HUMAN EAR –
STRUCTURE, FUNCTIONS AND PARTS
The Mammalian Ear
The mammalian ear performs two major functions: Hearing and detecting changes in the positions of the body to bring about balance and posture.
The ear is divided into three sections.
The Outer Ear
This consists of:
- An outer flap, the pinna which is made up of cartilage.
- The function of the pinna is to catch and direct sounds.
- The external auditory canal is a tube through which sound travel.
- The lining of the tube secretes wax, which traps dust particles and microorganisms.
- The tympanum is a membrane stretching across the inner end of the external auditory canal.
- The tympanum vibrates when it is hit by sound waves.
The Middle Ear
- This is a chamber containing three small bones called the ear ossic1es, the malleus, incus and stapes.
- The three ossic1es articulate with one another to amplify vibrations.
- The vibrations are transmitted from the tympanum to the oval window.
- At the end of the chamber is a membrane called the oval window.
- When the tympanum vibrates, it causes the ear ossic1es to move forwards and backwards.
- This causes the oval window to vibrate.
- The Eustachian tube connects the middle ear to the pharynx.
- It allows air to get in and out of the middle ear, thus equalising the pressure between the inside and the outside of the tympanum.
The Inner Ear
- This consists of a series of chambers filled with fluid.
- It comprises the cochlea and semicircular canals.
- Cochlea is a coiled tube that occupies a small space and accommodates a large number of sensory cells.
- The cells are connected to the brain through the auditory nerve.
- They detect vibrations which lead to hearing.
FUNCTIONS OF THE EAR
- The sound waves set the tympanum vibrating and are transformed into vibrations.
- The vibrations are transmitted to the oval window by the three ossicles.
- Vibrations of the oval window cause the fluids inside the cochlea tube to vibrate.
- The membranes inside the cochlea have sensory cells which change the sound vibrations to nerve impulses.
- These are transmitted to the brain through the auditory nerve.
- Hearing is perceived in the brain.
Balance and posture
- The semi-circular canals
- There are three semi-circular canals in each ear.
- They are situated at right angles to each other and each one is sensitive to movement in a different plane.
- They are filled with fluid and each has a swelling called the ampulla at one end.
- Inside the ampulla are sensory cells.
- Balance and posture are detected by these cells.
- Movement of the head in a given direction causes the fluid to move the hairs on sensory cells.
- This transmits impulses to the brain through the auditory nerve so that the movement is registered.
Defects of the ear
- This is an inflammation of the middle ear and cochlea.
- It may lead to deafness.
- It can be treated by using certain drugs but sometimes an operation may be necessary.
- This is a sensation of noises in the ear.
- It is caused among others by accumulation of wax in the ear or use of certain drugs e.g. quinine.
- Treatment is by removal of wax, stopping use of the causative drug. Vertigo – Giddiness
- This is disorientation of body in space – one of the causes is dilation of endolymph.
- Corrections: Use of appropriate drugs.
- This is inability to hear.
- It is presented in various degrees in various individuals, some have partial hearing, others are completely deaf.
This may be as a result of:
- Chronic infection of cochlea.
- Lack of sensory cells.
- Excess wax in external auditory canal.
- Fusion of ear ossicles.
- This is the inflammation of middle ear due to build-up of fluid.
- It is marked by the swelling of tissues surrounding the Eustachian tube due to infection or severe congestion.
- A strong negative pressure creates a vacuum in the middle ear.
- Treatment – use of antibiotics or surgery.