What are the three areas of the ear?
What comprises the outer ear?
Auricle and external auditory meatus
What are the borders of the middle ear?
Between tympanic membrane and petrous part of the temporal bone
What is the function of the outer ear?
To collect sound and localise sounds from different positions in space
What are the major features of the auricle?
Tragus - hair
What is the function of the external auditory meatus?
To transmit air towards the tympanic membrane
Describe the structure of the external auditory meatus?
Lateral 1/3 cartilagenous, medial 2/3 bony
Lined by hair skin and cerumen glands
What is the function of cerumen glands?
Produce waxy substance that prevents maceration of skin with water
Describe the innervation of the external auditory meatus?
Why is this important?
Auriculotemporal nerve (V3 branch - anterosuperior and external surface of tympanic membrane)
Important because EAM can refer pain to opther branches of V3 (eg. teeth)
Describe the strucutre of the tympanic membrane?
Concave externally, convex internally
Attached to ossicles
Describe the cone of light that should be seen when looking into the ear with an oroscope?
When might this change?
Cone of light in antero-inferior quadrant
When pressure builds up in middle ear, concavity of tympanic membrane will change and alter the position of the light
What is the function of the tympanic membrane?
Vibrates with same frequency and amplitude relative to sound waves > transmits energy into middle ear and beyond
Describe the two cavities in the inner ear?
Epitympanic recess: space above the tympanic membrane, communicates posteriroyl with spaces in mastoid bone
Tympanic cavity proper: directly medial to tympanic membrane
What is the significance of the communication between the epitympanic recess and the mastoid air cells?
Passage for infection
What is the function of the auditory tube?
Connects middle ear to nasopharynx
Allows communication between middle ear and atmosphere, therefore allowing equalisation of pressure to occur
Describe the arrangement of the ossicles?
Attached laterally to tympanic membrane, attached medially to hole in petrous part of the temporal bone
Lateral to medial: malleus, incus, stapes
How do the ossicles transmit sound through the middle ear?
Tympanic membrane vibrates > ossicles vibrate with same frequency and amplitude relative to that sound > sound waves transmitted through to inner ear
Describe tha major features of each of the three ossicles?
ALL: synovial joints
Malleus: handle, head
Incus: body, lenticular process
Stapes: head, base
Which two muscles are associated with the ossicles?
What are their functions and innervation?
Stapedius: attaches to stapes, innervated by CN VII
Tensor tympani: attaches to malleus, innervated by CN V
Both contract to dampen the amplitude of vibration of ossicles for loud sounds
What is the chorda tympani?
What is its function?
Branch of facial nerve that travels through middle ear
Carries PS nerve fibres to salivary glands and brings back info about taste from tongue
What are the major features of the medial wall of the middle ear?
What is the promontory?
Where do the oval and round window lie relative to it?
Basal turn of cochlea that impresses on the medial wall of the middle ear
Oval window is posterior and above
Round window is posterior and below
What are the oval and round windows?
Oval window: opening into inner ear
Round window: opening from inner ear back out into middle ear, which allows for pressure release
Which arterial structure lies close to the ear?
Internal carotid artery lies close to middle ear (runs straight underneath it)
Which structure lies over the oval window?
Describe the pathway of the facial nerve around the ear?
Enters petrous part of temporal bone through internal auditory meatus > travels in facial canal > emerges in stylomastoid foramen
What are the major strucutres of the inner ear?
Describe the structure of the cochlea and the semicircular canals?
Bony labyrinth: space in petrous part of temporal bone, filled with perilymph
Membranous labyrinth: closed sac that is suspended in perilymph of bony labyrinth, filled with endolymph
What is the function of the bony and membranous labyrinths?
Bony: transmits mechanical energy of vibration
Membranous: contains sensory receptors for hearing and balance
Where are the sensory receptors for hearing and balance located?
What is the connection between the cochlea and the semicircular canals called?
Where are the sensory receptors for hearing located?
In cochlear duct of membranous labyrinth
What are the componenets of the vestibule?
Utricle and saccule
What is the function of the utricle and saccule?
Contain sensory receptors for static equilibrium
What is the ampulla?
What is its function?
Swelling at the base of each semicircular canal
Contains sensory receptors for dynamic equilibrium
Describe the orientation of the semicircular ducts?
3: anterior, horizontal and posterior
Anterior and posterior lie at right angles to each other
Where are high and low frequency sounds detected?
High frequency: base of cochlea
Low frequency: apex of cochlea