Anatomy & Physiology Overview - The Ear
- Pinna (auricle) - visible part of the ear outside of the head.
- External auditory canal
- Ceruminous glands - specialized sudoriferous glands (sweat glands) located subcutaneously in the external auditory canal. They produce cerumen (earwax) by mixing their secretion with sebum and dead epidermal cells.
Middle ear: air filled
- Tympanic membrane - vibrates in response to sound waves
- Malleus, incus and stapes - 3 small bones that transmit vibrations to each other
Inner ear: fluid filled
- Mechanoreceptor for
hearing and balance
- Vesibular apparatus - balance
- Semicircular canals
- • Organ of Cor -
sensory epithelial cell
- Perilymph = similar
in compositon to
plasma – Na+
- Endolymph = high in
- Organ of Cor:
contains hair cells
– move due to
- 50-100 stereocilia
on each cell
- Longest embedded
In the cochlea that the vibrations transmitted from the eardrum through the tiny bones are converted into electrical impulses sent along the auditory nerve to the brain.
- The cochlea is a tapered tube which circles around itself
- The basilar membrane divides the tube lengthwise into two fluid-filled canals joined at the tapered end.
- ossicles transmit vibration to the cochlea where they attach at the oval window
- resultant waves travel down the basilar membrane where they are “sensed” by 16-20,000 hair cells (cilia) attached to it which poke up from a third canal called the organ of Corti.
- Organ of Corti transforms the stimulated hair cells into nerve impulses
- Waveforms travelling down the basilar membrane peak in amplitude at differing spots along the way according to their frequency
- Higher frequencies peak out at a shorter distance down the tube than lower frequencies
- The hair cells at that peak point give a sense of that particular frequency
- The distance between pitches follows the same logarithmic distance as our perception of pitch i.e. the placement of octaves are equidistant.