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Anatomy and Physiology lecture notes

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McMaster University
Health Sciences

There is the medial rectus and lateral rectus that are to adduct and abduct the eye respectively. The medial rectus pulls the eye nasally or abduct the eye. When looking upward, need two muscles, the third cranial nerve innervate the superior rectus muscle. The inferior oblique helps to correct the pulling of eyeball. When the two muscles work together, it gives a straight upward view of world. When accommodate, two things are happening. 1. Focusing eye convergent on the object, the contraction of cilary muscle allows the lens to round up increasing its magnifying power. So u are able to see that object. The lens cells that make up the lens, no nuclei, no mitochondria. It’s a big bag of protein. That makes it crystal clear, so u can see through it. Then lens doesn’t last u for 40 years. It became stiff, it also vulnerable to uv light. Pupil is to adjust the size of iris. Iris is a piece of tissue with two muscles in it. The very back of iris has a double layer of pigmented cells block all of the light. The eye color difference is due to the different deposition of melanin in the body in the stroma of iris, has nothing to do with the back of iris. We has the sphincter which closes the opening of the iris to make a small pupil and contraction of the pupilary sphincter and controlled by the parasympathetic nerve with third cranial nerve. When light is bright, it causes the contrain of the pupil sphincter and shuts the pupil. Pupilary dilator pull the iris open and its under control of sympathetic nervous system. Patient a, the left eye has a small pupil. It means the sympathetic is not operating the dilator. It suggests the damage to the sympathetic nervous
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