External ear
Consists of the:
- Auricle (pinna)
- External acoustic meatus (Auditory canal)
- Hairs
- Sebaceous and ceruminous glands
Tympanic membrane
- Also known as the eardrum
- Thin connective tissue membrane that transfers sound energy to the auditory ossicles
- Separate the outer and middle ear
Middle ear
- Also known as the tympanic cavity
- Small air-filled, mucosa-lined cavity in the temporal bone spanned by the auditory ossicles
Auditory ossicles
- Malleus
- Incus
- Stapes
Pharyngotympanic tube
- Also called the Eustachian tube
- links the middle ear with the nasopharynx allowing pressure to be equal between the middle and external ear
Inner ear
A bony labyrinth is a series of channels carved into the temporal bone including the:
- Scala vestibuli
- Scala tympani
- Filled with perilymph (similar to CSF)
Membranous labyrinth
Made up of membranous ducts within the bony labyrinth such as the scala media
Filled with endolymph (contains more K+ than perilymph)
Cochlea
- Spiral and snail-shaped
- Extends from the anterior part of the vestibule and contains the cochlear duct which houses the spiral organ (Organ of Corti), the receptor organ used for hearing
Three chambers of the bony cochlea
- Scala vestibuli: (next to the oval window)
- Scala media: Cochlear duct
- Scala tympani: terminates the round window
- Basilar membrane: the door of the cochlear duct that is important for sound reception
Organ of Corti
These are hair cells that detect vibrations between he basilar membrane and the tectorial membrane
Sound
Produced by a vibrating object and propagated by the molecules of the medium
Frequency
- Number of waves that pass a given point in a given time
- Measured in Hertz (Hz)
- Low frequency = long wavelength and high frequency = short wavelength
Amplitude (height)
- Reveals a sound’s intensity (loudness) in a wave
- Measured in decibels (dB)
Sound transmission
- Sound enters the auditory canal, causing the eardrum to vibrate
- Vibrations go from the ossicles to the oval window on the vestibule (amplified about 20-fold), producing a pressure wave within the perilymph
Resonance
- This is tuned to specific frequencies on the basilar membrane
In the cochlea: - Fibres close to the oval window are short and stiff and respond to high frequencies
- Fibres close to the apex resonate with low frequencies
