Hearing And Balance of Human Ear is very important for every science student.It is true the inner ear controls the hearing and balance of your body.We will discuss In details in the prespective of anatomy of ear.You can also see my article about Anatomy of ear
Hearing And the Taste of Sense:
Sounds are the result of the vibrations of a material body. The space between the source of sound and the receiver is known as the medium, this is usually air. In transmitting sound, the medium air vibrates. These vibrations, or waves, are collected by the external ear, and passed to the tympanic membrane, the vibration of which sets in motion the chain of ossicles: the vibration of the stapes affects the membrane covering the fenestra ovalis, and this sets up waves in the perilymph which causes the basilar membrane to vibrate, and the nerve endings in the organ of Corti receive a stimulus which passes by the cochlear (hearing) branch of the auditory nerve to the cerebral centre. Thus sounds are heard and distinguished.
Balance and the sense of direction.
The semicircular canals project from the back of the vestibule: their membranous canals open out of the utricle. On each side there are three canals arranged in the three planes of space, two vertical at right angles to one another, and one horizontal. Each is filled with endolymph, and is dilated at one end to form an ampulla. Into the ampullae run the endings of the vestibular branch of the auditory nerve.
Alterations in the position of the head cause pressure of the endolymph on the nerves in the ampulla to vary. The sensation will alter with altered position, and in this way is conveyed to the brain, by the vestibular nerve, the idea of the position of the head in space. Rapid rotary movements start movement in the endolymph and the semicircular canals and, by disturbing the reflexes by which balance is maintained, cause giddiness and staggering.
The Organ of Hearing And Balance In Ear Has been Divided Into External, Middle, And Internal ear.
The external ear consists of the pinna or auricle and the external auditory meatus. The pinna is situated outside of the skull and consists of an ovoid flap of cartilage covered with skin. The external auditory meatus is the channel leading from the pinna to the tympanic membrane; it is about an inch long, formed partly of cartilage and partly of bone, and is lined with skin, the sweat glands of which secrete a waxy substance, cerumen: the canal cm v little and is slightly constricted at the centre: it comm sound waves to the tympanic membrane.
The middle ear comprises (a) the tympanic cavity tympanum (drum), (b) the Eustachian tube, and mastoid antrum.The tympanum is a little air-containing chanibct in temporal bone. Its roof is formed of a thin plait which separates it from the cranial cavity and meninges. Its floor is also a thin bony plate and separates it from the jugular fossa and lateral sinus. Its outer wall is formed chiefly by the tympanic membrane, which separates it from the external ear. Its inner wall is bony and forms the outer wall of the internal ear: with it four important structures are connected:
- The delicate bony canal containing the seventh (facial) nerve which crosses it.
- An elevation, the promontory, corresponds with the first turn of the It is penetrated by two openings.
- The round window (fenestra rotunda).
- The oval window (fenestra ovalis), which communicates with the internal ear.
The windows are closed by membranes: that of the oval window is attached to a foot piece of a small bone, the stapes (stirrup).
The Eustachian tube is the channel of communication between the tympanum and the naso-pharynx. It is about one and a half inches in length and opens during the act of swallowing, serving to keep the pressure of air in the cavity equal to that of the atmosphere.
The mastoid antrum is an air-containing cavity in the temporal bone: with it the middle ear communicates by a little passage, the aditus ad antrum.
These three structures, tympanum, Eustachian tube, and mastoid antrum, are lined by a mucous membrane which is continuous.
The contents of the tympanum are the ossicles: these are three small bones which form a chain stretching across the cavity from the tympanic membrane to the fenestra ovalis and are called: the malleus or hammer; the incus or anvil; the stapes or stirrup.
The malleus is attached to the tympanic membrane by its handle: its head articulates with the incus which lies behind it: the incus articulates with the stapes, the foot of which is attached to the membrane closing the fenestra ovalis. These ossicles transmit the vibrations of sound from the tympanic membrane to the internal ear.
The internal ear. This is the part that influences and controls the hearing and balance of your ear.The petrous portion of the temporal bone contains a series of chambers which are together known as the labyrinth, comprising: the vestibule, Itio cochlea (like a snail shell), the semicircular canals.Inside the bony chambers lie membranous chamber! which fit the bony ones very loosely. Between the two If formed a fluid, the perilymph. Inside the membrane) chambers is found endolymph.
The vestibule is the central cavity behind the cochlea and in front of the semicircular canals: it contains two membranous sacs. From the larger sac, the utricle,there open out the three membranous semicircular canals: from the smaller sac, the saccule, a fine tube leads to the cochlea.From the modiolus a thin spiral lamina of bone pioja and from this the important basilar membrane stiffly to the outer wall of the cochlea, dividing it into two equal portions.
The basilar membrane supports the organ of corti.The organ of Corti consists of a great number of tiny arched rods, the rods of Corti, arranged so as to from a little tunnel, on either side of which, supported by the basilar membrane, are a number of sensory cells from which hair-like processes project.