Hearing and Equilibrium - Essay Example

The Auditory System The ear is divided into three parts: external or outer; middle, and; inner (see Fig The external ear is called pinna and isthe part of the ear that is visible. It is made of fibrocartilage, which makes it flexible. The lobe, the cochnea and the helix are all parts of the pinna. It functions to catch sound and direct it towards the auditory canal (or ear canal), a 24-inch long passageway between the external ear and the middle ear. At the end of the ear canal is the tympanic membrane or the eardrum, that part of the ear that separates the external ear from the middle ear and is part of the latter itself (Brooker & Nicol 2003, pp. 368) The middle ear consists of the following parts: tympanic membrane, and; ossicles.

The tympanic membrane is a three-layered structure at the end of the ear canal and fronting the inner ear’s cochlea. Its first layer is an epithelial lining while the second layer is fibrous giving strength to the eardrum as well as allows it to vibrate. The last layer is mucosal similar to that in the ear canal. The pars tensa, located in the lower of the tympanic membrane, is its main sound-transmitter while the pars flaccida, located in the upper portion of the membrane, is most vulnerable to infection.

On the other hand, the membrane has three ossicles or tiny bones. These three bones, viz. mallus, incus and stapes, are structured in a continuous order that allows sound to be carried from the vibrating eardrum and into the cochlea (Brooker 2003, pp. 368-369). The inner ear is consist of bony tubes all filled with fluid called perilymph. Within this bony labyrinth exists another series of cellular tubes or membranous labyrinth filled with fluid called endolymph. It is the latter labyrinth, which contains the actual hearing cells called the hair cells of the organ of Corti.

The bony labyrinth can be divided into three parts: the cochlea; the semi-circular canals, and; the vestibule, which connects the cochlea to the semi-circular canals. The inner ear is connected to the middle ear by the oval and round windows. The oval window, which is located next to the stapes of the middle ear, vibrates when struck by the stapes – a movement that sets off the sloshing motion of the fluid in the inner ear. The round window, on the other hand, functions as a pressure valve to regulate fluid pressure in the inner ear (Brooker P 369).. Figure 2 shows the auditory pathway where the sound collected by the external ear is directed to the ear canal and into the eardrum, which vibrates and moves the ossicles in the middle near.

The movements of the ossicles trigger the sloshing of fluid in the bony labyrinth, causing the vibration of the hair cells of the organ of Cotti in the cochlea. These hair cells are attached to auditory nerves that carry the sound to the spiral ganglion and onward to a network of subcortical nuclei and finally into the cerebral cortex (Smith 2008, pp. 150-151). The inner ear does not only function in the hearing process, but also helps a person maintain a sense of equilibrium. This is done through the vestibule, which is part of the bony labyrinth in the inner ear and it has the following purposes: it provides conscious awareness of balance; it helps maintain posture, and; it helps the image in the retina steady.

Aside from the vestibule, with its utricule and succule, the semicircular canals also contribute to equilibrium. All these three structures have, like the cochlea, contain endolymph and perilymph as well as hair cells that are sensitive to the movements of the fluids. The succule and utricule of the vestibule react to gravity while the semicircular canals to head and body rotations. For example, when the head is tilted the hairs in the utricle also bend in same direction because of the gravity exerted on them by the fluid.

On the other hand, succule hairs also respond to head tilting but only when the body switches from a horizontal position, such as in getting up from bed. The stimulus from the inner ear is sent to the vestibular bipolar ganglion in the internal acoustic meatus and further brought to the brainstem (England & Wakeley p. 271; Sherwood 2008, pp. 226-227). Bibliography Brooker, Christine & Nicol, Maggie. Nursing Adults: The Practice of Caring. Elsevier Health Sciences, 2003. England, Marjorie & Wakeley, Jennifer.

Color Atlas of the Brain and Spinal Cord: An Introduction to Normal Neuroanatomy. USA: Elsevier Health Sciences, 2005. Sherwood, Lauralee. Human physiology: from cells to systems. 7th Edition. Cengage Learning, 2008. Smith, C.U. Biology of Sensory Systems. 2nd Edition. John Wiley and Sons, 2008.