Outer Ear Flashcards
What is anatomy?
Physical part
What is Physiology
How the anatomy works
What types of tissue make up the outer ear?
Squamous epithelium
Mucous membrane
Cartilage
Name the parts of the pinna
Helix
Scaphoid fossa
Darwin’s tubercle
Antihelix
Concha
Antitragus
Lobe
Superior crus of antihelix
Triangular fossa
Inferior cris of antihelix
Crus of helix
Tragus
External auditory meatus
Intertragic notch
External Auditory Meatus dimensions
25mm long
7/8mm diameter
4cm squared volume
EAM features and labels
Tissue
1/3 cartilage
2/3 bone
1.5mm squamous epithelium
Glands
Ceruminous (sweat)
Sebaceous (oil)
Fine hairs
Skin at TM 0.5mm
2 bends
Isthmus is narrowest part
Properties of wax
(7 answers)
Colour variable
Water resistant
Hydroscopic
Bacterioscopic
Acidic
Lubricant
Self-cleaning
Tympanic membrane labels
(10)
Pars flaccida
Pars tends
Umbro
Annulus
Handle of malleus
Light reflex
Long process of incus
Anterior malleal fold
Posterior malleal fold
Short process of malleus
What layers is the tympanic membrane made up of? (3)
Squamous epithelium
Fibrous layer
Mucous membrane
Tympanic membrane dimensions and characteristics? (7)
10mm x 8mm wide 0.1mm thick
Approx 55 degrees
Concave, Umbo point ox max concavity
Translucent, pearly/grey
Handle of malleus attached
Light reflects
Annulux
What is the physiology of the outer ear?
C - collection
L - Localisation
A - Amplification
P - Protects
Collection
Collects sound in all directions
Pinna angles to front
Localisation
Ability to pinpoint source+ location of sound using input from both ears as well as cognitive processes
Amplification
Resonance in the concha 5500Hz
Resonance in the eam 2500Hz
Increased incoming signal by 12-20dB
Max amplification around 3000Hz
Protection
Pinna, tragus obstructs eam
Meatus, wax (infection) hair (filter) 2 bends (objects) sensitive bone (cough reflex)
What is the physiology of the Tympanic membrane?
V - Vibrates
A - Acoustic energy to mechanical energy (converts)
T - Transmits energy further into auditory system
S - Barrier between outer & middle ear
What is localisation?
Ability to pinpoint source & location of sound, using input from ears as well as cognitive processes
What are the types of side to side (horizontal) localisation?
Interaural time difference (ITD)
Interaural intensity difference (IID)
Interaural phase difference (IPD)
Explain Interaural time difference?
Sound from the side, arrives at the ear closest to to the source earlier and reaches opposite ear slightly later
Describe Interaural Intensity Difference
Sound dissipates over time and is heard louder in the ear closest to the source
Describe Interaural Phase Difference
When sound waves reach the other ear it is in a different phase (rarefaction / compression)
Only works for low frequencies (<1500Hz) due to long wavelength’s
Has to be in the same cycle, wavelength needs to be larger than head
What is head shadow effect?
- head acts as a barrier when sound is presented from one side, one ear is in shadow of head, 6dB average difference
- higher frequencies are less able, low frequencies more able
- sound arriving at opposite side to sound source will be lacking higher frequencies that were heard at closer ear
When will horizontal localisation reduced or not work?
If there is a hearing loss in one ear or if a hearing aid is only worn in one ear
How does vertical localisation work?
Determined by the size and shape of the pinna
Contours and fold of pinna create echoes as well as shoulder and torso reflections
Sound arriving at TM is combination of direct and reflected sound. Brain uses info to determine position of sound pressure.
Echo times in vertical localisation?
High frequencies reflect better
Sound from above = faster echo (100 micro-seconds)
Sound from below = later echo (300 micro-seconds)
Pinna echoes - difference between direct / reflected sound
How does front localisation work?
Pinna faces forward at an angle
HF are boosted by pinna resonance when they arrive from front
How does rear localisation work?
Sounds from behind reach the helix
- LF bends round helix and enters EAM
- HF sounds above 3k are less able to diffract
- brain uses loss of HF to identify sound source has come from behind
What are the sections of the inner ear or labyrinth?
Cochlea - hearing
Semi-circular canals - balance
Vestibule - posture
