structure and function of the ear
STRUCTURE:
Outer Ear
This consists of two parts:
FUNCTION:
When a sound is present it sets up vibrations in the ear which pass through the ear canal to the tympanic membrane and the three small bones in the middle ear. Together these structures increase the force of the vibrations entering the cochlea. The hair cells bend with this resonating vibration and stimulate its attached nerve fibre. The nerve fibres then pass information about the sound to the part of the brain that deals with hearing.
THE USHER SYNDROME EAR:
The affected genes that cause Usher Syndrome are also responsible for a number of proteins that are found in the hair cells of the inner ear. These proteins are required to ensure healthy growth of the hair cells. The hair cells are called stereocilia and are responsible for converting the vibrational waves of sound into the electrical signals sent to the brain. The lack of these proteins causes the majority of the stereocilia to be underdeveloped and non functional, therefore unable to convert the sound to electrical signals. When these electrical signals aren't able to get through to the auditory nerve and then onto the brain, it results in deafness in Usher syndrome patients.
Outer Ear
- Auricle: This is the outer part of the ear situated on either side of the head.
- Ear canal : This canal is lined by skin and passes from the hole in the auricle through cartilage and bone to the tympanic membrane (ear drum).
- Tympanic membrane: This is the thin transparent piece of skin which sits at the end of the ear canal
- This is a small, air-filled, bony chamber, that contains three small bones connecting the tympanic membrane to the inner ear.
This consists of two parts:
- Cochlea : This spiral shaped, fluid-filled structure has an elastic membrane along its entire length. Thousands of hair cells are aligned in 4 rows on top of the membrane. They are activated when the hairs on their upper end bend with resonating vibration. This "bending" is limited to the places where sound is resonating with the membrane. Each of the thousands of hair cells is connected to its own nerve and the brain is able to differentiate sounds based on where and which hair cells are triggered from the membrane's resonance. This association is called "tonotopic coding of sound".
- Semi circular canals: These 3 interconnecting tubes are also filled with fluid.
- Vestibulo-cochlear nerve : This nerve is connected to both the cochlea and the semi circular canals. Each nerve fibre in the cochlear part of this nerve is attached to just one hair cell. This nerve conducts messages to the hearing centre in the brain.
FUNCTION:
When a sound is present it sets up vibrations in the ear which pass through the ear canal to the tympanic membrane and the three small bones in the middle ear. Together these structures increase the force of the vibrations entering the cochlea. The hair cells bend with this resonating vibration and stimulate its attached nerve fibre. The nerve fibres then pass information about the sound to the part of the brain that deals with hearing.
THE USHER SYNDROME EAR:
The affected genes that cause Usher Syndrome are also responsible for a number of proteins that are found in the hair cells of the inner ear. These proteins are required to ensure healthy growth of the hair cells. The hair cells are called stereocilia and are responsible for converting the vibrational waves of sound into the electrical signals sent to the brain. The lack of these proteins causes the majority of the stereocilia to be underdeveloped and non functional, therefore unable to convert the sound to electrical signals. When these electrical signals aren't able to get through to the auditory nerve and then onto the brain, it results in deafness in Usher syndrome patients.