Auditory nerve damage symptoms 2014,pulsatile tinnitus headache dizziness weakness,sinus infection time to recover,ear ringing loud sound objects - Tips For You

An occasional tinnitus, especially within a very quiet environment, is not at all unusual and is reported by 90 to 95% of the population even in the absence of any ear disease or hearing disorders. The word tinnitus has its etymological root in the Latin tinnire meaning “to jingle.” However, the patient experiencing tinnitus may describe the sound as a ringing, roaring, hissing, whistling, chirping, rustling, clicking, buzzing, or some other similar term or description. The perceived loudness of tinnitus may be intense enough for some to be highly debilitating. To understand the pathopysiology of tinnitus it is first necessary to understand how the ear itself works. The cochlea is the portion of the inner ear responsible for hearing and it is within the cochlea that the origins of tinnitus arise. The sensory receptors, known as hair cells because of their appearance under magnification), are shown in Figure 2.
Figure 2: Cross-sectional schematic view of the single row of inner hair cells and the three rows of outer hair cells within the organ of Corti in the cochlea of the human ear.
The alterations in the normal random firings of the hair cells are “heard” only because they are a novelty: something new. The vestibulocochlear nerve is the eighth nerve of the twelve cranial nerves, which are all located in the brain's cranium.
Our hearing system is divided into four key areas: the outer ear, the middle ear, the inner ear and the central auditory pathways.
Damage or impairment to any one of these components that make up our hearing system can contribute to hearing impairment. Movement of the stereocilia of the hair cells causes the opening and closing of ion channels, thereby transducing mechanical movement into changes in electrical potential.
Afferents from the inner hair cells transmit auditory information first to the cochlear nuclei of the brainstem and then bilaterally to the superior olive, which in turn innervates the inferior colliculus.
At each level of the auditory system, sound frequencies are mapped in an orderly succession called tonotopic organization. Birds and mammals evolved different neural mechanisms for localizing sounds; in mammals the lateral superior olivary nucleus of the brainstem processes differences in intensity, and the medial superior olivary nucleus processes differences in time of arrival.
Nerve fibers from the vestibular receptors enter the brainstem and synapse in the vestibular nuclei, which send their outputs to the motor nuclei of numerous structures.
The tastes of salty and sour are evoked primarily by the action of simple ions on ion channels in the membranes of taste cells.
Humans can detect thousands of different odors, but some other species have more olfactory receptor cells and larger olfactory bulbs.
All olfactory neurons expressing a particular receptor synapse in the same glomerulus in the olfactory bulb. The vomeronasal organ contains receptors to detect pheromones released from other individuals of the species.
Ear and head noises are probably the most common complaints presented to hearing healthcare professionals.
Tinnitus becomes a problem for some when its intensity so overrides normal environmental sounds that it invades the consciousness. While most who have tinnitus report the presence of their tinnitus to be constant, others have reported it to be intermittent, fluctuant, or pulsating. The tinnitus itself may cause or be aggravated by difficulty sleeping, fatigue, difficulty relaxing, decreased ability to concentrate, increased levels of stress, depression and irritability. As can be seen in the accompanying cross section (Figure 1), the ear is comprised of much more than the visible skin and cartilage appendage on either side of our heads. Within this fluid-filled, snail-shaped, bony capsule, the mechanical energy of the vibrating ear bones changes into an electromechanical energy by triggering the microscopic sensory “hair cells.” These hair cells, so named because of their appearance, send neural impulses to the brain for interpretation.


If you can visualize a conch shell from the beach (similar in shape to the cochlea in the human ear which houses the organ responsible for hearing) with hair cells resting on a shelf that stretches throughout the coil of the shell, you can appreciate how many hair cells there are. The nerve receptors at the ends of your fingers are constantly “firing” and sending impulses to the brain. It is only when they are triggered by the patterns of sound waves that a pattern occurs in the sequence of neural firing so that the brain pays attention to it.
There are approximately 3,500 inner-hair cells, and it is these inner hair cells that are responsible for hearing.
Electron micrograph of a portion of the spiral curve of the human cochlea revealing a total obliteration of the outer hair cells and their accompanying nerve fibers following occupational noise exposure.
Novel sounds are always heard initially, but when they loose their novelty they leave our conscious attention. Its singular function is to transmit information from the cochlea and semi-circular canals to the brain for interpretation.
This system is a complex network of neural pathways in the brain that is responsible for sound localization, speech understanding in noisy listening situations, and other complex sounds, such as music perception.
Hearing loss can mislead our brain with a loss of audibility and distortion in the message that is trying to reach the brain. Vibrations of the tympanic membrane (eardrum) are focused by the three ossicles of the middle ear onto the oval window to stimulate the cochlea. High-frequency sounds affect the basilar membrane near the base of the cochlea; low-frequency sounds affect the apex. From there auditory information is relayed to the medial geniculate and then primary auditory cortex in the temporal lobe. Pitch is encoded two ways: as the place on the basilar membrane most strongly stimulated (place coding) and in the rate of firing in the auditory nerve (temporal coding).
For low-frequency sounds, differences in time of arrival at the two ears (latency differences) are especially important. Conduction deafness consists of impairments in the transmission of sound through the external or middle ear to the cochlea. In mammals the vestibular system consists of three semicircular canals, plus the utricle and the saccule. One important function of the vestibular system is the vestibulo-ocular reflex (VOR), which uses vestibular information about head rotations to precisely move the eyes to keep our gaze fixed.
In mammals, most taste receptor cells are located in clusters of cells called taste buds, situated within small projections from the surface of the tongue called papillae. Sweet and bitter tastes are perceived by specialized receptor molecules belonging to the T1R and T2R families, which are coupled to G proteins. Each olfactory receptor neuron has dendrites in the olfactory epithelium in the nose and a fine, unmyelinated axon that runs to a glomerulus within an olfactory bulb.
The projection from the epithelium to the bulb and then to the brain maintains a zonal distribution for different kinds of receptor molecules. These receptors transmit signals to the accessory olfactory bulb, which in turn communicates with the amygdala. Seventeen percent of the general population has tinnitus to a noticeable degree with as many as 30% of those over age 65 years reporting the presence of tinnitus. Tinnitus may be perceived as a high or low-pitched tone, a band of noise, or as a combination of these sounds. The degree to which these factors are present often far exceeds expectations based on the loudness levels of tinnitus as traditionally measured. A brief overview would begin with the outer ear, which extends from the auricle (what we call the “ear”) down the ear canal to the tympanic membrane, or eardrum.


These bones are used in transmitting the sound energy from the vibrating eardrum to the cochlea. What you see in Figure 2 is a representation of a slice of the long rows of hair cells revealing three rows next to each other called the outer hair cells (because they are positioned toward the outside of the snail-shaped cochlea) and a single row of inner hair cells. These random firings are filtered out as meaningless so that the brain pays them no attention. It is an alteration in the random neural activity of the hair cells in the absence of sound that the brain interprets as tinnitus. If we label the sound of the tinnitus as something negative (for example, a sign of impending deafness, a sound that may worsen and over-power us, an abnormality that signifies a significant pathology such as a tumor, etc.), then emotional reactions are attached to the sound. The ears and the brain work together in a sophisticated manner to process sound and allow us to hear as we do. The outer hair cells change their length under the control of the brain, tuning the basilar membrane. Sensorineural deafness arises in the cochlea, often because of the destruction of hair cells, or in the auditory nerve.
Within these structures hair cells detect rotation of the body in three planes, and the utricle and saccule sense static positions and linear accelerations.
The outer hair cells are much more plentiful than the inner hair cells, numbering about 12,000. Once this happens, we become increasingly aware of this sound that otherwise would have been filtered from our consciousness. The third bone, the stapes, transmits the vibrations of the middle ear to the inner ear through the stapes footplate. The cochlea is a snail-shaped bony structure that is responsible for receiving the sound signal by tiny hair cells. The gustatory system extends from the taste receptor cells through brainstem nuclei to the thalamus and then to the cerebral cortex. It is the patterned neural impulses that gain attention within the brain and that are assigned meaning. These cells, to the extent possible, will enhance the weak sounds that are received to make them more audible and they will attenuate the loud sounds to make them more comfortable.
Therefore, the primary difference between people who just notice their tinnitus, and those who suffer because of it, is the negative emotional attachments they may bring to its existence. These hair cells transmit the sound to the auditory nerve which will carry sound to the brain. Some forms of deafness may be alleviated by direct electrical stimulation of the auditory nerve (by a cochlear implant). The outer hair cells are more susceptible to damage from viral infections, exposure to intense sounds, and medications that can be toxic to the ear.
It is still there, of course; and is still heard if you think about it, as you probably are now. However, this damage can alter the random neural activity that is normally interpreted by the brain as a code of silence.
Now, the random firings, occurring in the absence of an actual sound, are “heard” by the brain. Rather, tinnitus is an alteration in the normal random firings of the nerve receptors of the ear.




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12.12.2015 admin



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