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מ: yaz
יוצר: yaz
אי-מייל: שלח אי-מייל
נוסף ב: אפריל 18, 2010
עודכן ב: אפריל 18, 2010
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המאמרים הפופולרים ביותר:
מה לקחת לטיול שנתי? (רשימה וטיפים)

 
סיכום שיעור אנטומיה בנושא העין
העין

ארובעת העין - orbit מהווה קופסה גרמית (עצם) בצורת פירמידה השוכבת על צידה. בתוכה יושבים גלגל העין ורצועות. גלגל העין מרופד ברקמה שומנית המגנה עליו מבחינה תרמית ומכנית. העפעפיים שנסגרים על גלגל העין הם כמו תריסים ומונעים חדירה של גופים זרים ואור חזק מדי. בפינה העליונה לטרלית (חיצונית) יושבת בלוטת הדמעות lacrimal gland. הדמעות שומרות של הקרנית מני התייבשות, ומסירה את הלכלוך מגלגל העין ליצירת תנאים לראייה טובה יותר. בנוסף לכך, נוזל הדמעות הינו אנטיבקטריאלי. לגלגל העין מבנה כדורי בקוטר 2.5 ס"מ.

דופן גלגל העין מורכב משלוש שכבות:
1. חיצוני - sclera, קרום הלובן. שכבה לבנה וסיבית. אטומה וקשה. ב80% מחלקה היא לבנה וב20% היא מהווה את העדשה שם היא שקופה וקמורה - הקרנית. משמשת כשמשה לחדירת של קרני אור לעין.
2. אמצעית - choroid, דמית. הרבה כלי דם ופיגמנטים.
3. פנימית retina - רשתית. מלאה בנוירונים ופיגמנטים. כשאר הפיגמנטים בצידה החיצוני - צמוד לשכבה הדמית. שכבה זו מורכבת משלוש שכבות.בכל שכבה ישנים נוירונים העושים סינפסה עם הנוירונים בשכבה הבאה. בשכבה הפנימית ביותר צרור האקסונים מתקבץ והופך להיות עצב II - optic nerve עצב הראיה שהולך ישירות למוח.

בשכבה הדמית בחלקה הקרוב לעדשה ישנן שתי בליטות היוצרות את הciliary body גוף ריסני ובתוכו שריר בעל אותו שם שנאחז בשכבה הדמית. שריר זה יוצר טבעת סביב לאישון. בין שתי הבליטות (בתוך הטבעת) נמצאת העדשה lens. העדשה מעוגנת ע"י רצועות העוברות באלכסון לciliary body ולchoroid. אלו נקראים suspensory ligaments. מהחלק הקדמי של הciliary בולטות 2 בליטות קשתיות (טוב, טבעת) בשם iris- קשתית. בתוכה שני שרירים: קונצנטרי (היקפי) ורדיאלי (רדיוס). בתוכה הפיגמנטים שנותנים לעין את צבעה. שרירים אלו מסודרים סביב חור - האישון. pupil. חור זה ניתן להרחבה וצמצום כתלות בכמות האור.
החלל בין העדשה והקרנית נחלק לשתי לשכות - קדמית ואחורית. (anterior, posterior chambers) המופרדות ע"י הקשתית. לשכות אלו מלאות בנוזל מימי משם aqueos humor המופרש לשם ע"י צינורות קטנים בciliary body. הנוזל מתנקז לוריד בפינה בין הקשתית לקרנית לתוך הcanal of schlemm. כאשר יש פהרעה בניקוז יכול להיווצר לחץ תוך עיני extra ocular pressure העלול לגרום לglaucoma. בנוסף, הקשית עלולה ליפול ולהידבק לעדשה. תפקיד הנוזל: לשמור על הלחץ התוך עיני ולשמש כגורם אופטי. החלל הגדול יותר, בין העדשה לרשתית מלא בנוזל זגוגי בשם vitreous humor. הנוזל צמיגי ומזכיר חלבון של ביצה. גם הוא שומר על הלחץ התוך עיני ומונע התמוטטות דפנות גלגל העין. משמש גם במרכיב אופטי. דואג להדק את השכבה הדמית לרשתית.

בתוך הרשתית, בתת השכבה הקיצונית, ישנם נוירונים רגישים לאור (פוטורצפטורים) משני סוגים. rods (מקלות) וcons (חרוטים) החרוטים נקראים מדוכים. קרני האור חודרים לגלגל העין דרך הקרנית השקופה. הפ נשברים עליה ואז מגיעים אל העדשה ונשברים גם שם. הם מתמקדים ברשתית מקום מזוים. הפוטורצפטורים קולטים אותם ונוצר דחף העובר לשכבות הבאות עד שהוא מגיע לאקסונים היוצרים את עצב הראיה ומשם לאזור הcalacarin sulcus במוח. במציאות, הקרנית מעט מוסטת מציר גלגל העין. ציר הראיה חוצה את הקרנית ובמקום אליו הוא מגיע ברשתית מתקבלת התמונה החדה ביותר. אזור זה נקרא הכתם הצהוב (macula lutea) ובמרכזה נמצאת גומה בשם fovea centralis. קוטר הכתם כ2 מ"מ. בגומה יש ריכוז גבוה של חרוטים האחראיים על ראיה חדה ואבחנה בין צבעים. במקום זה אין כלל מקלות. המקלות אחראיים על ראיה באור עמום ועוזרים להבחין בין צלליות וצורות. הם מפוזרים בכל הרשתית (שם ישנם גם חרוטים אך פחות).
קרני אור שנשברו מגיעות גםלאזורים אחרים ברשתית, אך שם לא רואים ברור כמו בשולי התמונה שאנו רואים, שם התמונה מטושטשת. ישנו אזור ברשתית שם לעולם לא תתקבל תמונה שנקרא blind spot או optic disk מכיוון ששם אין רצפטורים. שם יוצא עצב הראייה ויש שם אקסונים בלבד.





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