Week 3 midterm 2 Flashcards
What 2 functions is the ear specialized for?
- hearing
2. equilibrium
What is the visible part of the ear?
the pinna
What occurs in the middle ear? (primary function)
the amplification of sound waves in preparation for transmission from air to a fluid environment
Whats another words for the ear canal and what does it do?
the external auditory meatus - brings waves to the tympanic membrane
What is the primary function of the external ear?
to gather sound waves and conduct them to the tympanic membrane
What is the middle ear composed of (x4)?
- tympanic membrane (ear drum)
- ossicles (malleus, incus and stapes)
- oval window
- round window
What is the primary function of the inner ear?
the transduction/conversion of sound energy (fluid filled)
What is the inner ear composed of? (X2)
cochlea and vestibular apparatus
What is the external ear composed of?
ear canal (aka external auditory meatus) and pinna
What does the Eustachian tube do?
aka auditory tube, it connects the airfield middle ear with the pharynx (throat) to equilibrate pressure. Normally collapsed however it opens transiently to equilibrate middle ear pressure with atmospheric air
Malleus
aka hammer, first auditory ossicle
Incus
aka anvil, middle/second auditory ossicle
Stapes
aka stirrup, last/third auditory ossicle
What is the cochlea?
a coiled, bony, fluid filled tube in the inner ear through which sound waves trigger nerve impulses
What is the vestibular apparatus?
the receptive organs of the inner ear that contribute to balance and perception of head movement
How do sound waves work?
Don’t move from original position, they bump into adjacent molecules and transfer E which is transmitted in waves that radiate away from vibrating object (like ripples)
How do sound waves spread?
in 3 dimensions in a spherical way
What is amplitude?
intensity/loudness of sound (dB)
What is pitch?
frequency of waves/second (Hz)
What is pitch?
frequency of waves/second (Hz)
- low frequency = low pitch, vv
What exactly is sound?
the brains interpretation of the frequency, amplitude and duration of sound waves that reach the ears
What are infrasound waves?
sound waves with a frequency too low for the human ear to hear (whales, elephants and hippos) – can cause headaches and many other conditions when exposed to them for long periods of time
What are ultrasound waves?
Sound waves with a frequency too high for the human ear to hear (dogs, bats, insects and birds)
What happens when sound waves strike the tympanic membrane?
the membrane vibrates at the same frequency as the sound, which causes movement of ossicles (amplify sound waves) which then cause movement of the oval window (smaller than TM)
- mechanical vibrations from ossicles and oval window are converted into fluid waves
What are the 5 levels of amplification and transduction?
1st: movement of ossicles
2nd: movement of oval window
3rd: fluid waves bending hair cells in the cochlea, generating electrical signals
4th: elec. signals alter neurotransmitter release
5th: NT bind to primary auditory neurons, initiating APs
Which ossicle has the largest force and what does it force it on?
stapes - onto the oval window
What does the oval window do?
its the membrane at the entrance to the cochlea (top) through which the ossicles transmit vibrations (site of conversion of mechanical vibrations to fluid waves) (smaller than tympanic membrane)
What does the round window do?
a membrane covered opening in the inner wall of the middle ear that compensates for changes in cochlear pressure
What does the vestibular duct do?
aka scala vestibuli, is a perilymph filled cavity inside the cochlea of the inner ear that conducts sound vibrations to the cochlear duct
What is the tympanic duct?
aka scala tympani, it contains perilymph and is located at the bottom of the cochlea
What is the cochlear duct?
aka scala media, a fluid filled cavity within the cochlea that vibrates when sound waves strike it, contains endolymph and a high K+ concentration
What are hair cells and where are they located?
they are receptor cells for sound and are embedded in the basilar membrane of the cochlea
What are hair cells and where are they located?
they are receptor cells for sound and are on the organ of corti of the cochlea – located in the ampulla (end of the canal) – tonically active
What are stereocilia?
small hair like projections on the tops of auditory hair cell tips that are embedded in the tectorial membrane, organized from short to tall and surrounded by endolymph
What is endolymph and what does it do?
the fluid that fills the cochlear duct - plays a part in excitation of hair cells
What are tip links and how do they move?
they connect stereocilia of hair cells by protein bridges (move by mechanical stress which can open/close K+ channels)
- tall = open = depolarization = AP
- short = close = hyperpolarization = no AP
What does the vestibular membrane do?
it separates the cochlear duct from the scala vestibuli
Which neurotransmitter is the receptor for depolarization?
Glutamate – when theres sufficient membrane potential to admit calcium
What is the tectorial membrane?
a membrane located above the basilar membrane and serves as a shelf against which the cilia of the auditory hair cells move
What is the basilar membrane?
a structure in the inner ear that undulates when vibrations from the ossicles reach the cochlear fluid
How is amplitude coded (intensity coding)?
by the degree of deflection and opening of ion channels in the stereocilia (AP generated)
How is frequency coded?
by where on the basilar membrane the deflection occurs (location of hair cells)
Where do hair cells synapse?
afferent axons of CN 8
What is the CN8 aka vestibulocochlear nerve and what is it composed of?
the hearing and equilibrium nerve that travels to the brainstem - composed of the vestibular and cochlear nerves
What is the ratio of hair cell : cochlear nerve fiber?
1:1
What makes up the cochlear nerve and what is it?
made up of axons, is the cranial nerve responsible for hearing
Where does the second order neuron travel?
the medial geniculate nucleus