مدرسة ذكور سنيريا الثانوية
اهلا وسهلا بك في منتدى مدرسة ذكور سنيريا نتمنى لك عزيزي الاستفادة والافادة
المواضيع الأخيرة
» أجمل أربعين مثل في العالم
الثلاثاء يناير 22, 2013 2:13 pm من طرف yaheaissa

» 10 حقائق مثيرة ولا تصدق عن عالم الحيوان
الثلاثاء يناير 22, 2013 1:51 pm من طرف yaheaissa

» العام 2013 يحمل ستة ظواهر فلكية نادرة
الجمعة ديسمبر 28, 2012 3:27 pm من طرف yaheaissa

» معلومات_عن_الجنــة
السبت نوفمبر 24, 2012 10:04 am من طرف yaheaissa

» صور تحنيط للجنة العلمية
الخميس نوفمبر 22, 2012 5:56 pm من طرف yaheaissa

» فتنة المسيح الدجال
الإثنين نوفمبر 05, 2012 12:30 pm من طرف yaheaissa

» بصمات على جدار التاريخ
الأحد أكتوبر 21, 2012 1:08 pm من طرف yaheaissa

» كلمة المساء(الصداقة )
الأربعاء أكتوبر 17, 2012 6:45 pm من طرف الاستاذ عنان شواهنة

» كلمة المساء (احترام الوقت)
الأحد سبتمبر 30, 2012 7:39 pm من طرف الاستاذ عنان شواهنة

مكتبة الصور



عملية الاتزان

استعرض الموضوع السابق استعرض الموضوع التالي اذهب الى الأسفل

عملية الاتزان

مُساهمة من طرف yaheaissa في الجمعة نوفمبر 18, 2011 11:55 pm

عملية الاتزان وهي مرتبطة بما يعرف بجهاز الدهليز التيهي ((Vestibular labyrinth) وتتكفل القنوات الهلالية بهذه المَهمة، ولن يتم هنا التطرق إلى موضوع التوازن، إلا أن الجدير بالإشارة هو أن بعض المصابين بضعف السمع الوراثي يعانون خللًا في عملية التوازن إضافة إلى المشاكل السمعية

أما على نطاق الاتزان: فإن الأذن الداخلية تحتوي على القنوات الهلالية semicircular canals وهي سلسلة تحتوي على ثلاث حلقات متصلة مع بعضها، وظيفتها حفظ توازن الجسد. وعند حركة الرأس والجسم يتحرك السائل الذي بداخل هذه القنوات فينتج منه نبضات كهربائية لتصل إلى عصب الاتزان، والذي يلتقي بالعصب السمعي مشكلين بذلك العصب الثامن والذي يتصل بالدماغ. كما يلتقي العصب السمعي مع عصب الاتزان والعصب المسؤول عن تعبيرات الوجه (العصب الخامس) في منطقة في الدماغ، وهذه المنطقة تتكفل بوظائف حيوية عديدة كضغط الدم والنبض والتأهب الجسدي المفاجئ وغيرها.
The
Vestibular Labyrinth
The main peripheral component of the vestibular system is an elaborate set of interconnected canals—the labyrinth—that has much in common, and is in fact continuous with, the cochlea. Like the cochlea (see Chapter 13), the vestibular system is derived from the otic placode of the embryo, and it uses the same specialized set of sensory cells—hair cells—to transduce physical motion into neural impulses. In the cochlea, the motion is due to airborne sounds; in the vestibular system, the motions transduced arise from head movements, inertial effects due to gravity, and ground-borne vibrations
Hypothetical mechanism of Type 2 benign paroxysmal positioning vertigo. The right vestibular labyrinth is illustrated from the medial aspect. (A) Posterior cupula chronically deflected by the weight of the debris; the cupula becomes adapted to this extreme position. (B) Dix–Hallpike position. Particles fall down from the cupula. (C) Trunk oscillations during and shortly after sitting up. These may be caused by different mechanisms. By losing the mechanical load and because of the adaptation, the cupula over-reacts when, while sitting up, the endolymphatic flow pushes it toward the vestibulum. Thereby, the patients receive the impression that they are falling forward, and transient retropulsion occurs. Trunk oscillation immediately after sitting up may be elicited by particles falling back onto the cupula in the upright position. asc, anterior (superior) semicircular canal; hsc, horizontal semicircular canal; pa, posterior ampulla; psc, posterior (inferior) semicircular canal; um, utricular macula.
Responses to angular rotation
The responses of individuals to rotation have been studied quite thoroughly because understanding them is important to controlling performance in high speed aircraft or in spacecraft. When a person, with eyes closed, is submitted to angular rotation, for example in a Barany chair, he will accurately signal the direction of rotation when he first begins to move; however, after a period of rotation at constant velocity, he will report that he has ceased to rotate. This is precisely what is predicted from the rapid adaptation of receptors in the semicircular canals at constant velocity (Figs. 9-6 and 9-7). During the period of acceleration at the beginning of the rotation, the person will also experience a nystagmus in the direction of rotation, the eyes apparently attempting to stay fixated on some target. When the sensation of rotation fades at constant velocity, the nystagmus also disappears.
If the chair is abruptly stopped at this point, the person will have a sensation of rotation in the direction opposite to that he previously experienced, and that too will fade with time. In addition, there will be a postrotatory nystagmus also in the direction opposite to the previous rotation. Again, these are phenomena consistent with the discharge properties of receptors in the semicircular canals. When a rotation stops, the discharge frequency of the canal receptors (on the side toward which the head originally rotated) falls below resting levels and below the level of the contralateral canal, just as it would if there were actually a rotation in the opposite direction. Although rotation has ceased, the central nervous system cannot distinguish this signal from the signal that would occur for an opposite rotation and, therefore, it is interpreted as an opposite rotation. This sensation also fades with time because of receptor adaptation.
Another consequence of rotation in the postrotatory period is past-pointing. If a person is asked to point at a target immediately upon being stopped from a period of constant velocity rotation, he will consistently point inaccurately, with the deviation always in the direction of the previous rotation. Thus, if the previous rotation was clockwise, he will consistently point to the right of the target.
People who must undergo this kind of rotation frequently learn to ignore what their vestibular senses tell them. Figure skaters, for example, can spin for long periods without showing past-pointing or postrotatory nystagmus. Obviously, they must be able to do this if they are to continue skating after the spin. Airplane pilots can suffer what is called a Coriolis effect, a false sense of spinning. A pilot who has put his airplane into a spin, either intentionally or accidentally, may be unaware of it after a while if he relies upon his vestibular sense because of the adaptation of the receptors. When he stops the spin (usually because someone tells him to), he will experience a sensation of spinning in the opposite direction, the Coriolis effect. Were he then to attempt to correct for this illusory spin, he would set himself in a spin again. Many aircraft have been sent spinning to earth by pilots who failed to read their instruments and relied on the Coriolis effect to navigate.

_________________
][][§¤°^°¤§][ *****خلقني الله وابدع في تكويني وبث روح التحدي في شرايني ****انا الموقع على حبل مشنقتي كفاني فخر اني فلسطيني**** نحن الشعب المغوار نحن الثوار ****نحن ابناء فلسطين بلاد النار****اقتلوني مزقوني اغرقوني في دمائي****لن تعيشوا فوق ارضي لن تطيروا فوق سمائي*****
][§¤°^°¤§][][
avatar
yaheaissa
المدير
المدير

عدد الرسائل : 431
العمر : 33
تاريخ التسجيل : 24/02/2009

http://saneriaschool.mam9.com

الرجوع الى أعلى الصفحة اذهب الى الأسفل

استعرض الموضوع السابق استعرض الموضوع التالي الرجوع الى أعلى الصفحة


 
صلاحيات هذا المنتدى:
لاتستطيع الرد على المواضيع في هذا المنتدى