SS3 LESSON NOTE FOR WK4

ORGAN OF HEARING AND BALANCE

-The ear is the organ of hearing and balancing-A mammal has two ears ,one on each side of the head.The greater part of each ear is embedded in the scull for protection.

STRUCTURE OF THE EAR.Mammalian ear is divided into three parts:1. Outer ear2. Middle ear3.Inner earOUTER EAR.This consist of:1.Pinna-It is trumpet-shaped made of cartilage.-Pinna collects sound waves and directs them along the ear carnal.2.Ear canal/ External auditory meatus-It contains hairs, oil and wax3. Eardrum /tympanic membrane-This is located at the end of the ear canal. It is made of thin membrane-It vibrates and magnifies the sound waves.

MIDDLE EAR-It is an air-filled cavity behind the tympanic membrane-It has three bone s or ossiclesa. The malleus ( or hammer)b. Incus (or anvil),andc.Stapes (or stirrup).Middle ear also has:b. The oval and round windowsb.Eustachian tube-Ear ossicles transmit and magnify sound waves to the inner ear.-Eustachian tube equalizes the air pressure on either side of the eardrum-The windows act as gateways for sound waves to the inner ear.INNER EAR OR LABYRINTHThe inner ear is made up of: a. Three semicircular canals b. Utriculus/Utricles c.Sacculus/Saccules d. Cochlea e. Auditory nerves-send impulses to the brain. -The labyrinth is surrounded with the fluid called perilymph -The cavity of labyrinth contain endolymph

SEMICIRCULAR CANAL-The three semicircular are attached to the utricles-The point of attachment to the utricles form a swollen structure called ampulla.-The ampulla has sensitive cells. -The saccules, utricles and semicircular canal help in balancing and positioning the body. COCHLEA-The cochlea arises from the saccules. -It is a hallow structure and coiled like a snail`s shell -Cochlea has sensitive cells that form the organ of corti. -The sensitive cells of the cochlea help to amplify sound waves MECHANISM OF HEARING -The sound waves are collected by the pinna and passed along the ear the canal to the eardrum. -The eardrum magnifies the vibration and transmits

It to the ossicles which in turn amplify and transmit it to the oval window-The oscillations of the oval window set the fluid in the inner ear to vibrate especially in the cochlea. -Perilymph and endolymph are stimulated and in turn oscillated the sensory hair cell and nerve fibre in the cochlea. -The nerve fibres then convert the sound vibrations to impulses which are relayed to the brain for interpretation.MECHANISM OF BALANCE -The semicircular canal which contain the endolymph are at the right angles to each other. -The ampullae contain sensory hair cells. -When the head rotates ,the vibration of the endolymphs stimulates the sensory hair cells -The auditory nerve then transmits the impulses to the brain which interpretes them and direct response. -The balance is therefore maintained. DEAFNESS -Deafness can be described as inability to hear. Deafness can be temporary or permanent

CAUSES OF DEAFNESS -Damage to the eardrum. -Blocking of the eustachian tube. -Blocking of ear canal by wax. -Infection of the middle and inner ear. -Damage to the sensory cells in the cochlea. -Exposure to sound of high decibe(Db) CARE OF THE EAR 1.Do not use sharp or pointed objects in cleaning the ear, to avoid damage to the eardrum. 2.High noise level over a long period of time should be avoided to prevent deafness. 3.Hard wax should be removed with syringe and warm water by a doctor. 4.Receiving blows on or around the ear should be avoided. 5.Any ear problem should be immediately directed to a doctor.

ASSIGNMENT1. Make a well labelled drawing of the mammalian ear.2. Describe any five defects of the mammalian ear.