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 the vestibular system and what is it’s function?
- sensory system
- contributes to our sense of balance and spatial orientation
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
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
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 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
