Section 1.1 Outer Ear Flashcards
What is Resonance?
Phenomenon that amplifies a vibration.
Vibration is transmitted to another object whose natural frequency is at or very close to the source’s.
What are the main structures for the pathway from the peripheral to the central nervous system? (7)
External ear, Middle Ear, Basilar Membrane, Receptor Cells, Auditory Nerve, Brainstem, Cortex
What of are the functions of the EE structure?
Gather/Reflect and conducting sound protect eardrum.
What of are the functions of the ME structure?
Conducting/modification of sound protect cochlea against loud sound
What of are the functions of the Basilar Membrane structure?
Filtering (frequency analysis)
What of are the functions of the Receptor Cells structure?
Signal Transduction
What of are the functions of the Auditory Nerve structure?
Simple coding (transmission) convert the signal into readable for the cortex
What of are the functions of the brainstem structure?
Complex Coding, feature abstraction.
What of are the functions of the Cortex structure?
Perception
What is the nature of the signal processing at EE step?
Mechanical
What is the nature of the signal processing at ME step?
Mechanical
What is the nature of the signal processing at Basilar Membrane step?
Mechanical to Hydrodynamics
What is the nature of the signal processing at Receptor Cells step?
Mechanical to Electrochemical
What is the nature of the signal processing at Auditory Nerve step?
Electrochemical
What is the nature of the signal processing at Brainstem step?
Electrochemical
What is the nature of the signal processing at Cortex step?
Electrochemical
Describe the change that occurs in the way sound travels once it goes from the external ear to the inner ear (hint: impedance).
Sound is passing through fluid in IE.
Compared to air, there is much greater impedance in fluid (mechanical hydrodynamics). There is therefore a loss of energy (33 dB) from the impedance mismatch. In the middle ear, the sound is amplified to accommodate for this.
What is transduction (and steps) and what is it specific to the auditory system?
Mechanical signal is converted to electrical signal (receptor potential) at the top of the hair cells (via the MET channel).
What is included in the peripheral auditory system?(3)
External Middle and inner ear
what is included in the central auditory system? (4)
Auditory brainstem, mid-brain, Thalamus, Cortex
What is at the border PAS and the CAS?
Auditory nerve
What are the shapes of the external, middle and inner ear?
External ear shape: S shape
Middle ear: Cubic
Inner ear: Snail Shape
What is a unique feature of the auditory peripheral organ?
The structural features of the auditory peripheral organ are closely related to their functions.
What do the external, middle and inner ear contain?
External ear: Hairs, Wax
Middle ear: Bone chain, ligaments and muscles.
Inner ear: Cochlea semi-circular canals
What are the 4 main functions of the external ear canal (briefly)?
- Gathering/conducting sound
- Signal processing: ear canal resonance modifies sound in frequency and amplitude (Especially in high frequencies)
- Provide cues for localization
- Protect against foreign bodies
Where does the ear lobe block more sound from (i.e., which direction)?
From behind
What are examples of foreign bodies that the external ear canal provides protection from?
Insects, qtips, Toys
What are the THREE main middle ear functions?
- Sound conduction from eardrum to inner ear via bone chain
- Impedance match by amplification
- Protect IE from loud noises
What is impedance?
resistance to displacement
What are the three components of Impedance?
Mass, Stiffness and Resistance (friction)
What and why is their impedance matching?
ME transfers incoming vibration from larger, low impedance tympanic membrane to much smaller, high impedance oval window. If not there would be a 33dB loss.
What is the difference in what the middle ear is protecting compared to the external ear canal?
ME protects against loud sounds EE protects against foreign objects.
What does the eustachian tube balance? What happens if it is unbalanced?
Balances air pressure in the ME. Distorted hearing, muffled sounds, ear pain.
What are the 4 functions of the cochlea (for hearing)?
- Converting Acoustic signal to biochemical-electrical signals-by receptor sensor cells
- Frequency processing-
- Encoding of sound features to action potential in auditory nerve neurons
- Feedback control
What occurs in encoding: what is the signal being processed from and to?
Encoding: Sound features being converted to something that can be understood and processed by the AN e.g. action potentials
What is the difference between an action potential and receptor potential?
Action potential carries signal (communicates) up to the brain however the receptor potential is limited to the sensory cells (in this case, the hair cells).
What are the three steps of signal processing in for the auditory peripheral organs?
- Conduction
- Transduction
- Transmission
Recreate the diagram on slide number 3 of PowerPoint week 1!
What is transduction and what is it specific too in the auditory system?
Transduction is the conversion of mechanical signal to electrical signal. , In As, it’s when the receptor cells convert the incoming mechanical vibration to electrochemical signal via the MET (Mechanically gated channels) at the top of the hair cells.
Another word for hair cells.
Stereocilia
What is included in the PAS? (3)
Outer ear, middle ear, cochlea
What is included in the border of the PAS and the CAS?
Auditory nerve
What is included in the the CAS? (4)
Brainstem, midbrain, thalamus, cortex
What are the shapes of the external, middle and inner ear?
External ear: S-shape
Middle ear: Cube
Inner ear: Snail shape
What is a unique feature of the auditory peripheral organ?
Structure features are closely associated with function.
What do the external, middle and inner ear contain?
External: hair/wax
Middle: Bone chain, ligaments and muscles
Inner ear: Basilar membrane, hair cells, cochlear fluid, Organ of Corti
What is transmission?
The receptor potential is converted to the action potential.
What are the steps in conduction? (2)
- External sound collected by earlobe.
- It travels along the OE, ME (it is modified here), and IE to stimulate the hair cells.
What are the steps in transmission? What kind of process is this (electrical, mechanical, chemical)?
RP is converted to AP across the synapses between the hair cells and the spiral ganglion neurons. Electrochemical process.
What are the 4 major jobs of the CAS? (ETSD)
Encoding of sound features
Transmission (APs) from one neuron to another
Signal processing (analysis an intergration)
Decoding (perception, APs become sense at cortex)
What are the three major differences the CAS has compared to the PAS? (3)
- Diversity and segregation
- Nuclei and stations
- Increased number complexity in organization from low to high level
The mastoid section forms the p___________ wall of the MIDDLE EAR CAVITIY.
Posterior wall
What are the four main parts of the temporal bone? (draw them)
Mastoid, squamous section, tympanic bone, petrous section
Which Temporal bones are visible from both the lateral and medial view?
Mastoid, squamous
Which Temporal bone section is lateral only?
Tympanic
Which Temporal bone section is medial only?
Petrous
Which is the largest Temporal section?
Squamous
Which is the smallest Temporal section?
tympanic
What is partially responsible for the middle ear resonance?
The air cells that are connected to the middle ear
Why is the mastoid an ideal surface to place the electrode and bone vibrator? (3)
- Short distance to IE and brainstem
- Thin soft tissue, less bone conduction attenuation and smaller impedance to electrical signal
- Inertia for bone conduction
What are two examples of infections that occur at the mastoid? Why is it an easy target?
Mastoiditis and Cholesteatoma. Due to its location and proximity to the middle ear (remember, it has air cells that are connected to the middle ear), it is relatively easy for otitis media to spread to it and infect the air cells.
What are air cells?
Air filled cavities in bones.
With reference to the EAR CANAL, how can the squamous section be described (locational-wise)
forms the roof of the ear canal
With reference to the EAR CANAL, how can the tympanic bone be described (location-wise)?
forms the floor and walls of the ear canal.
What is another name for external auditory meatus?
External ear canal
Which Section of the temporal bone houses the sensory organs? ( cochlea, the semicircular canals, and the vestibule)
Petrous section
What fraction and which location (lateral/medial) is cartilage versus bony composition in the canal?
The lateral 1/3 is cartilage, and the medial 2/3 is bone
What seals the ear canal?
Tympanic Membrane
Describe 5 traits of the earlobe. (5)
- fibrous cartilage
- Covered with cutaneous tissue
- No fat under the skin
- Rich in blood supply
- 3 auricular muscles (anterior, superior and posterior)
What are 2 functions of the ear lobe?
Pinna reflects sound (Pinna Cues)
Heat dissipation (rich blood supplies circulate heat from inside to surface)
What are the 8 earlobe landmarks? Draw them
Helix
Antihelix
Triangular fossa
Scaphoid fossa
Concha
Tragus
Lobule
External auditory meatus (canal)
What was the difference between animal and human pinnae?
Humans can’t move their pinnae to help with sound localization like many other mammals can
What are two practical uses of knowing the landmarks?
- Reconstruction surgery purposes for ENTs,
- Earmolds for hearing aid fittings,
- To communicate with the HA manufacturers.
How is the pinna useful for sound localization (briefly)?
Pinna will reflect the sound differently depending on where it’s coming from.
What are two traits of the general shape of the external ear canal (external auditory meatus)
Irregular S-shape
One end sealed.
What kind of tissue lines the external ear canal?
Cutaneous tissue
What is gain and its relation to the ear?
Gain = output/input
Related to the ear, gain shows the change in signal amplitude between what is entering the ear medially and what is entering the pinna.
What gain ratio shows attenuation and what shows amplification?
Gain of less than 1 is attenuated and greater than 1 it is amplified
What does the pinna do?
Gathers/funnels sound to the ear canal (conduction). It also acts as an acoustic obstacle—its irregular surface alters the frequency and amplitude of sounds coming from different directions
What effect does the irregular surface of the pinna have?
Filtering and reflecting. Altering the frequency amplitude of sound coming from different directions.
Which section of the temporal bone houses the sensory organs of hearing and balance?
Petrous section
What are the roles of Ceruminous (wax) and Sebaceous (oil) glands?
To lubricate the canal
What is the formula for mass component?
Xm=2πfm
What is the formula for stiffness component?
Xc=S/2πf
When Xm = Xc, the total reactance is ____.
0
At NF the impedance is the ______.
NF the impedance is the least.
