Sem 2 - Z(2) - The Ear - Divisions, external auditory meautus, External/middle/inner ear

Question 1

The ear can be divided into the external (outer), middle and internal (inner) ear What makes up the external ear?

Answer 1

• * The auricle
• * External auditory meatus
• * External surface of the tympanic membrane

Question 2

What makes up the middle ear?

Answer 2

• * The internal surface of the tympanic membrane
• * The tympanic cavity
• * The ossicles
• * The pharyngotympanic (aka Eustachian, aka auditory) tube

Question 3

What makes up the inner ear?

Answer 3

• * Auditory apparatus
• * Vestibular apparatus
• * Internal auditory meatus
• * Vestibulocochlear nerve (CN VIII)
• * Oval window
• * Round window

Question 4

Is it the auditory system or vestibular system involved in hearing? Which system is involved in balance?

Answer 4

The auditory system is involved in hearing with the cochlear part of CN VIII innervating this The vestibular system is involved in balance with the vestibular part of CN VIII innervating this

Question 5

We will now discuss the external ear in more depth

• * The auricle
• * External auditory meatus
• * External surface of the tympanic membrane

What type of cartilage makes up the auricle? What part of the auricle is not supported by cartilage?

Is the ear a muscle of facial expression?

Answer 5

The auricle is mostly elastic cartilage with the earlobe (lobule) not being supported by any cartilage

In some mammals, the ear has muscles of facial expression but these are vestigial structures in humans

Question 6

What is the outer curvature formed by the cartilaginous part of the auricle?

What is the inner curvature formed by the cartilaginous aspect of the auricle? This divides into two crus known as what?

What is the hollow depression in the middle of the auricle?

Answer 6

• Outer curvature of the auricle is known as the helix
• Inner curvature of the auricle is known as the antihelix - can be divided into the superoposterior crus and the inferoanterior crus

Hollow depression in the middle of the auricle is known as the concha

Question 7

The conchae can be divided into two parts Where do these two parts lie and what are they known as?

Answer 7

We have the cymba concha -located between the inferoanterior crus of the antiheli and the crus of the helix

We have the cavity of the concha next at the external auditory meatus

Question 8

Label the diagram

• Start with horizontal arrows
• Then downwards arrows
• Then upwards arrows
• Then white circles

Also state where does the external ear lymphatics drain?

Answer 8

• Horizontal arrows - Helix, antihelix, antitragus
• Downwards arrows - Superoposterior and inferoanterior crus of antihelix, crus of helix
• Upwards arrows - lobule, tragus
• White circle - cymba conchae, cavity of concha

Lymph from auricle drains to the parotid and cervical lymph nodes

Question 9

What is the arterial supply to the auricle?

Answer 9

• Posterior auricular artery (from ECA) gives perforating branches
• and Superior, middle and inferior anterior auricular arteries (from superficial temporal artery)

Question 10

What is the sensory innervation to the ear?

Answer 10

• Lesser occipital (C2) - superior helix
• Greater auricular (C2,3) - posterior and inferior helix
• Auriculotemporal branch of CN V3 - anterior helix, tragus and side of face
• CN IX and CN X - concha of auricle
• CN VII - most of auricle surface

Question 11

Lesser occipital (C2), greater auricular (C2,3) and auriculotemporal all innervate helix, CN IX and X concha, CN VII most of auricle

NOW WE DISCUSS THE EXTERNAL AUDITORY MEATUS

• How long is this?

Answer 11

The external auditory meatus is approximately 2.5cm long

Question 12

The external auditory meatus is a tube that extends from the deep part of the concha to the tympanic membrane. What forms the walls of the meatus? (lateral third and medial two thirds)

Answer 12

• Lateral third is formed by elastic cartilage, hair follicles, sweat & sebaceous glands
• Medial two thirds are formed by temporal bone lined with statified squamous epithelium

Question 13

What is the blood supply to the external auditory meatus?

Answer 13

Auricular branches from branches of ECA

• Posterior auricular branch from ECA
• Anterior auricular branches from superficial temporal artery (terminal branch of ECA)
• Deep auricular branches from the mandibular part of the maxillary artery

Question 14

What is the innervation of the external auditory meatus?

Answer 14

The innervation of the external auditory meatus is mainly from the auriculotemporal branch of CN V3

But also branches from CN VII and CNX will contribute

Question 15

The tympanic membrane is a roughly circular shape What is the approximate diameter of this? What lines the outer (external ear) and inner (middle ear) surfaces?

Answer 15

The tympanic membrane is approximately 8mm in diameter The outer surface is lined by stratified squamous epithelium and the inner surface has a mucous membrane lining

Question 16

What bone attaches to the tympanic membrane?

• What its the point of most depression into the tympanic membrane caused by this bone?
• The bone continues superiorly until its highest point which is known as what?

What is the thickest and thinnest parts of the tympanic membrane known as?

Answer 16

The handle of the malleus attaches to the tympanic membrane at a point called the umbo of the tympanic membrane

• The handle of the malleus continues superiorly until its highest point known as the lateral process of the malleus

Thickest - pars tensa Thinnest - pars flaccida

Question 17

Which nerve travels across the medial surface of the tympanic membrane?

Answer 17

The chorda tympani travels across the medial surface of the tympanic membrane and between the malleus and incus to exit the cranial cavity via the petrotympanic fissure

Question 18

What is the innervation of the tympanic membrane? (lateral and medial surface)

Answer 18

• The lateral surface (external ear) is innervated by the auriculotemporal nerve and auricular branch of the vagus nerve
• The medial surface (middle ear) is innervated by the tympanic branch of the glossopharyngeal nerve

Question 19

The tympanic cavity is immediately medial to the tympanic membrane

• What are the three small bones transmitting sound vibrations through the middle ear?
• What are the two muscles attaching to these bones?

Answer 19

We have the malleus, incus and stapes (hammer, anvil and stirrup)

The tensor tympani attaches to the malleus and the stapedius muscle attaches to the stapes

Question 20

What is the space lying adjacent to the mastoid air cells where two of the three ossicles extend into?

Answer 20

The epitympanic recess is superior to the tympanic cavity adjacent to the mastoid air cells The malleus and incus extend into this recess

Question 21

What is the origin and insertion of the tensor tympani and the stapedius muscle?

Answer 21

The tensor tympani attaches from the wall of the auditory tube to the handle of the malleus

The stapedius muscle attaches from the pyramid of the middle ear to the neck of the stapes

Question 22

What is the function and innervation of the tensor tympani and stapedius muscles?

• What is their combined action?

Answer 22

• Tensor tympani - tenses the tympanic membrane - tensor tympani branch of the nerve to the medial pterygoid from the main trunk of CN V3
• Stapedius - pulls the footplate of the stapedius laterally - stapedial branch of the facial nerve (CN VII)

Combined action - reduce vibration passing to the delicate inner ear

Question 23

RESTATE the attachments, function, combined action and innervation of the tensor tympani and stapedius

Answer 23

• * Tensor tympani - wall of auditory tube to the handle of the malleus - tenses the tympanic membrane - CN V3 (branch of the nerve to medial pterygoid from main trunk of CN V3)
• * Stapedius - pyramid of middle ear to the neck of the malleus - pulls footplate of malleus laterally - CN VII (stapedial branch of facial nerve)

* Combined action - Reduces vibration passing to delicate inner ear

Question 24

What provides sensory innervation to the tympanic cavity and medial surface of tympanic membrane? What is the blood supply to the tympanic cavity?

Answer 24

CN IX provides sensory innervation to the tympanic cavity and medial (inner) surface of the tympanic membrane

Blood supply to tympanic cavity

• Tympanic branches of posterior auricular (from ECA),
• ascending pharyngeal (from ECA) and
• maxillary arteries (anterior tympanic branch)
• Also caroticotympanic artery from ICA

Question 25

How does the chorda tympani branch travel from facial nerve to exit the cranial cavity?

Answer 25

The chorda tympani branches off the facial nerve in the facial canal and enters the tympanic cavity where it crosses the medial (inner) surface of the tympanic membrane between malleus and incus to leave the tympanic cavity via the petrotympanic (aka glaserian) fissure and enters the infratemporal fossa

Question 26

What nerve does the chorda tympani then hitch a ride on and what does it supply with what?

Answer 26

The chorda tympani then joins the lingual nerve before synapsing in the submandibular ganglion * Parasympathetic secretomotor fibres will go to the submandibular and sublingual salivary glands * Fibres for the special sense of taste will go to the anterior 2/3rds of the tongue

Question 27

What connects the nasopharynx to the tympanic cavity? What is the function of this tube?

Answer 27

The eustachian (auditory/pharyngotympanic) tube connects the tympanic cavity to the lateral wall of the nasopharynx The function of the tube is to equalize pressure on both sides of the tympanic membrane (between middle ear and external ear)

Question 28

What makes up the lateral (ear end) and medial aspects (nose end) of the eustachian tube? What length is the lateral end and medial end?

Answer 28

Lateral end of the eustachian tube is approximately 1.2cm long and is a bony canal lined with mucous membrane The medial end of the eustachian tube is approximately 2.5cm long and is a cartilaginous and membranous tube

Question 29

When is the eustachian tube open? What provides sensory innervation to the esutachian tube?

Answer 29

Eustachian tube is normally closed but opens when the tensor veli palatini and levator veli palatini contract (swallow, yawn etc) Sensory innervation to the auditory tube is via CN IX

Question 30

So many arteries give some branches to the middle ear What were the main one mentioned earlier?

Answer 30

Blood supply is mostly from * Tympanic branches from posterior auricular (from ECA), * ascending pharyngeal (from ECA), * and the maxillary arteries (anterior tympanic artery from mandibular (1st part) part of maxillary artery) * Also from caroticotympanic artery from ICA

Question 31

We have now discussed the external and middle ear Time to discuss the inner ear What are the two main functions of the inner ear?

Answer 31

* To convert mechanical signals from the ear (vibrations) to electric signals which can transfer information to the auditory pathway * To maintain balance by detecting position and motion

Question 32

Within the inner ear we have the bony labyrinth and the membranous labyrinth What is the bony labyrinth? What are the three important parts of the bony labrynth?

Answer 32

The bony labyrinth is a system of canals filled with perilymph which surrounds the membranous labyrinth (similar to extracellular fluid) * The bony labyrinth consists of the cochlea, vestibule and the semicircular canals

Question 33

Are the bony labyrinth and the otic capsule the same thing? If not then whats the different?

Answer 33

The bony labyrinth and otic capsule are NOT the same thing The otic capsule is very dense bone within the petrous temporal bone that surrounds the bony labyrinth (the system of canals filled with perilymph) Image doesnt show otic capsule over bony labyrinth

Question 34

What is the membranous labyrinth? What are the three parts it consists of? What does the membranous labyrinth contain?

Answer 34

The membranous labyrinth is a continuous system of ducts and sacs suspended within the bony labryrinth * Consists of * \* Cochlear duct located in the cochlea * \* Utricle and saccule within the vestibule * \* Semicircular ducts within the semicircular canal The membranous labyrinth contains endolymph (similar to intracellular fluid)

Question 35

State which labyrinth I am describing * \* System of canals filled with perilymph * \* System of ducts and sacs * \* Suspended in perilymph and contains endolymph * \* Surrounded by the otic capsule

Answer 35

* System of canals filled with perilymph - bony * System of ducts and sacs - membranous * Suspended in perilymph and contains endolymph - membranous * Surrounded by the otic capsule - bony

Question 36

The presence of the cochlear duct within the perilymph creates a perilymph filled chamber above and below When stapes vibrates on the oval window, describe what happens to the vibrations to reach the round window? * Include terms such as: * \* Scala vestibuli * \* Scala tympani * \* Perilymph * \* Hair cells * \* Round window

Answer 36

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Question 37

Anterior to the vestibule of the bony labyrinth lies the cochlea What lies posterior and lateral to the vestibule?

Answer 37

The semicrcular canals containing the semicircular ducts lie posterior and lateral to the vestibule

Question 38

What are the three semicircular canals? What orientation are they in to one another?

Answer 38

We have an anterior, posterior and lateral semicircular canal * The anterior and posterior semicircular canals are at right angles to one another * The lateral canal lies horizontally

Question 39

Within the semicircular canals are the semicircular ducts. What are these continous from? What are the swellings of each duct known as?

Answer 39

The semicircular ducts are continous with the utricle which is located in the vestibule (bony labyrinth) The swellings at the end of each duct are known as the ampullae

Question 40

The ampullae contains cells sensitive to change in flow of the endolymph (known as equlibirum receptors) through the semicircular duct What are these equilibirum receptor cells known as in the ampulla? What type of movement does it respond to?

Answer 40

The ampullae houses equilibrium receptor called crista ampullaris which responds to angular (rotational) movement of the head

Question 41

How long is the vestibule and what 2 membranous sacs does it contain?

Answer 41

The vestibule is approximately 5cm long and contains the saccule and utricle

Question 42

What are the equilibrium receptors housed in the saccule and ventricle known as? What do they respond to?

Answer 42

The equilibrium receptors in the saccule and ventricle are known as maculae and these respond to the pull of gravity and changes in head position

Question 43

What are the small gravel like crystals that move when there is change in the angular movement, position of the head or the pull of gravity? What nerve connects to the maculae of the saccule and utricle and the crista ampullaris of the ampulla of the semicircular ducts?

Answer 43

These are known as otolith crystals The vestibular part of CN VIII connects to the maculae and ampullae of the vestibular part of the membranous labyrinth

Question 44

What is the blood supply to the internal ear? Where does this branch most commonly come from and where can it arise from?

Answer 44

The blood supply is mainly from the labyrinthine artery (internal auditory artery) which arises from a branch of the anteroinferior cerebellar artery 80% of the time or the basilar artery

Question 45

The internal auditory artery arises from the anterior inferior cerebellar artery 80% of the time or directly from the basilar artery What branches does the internal auditory artery give?

Answer 45

It gives the common cochlear artery and 2x vestibular arteries