Receptors (The Ear) - Slides

Receptors (the ear) The Ear  The ear is a complicated receptor organ as it enables us to hear as well as to maintain our balance. Structure of the ear  The ear may be divided into THREE regions:  1. The outer ear  2. The middle ear  3. The inner ear  Each of these are surrounded by a temporal bone. ** Be able to label the ear. No functions need to be known Structure of the ear  1. The Outer Ear  Pinna  Auditory canal Structure of the ear  2. The Middle Ear  Eardrum (also called tympanum)  Ossicles (hammer, anvil and stirrup)  Eustachian tube  Oval windows Structure of the ear 3. The Inner ear The inner ear is made up of:  The bony labyrinth - a series of canals and cavities within the temporal bone, filled with a fluid called perilymph. peri = around  The membranous labyrinth - floats in the perilymph and is filled with a fluid called endolymph. endo = inside labyrinth = passage These two labyrinths form two structurally and functionally different regions: A. Cochlea B. Vestibular apparatus Structure of the ear  A. Cochlea (where sound vibrations move fluid to stimulate hearing receptors)  1. The Scalas  2. The membranes  3. Organs of Corti  4. Auditory nerve Structure of the ear  B. Vestibular apparatus  1. Utriculus  2. Sacculus  3. Semicircular canals Hearing defects  1. Middle ear infections  2. Deafness Hearing defects 1. Middle ear Infections Inflammation of the middle ear, also known as otitis media is very common in early childhood. It is caused by a bacterial or viral infection which can initially cause sore throats, colds or other respiratory problems and then spread to the middle ear through the Eustachian tube. The signs and symptoms are:  swelling of the lining of the middle ear which blocks the eustachian tube, causing the buildup of fluid in the normally air-filled cavity. This discharge may include pus (dead white cells) and when it becomes sticky, it is known as ‘glue ear’.  conductive hearing loss as the eardrum and ossicles are unable to move as freely as they should and therefore prevent the transmission of sound waves through the middle ear.  tearing of the eardrum as the pressure build up.  severe pain. Unchecked, it can become a chronic condition and can impair a young child’s hearing at a time when it is crucial for speech and language development. Hearing defects  2. Deafness  Hearing loss, or deafness, is the partial or total inability to hear sound.  Pre-lingual deafness is hearing loss that occurs before a child has acquired a spoken language. A child learns to speak a language by hearing others speak. A deaf child therefore cannot acquire a language. This can have severe consequences as it not only interferes with learning to speak but also with psychological and emotional development.  Children born into families that use sign language, however, rarely have delays in language development.  Post-lingual deafness is hearing loss after the child has learnt to speak a language; usually after the age of six.  When hearing loss occurs early in childhood, it makes learning very difficult and can cause frustration or isolation.  This type of deafness is far more common than pre- lingual deafness. Causes of hearing defects  What causes loss of hearing?  • Hearing loss can be inherited. Both dominant and recessive genes exist which can cause mild to severe impairment. - If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent. - If a family has genetic hearing impairment caused by a recessive gene it will only manifest itself in the offspring if it is passed on by both parents.  • Meningitis is a common cause of severe acquired deafness in infants and children.  • Trauma or disease can cause hearing defects. There are different types of hearing loss, depending on which part of the hearing pathway is affected. Treatment for hearing loss  How can hearing loss be treated?  Middle ear infections are usually treated with antibiotics but if glue ear or acute middle ear infections persist, grommets may be recommended.  Loss of hearing can be treated in the following ways:  A. Grommets  B. Hearing Aid  C. Cochlear implants Treatment for hearing loss  A. Grommets  Grommets are small ventilation tubes made of either plastic or metal. They are inserted through an incision in the eardrum after all the mucus has been sucked out. They perform the function of the Eustachian tube, allowing air into the middle ear and reducing the build up of fluid. If an infection does occur, the excess mucus and pus can flow out through the grommet.  Most grommets usually stay in place for about six to 18 months after which they fall out naturally and the eardrum closes up. Treatment for hearing loss  B. Hearing Aids A hearing aid is a small electronic device that amplifies incoming sound. It fits into the ear and consists of:  • a tiny microphone to pick up the sounds  • an amplifier that increases the volume  • a tiny speaker that transmits sounds to the ear. They can only be fitted to patients who are not totally deaf. Although they might alleviate some of the problems caused by hearing loss, they are often not totally satisfactory. Treatment for hearing loss  C. Cochlear implants  A cochlear implant is an electronic device that restores hearing to people with very severe or profound deafness.  The implant consists of two parts - the internal part is surgically placed inside the inner ear and the external part is worn behind the ear.  They compensate for damaged hair cells on the organ of Corti by artificially stimulating the auditory nerve and bypassing the affected areas.  While hearing is not restored to its natural state after a cochlear implant, the recipient will be able to hear common sounds such as a telephone or doorbell and will be able to interact with others and have a normal conversation.  The disadvantage is that cochlear implants and hearing aids are expensive and therefore not available to many who would benefit from them.  There are many assistive devices that help deaf people from becoming isolated, such as TV listening devices, telephones that use text instead of sound and flashing or vibrating alarm clocks and doorbells. Sign Language  Sign Language developed as a result of the need to communicate among members of Deaf communities. Movements of hands, face, head and upper torso are all used to communicate and the information is processed by the eyes.  South Africa is one of a few countries to recognise and protect sign language. South African Sign Language (SASL) is protected in various legislative and governmental policies (and even acknowledged as a language equal in status to the 11 official languages in the country) and is accepted as the language of instruction in the education of Deaf learners. In addition, there is a program, Deaf TV on South African Broadcasting Corporation’s SABC3 channel.