ear Essay -- essays research papers

The ear is an organ of the body that is used for hearing and balance. It is connected to the brain by the auditory nerve and is composed of three divisions, the external ear, the middle ear, and the inner ear. The greater part of which is enclosed within the temporal bone. The ear is looked upon as a miniature receiver, amplifier and signal-processing system. The structure of the outer ear catching sound waves as they move into the external auditory canal. The sound waves then hit the eardrum and the pressure of the air causes the drum to vibrate back and forth. When the eardrum vibrates its neighbour the malleus then vibrates too. The vibrations are then transmitted from the malleus to the incus and then to the stapes. Together the three bones increase the pressure which in turn pushes the membrane of the oval window in and out. This movement sets up fluid pressure waves in the perilymph of the cochlea. The bulging of the oval window then pushes on the perilymph of the scala vestibuli. From here the pressure waves are transmitted from the scala vestibuli to the scala tympani and then eventually finds its way to the round window. This causes the round window to bulge outward into the middle ear. The scala vestibuli and scala tympani walls are now defor med with the pressure waves and the vestibular membrane is also pushed back and forth creating pressure waves in the endolymph inside the cochlear duct. These waves then causes the membrane to vibrate, which in turn cause the hairs cells of the spiral organ to move against the tectorial membrane. The bending of the stereo cilia produces receptor potentials that in the end lead to the generation of nerve impulses. The External or Outer Ear - comprises of the auricle or pinna which is the fleshy part of the outer ear. It is cup-shaped and collects and amplifies sound waves which then passes along the ear canal to the ear drum or tympanic membrane. The rim of the auricle is called the helix and the inferior portion is called the lobule. The external auditory canal is a carved tube and contains a few hair and ceruminous glands which are specialized sebaceous or oil glands. These secrete ear wax or cerumen. Both the hairs and the cerumen help prevent dust and foreign objects from entering the ear. A number of people produce large amounts of cerumen, and this sometimes cause the build up to be impacted and can bri... ...on on the position of the head in space for static equilibrium making it essential for maintaining appropriate posture and balance, where as dynamic they detect linear acceleration and deceleration. There are two kinds of cells in the two maculae, hair cells and supporting cells. The hair cells are the sensory receptors. Laying over the hair cells are columnar supporting cells that probably secrete the thick, gelatinous, glycoprotein layer called the otolithic membrane and over the membrane is a layer of dense calcium carbonate crystals called otoliths. When the head is tilted, the otoliths shift, and the hairs beneath respond to the change in pressure and bending the hair bundles. Dynamic equilibrium functions in the three semicircular ducts, the saccule and the utricle. The two ventical ducts are the anterior and posterior semicircular ducts. The lateral semicircular duct is horizontal. In the dilated portion of each duct, the ampulla, is a small elevation called the crista. This contains hair cells and supporting cells which are also covered by a mass of gelatinous material which is called cupula. When the head moves the attached semicircular ducts and hair cells move with it.