<P> Unlike structures of the inner and middle ear, which develop from pharyngeal pouches, the ear canal originates from the dorsal portion of the first pharyngeal cleft . It is fully expanded by the end of the 18th week of development . The eardrum is made up of three layers (ectoderm, endoderm and connective tissue). The pinna originates as a fusion of six hillocks . The first three hillocks are derived from the lower part of the first pharyngeal arch and form the tragus, crus of the helix, and helix, respectively . The final three hillocks are derived from the upper part of the second pharyngeal arch and form the antihelix, antitragus, and earlobe . The outer ears develop in the lower neck . As the mandible forms they move towards their final position level with the eyes . </P> <P> Hearing loss may be either partial or total . This may be a result of injury or damage, congenital disease, or physiological causes . When hearing loss is a result of injury or damage to the outer ear or middle ear, it is known as conductive hearing loss . When deafness is a result of injury or damage to the inner ear, vestibulochoclear nerve, or brain, it is known as sensorineural hearing loss . </P> <P> Causes of conductive hearing loss include an ear canal blocked by ear wax, ossicles that are fixed together or absent, or holes in the eardrum . Conductive hearing loss may also result from middle ear inflammation causing fluid build - up in the normally air - filled space, such as by otitis media . Tympanoplasty is the general name of the operation to repair the middle ear's eardrum and ossicles . Grafts from muscle fascia are ordinarily used to rebuild an intact eardrum . Sometimes artificial ear bones are placed to substitute for damaged ones, or a disrupted ossicular chain is rebuilt in order to conduct sound effectively . </P> <P> Hearing aids or cochlear implants may be used if the hearing loss is severe or prolonged . Hearing aids work by amplifying the sound of the local environment and are best suited to conductive hearing loss . Cochlear implants transmit the sound that is heard as if it were a nervous signal, bypassing the cochlea . </P>

How many muscles are in a human ear