Region 14 - Ear Flashcards
What structures make up the external ear?
Auricle
External auditory meatus
External surface of tympanic membrane
What structures make up the middle ear?
Internal surface of tympanic membrane
Tympanic cavity
Ossicles
Pharyngotympanic tube
What structures make up the inner ear?
Auditory apparatus Vestibular apparatus Internal acoustic meatus CN VIII Oval window Round window
What is the auricle made up of?
Irregularly-shaped plate of elastic cartilage
Where does lymph from the auricle drain to?
Parotid and cervical nodes
What is the arterial supply to the auricle from?
Anterior auricular branches of superficial temporal artery
Posterior auricular artery perforating branches
What is the concha of the auricle? What is it made up of?
The deepest depression
Formed from:
- Cymba (superiorly)
- Cavity (inferiorly)
What is the sensory innervation to the auricle?
Anteriorly = Auriculotemporal nerve (CN V3)
Posteriorly = Lesser occipital nerve (C2) and Greater auricular nerve (C2-C3)
Entire auricle = Facial nerve contributions
Concha = Vagus nerve contributions
How long is the EAM?
~2.5cm
What type of cartilage makes up the lateral 1/3 of the EAM?
Elastic
What features are present in the lateral 1/3 of the EAM?
Hair follicles
Sweat glands:
- Ceruminous glands
Sebaceous glands
How does earwax form?
Mixing of secretions from sweat glands and sebaceous glands in lateral 1/3 of EAM
What is the structure of the medial 2/3 of the EAM?
Bone
Lined with stratified squamous epithelium
What is the arterial supply to the EAM?
Auricular branches of ECA
What is the sensory supply to the EAM?
External surface = Auriculotemporal nerve (CN V3)
Anterosuperiorly = Auriculotemporal nerve
Posteroinferiorly = Auricular branch of CN X
Posteriorly = Posterior auricular branch of CN VII
What is the diameter of the tympanic membrane?
~8mm
What is the outer surface of the tympanic membrane lined with?
Stratified squamous epithelium
What is the inner surface of the tympanic membrane line with?
Mucous membrane
What neurovascular structure crosses the inner surface of the tympanic membrane?
Chorda tympani of CN VII
What ossicle attaches to the inner surface of the tympanic membrane?
Malleus
What is the innervation to the lateral (external) surface of the tympanic membrane?
Auriculotemporal nerve (anteriorly and superiorly) Auricular branch of CN X (posteroinferiorly)
What is the innervation to the medial surface of the tympanic membrane?
Tympanic branches of CN IX
What forms the roof of the tympanic cavity (middle ear)?
Tegmen tympani:
- Part of petrous temporal bone
- Separates middle ear from dura of middle cranial fossa
What forms the floor/jugular wall of the tympanic cavity (middle ear)?
Layer of bone between:
- Tympanic cavity AND
- Superior bulb of IJV
What forms the membranous/lateral wall of the tympanic cavity (middle ear)?
Tympanic membrane
Superiorly:
- Lateral bony wall of epitympanic recess
- Head of malleus extends into recess
What forms the labyrinthine/medial wall of the tympanic cavity (middle ear)?
Promontory of labyrinthine wall:
- Basal turn of cochlea
- Oval and round windows
What overlies the promontory of the labyrinthine wall of the tympanic cavity?
Tympanic plexus:
- Lesser petrosal nerve
- Tympanic nerve
(Both CN IX)
What forms the mastoid/posterior wall of the tympanic cavity (middle ear)?
Aditus:
- Opening in superior aspect of cavity
- Opens into mastoid antrum
What forms the carotid/anterior wall of the tympanic cavity (middle ear)?
A thin bone between the tympanic cavity and the carotid canal
What features are in the superior part of the anterior wall of the tympanic cavity?
Opening for pharyngotympanic tube
Canal for tensor tympani
What is the origin and insertion of tensor tympani?
Origin = Wall of pharyngotympanic tube Insertion = Handle of malleus
What is the function of tensor tympani?
Tenses tympanic membrane by pulling handle of malleus medially
What is the innervation to tensor tympani?
CN V3
What is the origin and insertion of stapedius?
Origin = Pyramidic eminence on posterior wall of tympanic cavity Insertion = Neck of stapes
What is the function of stapedius?
Pulls ‘footplate’ of stapes laterally
What is the innervation to stapedius?
Nerve to stapedius from CN VII
What is the combined action of tensor tympani and stapedius?
Reduces vibration passing to delicate inner ear at the oval window
What nerve provides sensory supply to the tympanic cavity?
CN IX
What is the arterial supply to the tympanic cavity?
Tympanic branches of: - Posterior auricular artery - Ascending pharyngeal artery - Maxillary artery Caroticotympanic artery from ICA
How does the chorda tympani leave the tympanic cavity?
Via the petrotympanic fissure
What is the structure of the lateral part of the pharyngotympanic tube?
1.2cm long
Bony canal
Lined with mucous membrane
What is the structure of the medial part of the pharyngotympanic tube?
2.5cm
Cartilaginous and membranous tube
What causes the pharyngotympanic tube to open?
Swallowing or yawning:
- Tensor veli palatini contracts
- Lumen opens
What is the purpose of opening the pharyngotympanic tube?
Equalises pressure on both side of tympanic membrane
What is the sensory supply to the pharyngotympanic tube?
Nerves from tympanic plexus (CN IX)
What is the main arterial supply to the middle ear?
Anterior tympanic (glaserion) artery from 1st part (mandibular) of maxillary artery
What other arteries supply the middle ear?
Ascending pharyngeal (inf. tympanic artery)
Middle meningeal (superior tympanic artery)
Posterior auricular:
- Stylomastoid artery
- Posterior tympanic artery
Artery of pterygoid canal
Caroticotympanic branch of ICA
What surrounds the bone labyrinth of the inner ear?
Otic capsule:
- Very dense bone within petrous temporal bone
- NOT a part of bony labyrinth
What are the canals of the bony labyrinth filled with?
Perilymph (similar to ECF)
What are the structures of the bony labyrinth?
Cochlea
Vestibule
Semicircular canals
What is the membranous labyrinth?
A continuous system of ducts and sacs within bony labyrinth
What is the membranous labyrinth suspended in?
Perilymph
What is the membranous labyrinth filled with?
Endolymph (similar to potassium ion-rich ICF)
What are the functions of perilymph and endolymph?
Conduct sound vibrations
Respond to mechanical forces:
- Movement
- Acceleration
What are the three main canals within the cochlea?
Scala vestibuli
Scala tympani
Cochlear duct
What canal within the cochlea communicates with the stapes and where?
Scala vestibuli
At the oval window
What canal within the cochlear communicates with the tympanic cavity and where?
Scala tympani
At the round window
What are the scala vestibuli and scala tympani filled with?
Perilymph
What separates the scala vestibuli and scala tympani?
Reissner’s membrane
What is the cochlear duct filled with?
Endolymph
What organ of hearing is found within the cochlear duct?
Organ of Corti
How many turns does the cochlear have?
2.5
What does the spiral canal of the cochlea turn around?
A bony core = Modiolus
Where do the scala vestibuli and scala tympani communicate?
Helicotrema
Where do the semicircular canals lie in relation to the vestibule?
Posterolaterally
What is the structure of a semicircular canal?
2/3 of a circle
Diameter of ~1.5mm
What are the semicircular canals?
Anterior and posterior (lie at right angles)
Lateral (lies horizontally)
What are the semicircular ducts continuous with?
Utricle
What is the swelling at the end of each semicircular canal? What does this contain?
Ampulla
Contains:
- Crista ampullaris which contains equilibrium sensors
What do the ampullae of the semicircular canals respond to?
Angular (rotational) movements of the head
How long is the vestibule of the bony labyrinth?
~5mm
What membranous sacs are within the vestibule of the bony labyrinth?
Utricle
Saccule
What equilibrium sensors are contained within the utricle and saccule? What movements do they respond to?
Maculae
Respond to:
- Gravity
- Changes in head position
What is the main arterial supply to the inner ear?
Internal auditory (labyrinthine) artery
What is the origin of the main arterial supply to the inner ear?
Anterior inferior cerebellar artery (85%) Basilar artery (15%)
What are the branches of the main arterial supply to the inner ear?
Common cochlear artery
Vestibular artery