Theme 8a Flashcards
The Ear
3 Sections of the Ear
What are they?
What does each consist of?
What ois the role of each?
External Ear: funnels air vibrations towards tympanic membrane
- External auditory meatus
- Tympanic Membrane
Middle Ear: conducts vibrations from tympanic membrane to inner ear
- Tympanic cavity
- Pharyngotympanic tube
- Ossicles & muscles
- Air-filled
Inner Ear: Hearing & Balance
- Bony labyrinth
- Membranous labyrinth
What are the two parts of the Temporal Bone?
What does each part consist off?
Petromastoid part: Tympanic ring
Squamous part:
- Styloid process
- Jugular Foramen – Transmits Internal Jugular Vein, CN IX, X and XI
- Carotid Canal
- Stylomastoid Foramen – Transmits CNVII (after emerging through Internal Auditory Meatus)
- Internal Auditory Meatus – Transmits CN VII and VIII
- Greater Petrosal Hiatus – Transmits Greater Petrosal Nerve of CNVII
- Lesser Petrosal Hiatus – Transmits Lesser Petrosal Nerve of CNIX
What are the Borders of the Middle Ear?
Anterior:
- Pharyngotympanic (Auditory) Tube which leads to the
- Nasopharynx.
Medial:
- Promontory (rounded projection)
- Fenestra Vestibuli (Vestibular Window opens to inner ear)
- Fenestra Cochleae (Cochlear Window) is a smaller, inferior membrane covered opening
.Lateral:
- Tympanic membrane
- Epitympanic Recess (slight upward extension of the middle ear above the Tympanic Membrane)
- Chorda Tympani (branch of CNVII, crosses medial side of Tympoanic Membrane)
What are the muscles of the Middle Ear?
- Role?
Tensor tympani:
- attaches to the ossicle to protect again loud sounds and modulate the frequency response of the ossicles - reducing their ability to conduct sounds of low frequency.
Stapedius:
- Contracts to pull the stapes foot plate laterally: counteracts loud, low sounds
- What are Ossicles?
- What is the role of Ossicles?
- What are the 3 different bones?
1 .3 small articulating bones from tympanic membrane to vestibular window
- transmit sounds from the air to the fluid-filled labyrinth (cochlea)
3.
- Malleus
- Incus
- Stapes
Movement of Ossicles
- Increase in air pressure moves tympanic membrane medially
- The long process of malleus moves medially
- Head of malleus rotates laterally on an axis in the epitympanic recess
- The body of the incus moves medially
- Stapes base pushes on oval window (fenestra vestibuli)
- Movement is like a banging door
Inner ear
What are the two divisions of the inner ear?
What fluid does division contain?
- Bony labryinth - perilymph
- Membranous Labyrinth - endolymph
Facial Nerve
Where does it enter and leave?
What are gthe branches?
In: through the internal auditory meatus in the petrous temporal bone
Out: stylomastoid foramen where it pierces parotid gland & the five facial branches
Branches:
- Greater Petrosal Nerve: arises from the geniculate ganglion into middle cranial fossa, through Fo. Lacerum, into Pterygoid Canal to ~+ deep petrosal nerve = N of Pterygoid Canal and then joining Pterygopalatine Ganglion
- N to Stapedius
- Chorda Tympani: enters the middle ear across the tympanic membrane, enters the infratemporal fossa via petrotympanic fissure where it joins lingual nerve to go to submandibular ganglion
- Lesser Petrosal Nerve:
- aves tympanic plexus IX to join V otic ganglion via ovale
Lesions of the Facial Nerve
- What aspcts of the Facial Nerve Function can be tested?
- Where can lesions be present?
1.
- Lacrimation (pterygopalatine ganglion)
- Stapedius Reflex
- Taste (chorda tympani)
2.
Taste only = between N to Stapedius & Chorda Tympani
S.R. & Taste = between Geniculate ganglion & N to Stapedius
What would damage to CNVII in the Internal Auditory Meatus result in?
ipsilateral facial paralysis combined with a loss of taste to the anterior 2/3 of the tongue, loss of the stapedial reflex and loss of lacrimal gland secretion
Sensory transuction
- Stapes presses on fenestra vestibuli
- Fluid vibrations are transmitted to the scala vestibuli
- Basilar membrane is displaced
- Displacement is greatest at the base for high freuency & greatest at the apex for low frequency
- Hairs of the hair cells are displaced
- Fenestra cochlea is displaced
