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.
Table of Contents
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.