Lecture 19 - Visual System PDF

The EYE Lec. 19 lad  Orbit (“Eye socket”) Composed of Bone  frontal,  maxillary,  Zygomatic Also a tremendous amount of fat protects the eyeball Eyebrow/ lashes/ Eyelid  Brow/Lashes=Protects eye from dust &foreign objects  Lid=Protects eye from fo...

The EYE Lec. 19 lad  Orbit (“Eye socket”) Composed of Bone  frontal,  maxillary,  Zygomatic Also a tremendous amount of fat protects the eyeball Eyebrow/ lashes/ Eyelid  Brow/Lashes=Protects eye from dust &foreign objects  Lid=Protects eye from foreign objects  Keeps eyeball moist  contains a small amount of cartilage  Conjunctiva Structure: thin mucous membrane Location: on the inner surface (back part) of the eyelid & white part (sclera) of the anterior surface of the eyeball/ does not cover cornea. Conjunctivitis “Pink Eye”  Lacrimal Gland Nasolacrimal Duct  Location:  Location : upper lateral corner of the orbit. passes from medial corner of the orbit &lateral nose  Secretes tears with path of to the nasal cavity. flow from upper lateral portion of eye to inferior medial part. That’s why-  when we cry, we often Controlled by : facial nerve. ( CN VII ) get a “runny nose”! Used with permission pinterist.com https://i.pinimg.com/736x/a5/31/8f/a5318f771e7d5938975e019f7ec5a736--medical-school-medicine.jpg  Extrinsic Muscles of the Eye  These muscles allow for superior, inferior, medial & lateral rotational movement of eyeball.  All under voluntary control : CN III, IV, VI. Three Major Layers of the Eye  1. OUTER a.) Sclera b.) Cornea Tough outermost layer of CT Called :  Transparent anterior portion white of eye that bulges—  covers iris, pupil & Continuous with Dura Extrinsic muscles attach here anterior chamber  Avascular: Oxygen diffuses Protects the sensitive inner structures from vessels in sclera & gives shape to eyeball 2. Middle or Vascular Layer 1. Choroid – contains blood vessels supplying interior of eyeball. 2. Ciliary Body – contains muscles which change shape of the lens. 3. Iris – colored / pigmented - contains SMOOTH muscle that regulates the size of the pupil to protect retina from strong light. 3. Innermost Layer: Retina - Composed of 10 layers 1. Pigmented layer – outer layer that is BLACK in color so it absorbs light rays. 2. Nine nervous layers : Three layers involved in the conduction of an image  1. rods ( dim light) & cones ( color)  2. bipolar cells  3. ganglionic cells. Visual Response Light is converted to an electrical impulse in the retina and then is transmitted to occipital lobe of brain. Photoreceptor Cells ( not test question) RODS CONES  More numerous  Operate best in bright  More sensitive to light light  Permit vision in dim light  Enable high acuity for (gray/ fuzzy) color vision  Provide neither sharp  Sensitive to red, green images or color vision and blue light Optic Nerve  Extends from posterior side of the eye  Transmits impulse to the visual pathway  Composed of axons from ganglion cells Fovea Centralis & Optic Disc Fovea Centralis – area of most acute vision / sharpest vision. Optic Disc – called “Blind Spot”  This is where optic nerve enters with blood vessels.  Thereare no cells of the retina at the blind Visual Pathway: Retina  Optic Nerve  Optic Chiasm  Thalamus Optic Radiations  Occipital Cortex ( Visual Cortex)  5. Lens of the Eye Changes shape to help bend light rays & bring them into sharp focus on the retina.  This adaptability is “Accommodation”  Crystal clear/ transparent. -contains elastic CT.  Composed of protein. - If protein amount increases; lens becomes cloudy. Normal Cloudy = CATARACT 6. Cavities & Chambers of the Eye 1. Anterior Cavity 2. Posterior Cavity – front 1/3rd anterior to lens -Posterior to lens ( 2/3rds ) has an anterior & posterior chamber. Contains : Contains : Vitreous Chamber/ Aqueous Humor. Vitreous Humor  a clear liquid produced by  Clear gelatinous (jelly “Ciliary body “ like) substance  continually produced. produced during embryonic development. note: If not drained off  Function: maintain through channels there is an increase in pressure causing pressure & shape of blindness: Glaucoma eyeball.  Cavities of the Eye http://upload.wikimedia.org/wikipedia/commons/d/d0/Three_Main_Layers_of_the_Eye.png  Blood Supply  Vessels in choroid layer come in laterally.  Vessels enter with optic nerve coming off branches of the internal carotid artery & look like “spokes of a wheel” when we look at the back of the eye.  Function of the Eye  Refraction and transmission of light waves to photoreceptor cells of retina  Theamount of light and the focus of light must be regulated  The AUTONOMIC NERVOUS SYSTEM (CN III) controls this with NO CONSIOUS EFFORT HOW?? Two ways: 1.) Accommodation Changing shape of lens through contraction / relaxation of the suspensory ligament Focus FAR = lens becomes THIN Focus NEAR = lens becomes Thick  2. Iris alters the size of pupil aperture a. Dilation  Muscle that runs radially like spokes of a wheel b. Constriction  Muscle runs in circular direction to Clinical Conditions of Retina END SLIDE NO TEST QUESTIONS avoid THIS fad