Monday, 2 February 2015

Human ear

Human ear is auditory and balancing organ. It not only captures the sounds, but also helps in maintaining body balance and posture.The outer visible part of ear is called external ear or Ear pinna. It is composed of flexible tissue called Cartilage.Ear pinna or auricle is characteristic feature of mammals. It is useful in animals like cat, dear, cow to localize the source of sounds. It acts as dish antenna to converge sound waves in to internal ear. Ear pinna and ear muscles are considered as vestigial organs in human, since they are useless.

Ear can be divided into three parts namely Outer ear, Middle ear, Inner ear.

Outer ear

Outer ear has visible fleshy flexible ear pinna and deep external auditory canal.The external auditory canal is a slightly curved tube  and ends blindly at the tympanic membrane other wise called as ear drum. Auditory canal has lined ceruminous gland which produces a waxy secretion called Cerumen.It protects  external ear from infections.

Middle ear

Middle ear is narrow and filled with air.It encloses the auditory ossicles namely malleus (hammer), the incus (anvil), and the stapes (stirrup) and Tymphanic membrane.Tympanic membrane is semitransparent which form barrier between external ear and middle ear with diameter of 9mm.The three bones are suspended by ligaments which allow them to vibrate freely. Two minuscule muscles reduce the intensity of sound by adjusting the stapes. The tensor tympani dampens noise, and the stapedius decreases the receptivity to high-frequency noise Tymphanic membrane is in contact with malleus. When Tymphanic membrane vibrates due to sound waves entering through auditory canal, the sound energy is converted to mechanical energy and is transferred along three auditory bones. Stapes is in contact with oval window of Cochlea a spiral structure in middle ear..The middle ear also connects to the upper throat via the Eustachian tube. It is made up of cartilage and helps in maintaining balance in air pressure on either sides of Tymphanic membrane.

Inner ear

There are actually two labyrinths of the inner ear, membranous labyrinth contained within the bony labyrinth. The bony labyrinth consists of a central chamber called the vestibule, the three semicircular canals, and the spirally coiled cochlea. The hollow spaces of these chambers are filled with liquid, and contain a sensory epithelium that is lined with hair cells.Vibration of the oval window causes vibration of  fluid  endolymph in Cochlea.The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated.They send information through the auditory portion of the vestibulocochlear nerve to the temporal lobe of the brain.The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz. The vestibule and the semicircular canals are involved in the sense of equilibrium.Motions of the head cause the otoliths (calcium carbonate particles) to move the hair cells, stimulating  vestibular nerve, which signals the position of the head with respect to the rest of the body.The three semicircular canals are arranged at right angles to each other, so that they measure motions in all three planes.

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