Auditory and vestibular system Flashcards
What is sound?
Sound is produced when an object vibrates; causing small changes in air pressure.
What is the function of the outer ear?
- Collects sound
What is the function of the middle ear?
- Amplifies the sound pressure
- Protects ear against loud noise
what is the pitch of sound & what does it depend on?
the tone of sound
it depends on the freq of the air waves
what is the intensity of sound and what does it depend on?
-loudness of sound
-depends on amplitude of air waves
What is the function of the inner ear?
- Converts sound waves into nerve impulses
- Also involved with vestibular system- balance and proprioception
What is the tympanic membrane ?
- The ear drum which vibrates in response to a a change in air pressure in the auditory canal
- Converts sound energy into mechanical energy
What are these 3 bones in the middle ear called? What is there function?
- Auditory ossicles - malleus, incus and strapes
- They convert sound energy into mechanical energy and transport it into the cochlea.
What is the acoustic reflex?
- an involuntary contraction of the tensor tympani & stapedius muscle that protects the ear from loud noise
- The contraction prevents the movements of the ossicles in the middle ear
What is the oval window?
- membrane covered opening from middle-inner ear
- vibrations from tympanic membrane travel through the 3 ossicles and enter the inner ear @ oval window
What is the inner ear composed of?
- semicircular canals (vestibular)
- cochlea
- filled with perilymph
What is the structure of the cochlea?
- 3 chambers - scala media, scala vestibule and scala tympani
- basilar membrane - seperates the media and tympani
What is the organ of corti?
- located in the cochlear duct in cochlea
- contains specialised receptors called hair cells
- the receptor organ for hearing
describe the structure of the vestibular apparatus in the inner ?
-includes the utricle, saccule and 3 semicircular canals
-sends info to the temporal lobe of brain on balance motion and head position
What are hair cells?
- specialised receptor cells
- the movement of the basicular membrane causes them to move back and forth and they become excited
How is sensory information converted to nerve impulses in hair cells?
- movement of the basicular membrane ( movement of sound along Scala V and back along Scala T) causes hair cells to become excited
- excitation= K+ channels open, K+ conc higher in endolymph so it rapidly enters cell
- this causes membrane depolarisation
- This causes voltage gated Ca2+ channels to open, therefore influx of Ca2+ causes release of nuerotransmitter
- action potential
What is coding of Sound frequency
- Frequency coded by place on basicular membrane where AP generated
- Intensity coded by number of AP’s generated
What is the vestibular system and what is it’s function?
- sensory system
- contributes to our sense of balance and spatial orientation
What are the important components of the vestibular system?
The semicircular canals, utricle and saccule and the otolith organs
Describe the structure of the semi circular canals
- 3 canals
- at the end of each canal there is a swelling called an ampula
- There is a crista ampullaris in each ampula which contains motion receptors - hair cells
How is sensory information from hair cells in ampula relayed to brain?
Through the vestibulocochlear nerve (VIII)
Describe the importance of the stereocilia movement
- stereocilia are displaced toward kinocilium - excited hair cell
- stereocilia displaced away from kinocilium- inhibited hair cell
mechanism is similar to cochlear hair cells
How do vestibular hair cells produce action potentials?
- head tilting- canals and hair cells move but endolymph lags behind
- bending of hair cells dragging endolymph causes receptor potentials
- if depolarisation reaches threshold- action potential generated
What is the push pull symmetry in vestibular hair cells?
- hair cells in opposite ears compliment each other
- ie left ear hair cells depolarise (+), right hyperpolarises (-)
What are the otolith organs?
- Sensory motion receptors in utricle and saccule
- These hair cells have similar structure & function to cochlear and vestibular hair cells
What is the otolithic membrane and function?
- Glycoprotein layer that sits on top of hair cells
- function: motion detection (ie head tilt foward, membrane slides over cells and bends them- causing depolarisation or hyperpolarisation
what is impedance?
resistance to the flow of energy
what is impedance matching of the middle ear?
-process by which the mechanical energy of sound waves traveling through air is efficiently transmitted to the fluid-filled inner ear (cochlea)
-middle ear performs this function through the 3 bones, and the timpani membrane
describe sound transduction in 7 steps
- sound waves are captured by the pinna and channelled into the auditory canal
- they hit the tympanic membrane and cause it to vibrate
- malleus starts the ossicles into motion
- stapes moves in & out of the oval window of the cochlea - fluid motion
- fluid movement causes organ of corticosteroid membrane to shear against the cilia of the hair cells creating electrical energy
-6. signals are transmitted to the temporal love via cochlear nerve - brain interprets it as sound
what does an audiometry exam test?
your ability to hear sounds
what range of frequencies (in Hz) can humans detect ?
20-20,000 Hz
what is sensorineural deafness?
degeneration of the hair cells of the organ of corticosteroid and or cochlea nerve fibres
what is conductive deafness?
-impaired sound transmission in the external or middle ear
what are the 2 clinical tests that differentiate between conductive vs sensorineural deafness?
-Weber and Rinne tests
what does the Rinne test evaluate?
-evaluates air and bone conduction
-vibrating tuning fork is placed on mastoid process until patient can no longer hear sound
-it is then quickly placed near the ear canal
what does the weber test detect ?
-detects unilateral hearing loss (loss on one side)
-using vibrator tuning forks on top of patients head, ask patient where he hears it - one or both sides
In the Rinne test, what is considered normal vs abnormal?
- if air conduction (AC) is greater than bone conduction (BC) = normal
- if BC is less than AC - conductive hearing loss
what us presbycusis?
-common age related hearing loss
-ability to hear high frequencies diminishes
-men more affected than women
what are examples of risk factors for presbycusis?
-noise exposure
-infections
-smoking
-hypertension
-vascular disease
-diabetes
Describe the 3 different ways that presbycusis can occur
-sensorineural - degeneration of cilia on hair cells of organ of corti
-conductive - stiffening of basilar membrane of cochlea and or the ossicles
-metabolic - atrophy of the stria vascular
what do the semi circular canals detect?
angular acceleration
what its Meniere’s disease?
-unilateral fluid imbalances in the inner ear which affect the cochlea and the vestibular apparatus
