Anp 1 with a detailed breakdown of the human eye, Cheat Sheet of Biology

Download Anp 1 with a detailed breakdown of the human eye and more Cheat Sheet Biology in PDF only on Docsity! 1 | P a g e Lab 11 Special Sense - Vision (Image by StarGladeVintage) https://pixabay.com/users/stargladevintage-17411787/ The original text of the skeletal system chapter was created by Daniel McNabney and Deloris Hesse Part of the GALILEO, University System of Georgia GALILEO Open Learning Materials Biological Sciences Open Textbooks Laboratory exercises are Part of Skyline College Faculty Laboratory Manual (Summer 2019) Second Edition compiled by Professor Yancy Aquino Licensed under CC BY-NC-SA 4.0 Edited by Drs Andrew Nguyen and Areti Tsimounis 2 | P a g e Special Senses – Vision Created by Nurgul Kaya Introduction Of the five special senses, vision is the sense that humans rely on most to interact with our external environment. In this lesson you will learn the basic anatomy of eye, along with some accessory structures. By the end this lesson, students will be able to: 1. Identify external and accessory structures of the eye on a model, diagram, or dissected specimen. 2. Identify the structures and functions of muscles associated with movement of the eye. 3. Identify interior structures of the eye on a model, diagram, or dissected specimen. 4. Trace the pathway of light as it moves through the eyeball. Background Information Sensation vs. Perception The sensory portion of our nervous system allows us to interact with the external and internal environment. Stimuli from varying sources, and of different types, are received and translated into the electrochemical signals of the nervous system. This occurs when a stimulus changes the membrane potential of a sensory neuron which causes the sensory receptor to produce an action potential that is eventually relayed to a specific part of the cerebral cortex. This allows for detecting or sensing a stimulus. The conscious interpretation of the stimulus, i.e., perception, requires higher cognitive functions involving additional areas of the CNS. Perception is dependent on sensation, but not all sensations are perceived. For example, when one looks at and visually senses an object, one detects its presence; understanding what the object is, is part of perception. For the purposes of this lab, we will focus on the sensation (not perception) associated with the eye (vision). We will then focus on the sensations associated with the ear (hearing and equilibrium). Vision Anatomy Vision is the special sense of sight that is based on the transduction of light stimuli received through the eye. The primary structure associated with vision is the eyeball but there are also several accessory structures that are critical for our ability to see the world around us. Accessory Structures of the Eye Several accessory structures function to protect the eyeball and otherwise support its function (Figure 11.1). Each eyeball is located within an orbit in the skull. The bony orbit surrounds the eyeball, protecting it and serving as an anchor for soft tissues that support the eyeball. Eyelids (palpebrae), with lashes at their leading edges, help to protect the eye from abrasions by blocking particles that may land on the surface of the eye. The production of tears by the lacrimal gland washes the surface of the eyeball to prevent the accumulation of foreign material and nourish the cells of the cornea. The lacrimal gland, found in the superolateral portion of the orbit, releases fluid through lacrimal ducts onto the surface of the eye where the fluid eventually flows through the nasolacrimal duct, into the back of the 5 | P a g e Figure 11.3 The Eyeball. The Retina The retina is composed of several cellular layers and contains specialized neuronal cells for the initial processing of visual stimuli (Figure 11.4). There are two types of photoreceptors: rods and cones. These photoreceptors contain different light-sensitive molecules called photopigments. There are 3 different types of cones depending on the type of photopigment they contain. The photopigments of cones are called opsins. There are 3 different opsins, each sensitive to a particular wavelength of light within the human visible spectrum. These wavelengths correspond to the primary colors red, green, and blue. Thus, cones are responsible for human color vision. Rods, on the other hand, contain 1 type of photopigment and are responsible for vision under dim-light conditions, where different colors cannot be distinguished. Note the morphological differences between rods and cones as shown in Figure 11.4. Photoreceptors are stimulated upon exposure to light which affects their release of signaling molecules and initiates an electrical signal (a change in membrane potential in neurons of the retina). This electrical signal is carried out of the eye along axons that form the optic nerve. These axons lie on the innermost layer of the retina and exit it at the optic disc (Figure 11.3). Because these axons pass through the retina, there are no photoreceptors at the optic disc. This creates a “blind spot” in the retina, and a corresponding blind spot in our visual field. At the center of the posterior portion of the retina is a small area known as the fovea centralis (Figure 11.3). At the fovea, the supporting cells and blood vessels are pushed away and light can directly hit photoreceptors. This area looks like a pit and hence its name (fovea means “pit”). Visual acuity, or the sharpness of vision, is greatest at the fovea. As one moves in any direction from this central point of the retina, visual acuity drops significantly. The difference in visual acuity between the fovea and peripheral retina is easily illustrated by looking at a word in the middle of this paragraph. The visual stimulus in the middle of the field of view falls on the fovea and is in the sharpest focus allowing you to clearly read that word. Without moving your eyes off that word, notice that words at the beginning or 6 | P a g e end of the paragraph are not in focus. The images in the peripheral vision are focused on the peripheral retina, and have vague, blurry edges and are not clearly focused. As a result, a large part of vision involves moving the eyes and head so that visual stimuli are centered on the fovea which leads to greater visual acuity. Figure 11.4 Photoreceptors (a) All photoreceptors have inner segments containing the nucleus and other important organelles and outer segments with membrane arrays containing the photosensitive opsin molecules. Rod outer segments are long columnar shapes with stacks of membrane-bound discs that contain rhodopsin. Cone outer segments are short, tapered shapes with folds of membrane in place of the discs in the rods. (b) Tissue of the retina shows a dense layer of nuclei of the rods and cones. LM × 800. (Micrograph provided by the Regents of University of Michigan Medical School © 2012) 7 | P a g e Pathway of the Light Photons of light enter the eye through the cornea and refraction occurs as the rays that pass through anterior chamber, aqueous humor, and pupil. The iris surrounding the pupil has the ability to expand and contract, to regulate the amount of the light travelling through the pupil. Light then passes through the lens which further bends light rays to focus them onto the photoreceptors of the retina. Common Eye Conditions: Emmetropia Normal vision Hyperopia Farsightedness Myopia Nearsightedness Astigmatism Condition where light passing through cornea and lens is not refracted properly. Often due to an abnormality in the curvature of the cornea. Color blindness Inability to detect certain colors due to defective cones. Glaucoma Increase in intraocular pressure due to the blockage of the canal of Schlemm. If the optic nerve is damaged, it can lead to blindness. Cataract The lens is cloudy or progressively opaque. Source Material Except where it is noted, all images and text found in this section are a derivative of "Anatomy and Physiology" by OpenStax CNX used under CC BY 4.0. Aug 2, 2019. Download the original text for free at http://cnx.org/contents/14fb4ad7-39a14eee-ab6e-3ef2482e3e22@16.1. 10 | P a g e Use similar models as shown below. When possible, open up the model to study the internal structures. 11 | P a g e Exercise 3: Label the structures of the eye IDENTIFY INTERNAL REGIONS AND LAYERS OF THE EYE: FIBROUS TUNIC, VASCULAR TUNIC, NEURAL TUNIC, IRIS, LENS, CORNEA, SCLERA, OPTIC NERVE, VITREOUS HUMOR, AQUEOUS HUMOR, CILIARY BoDy, SUSPENSORY LIGAMENTS. 1 6 12|Page  15 | P a g e 1. ______________________ 2. ______________________ 3. ______________________ 4. ______________________ 16 | P a g e Exercise 4: Cow or Sheep Eye Dissection The cow/sheep eyes are functionally and structurally similar to the human eye. During this activity, you will dissect a cow/sheep eye, identify several structures of a cow/sheep eye and learn their functions. Associated SLOs Identify and describe external and internal eye structures on a dissected eye. Required Materials (Provided) • Preserved cow’s or sheep’s eye • Single-edged razor blade or scalpel • Dissection scissors • Dissection tray • Forceps • Gloves • Paper towel • Plastic trash bag Procedure: 1. You will complete this activity in dissection lab as group of 2. Please read the following steps carefully before you begin and while doing dissection. 2. Put on your personal protective gloves and get a cow or sheep eye from your instructor. Place the preserved cow or sheep eye on a dissecting tray. 3. Examine the external features of the eye. - Note the large amount of fatty tissue and muscles surrounding the eye. 17 | P a g e 4. Cut away all the thick fat and the muscle surrounding the eyeball. Avoid cutting the tough optic nerve on the back of the eye. 5. Using a scissor or scalpel, carefully cut through the sclera around the middle of the eye. - While cutting through the sclera, a clear watery fluid will seep out which is aqueous humor. - Note the tough consistency of the sclera and relate that to this layer’s function. Fat Muscle Cornea Optic nerve Fat Cornea Optic nerve 20 | P a g e 11. When you are done with the eye dissection, dispose of the eyeball in the biohazard bin and wash the dissection tray, scalpels and scissors. Place the dissecting tools back into the tray. Retina Optic disc Optic nerve Optic disc Tapetum lucidum Choroid Retina 21 | P a g e Eye Dissection Lab Observation Sheet Describe your observations of the parts of the sheep’s or cow’s eye as you worked through the dissection and connect structure to function for each of the given structures: Sclera: Cornea: Muscles and Fat: Pupil: Iris: Lens: Optic Nerve: Aqueous Humor Vitreous Humor: Retina: Tapetum Lucidum: Notes: 22 | P a g e Check Your Understanding 1. Name the major anatomical difference between the sheep eye and human eye that you observed. ________________________________________________________________________________ 2. Why does the optic nerve cause a blind spot? _______________________________________________________________________________. 3. If you enter a dark room after being in a bright room, would your pupil constrict (get smaller) or would it dilate (get larger)? Why? _______________________________________________________________________________. 4.What is the function of the muscles surrounding the eye? How do they affect vision? _______________________________________________________________________________. 5. Light first enters the eye through the lens. A) True B) False 6. What is the white layer that surrounds eye called? A) Cornea B) Sclera C) Retina D) Ciliary body