Ear Flashcards
Arrangement of the Ear
- Auditory system (hearing)
- Vestibular system (balance)
Auditory system
(Outer Ear)
- Air pressure waves gather at the outer ear, where the Pinna is.
- The Pinna is our outer ear cartilage that alters sound helps us determine where it’s coming from
- The air pressure waves pass through the out ear canal / auditory canal till the ear drums
- The waves create vibration at the Ear drum membrane
Middle Ear
- The vibration (mechanical energy) is transferred by 3 bones (Malleus, Incus and Stapes)
- Those 3 bones that the vibrations are passing through are in an ‘Air filled’ middle ear and are converted to mechanical energy
- Vibrations are passed to the Oval Window membrane & Round Window membranes
- Oval Window separates Air middle ear from Liquid Inner ear
- The vibration in oval window get set up as pressure waves
Inner Ear
- Pressure waves travel through liquid inner ear/ Cochlea
- Cochlea is split into 3 chambers by membranes
- The pressure waves in the guilt set up a patter of waves in the Basilar Membrane
- Different frequencies produce different vibrations along the basilar membrane
High frequency cause a peak near the Round Membrane
Low frequency cause a peak near the end of Cochlea - Hair like sensors in the Basilar membrane translate membrane movement into electrical signals to the brain via auditory nerve
Equalization of the ear
when air pressure in middle ear and outer ear (either side of ear drum) are equal
The pressure between the middle ear and atmospheric need to be equalised.
what is the name of the tube that helps with ear equalization
Eustachian tube
Explain how it works
The tube is a like a one way valve
it connect middle ear cavity to the back of the nose
it allows air flow from middle ear out to release pressure.
when you swallow, the flows out the tube.
Air pressure when ascending
the pressure in the middle ear is higher than outside, so the air pressure is released from the middle ear via Eustachian tube via swallowing
Air pressure when descending
pressure is lower in the middle ear than outside
however the eustachian tube in just one way valve, so this can cause ear drum to stretch (possibly rupture)
What is Barotrauma
when the ear drum over stretches and ruptures or gets injured due to unequal pressures in the middle ear and outside
What happens during a cold/infection
Eustachian tube becomes swollen or blocked, not allowing to release pressure
what happens during sinuses
sinuses are airfilled cavities within the skull
if there differential pressure between the outside and the sinuses cavity, you will have headaches, watery eye
Solutions?
don’t fly if you have a cold, infection or sinuses because pressures between the middlea ear and the atmosphere is not equalized
swallow or yawn
Valsalva manoevre - pinch your nose and blow hard through it.
in what 3 ways can the ear distinguish sound
frequency
timbre
loudness
what is the auditory range for an average human
20 Hz to 20,000 Hz
(1Hz is 1 vibration per second)
sound is perceived as 3 elements
Frequency: Is the pressure waves per second that sound produces measured in Hz
Loudness: Amplitude/strength of the sound wave measured in Db
Duration : how long the sound lasts
what is the scale used to measure loudness
Decible scale - ratio between sound heard and reference level
every 20db is 10x lounder than 0db
40db is 100 x louder
60 db is 1000 x louder…
What is the full range of decible scale
0 - 180 dba
explain the range of safe to unsafe dba..
below 80 dba = speech
above 80 - 90 dba = chronic exposure that can lead to hearing loss
100 dba= level of physical discomfort
140 - 160 dba=level of paint threshold, ear drum rupture or middle ear ossicles
180 dba=instant hear loss
loud sound can cause fatigue, pain, lack of concentration, inability to communicate over radio
What is Noise induced hearing loss
2)Temporary:
hearing might disapper for few hours or days.
**Long terms: **
when you expose yourself to prolonged high intensity sound at 90dba
usually causes damage to the Basilar membrane in inner ear or the hairs inside it
Unable to hear certain sounds clearly/completely or complete loss.
you will gradually 3 to 6 KHZ over in intervals over time
Conductive deafness
failure to conduct sounds from outer ear to middle ear due to a defect
caused by:
1) ear drum rupture
2) wax build up in auditory canal
3) Otits Media (ear glue)
4) Osteorclosis - bone build up in the oval window affecting the stapes in the middle ear
5) Barotrauma (air pressure building up) from sinus or infection
6) fluid build up
7) faulty ossicles
Presbycusis
age induced hearing loss (usualy higher frequencies are lost)
Tinnitus
constant sound being heard, usually high pitched tone.
it can obscure other sounds of similar pitch
can be caused by an infection or injury - where the hairs in the chochiela or the auditory nerve are damaged
Vestibular system
In the inner ear
provide info to allow the body to maintain stable posture/balance and stable retina image during movement
How does vestibular system help?
- sensing accleration of head movement
-sensing direction of gravitational pull
- controls eye movement
if the system is damaged?
not able to balance, dizzy, unsafe vision
How does the vestibular system work - linear acceleration
It detects acceleration in linear axis and vertical access (gravity)
- The (static organ) is connect via a passage from middle ear
- The organ has 2 chambers- Utricle and Saccule filled with liquid (cupula)
- There are hairs with crystals called Otolith inside the utricle and saccule
Gravity:
If you tilt your head and there is a 1g gravitational pull, the top heavy hairs will bend in the direction of the gravity, and sends signals to the brain via vestibular nerves.
The brain understand the direction of the tilt with respect to gravity
**In linear accelaration: **
The cupula in the static organ also detects linear accelerations. During a linear acceleration, the body accelerates away from it and the cupula is temporarily ‘left behind’, causing the hairs to bend and send a new signal to the brain. They will return to their normal position once the body is no longer accelerating and is moving at a steady speed (which may be zero).
if your head is tilted back but you are accellerated forward, your braind thinks you are tumbling backwards
How does the vestibular system work - angular acceleration
It detects angular acceleration (rotation of the head) in 3 planes
- There are 3 semi-circular canals integral to the skull positioned at right angles, with fluid inside them (pitch, role, yaw)
- The semi circular canals end in little bulbs called ampula which have hairs in them
When you rotate your head, the canals move with it.
But since the canals have their own fluid, they have their own inertia - the fluid moves later after the head as moved and in the opposite direction, pushing the hairs into the direction of the head movement (ie head/hair moves opposite of the fluid, during accerlation)
The movement of the fluid in canals cause the hairs in the ampula to bend in the same direction
Each signal from a canal is sensed by the brain as a rotation in each plane
when the angular accelleration is ceased: the fluid moves with the canal in the same direction. Hairs will no longer bend.
Brain will no longer sense any angular accelleration, even if steady angular turn is happening.
Spacial Disorientation
Mismatch between the signals recieved by the brain from vestibular system and the visuals seen by your eyes
Such as motion sickness
most reliable sense here is vision to help with this
rely on your instruments
symptoms of motion sickness
dizzy, nausea, vomit
hot flushes, clammy hands
headache
fatigue and yawning
salivation
Hyperventilation (fear and anxiety induced)
Causes of motion sickness
**vibration of eyeballs **(rapid intake of visual field vs intake from the eye)
simulator sickness: due to the different between simular display and its motion, or its motion vs motion perceived by the pilot
**mismatch accelration:
**when you change acceleration suddenly after being on a constant speed. If you bank after cruising, the change of g force can create a mismatch
Solutions to motion sickness
Address the mismatch ideally by
1) fillin in the visual fields with cueues such as focusing on the horizon
2)removing inputs by standing up to gain balance, distracting yourself
3)hydration
4) control breathing and breath more/deeply
5) lay flat/horizontally
Vestibular illusions
3 root causes
- system assumes your body’s linear acceleration is 1 g from head to toe due to gravity.
- system only detects initial rotational movement
3.system has a threshold under which external stimuli doesn’t trigger any action
what is the illusion triggered by linear acceleration
Somatogravic illusion
explain this illusion
- Illusion related to linear acceleration
- Usually happens when visual cues are absent
- Example
- If the head is upright and then tilted back, the hairs are deflected back to sense the tilt.
- But if the head then moves forward but the hairs are still deflected back, the brand doesn’t sense the change
- Happens with the hair crystals in the Utricle and saccule are deflected and the brain serene the deflection as title even though that head isn’t tilted anymore
Scenario: take off
A large forward acceleration feels like you are pitching up and you end up pushing forward with the controls away
Scenario: landing
A slow forward acceleration feels like you are pitching down
what is the illusion affection rotation
**Somotagyral illusion - false perception of rotation
**
Visual queues are not present (ie orbiting at night or in cloud)
The semicircular canals detect an initial angular accerlation.
The natural inertia of the fluid inside the canal causes a pronounced relative movement between the fluid and canal
The hairs of the ampulla are bent
But in a prolonged acceleration, the fluid accelerates at the same speed as the rotation, and hairs stand straight so the body doesn’t sense the angular rotation anymore.
If you stop suddenly, the inertia of the fluid causes the fluid to continue rotation even if the canals stoped. The hair is bent the opposite direction so senses opposite rotation
What is LEANS
it’s a type of somotogyral illusion
when you feel that the **aircraft is pitching or rolling **despite the instuments proving otherwise or despite you are at win level - due to the **detection below threshold of the canals (ie movement not detected) **
**Scenario 1
**1)if you make tip to one side quickly that you feel the tilt, and you make and adjustment to wing level slowly/below the detection threshold of the semi circular canals. Your body feels like it’s still tilted to that side and you will lean away from the perceived tilting
Scenario 2
You come to know of a long turn that went un noticed and you make a sudden adjustment to wing level. Your body feels like it’s banking in the opposite direction.
Scenario 3
if let’s say you roll left, you sense this angular accelration
But if you stay in the left turn for 15 sec, the motion is no longer sense and you think you are wing levelled.
you then might roll to the right to try to ‘level’ the wing
the vesitublar system registers you are rolling right from the ‘wing level’,so you are sensing rolling to the right unwantendly
‘graveyeard spiral’
Look at your insturments
Coriolis illusion
shifting of the semicircular canals out of their plan of rotaion
Cross coupled stimulation from 2 or more canals
caused by head movement while aircraft is turning - without visual queue
Scenario:
if you look down at your chart while aircraft is turning..and you look up again, Feeling of pitching, rolling or tumbling at the same time
can cause motion sickness and losing control of aircraft
solution: keep head straight relative to the body and avoid extreme head movements while making turns
Vertigo
feeling of spinning while stationary / or feeling stationary while you are spinning
brought on by moving the head, heavy accleration
usually a defect in the vestibular system
infection or alchol
sudden pressure change (ie. blowing nose strongly)
flicker vertigo (brought on by flashing light or sunlight reflecting on rotating propellors)
pressure vertigo: flying with block eustachian tube
losing visual reference / horizon reference
going into spins , spiral dives
avoid alchol 3 days prior to flight
What is Motion illusion
Inner ear balance mechanism is over stimulated
high g, turbulence
fear and anxity
misbalance from the ear and eye signals (like doing a bank in a simulator visually gives the illusion of a turn, but vestibular signals show straight and not moving)
when your body can’t detect small accelerations making it difficult to sense movement.
Example: train accelerates slowly and vestibular system doesn’t detect this. Without looking out to a fixed reference like the platform, you can’t tell if your train is moving or the other train next to you.
to avoid:
fly aircraft sensibly with control
avoid manoevres that involve unusual gforce
avoid turbelence
ventilate cabin
look out at a distance
recline seat vertically
land if required
Habituation
When you have prolonged exposure to stimuli resulting in decreased responses from sensory neurons
Example: If you drive at high speed for a prolonged time and come to exit at low speed, this low speed feels ‘very slow’ because the motion detection apparatus of our visual system has ‘habituated’ to a higher speed
what is cocktail party effect
when you can hear a message important to you despite various noises and stimuli
how does alchol affect hearing
can induce long/short term hearing.
also drugs/meds
How to prevent hearing loss
wear hearing protection like noise canceling headsets, ear plugs and ear muffs
when using radio - lower the volume, and use squelch to control the hash/static
can the body sense speed?
no it cannot sense stead speed in a straight line, it can only sense acceleration ( change of speed)
what is seat of the pants mean
signals connecting brain to
ear balancing (vestibular) + vision + muscle/tendon and organ propioceptors to sense
these help body react to acceleration, change of speed and direction
Types of accerlation: angular and linear
Linear: you go up the elevator and you experience a change in ‘g’ compared to normal
angular: when you spin
Vestibullar illusion
of level flight during turning “false up’
Up is always the direction of the g force on your body according to the static organ
if you roll at 60 degrees, you will experience a 2g force on yoru body.
you will feel the anuglar accellartion at tehe beginning when you are in/out of hte turn. However, when the motion stops or stays constant, the fluid goes back to being steady and stops sensing the turn
if your eyes are shut, it will still feel like you are sitting upright but you need your eyes or instruments to confirm that you are not.
Orientation - what is it?
ability to determine your position
achieved by:
Vision (strongest sense)
balance (gravity, linear and angular)
seat of the pants( proprioceptive)
Vestibullar illusion
of level flight during banking in shallow turn “false up’
pilot might look down at the charts an make a very slow bank and not realize it
its’ because that small rolle was insignificant and the fuid didn’t move in the canals to sense the accleration
turns that feel like climb
In a turn, the body experiences a force on the seat-of-the-pants greater than 1g normally exerted on it by the seat in straight-andlevel flight, the same feeling as if the aeroplane was being pulled up from straight-and-level into a climb.
pilot tends to push the control column forward thinking he’ll climb but in fact he’ll descend
rolling for lengthy period may feel like a descend
After being in a steady turn for some time, the body gradually gets used to the increased g-forces. Immediately after rolling back to wings-level, and reducing the g-forces to just 1g, the body feels this reduced g-force as less than 1g, the same effect as pushing the nose over into a descent. Use your eyes to check the horizon or the flight instruments to avoid making incorrect inputs on the controls.
The Tumbling-Backwards Illusion Caused by Strong Linear Acceleration
In a state of rest or steady velocity (i.e. no acceleration), the body experiences an upward force from the seat. If you now accelerate strongly, there is a further force from the back of the seat accelerating you forwards, and your vestibular apparatus, as well as the seat-of-your-pants, interprets this as a g-force angled forwards.
Since you are used to g-forces always being ‘up’, you interpret the tilted direction of the new g-force as being ‘up’; in other words, you must have tumbled backwards. This is known as the oculogravic illusion or the somatogravic illusion.
a result of this illusion of tumbling backwards during strong accelerations, to want to push the nose of the aeroplane down – a tendency which you can avoid if you use your eyes.
The Illusion of Pitching Forwards Caused by Strong Linear Deceleration
**Slowing down may feel like tumbling forwards.
**
The converse happens when you are travelling fast, and then decelerate rapidly. The seat-belt now exerts a force on you, and the resultant g-force from this and the force of gravity is now angled backwards. You sense this direction as ‘up’, so you imagine that you must have pitched forward. The tendency is to pull the control column back, which you can resist if you use your eyes.
what happens at the oval window in inner ear?
the vibrating chain of ossicles induces pressure waves in the endolymph
inner ear can sense
angular acceleration
linear acceleration
noise
human vestibular system performs spatial orientation by
measuring linear and radial acceleration within the inner ear
