Clinical anatomy of the ear Flashcards
what are the 2 parts of the temporal bone?
- squamous part
- petrous part
what makes up the external ear and whats it function?
- auricle to tympanic membrane
- via external acoustic meatus
- collects and conveys sound waves to tympanic membrane
what makes up the middle ear and whats it function?
- tympanic membrane to oval window
- also eustachian tube
- amplifies & conducts sound waves to the internal ear
what makes the internal ear and whats it function?
-oval window to internal acoustic meatus
-converts special sensory information-into fluid waves,
then APs,conducts APs to brain
what is the external ear made of and whats it’s properties?
- temporal bone
- elastic cartilage
- avascular
- nutrients from skin
- do not use anaesthetic containing adrenaline on external ear
what is the ear canal made of?
- 1/3 cratilage
- 2/3 bony and is lined with skin
what is the nerve supply to the auricle?
- C2,3
- CN VII
- CN V3
- CN X (look at lecture side 8)
what lymph nodes drain the auricle?
- Lateral surface of superior half -parotid lymph nodes
- Cranial surface of superior half-mastoid lymph nodes (and deep cervical)
- Rest of auricle, including lobe- superficial cervical lymph nodes
where does the lymph eventually drain to?
deep cervical lymph nodes (in carotid sheath) then into the thoracic duct or right lymphatic duct then into the
venous angle
what is the difference between a child’s EAM and an adults?
- childs is short and straight (gently pull auricle posteroinferiorly)
- adults is curved and gently pull auricle posterosuperiorly
what are the 4 parts of the ear of the otoscopic examination?
- pars flaccida (thin part of the tympanic membrane superiorly)
- the jumbo
- the cone of light
- pars tensa (thick part of the tympanic membrane posteroinferiorly)
what is the general sensory nerve supply to the tympanic membrane?
external surface- mostly CN V3
internal surface- CN IX
where does the glossopahrygeal nerve provide sensory innervation to?
middle ear cavity eustachian tube nasopharynx oropharynx tonsils
what is the function of the Eustachian tube ?
connects middle ear cavity to nasopharynx
what are the 3 auditory ossicles?
- malleus
- incus
- stapes
how do the 3 ossicles articulate to each other?
synovial joints
what fits into the base of the stapes?
oval window into internal ear
what forms the bony swelling on the medial wall?
Formed by the cochlea of the internal ear
what causes mastoiditis?
spread of infection from middle ear cavity
what is the aditus?
doorway into the mastoid antrum from the epitympanic recess
what does the chord tympani (branch of CN VII) supply?
- taste buds of the anterior 2/3rds of the tongue
- parasympathetic supply to the submandibular & sublingual salivary glands (salivation)
what is the role of the right stapedius?
reduces stapes movement to protect the internal ear from excessive noise
what course does the facial nerve take through the base of the skull?
- through internal acoustic meatus
- in the facial canal of the petrous temporal bone
- stylomastoid foramen
what does the internal ear consist of and whats its function?
- oval window to internal acoustic meatus
- petrous part of temporal bone
- converts special sensory information
what are the 2 parts of the CN VIII?
-the cochlear nerve (hearing) - the vestibular nerve (balance)
where does the dense otic capsule sit?
in the temporal bone
what does the otic capsule contain?
Bony labyrinth - filled with perilymph
what is suspended within the perilymph of bony labyrinth?
- membranous labyrinth
- communicating sacs and ducts
- contains endolymph fluid
how many turns does the cochlea have?
2
what are the 3 semicircular canals and whats their function?
- anterior
- lateral
- posterior
- associated with balance
what is the cochlear duct and what conducts their action potentials?
- a long balloon-like structure within the cochlea filled with endolymph
- cochlear nerve
what is the semicircular duct and what conducts their action potentials?
- inter-linked balloon-like structures within the semicircular canals filled with endolymph
- vestibular nerve
what stimulates hair cells?
movement of endolymph
what are clusters of hair cells called?
maculae
what detects angular movement change?
semicircular ducts
what detects linear movement change?
- utricle (horizontal)
- saccule (vertical)
what are the steps of sound transmission?
1) Sound waves make tympanic membrane vibrate
2) Vibrations transmitted through ossicles
3) Base of stapes vibrates in oval window
4) Vibration of stapes creates pressure waves in perilymph
5) Hair cells in the cochlea are moved, neurotransmitter is released, APs stimulated and conveyed to brain by cochlear nerve
6) Pressure waves descend and become vibrations again
7) Pressure waves are dampened at the round window
where does CN VII and VIII connect with the brainstem?
junctions between the pons and the medulla oblongata
what are symptoms associated with pathology at the internal acoustic meatus regarding the CN VII?
- ipsilateral loss of facial expression
- ipsilateral loss of taste
- dry mouth (reduced ipsilateral salivation)
- reduced general sensation in the auricle (immediately posterior to the tragus)
what are symptoms associated with pathology at the internal acoustic meatus regarding the CN VIII?
- ipsilateral loss of hearing (cochlear nerve)
- ipsilateral loss of balance (vestibular nerve)
