Sem 2 - Z(2) - The Ear - Divisions, external auditory meautus, External/middle/inner ear Flashcards
The ear can be divided into the external (outer), middle and internal (inner) ear What makes up the external ear?
- * The auricle
- * External auditory meatus
- * External surface of the tympanic membrane
What makes up the middle ear?
- * The internal surface of the tympanic membrane
- * The tympanic cavity
- * The ossicles
- * The pharyngotympanic (aka Eustachian, aka auditory) tube
What makes up the inner ear?
- * Auditory apparatus
- * Vestibular apparatus
- * Internal auditory meatus
- * Vestibulocochlear nerve (CN VIII)
- * Oval window
- * Round window
Is it the auditory system or vestibular system involved in hearing? Which system is involved in balance?
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
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?
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
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?
- 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
The conchae can be divided into two parts Where do these two parts lie and what are they known as?
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
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?
- 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
What is the arterial supply to the auricle?
- Posterior auricular artery (from ECA) gives perforating branches
- and Superior, middle and inferior anterior auricular arteries (from superficial temporal artery)
What is the sensory innervation to the ear?
- 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
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?
The external auditory meatus is approximately 2.5cm long
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)
- 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
What is the blood supply to the external auditory meatus?
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
What is the innervation of the external auditory meatus?
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
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?
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
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?
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
Which nerve travels across the medial surface of the tympanic membrane?
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
What is the innervation of the tympanic membrane? (lateral and medial surface)
- 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
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?
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
What is the space lying adjacent to the mastoid air cells where two of the three ossicles extend into?
The epitympanic recess is superior to the tympanic cavity adjacent to the mastoid air cells The malleus and incus extend into this recess
What is the origin and insertion of the tensor tympani and the stapedius muscle?
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
What is the function and innervation of the tensor tympani and stapedius muscles?
- What is their combined action?
- 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
RESTATE the attachments, function, combined action and innervation of the tensor tympani and stapedius
- * 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
What provides sensory innervation to the tympanic cavity and medial surface of tympanic membrane? What is the blood supply to the tympanic cavity?
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
How does the chorda tympani branch travel from facial nerve to exit the cranial cavity?
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
What nerve does the chorda tympani then hitch a ride on and what does it supply with what?
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
What connects the nasopharynx to the tympanic cavity? What is the function of this tube?
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)
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?
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
When is the eustachian tube open? What provides sensory innervation to the esutachian tube?
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
So many arteries give some branches to the middle ear What were the main one mentioned earlier?
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
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?
- 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
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?
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
Are the bony labyrinth and the otic capsule the same thing? If not then whats the different?
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
What is the membranous labyrinth? What are the three parts it consists of?
What does the membranous labyrinth contain?
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)
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
- 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
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
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Anterior to the vestibule of the bony labyrinth lies the cochlea What lies posterior and lateral to the vestibule?
The semicrcular canals containing the semicircular ducts lie posterior and lateral to the vestibule
What are the three semicircular canals? What orientation are they in to one another?
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
Within the semicircular canals are the semicircular ducts. What are these continous from? What are the swellings of each duct known as?
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
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?
The ampullae houses equilibrium receptor called crista ampullaris which responds to angular (rotational) movement of the head
How long is the vestibule and what 2 membranous sacs does it contain?
The vestibule is approximately 5cm long and contains the saccule and utricle
What are the equilibrium receptors housed in the saccule and ventricle known as? What do they respond to?
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
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?
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
What is the blood supply to the internal ear? Where does this branch most commonly come from and where can it arise from?
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
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?
It gives the common cochlear artery and 2x vestibular arteries
