Chapter 6-7 Flashcards
Names of the outer ear
Pinna / Auricle
Wherein the 8th cranial nerve located
Inner ear
What is the pinna and what the framework is made up of
- flap-like appendage on sides on ears
- framework made-up of cartilage
What does the pinna funnel into
The EAC , external auditory canal
What is the External auditory canal made-up of
Lateral side made up go cartilage , and leads medially to bone
What’s is the (EAC) External Auditory Canal ?
- bent tube 25/35mm long ( 1-1 1/4 inches)
- 5-7 mm in diameter
- covered in skin
Cartilage portion secretes …
Cerumen
What does the outer ear effect ? (3)
- protection for delicate middle and inner ear structures
- enhancement go mid-high frequency region ( improves sensitivity)
- improves in directional hearing
Why is there improved sensitivity ?
Because its a tube with 1 open and 1closed end
- standing wave starts at odd integer multiples of frequencies with wave length of 4x length of tube
How can you find the frequency of a external auditory canal
- average adult canal is approximately 25 mm
- the frequency = c (344) / 4X length of the canal
When is there a sound pressure gain in the EAC ?
Sound pressure gain at the medial end of pipe of about 12-15 dB at around 3400 Hz
How does the outer ear aid in directional hearing?
- two ears on opposite sides of the head
- Head ( .18m in diameter ) and torso create a baffle effect
- sound from air travels through EAC
What restriction are present on hearing
- Frequency below 1900 Hz (344/.18) are diffracted around head
- > 1900 Hz are reflected => constructive reinforcement
- cues to localize sound
- complex , involve differences in time of arrival and level between the ears
What leads to the beginning if the middle ear
Tympanic membrane
Characteristics of TM ; diameter , location , substance and sections
- 8-9 mm in diameter
- medially end = eustation tube
- laterally near EAC
- layered cone shaped membrane
- superior area is the location of pars flaccida (2 layered)
- inferior layer locates the pars tensa (3 - 4 tissue layers )
What is pars tensa made up of ?
(Sandwich) made up of skin and mucosa with fibrous tissue inter twining making it stiff
What ear has the head of the malleus facing 11:00 o’clock ?
Left ear
What ear has the head of the malleus facing 1:00 o’clock ?
Right ear
What ossicles are visually present while looking at the TM from and exterior view ?
- the short process of the malleus
- incus
- handle of the malleus
- sometimes the incus
What three middle ear ossicles are all attached ? Which attaches to the tympanic membrane ?
The malleus is attached to the tympanic membrane which also attaches to the incus and the stapes
What are the position of the ossicles on the malleus , starting laterally leading to the medial most part connecting to the stapes ?
Umbo - handle of malleus (aka manubrium) - head of malleus
What are the cavities called that are located in the middle ear , listed superior to inferior ?
- tympanic cavity
- epitympatic recess (aka attic) > aditus : opening to two landmarks
- mastoid Antrum
What is the middle ear made up of ?
ME bones, ligaments and muscles
What does the middle ear connect to , what does it do ?
ME connects to nasopharynx by eustachion tube which ventilates and drains the middle ear space
What is the difference in the eustachion tubes in children and adults , what difficulties occur ?
They are horizontal in children , adenoids swelling can cause difficulties because they may block tubes …. Causes an uneven distribution of pressure due to tubes
What happens when eustachion tubes are not working ?
If tube is blocked / swelling occurs it creates a negative pressure because air can’t enter . The ME secretes fluid to fill the space
What is located inside of the tympanic cavity ? ( 6) walls
Lateral wall: tympatic membrane
Anterior wall : carotid wall ( caractid artery)
Posterior wall : mastoid wall (aditus location)
Superior wall : tegmental wall ( thin plate of bone)
Inferior side : jugular wall (jugular vein below)
Medial side: labyrinth wall (oval/ round window)
Ossicular chain and parts of the each piece ?
- malleus ( head & manubrium)
- incus ( body & legs)
- stapes (head, crura and footplate)
Facts about stapes , where does it insert, how large is the footplate .
- smallest bone in the human body
- foot plate sits in the oval window in the inner ear , supported in place by the annular ligament
- area of foot plate is approximately 3.2mm^2
What influences the movement of the ossicles in the middle ear?
- ligaments suspend the ossicles in cavity
- ME muscles that influence ;
1. Tensor tympani
2. Stapedius
Tensor tympani
Attached to the manubrium , innervated by the 5th cranial nerve
- if muscles contracts it limits movement for ossicles
Stapedius
Attached to the head of stapes , innervated by the facial nerve 7
- if muscles contract it limits movement
How big is the middle ear and what does it hold ?
Two cubic cm , cavity comprising three air-filters
