The Ear Flashcards
3 main sections of the ear
outer
middle
inner
outer ear
pinna
external auditory meatus (EAM - ear canal)
tympanic membrane (ear drum)
function of outer ear
collect and funnal sound into skull towards inner ear
role of tympanic membrane
boundary between external and middle ear
○ Collection vibrations and pressure waves down the EAM and the TM vibrates and transfers them to middle ear
shape of EAM
sigmoid shaped and not straight
division of tympanic membrane
- Subdivided into anterior and posterior or superior and inferior
- Quarters:
○ ASQ - anterior superior
○ AIQ - anterior inferior
○ PSQ - posterior superior
○ PIQ - posterior inferior
- Quarters:
parts of the tympanic membrane
handle of malleous (short process of malleous at top)
pars flaccida at top of membrane
pars tensa is around the handle of malleous
middle ear
empty cavity sitting in the temporal bone
middle ear connection to outside world
via a small Eustachian tube that enters the nasal canal cavity
ossicles (bones) in the inner ear
malleus
incus
stapes
descending size from lateral to medial
role of ossicles
transmit vibration from the tympanic membrane to the sensitive inner ear via an oval window
role of middle ear
amplifying vibrations of tympanic membrane
impedance matching the vibration of air and liquid (from the outside world to fluid inside the inner ear)
nerve transversing middle ear
facial nerve
Tensor tympani
attaches to malleus and dampens very loud sounds
Stapedius muscle
(1mm long)
○ Dampens and limits the vibrations/movements of stapes
○ Nerve to stapedius is literally called ‘nerve to stapedius’
○ Branch of facial nerve (7)
○ If nerve to stapedius is damaged e.g. in Bell’s palsy and the stapedius muslce doesn’t work then normal sounds will seem so loud
where is the inner ear
petrous part of temporal bone
role of inner ear
transduce vibration/sound into electrical activity or AP and to provide balance
2 parts/layers of labyrinth
bony and membranous labyrinth
fluid in the membranous labyrinth and its function
endolymph fluid - bathes the whole of the sensory epithelium inside the inner ear
fluid between the bony and membranous labyrinth
perilymph
where are endolymph and perilymph fluids
endolymph - in membranous labyrinth
perilymph - between bony and membranous labyrinth
2 functional parts of the inner ear
cochlear - hearing
vestibular system - balance
nerve wired to the special sensory organs of hearing and balance
vestibulocochlear nerve (CNVIII)
vestibular system is responsible for…
balance
vestibular system consists of…
2 sacs called the utricle and sacculle
3 semi-circular canals (horizontal, posterior, superior)
what is at the end of the semicircular canals
swellings called ampulla
where is the oval window
under stapes
flow around the cochlear
- Scala vestibular (vestibular duct)
○ Carries vibrations to tip of cochlea- Scala tympani (deep to the bone)
○ Carries vibrations back to the round window
- Scala tympani (deep to the bone)
role of endolymph in cochlear duct
in the cochlea duct
- Lots of potassium ions so AP triggered well
- If mixed with perilymph then the concentration of potassium ions lost and hearing effected.
role of utricle
(detects horizontal movements)
§ Contains a macula
role of sacculle
(detect vertical movements)
§ Contains a macula
sensory organ of vestibular system
hair cell
clusters of hair cells form…
modified sensory epithelium floating in the endolymph
structure of hair cells in the vestibular system
clusters of hair cells form modified sensory epithelium floating in the endolymph
each hair cell is connected to vestibular neuron consisting of a body and stereocilia projecting outwards (longest one is kinocilium) (encased in gel)
hair cells are constantly doing what?
firing AP down their vestibular neurons towards the brain
hair cells are found where?
in macula in utricle and sacculle
what is special about the hair cells in the macula?
otoconia (crystals) on top of the gel layer that add inertia to the system and emphasise movements.
direction of macula in utricle
dangle from roof
role of macula in utricle
detect linear or horizontal acceleration
direction of macula in sacculle
hang from wall
role of macula in sacculle
detect vertical acceleration
hair cells in the semicircular canals
cup shaped layer called cupula
sensory epithelium called crista
no otoconia
role of crista
detect angular acceleration but only in the same plane as the movement
when is horizontal canal stimulated
when you look left or right
when is superior canal stimulated
when you look up or down
when is posterior canal stimulated
lookup as laid down
majority of info provided by semicircular canals is destined to go where?
extraocular eye muscles
how does the majority of info provided by semicircular canals is destined to go to the extraocular eye muscles?
achieved in the brainstem by relays from the vestibular nuclei to the nuclei of CN3, 4 and 6.
vestibulo-ocular reflex (VOR)
keep the vision and gaze fixed on the object despite the head, body or object moving.
transduction of sound is conducted by what?
hair cells in the cochlear
blood supply to the ear
○ Posterior and anterior to the EAM
○ Posterior auricular artery supplies posterior part of the ear
○ Anterior part (anterior to EAM) is supplied by superficial temporal artery
○ Both branches of external carotid artery
○ Posterior part of ear is innervated by branches from spinal level c2 and c3 and cervical plexus
○ Anterior ear is innervated by trigeminal nerve (3rd branch - mandibular branch), vagus and facial nerve
