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Editorial note: This chapter on the olivocochlear efferents has been written preliminary in English, in order to ask professor John Guinan Jr.
The Editorial Board of the Textbook greatly appreciates that  professor John Guinan Jr.
The auditory pathway is a huge and complex system of bundles of neurons, which send information from the cochlea to higher auditory nuclei.
The present chapter presents some striking examples of the reflexes (feedbacks) generated via the olivocochlear acoustic reflex bundles. These topics have been selected too because they are a further step in understanding auditory mechanisms like the detection of signals in noise and the protection of hearing against damaging high sound levels. The way in which, via these efferents, the cochlear gain and the frequency selectivity of the outer hair cells are regulated, both in quiet and in noise, and the potential function of these reflexes in protecting the auditory system against damage due to high sound levels. Effects on cochlear gain in quietActivation of outer hair cells by efferent fibers regulates the gain of these cells at low stimulation levels. Decrease of gain, under MOC stimulation, is maximum at the characteristic frequencies of the fibers involved, as shown in Fig.3B. Effects on cochlear gain in the presence of noiseIn the former section tone bursts in quiet were used in order to show the effect of MOC stimulation. Effects on Otoacoustic EmissionsGood insight in the effects of the olivocochleair efferents on otoacoustic emissions is obtained from several experiments carried out by Liberman et al. When the uncrossed bundles (UOCB) and crossed bundles (OCB) are intact the DPOAE amplitude in the right ear follows the red curve. As already mentioned these highly interesting experimental results are fully in line with the anatomy of the olivocochlear bundles: the ipsilateral acoustic reflex (MOC) going via the contralateral pathway (vice versa) and the contralateral reflex going from the contralateral side to the ipsilateral one. Protection against high sound levelsThe decrease of cochlear gain in outer hair cells under MOC stimulation might have a function in protecting the cochlea against damage due to high sound levels. Mechanisms (role of transmitters)The mechanisms responsible for the influencing of the cochlear gain in the outer hair cells and the role of the neurotransmitters are not discussed in this textbook.
This chapter describes some experiments that are illustrative for the way in which olivocochlear efferents modulate the cochlear gain of the outer hair cells.
Decrease of temporary threshold shift (TTS) under electric (MOC) and acoustic stimulation of the olivocochlear efferents at the contralateral side of the traumatized ear. The individuals rendering the military service are often liable to frequent noise in factories and discharge sounds deriving from firearms and detonations. INTRODUCTIONHigh intensity impulse noises caused by explosions are the most common cause for militaries to look for medical help in the United States, as well as in other countries 1.
The access to article's content is restricted to members of ABORL-CCF (Brazilian Association of Otolaryngology and Cervico-Facial Surgery). So let us turn to the causes instead, and see whether we can try to solve the issue from this end. You could begin to hear all kinds of noises if you have been exposed to just a single high-pitched noise. Take care of your head because a severe blow or a slight bang could make you hear the tinnitus noises. Ear infections and other ear problems – An ear infection, and even sinus can lead to tinnitus as well. The only way you could ever get rid of your tinnitus for good is by following the holistic approach to healing. Appliance Transporter Wity Solid Tyres Made From Sheet Steel, Drag Bearing With Double Ball Race, Bolted Axle Tree.
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Whereas the functions of the efferent pathways from colliculus inferior and from cortex are unclear and unknown for a great deal, the anatomy and properties of the olivocochlear efferents, that connect the olivary complexes to the inner and outer hair cells, are well understood now. Although this evidence is based on animal experiments, the scientific experience at this moment is enough far developed for extending the findings reliably to humans. The medial bundles are connected with the outer hair cells (OHC) and the lateral ones with auditory-nerve fibers under the inner hair cells (IHC), as illustrated schematically in Fig.1. Schematical representation of the courses of the olivocochlear acoustic reflex bundles (OCB) to the right ear. Sound presented to the right cochlea (at the right in this figure) causes excitation of afferente neurons from the inner hair cells (indicated in black). Schematical representation of the generation of the ipsilateral reflex in the right ear via the crossed olivocochleaire (OCCB - MOC) bundle (green and thick).
In this case the afferent neurons run via the left cochlear nucleus to the (medial) MOC neurons in the ipsilateral (right) olivary nucleus (the dashed black line).
This conclusion is only applicable to animals, especially for the higher (basal) frequency regions. With these stimuli electric stimulation of MOC neurons (at the contralateral side of the brainstem) reduced the firing rates of the afferent neurons from the ipsilateral cochlea.
Schematic representation of the effect of electric stimulation of the contralateral (crossed) medial olivocochleaire bundle (MOC stimulation) on the gain in the outer hair cells during ipsilateral stimulation with tone bursts in noise, measured in cats. In case of the blue curve continuous noise is presented to the right ear, simultaneously with the tone bursts.
Schematic representation of the effects of acoustic stimulation of the contralateral (left) ear on the size of the DPEAO in the ipsilateral (right) ear of a cat, before and after cutting the medial olivocochlear bundle at two places, respectively. The curve is characterized by a fast decrease (adaptation) at the beginning and again a fast decrease when the contralateral noise is turned on.

It is highly probable that this fast adaptation reflects the ipsilateral (right ear) acoustic MOC reflex. An illustration of such a protection is the effect of MOC stimulation on the size of the temporary threshold shift (TTS) induced by high level sounds in guinea pigs, as investigated by Rajan (1988a,b) and Rajan end Johnstone (1988). The threshold was measured by means of the N1 of the Compound Action Potential (CAP), starting 5 minutes after the end of the traumatizing sound. CAP thresholds (N1) in guinea pigs as a function of frequency as a result of TTS, elicited by traumatizing the right ear the animal with a 10 kHz tone of 103 dB SPL during 1 minute The measurement of the thresholds was started 5 minutes after the end of the traumatizing sound. Then the CAP thresholds are similar to the case in which the COCB is intact and the contralateral stimulus is absent (red triangle in Fig.6B). Olivocochlear Efferents: Anatomy, Physiology, Function, and the Measurement of Efferent Effects in Humans. The ipsilateral evoked olivocochlear reflex causes rapid adaptation of the 2f1-f2 distortion product otoacoustic emission. Effect of electrical stimulation of the crossed olivocochlear bundle on temporary threshold shifts in auditory sensitivity I. Effect of electrical stimulation of the crossed olivocochlear bundle on temporary threshold shifts in auditory sensitivity II. Centrifugal pathways protect hearing sensitivity at the cochlea in noisy environments that exacerbate the damage induced by loud sound. Binaural acoustic stimulation exercises effect protective effects at the cochlea that mimic the effectc of electrical stimulation of an auditory efferent pathway.
Medial efferent inhibition suppresses basilar membrane responses to near characteristic frequency tones of moderate to high intensities. These sort of undesirable sounds cause lesions the auditory system, which are sometimes irreversible, besides provoking bad effects to the body as a whole.
Thomas is an author, researcher, nutritionist and health consultant who dedicated his life to creating the ultimate Tinnitus solution to permanently reverse the root of ear ringing and naturally and dramatically improve the overall quality of your life, without the use prescription medication or any surgical procedures.
When there is an allergy or a sinus infection, the mucous thickens within the inner ear, and this causes more pressure. By using a multidimensional treatment for tinnitus, we are tackling all tinnitus causative factors and eliminating these triggering elements from the root. Thomas is an author, researcher, nutritionist and health consultant who dedicated his life to creating the ultimate Tinnitus solution guaranteed to permanently reverse the root of ear ringing and naturally and dramatically improve the overall quality of your life, without the use prescription medication and without any surgical procedures. The afferent neurons are connected with the bases of the inner hair cells via about 30.000 ganglion cells. These efferents, called the olivocochlear acoustic reflex bundles, regulate the cochlear gain and frequency selectivity of the outer hair cells under acoustic stimulation. Moreover several psychophysical experiments with efferent stimulation have been carried out already for humans (see e.g. This is schematized from a transverse section of the brainstem and the right cochlea of the cat.
These afferents innervate reflex interneurons in the posteroventral part of the ipsilateral cochleaire nucleus (CN). From there the efferent neurons follow the thin green line at the right hand side in Fig.2, ending on the ipsilateral outer hair cells.
The dendrites of these afferents run into basal direction and thereby contact several outer hair cells. This has been demonstrated experimentally by presenting tone bursts to the ipsilateral ear of a cat and electrically stimulating MOC neurons at the contralateral side of the brainstem (Fig.2). The opposite effect, an increase of firing rate ipsilaterally, occurs too under certain conditions.
From 3 seconds after the beginning, a broadband noise is presented to the contralateral ear during an interval indicated by the black bar.
This effect crosses the brainstem twice, firstly via the afferents to the contralateral medial olivary complex and subsequently back, along the efferent MOC bundle to the ipsilateral outer hair cells. Aim: Evaluating the auditory profiles from a specific group of military personnel, and according to the achieved results to promote the incentive towards the implantation of preventive measures related to auditory losses, such as auditory preservation programs. But some people cannot live without an injury, such as those who are into sports – boxers and football players. Such as antibiotics like Aminoglycosides, Erythromycin and Vancomycin, Aspirin or medicines containing it.
In the auditory nerve the number of (afferent) neurons is much bigger than the number of hair cells, because between 10 and 20 neurons have connection with one single inner hair cell. The abbreviation COCB refers to crossed bundles and the abbreviation UOCB represents uncrossed bundles. Most anatomic connections originate from investigations of Warr (1978) and Warren & Liberman (1989).
These in turn innervate MOC neurons in the contralateral olivary complex which cross again (back) the brainstem and innervate the ipsilateral outer hair cells. A possible reason for this might be the fact that the maximum sensitivity for sound is in a lower frequency region in humans than for the experimental animals investigated.
The blue curve at the left represents the firing rates without MOC stimulation and the green curve is the result obtained with MOC stimulation. For transient stimuli, like tone bursts, presented to the right ear, now in a background of continuous noise, MOC stimulation causes an re-increase of firing rate in the afferent neurons.
In case of the blue curve is continuous noise has been presented the right ear simultaneously with the tone bursts. Probably, now the neural transmitter is partly used by the noise and therefore not available for the production of a sufficient high spike rate at high level tone burst. Contrary the effect of the noise in the left ear on the amplitude remains, because this activates the medial bundle at the right (ipsilateral) side which reduces the cochlear gain in the outer hair cells of the right ear.
When, simultaneously with the conditioning sound, the COCB is stimulated electrically (MOC stimulation, thus at the contralateral side) the TTS is much less (10 dB, the green triangle). Decrease of TTS after simultaneous acoustic stimulation of the contralateral ear with noise (COCB intact). Sure enough, your doctor would suggest a few remedies, and it may seem to you that the noises you hear are going down. Meniere’s disease, where the fluid level goes up inside the middle ear is another reason.
Anti inflammatory drugs like Advil, Aleve, Anaprox, Clinoril, Feldene, Indocin, Lodine and Motrin have also been blamed.
The afferent bundle ascending from the inner hair cells to the (ventral) Cochlear Nucleus (CN), and farther on (see Fig.2) is indicated in black.
We here stress again that effects on otoacoustic emissions mean effects on the cochlear gain in the outer hair cells. The blue curve represents the situation with the crossed bundle (COCB) cut and the green curve the cutting of the whole olivocochlear bundle (OCB). Material and Method: Auditory evaluation of 97 individuals working in a military organization, which included interviews, as well as otoscopic and audiometric tests. These sounds can reach intensity and frequency of about 140dB SPL and 2 to 3 kHz, respectively, and can for this reason, be harmful to human ear.The effects of impact noise can be innocuous, such as a round of applause, or dangerous, such as explosions.

Sometimes people heard noises after taking chemotherapy agents such as Cisplatin, Nitrogen Mustard and Vincristine. In general it is 10 to 25 dB, depending on the specific measuring position within the dynamic range. Finally, as expected now, MOC stimulation causes a reduction of the amplitude of basilar membrane displacement in the ipsilateral cochlea. Results: From the total examined personnel, 38,1% presented audiometric changes supposedly noise-induced since these changes prevailed in the artillerymen, being the unilateral hearing loss predominant.
The cochlear gain and, thus, the decrease of it too are maximum at relatively low stimulation levels. The illustration at the right is the same one as that in Fig.2 and has been added for better understanding the one at the left. The use of no proper protection equipment was observed in 64,5% of the total examined military personnel.
Sound load will produce severe lesions in the cochlea, such as rupture of basilar membrane, disorganization of tissues and hair cells, in an abrupt fashion.
Conclusion: The high level of hearing loss occurrences found between the military personnel joined to the absence of proper protection equipment for the exposition to noises, indicate the need of implanting prevention measures to avoid hearing losses among theses professionals. Clinically, there is immediate and permanent sensorineural hearing loss, uni or bilateral, with presence of constant tinnitus. In some cases, the auditory loss can present improvement for some days, recovering social hearing in many occasions 5.In explosions, there may be simultaneous damage to the middle ear, such as tympanic membrane rupture, disarticulation of ossicles or vestibular system damage. If there is impairment of middle ear, the mechanism of natural protection of Corti's organ gets into action.
The sudden increase in acoustic pressure results in immediate and severe auditory sequel (profound hearing loss), as well as tinnitus. As a result of increase in shooting as sport, a larger number of people suffer acoustic trauma or gradual sensorineural loss secondary to excessive noise caused by firearm.
Sudden hearing loss results from high sound pressure level of impulse noise that exceeds critical level, which can cause mechanical or metabolic damage to inner ear structures. Gradual hearing loss is the result of exposure during many years to impulse noise of firearms that are not sufficiently loud to cause acoustic trauma, but cause harmful effects to inner ear structures in the long run.
Some patients come to the service of audiology owing to difficulty in understanding speech and others owing to tinnitus.In Brazil, Godoy (1991)4 conducted an auditory assessment study in the Formation of Army Military Course through interviews and audiometric assessment of participants at the beginning and at the end of the course. The author detected changes to hearing in a significant number of students (24%) within a period of 20 months. These changes occurred predominantly among those exposed to noise levels higher than 80dB.Seballos (1995)9 conducted a study about assessment of auditory conditions in subjects exposed to noise from firearms caliber 12. They detected that the occurrence of auditory affections caused by acoustic trauma in subjects exposed to noise of firearms was greater when exposure time to noise was higher than 10 years and in subjects with advanced age. In the audiometric exam, they detected significant changes in frequencies of 4 to 8kHz.Neves-Pinto et al. The same authors conducted many different studies with airplane crew and found significant affections to hearing of studied subjects.Brito (1998)11 conducted a study of auditory assessment of civil and military flying crew of the Air Force to detect early hearing losses. The subjects were submitted to conventional audiometric tests and high frequency audiometry (12Kz). The results showed changes to frequencies of 12,000Hz in subjects that were considered normal in the conventional exam, allowing early detection of cochlear problems by noise exposure.Bandeira (1979)12 conducted a study of auditory assessment in 54 military men that worked for security services, conducting weekly shooting exercises. 15 (1978) defined tolerance limits to continuous or intermittent and impact noise, respectively. Considering distribution by time in service, on average it was 12.75 years, ranging from 2 to 32 years.
We used acoustically treated booth (Vibrasom VSA40), audiometer (Siemens SD25) and impedanciometer (Dicton ZA44).Figure 1.
Continuous lines represent mean, minimum, maximum values and dotted lines are standard deviation.Figure 2. Continuous lines represent mean, minimum, maximum values and dotted lines are standard deviation.Graph 1. As to the most affected ear, the left side presented more affections in frequencies higher than 2KHz (Table 9 and Graph 6).Table 1. Distribution by age range and abnormal audiometric findings versus those within acceptable limits.Table 2. Distribution by time in service and abnormal audiometric findings versus those within acceptable limits.Table 3. Distribution by job and abnormal audiometric findings versus those within normal range.Table 4. Relation of type of arms and exposure to impact noise.DISCUSSIONCox & Ford14 confirmed that 20 to 30% of the militaries have some hearing loss caused by exposure to firearm noise. These results are in accordance with the study by Seballos 9, which detected that occurrence of auditory affection caused by acoustic trauma in subjects exposed to noise caused by firearm was greater in older subjects.As to distribution by time in service, subjects with over 15 years exposure presented the highest percentage of abnormal audiometric tests and the tendency was that the longer the time in service, the greater the number of affected tests, in agreement with what was found by Cox & Ford14, in which subjects with over 15 years in the military service the percentage of hearing loss was over 50%.
In the studies by Axelsson & Hamernik15 the maximum hearing loss was reached within five years of military service, as well as in the study by Alvarez16, which showed hearing disorders occurred when duration of exposure was higher than six years.As to subjects' jobs, the most affected group was that of artillery, probably because they were exposed directly in the shooting exercise field to weapons and howitzer, either not protected or inappropriately protected.
In the study by Alvarez16 about incidence of acoustic trauma in units of tanks and artillery, the most affected group was that of artillerymen, probably attributed to lack of appropriate hearing protection.Out of interviewed subjects that reported good hearing, one third presented abnormal audiometry, which is probably due to the fact that most hearing losses were in high frequencies.
Alvarez16 explained that hearing loss was not much manifested by the studied subjects, since the affected frequencies were 4 to 8kHz.Out of those that reported average hearing reduction, 40% presented audiometry within the normal range. Among them only 20% reported that hearing loss was of sudden onset, reporting exposure to firearm or loud noise. Tinnitus is the most common symptom found in many other studies, being that in the present study it was reported in only 16.49% of the subjects. According to Mrena et al.17, tinnitus and hearing loss are the most common symptoms reported after exposure to noise that causes acoustic trauma. Tinnitus can disappear after some time or persist for a long period, affecting people's quality of life 17.Currently, it is known that many types of high intensity noise are capable of causing hearing loss.
Konopka et al.18 studied 10 soldiers aged 20 years exposed to impact noise of automatic firearms without hearing protection and they detected hearing disorders in these subjects.
The author believed that the lesion depended on the ear that was closer to the sound source (given the positions that each one holds the gun in combat situations).The authors observed that the interviewed subjects did not have any information about auditory risks caused by impact noise of the arsenal used, nor the way in which they could protect themselves and prevent hearing loss. For this reason, it is critical to implement preventive measures in military units.CONCLUSION1.
Perda auditiva induzida pelo ruido: revisao das Publicacoes por Brasileiros no periodo 1938-1970. Diretrizes e parametros minimos para avaliacao e acompanhamento da audicao em trabalhadores expostos a niveis de pressao sonora elevado. Hearing loss associated with weapons noise exposure: when to investigate an asymmetrical loss.

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