oval window
round window
prominence of facial canal
prominence of lateral semicircular canal

Answer 17

promontory - a bulge caused by the basal turn of the cochlea
tympanic plexus – a nerve plexus located on the promontory
oval window – opening between middle ear and the vestibule (sealed by a membrane)
round window – opening between middle ear and the cochlea (sealed by a membrane)
prominence of facial canal – a bump that marks the position of the facial canal, which contains the facial nerve
prominence of lateral semicircular canal – a bump that marks the position of the lateral semicircular canal

Question 18

What are the structures of the posterior wall?

Answer 18

entrance to (aditus of) mastoid antrum – opening that leads into mastoid air cells
pyramidal eminence – a small piece of bone that serves as the origin of the stapedius muscle
facial canal – canal for the facial nerve that is posterior to the posterior wall
opening for the chorda tympani n. (doesn’t have a name)

Question 19

Of the posterior wall what are the following?

entrance to (aditus of) mastoid antrum
pyramidal eminence
facial canal
opening for the chorda tympani n.

Answer 19

entrance to (aditus of) mastoid antrum – opening that leads into mastoid air cells
pyramidal eminence – a small piece of bone that serves as the origin of the stapedius muscle
facial canal – canal for the facial nerve that is posterior to the posterior wall
opening for the chorda tympani n. (doesn’t have a name)

Question 20

What is the Tegman Tympani?

Answer 20

The roof of the tympanic cavity is called the tegmen tympani.

Question 21

What is the Epitympanic Recess?

Answer 21

The space between the ossicles and the tegmen tympani is called the epitympanic recess (clinicians call this space the “attic”).

Question 22

What is the Jugular Fossa? What is the Jugular Bulb?

Answer 22

The jugular fossa is found just inferior to the floor of the tympanic cavity. This depression of bone contains the jugular bulb – the point of transition between the sigmoid sinus and superior part of the internal jugular vein.

Question 23

What provides sensory innervation of the middle ear cavity and the eustachian tube? Where does this nerve enter the middle ear?

Answer 23

tympanic branch of CN IX, which enters the middle ear cavity through a small hole in the floor near the jugular fossa (this should make sense because you know that CN IX emerges from the jugular foramen). The tympanic nerve forms a plexus on the promontory.

Question 24

What is the lesser petrosal nerve? Name its course to the parotid gland.

Answer 24

A few nerve fibers leave the tympanic nerve promontory plexus as the lesser petrosal nerve (turquoise arrow)
These preganglionic parasympathetic fibers are destined for the otic ganglion. Then postganglionic fibers from this ganglion travel to the parotid gland in the auriculotemporal nerve.
The lesser petrosal nerve reaches the otic ganglion by exiting the middle ear cavity through a hole in the tegmen tympani, and then traveling through the foramen ovale or spinosum to enter the infratemporal fossa.

Question 25

Recap: What is the course of CN IX from the jugular foramen to the parotid gland?

Answer 25

This is a cranial nerve map of CN IX. Focus on the upper half of the diagram at this time (the branches in the lower half will be discussed later). The tympanic nerve is the first branch of CN IX. It enters the middle ear cavity through a small foramen and forms a plexus on the promontory. It provides sensory innervation to the middle ear cavity. The parasympathetic neurons that are traveling in CN IX travel through the plexus (without innervating anything) and leave the plexus as the lesser petrosal nerve. These neurons will synapse in the otic ganglion (we will eventually see where this is!). The postganglionic neurons join the auriculotemporal nerve to travel to the parotid gland (they cause secretion of the parotid gland).

Question 26

What is the blood supply of the middle ear?

Answer 26

deep auricular artery and anterior tympanic artery, both branches of the maxillary artery. There are others, but we don’t need to know them.

Question 27

What is the nerve that passes through the middle ear? What cranial nerve is this a branch of?

Answer 27

The nerve is the chorda tympani nerve, a branch of the facial nerve.

Question 28

What is the course of CN VII from the brainstem through the middle ear and finally to the face? What is the genu? What is the first branch of the facial nerve? What are the two branches it gives off in the facial canal? At what point does it give off branches to the digastric and stylohyoid muscles? When does it give off its five facial branches? What are they?

Answer 28

CN VII emerges from the brainstem and enters the temporal bone via the internal acoustic meatus (IAM). It travels within the facial canal between the cochlea and semicircular canals, and then proceeds towards the middle ear turning abruptly posterior (this location is called the genu). Its sensory ganglion, the geniculate ganglion, is found at the genu. The first branch of the facial nerve arises here also, the greater petrosal nerve (contains preganglionic parasympathetic fibers traveling to the pterygopalatine fossa – more about these later).

After giving off the greater petrosal nerve, the remaining part of CN VII descends within the facial canal posterior to the middle ear cavity. CN VII gives off two branches while in the canal (nerve to stapedius and the chorda tympani nerve) then continues inferiorly to exit the facial canal via the stylomastoid foramen. At this point it gives off branches to the posterior digastric and stylohyoid muscles, and then enters the parotid gland. Within the gland it divides into its five terminal branches that innervate the muscles of facial expression (temporal, zygomatic, buccal, marginal mandibular, cervical).

Question 29

What is the origin and insertion of the Stapedius? What is its function? What embryological arch did the Stapedius nerve originate from?

Answer 29

The stapedius originates from the pyramidal eminence and inserts on the stapes. It has the same function as tensor tympani (to protect the ear from loud sounds), although it accomplishes this by preventing excessive oscillations of the stapes rather than the tympanic membrane. Since stapedius is innervated by the facial nerve, it should make sense that it is derived from the 2nd pharyngeal arch.

Question 30

What is the course of the Chorda Tympani? What are its final innervations?

Answer 30

The chorda tympani arises from the facial nerve within the facial canal. It enters the middle ear cavity through an unnamed foramen and courses between the malleus and incus. It exits the middle ear and enters the infratemporal fossa through the petrotympanic fissure. Here it joins the lingual branch of CN V3 to transmit taste fibers to the anterior 2/3 of the tongue and preganglionic parasympathetic fibers to the submandibular ganglion.

Question 31

What do the cochlea and semicircle canals do?

Answer 31

The inner ear is functionally divided into two parts: the more anterior cochlea that functions in hearing, and the more posterior semicircular canals that are concerned with balance. Anatomically, the inner ear is a series of cavities within the petrous part of the temporal bone.

Question 32

What are the cavities of the bony labyrinth?

Answer 32

The cavities are the cochlea, vestibule and semicircular canals (listed from anterior to posterior). Collectively they are known as the bony labyrinth.

Question 33

What is the vestibule? What is the relationship between the middle ear, the inner ear, and the oval and round window?

Answer 33

The vestibule is a “common area” between the cochlea and semicircular canals. It is connected to the middle ear cavity via the oval window. The cochlea is a snail-shaped coiled tube that is continuous with the vestibule and connected to the middle ear cavity via the round window. Thus the oval and round windows are sites of communication between the middle and inner ear (although neither are “open” as there is a membrane across each opening).

Question 34

What is the vestibular aqueduct?

Answer 34

There are three semicircular canals that project from the vestibule at right angles to each other, and they are designated superior (a.k.a. anterior), posterior and lateral. A small channel called the vestibular aqueduct connects the vestibule with the posterior cranial fossa.

Question 35

What are the specific components of the membranous labyrinth?

Answer 35

cochlear duct, utricle, saccule and semicircular ducts. Semicircular ducts have a dilated area called the ampulla.

Question 36

What is the fluid within the membranous labyrinth?

Answer 36

endolymph.

Question 37

What is the fluid between the membranous labyrinth and the bony labyrinth?

Answer 37

Perilymph.

Question 38

What are the Endoymphatic duct and the Endoylymphatic Sac?

Answer 38

Arising from the utricle and saccule is the endolymphatic duct that ends at the endolymphatic sac. These structures have cells that resorb and filter endolymph.

Question 39

What is the Modiolus?

Answer 39

The central core of bone that the cochlea canal spirals around is called the modiolus.

Question 40

What is the cochlear duct? What is the scala vestibuli? What is the scala tympani? What is the Helicotrema?

Answer 40

Within the bony canal is a membranous tube called the cochlear duct. Note in the drawing that the cochlear duct (shaded blue) does not completely fill the bony cochlea – it assumes only the central portion, thereby creating “compartments” on either side of it (scala vestibuli and scala tympani). The scala vestibuli and scala tympani are in continuity with each other at the apex of the cochlea at the helicotrema. If a cross-section is taken across one portion of the cochlea (where the dotted line is), a view is seen as shown in the picture at the bottom right.

Question 41

What is the spiral lamina? What is the spiral ligament?

Answer 41

The cochlear duct (silver) is anchored inside the cochlea by attaching to a shelf of bone called the spiral lamina that projects out from the modiolus (similar to the threads of a screw). The outer portion of the cochlear duct (spiral ligament) is thickened and it also has a tethering function.

Question 42

What is the Vestibular (Reissner’s) membrane?

What is the Basilar Membrane?

Answer 42

The vestibular (Reissner’s) membrane separates the cochlear duct and scala vestibuli. The basilar membrane separates the cochlear duct and scala tympani.

Question 43

Perilymph vs endolymph is found in what cavities?

Answer 43

Both the scala vestibuli and scala tympani are lined with simple squamous epithelium and contain perilymph, which has a composition similar to cerebrospinal fluid.
In contrast, the cochlear duct (also called scala media) is filled with endolymph that has a composition similar to intracellular fluid.

Question 44

What is the stria vascularis?

What is the endolymphatic sac?

Answer 44

Endolymph is produced by a population of cells along the inner surface of the spiral ligament – the stria vascularis. Endolymph is resorbed into venous blood via the endolymphatic sac (cells in the sac are columnar with microvilli).

Question 45

Explain the Organ of Corti. Key words: basilar membrane, Sensory hair cells, support cells, stereocilia, tectorial membrane, tip links.

Answer 45

The cochlear duct contains the organ of hearing (organ of Corti); it rests on the basilar membrane. The organ of Corti consists of two major groups of cells – sensory hair cells and underlying support cells. The hair cells are in two rows – an outer row consisting of 3-5 cells, and an inner row of 1 cell thickness. The hair cells have stereocilia on their free surface that project into the endolymph and overlying tectorial membrane. The tectorial membrane is a gelatinous mass that is anchored to the spiral lamina via the spiral limbus. The stereocilia of the hair cells are connected to each other by filaments known as tip links. These tip links are important for the function of hair cells, and will be discussed in depth in the Neuroscience course.

Question 46

Hair cells generate action potential that is conveyed to the brain via what nerve?

Answer 46

in the bipolar neurons forming the cochlear division of CN VIII.

Question 47

Explain the production of sound

Answer 47

sound waves in the air are collected by the external ear and “funneled down” to the tympanic membrane – the waves cause the tympanic membrane to vibrate
vibrations of the tympanic membrane are transmitted to the oval window via the ossicles (sound waves are amplified during this process due to the architecture of the ossicles and the difference in size between the tympanic membrane and oval window)
vibration of the oval window creates pressure waves in perilymph of the scala vestibuli
vibration of the vestibular membrane transfers the pressure waves to the endolymph in the cochlear duct
pressure waves in the cochlear duct cause vibration of the basilar membrane
vibration of the basilar membrane induces shearing of the apical ends of the hair cells against the tectorial membrane. This bends the bundle of stereocilia on each hair cell and opens ion channels, causing depolarization of the hair cell. The resultant release of neurotransmitter generates an action potential that is propagated along the sensory neurons of the cochlear division of CN VIII.
different frequencies of sound are detected in different locations along the basilar membrane – this is partially due to variations in the structure of the basilar membrane, e.g. it is narrower at the base of the cochlea and wider at the apex.
vibration of the basilar membrane also transfers the pressure waves to the perilymph in the scala tympani – the waves “push out” the secondary tympanic membrane in the round window and dissipate

Question 48

What is the spiral ganglia in the modiolus?

Answer 48

Neurons from the cochlea conducting auditory information have cell bodies in one of the many spiral ganglia (cochlear division of CN VII) found within the modiolus.

Question 49

What are the Sacule and the Utricle? What kind of cells are they lined with? What is the Maculae?

Answer 49

The vestibule contains two sac-like regions of the membranous labyrinth called the saccule and utricle. Both are lined with simple cuboidal epithelium, except in two specialized areas called maculae. The maculae are the receptor organs for balance, which like the organ of Corti, are comprised of hair cells and columnar support cells.

Question 50

What are the Semicircle canals? What kind of cells are they lined with? What is the Cristae Ampullares?

Answer 50

The semicircular canals contain semicircular ducts, which are lined with simple cuboidal epithelium. The ampullae of the semicircular ducts contain the receptor organs that are called cristae ampullares.

Question 51

What is the Kinocilium? What is the Otolithic Membrane? What are Otoliths/Otoconia?

Answer 51

In addition to stereocilia, the hair cells in the macula also have one long cilium that projects from the apical surface called a kinocilium. The stereocilia and kinocilium project into a gelatinous glycoprotein layer called the otolithic membrane. The otolithic membrane has crystals embedded in its surface called otoliths (or otoconia).

Question 52

What kinds of movement does the Macula (from the utricle) detect?
What kinds of movement do the semicircle canals detect?

Answer 52

The maculae detect gravity and linear acceleration. Linear acceleration is moving along the x, y, and z axes.
The cristae ampullares detect angular acceleration (rotations of the head).The rotational movements shown in this diagram (roll, pitch and yaw) will be detected by the semicircular canals.

Question 53

What are the Semicircle canals? What kind of cells are they lined with? What is the Cristae Ampullares?

Answer 53

The semicircular canals contain semicircular ducts, which are lined with simple cuboidal epithelium. The ampullae of the semicircular ducts contain the receptor organs that are called cristae ampullares.

Question 54

What is the cupula?

Answer 54

The structure of a cristae ampulla is similar to the macula (i.e. hair cells with stereocilia and kinocilium, columnar support cells), except that the gelatinous mass (cupula) is thicker and does not contain otoliths. In addition, the epithelium of the crista forms a ridge while that of the macula is flat.

Question 55

What supplies innervation of the inner ear? What do each of its divisions do?

Answer 55

The innervation of the inner ear is provided by CN VIII, the vestibulocochlear nerve. CN VIII has two divisions, one that conveys neurons for hearing, and one that conveys neurons for balance.

Question 56

What is the labyrinth artery? What is this a branch of? Trace its route. What are the clinical consequences of ischemia of the Labyrinth artery?

Answer 56

The inner ear receives its blood supply from the labyrinthine artery.

The labyrinthine artery typically arises from the anterior inferior cerebellar artery (a branch of basilar a.) or the basilar artery itself and travels through the internal acoustic meatus with CN VII and CN VIII. Ischemia in the labyrinthine artery (e.g. during a stroke) produces immediate vertigo and unilateral deafness on the affected side.

Question 57

Explain the location and function of the vestibular ganglion and the Spiral ganglion.

Answer 57

Neurons from the semicircular canals, utricle and saccule form the vestibular division of CN VIII that conveys information for balance. The sensory cell bodies of these neurons are located in the vestibular ganglion in the lateral part of the internal acoustic meatus.
Neurons from the cochlea conducting auditory information have cell bodies in one of the many spiral ganglia found within the modiolus. Axons leaving the spiral ganglia converge to form the cochlear division of CN VIII. The two divisions of CN VIII merge within the internal acoustic meatus. CN VIII enters the brainstem at the junction of the pons and medulla.