For this lab you will use parts of Exercise #18 in your Wise lab manual. Please be sure to read those sections before coming to lab

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1 Bio 322 Human Anatomy Objectives for the laboratory exercise The Eye and Ear Required reading before beginning this lab: Saladin, KS: Human Anatomy 5 th ed (2017) Chapter 17 For this lab you will use parts of Exercise #18 in your Wise lab manual. Please be sure to read those sections before coming to lab Introduction: Humans have five special senses: vision, hearing, equilibrium, smell, and taste. All of these are mediated by specialized sensory organs located in the head, send their information back to the brain through cranial nerves, and distribute that information to specific regions of the cerebral cortex for processing and response. The eye is probably the most complex of all of our sensory organs. It not only includes receptors which are stimulated when light strikes them and send electrical signals to the brain, but it is also able to modify how much these receptors are stimulated by allowing more or less light to enter the eye and to focus it specifically on the receptor cells. Unlike any other sensory organ in the body, the eye is also able to begin processing information from the receptor cells before it is sent to the central nervous system. The ear is also highly complex. It receives sound waves and transforms them into physical movement of bones and fluid which stimulate specific receptors in the inner ear for hearing. The inner ear also houses structures for detecting both static equilibrium (position of the head when you are not moving) and dynamic equilibrium (acceleration and movement of the head). We will examine the eye and the ear in this lab. We will not examine the structures related to taste or smell. Objectives: 1) Obtain a human skull from the back or side of the room a) Identify the orbits, noting their position medial to the nasal cavity and inferior to the anterior cranial fossa. Identify both the optic canal and the superior orbital fissure leading from each orbit back into the cranial cavity. You should know which cranial nerves pass through each of those.

2 b) Identify the external auditory (acoustic) meatus on each side of the skull and note that it leads into the auditory canal of the temporal bone. Identify the petrous ridge of the temporal bone on each side, separating the middle and posterior fossae of the cranial cavity. The auditory canal, middle ear, and inner ear are all located within this ridge. Identify the internal auditory (acoustic) meatus on the posterior aspect of the petrous ridge. You should know which cranial nerves pass through this (only one of which is actually involved with hearing or equilibrium). 2) Begin Exercise #18 in your Wise lab manual with External Features of the Eye on page 247. You can skip the sections before that on touch receptors, taste buds, and olfaction. a) Examine one of your lab partner s eyes. You should be able to identify the structures shown on Figure 18.4 of your Wise Lab manual, and you should know the locations of the structures shown in Figure b) On a model showing the eye and the extraocular muscles, you should be able to identify all six of these muscles. You should know which cranial nerves innervate each of them, what movement each creates, and what would happen if each of them were damaged, c) On Figure 18.7 of your Wise lab manual and on a model, you should be able to identify the structures described in Interior of the Eye. You should be able to describe the pathway which light follows from the time it passes through the cornea to the time it hits the photoreceptor layer of the retina. From the reading in your Saladin text, you should be able to describe to your lab partners how the iris changes the size of the pupil to regulate how much light enters your eye. From the reading in your Saladin text, you should be able to describe to your lab partners how the ciliary body, suspensory ligaments, and lens work together to change the focus of light on the macula lutea and fovea centralis of your retina. You should know the layers of the retina as shown on Figure 18.9 of your Wise lab manual, but we will not examine a slide of this. You should understand the pathways which nerve signals follow from the retina to the brain as shown in Figure 18.8 of your Wise Lab Manual, including which specific signals pass through different parts of the optic chiasm. d) We will not be dissecting the eye from a cow or sheep.

3 3) Continue Exercise #18 with Anatomy of the Ear on page 254. a) On a model of the ear and on Figure of your Wise lab manual you should be able to identify all of the structures listed under Outer Ear, Middle Ear, and Inner Ear. This includes the structures of the cochlea (Figure 18.16), the vestibule, and the semicircular ducts (both Figure 18.14). b) We have just one model of the chambers of the cochlea. On this you should be able to identify the scala vestibuli, cochlear duct, scala tympani, basilar membrane, and spiral organ ( of Corti ) as shown in Figure 18.16b of your Wise lab manual. c) You should understand and be able to explain to your lab partners how otoliths, the otolithic membrane, and hair cells in the maculae of the vestibule regulate static equilibrium when the head changes position (Figure 18.19). You should understand and be able to explain to your lab partners how the endolymph, cupula, and hair cells in the ampullae of the semicircular ducts regulate dynamic equilibrium when the head moves. Review: After you have completed this lab exercise, be sure you can answer the questions at the end of Exercise #18 which relate to the eye and the ear (9-29) in your Wise lab manual, but you should do this verbally with your lab partners rather than in written form. The purpose of doing this should not be to write down the correct answer, but rather to be sure that everyone in your lab group understands the information presented in the exercise and to identify any areas which you still do not understand. Remember: one of the best ways to learn new information and to be sure you understand it is to discuss it with another person. If you can t easily answer one of the questions, go back to your Saladin textbook and re-read the relevant section(s), It is also an excellent idea for members of a lab group to set up small quizzes for each other. Ask each other to identify structures on diagrams and models and microscope slides. Ask each other to explain the functions of those structures. Here are some additional questions and discussions which may help you understand the human eye and ear. Remember these are for discussion, not writing. That s the best way to be sure your brain can explain what you have learned.

4 In what order does light pass through the three layers of cells in the retina? Which neurons send their axons through the optic nerve toward the brain? Explain to your lab partners what would happen to your vision if your corneas were damaged and became opaque so they could no longer allow light through. Explain to your lab partners what would happen if your aqueous humor became cloudy and could no longer transmit light. Explain to your lab partners what would happen if your lens became cloudy and could not transmit light. Have your ever stepped directly from a dark room into bright sunlight, or from sunlight into a dark room? You had trouble seeing for a couple of seconds. Explain to your lab partners what is happening to your pupil during those few seconds. Explain to your lab partners how would it affect your vision if your lens became inflexible and could no longer change its shape? (you might want to look up presbyopia in your medical dictionary) Each of the extrinsic muscles receives its stimulus through one of the cranial nerves. List the proper nerve for each of the muscles above (hint: you may need to use an earlier chapter in your text) Explain to your lab partners which of these muscles contract when you look to the left with both eyes? (Caution: it may not be the same muscle for both eyes) Explain to your lab partners which of these muscles contract when you look to the right with both eyes? (see caution above) Explain to your lab partners which of these muscles contract when you look cross-eyed? (see caution above) Explain to your lab partners what effect would it have on your vision if each of the following were damaged: The right optic nerve The left optic nerve The right optic tract The left optic tract The optic chiasm

5 Explain to other members of your lab group how it would affect your hearing (if at all) if your pinna/auricle was removed? Explain to other members of your lab group how vibrations of air create vibrations of the tympanic membrane, ossicles, and oval window to reach the inner ear. external auditory canal were blocked tympanic membrane could not vibrate ossicles could not vibrate Explain to other members of your lab group the function of the auditory tube between the middle ear cavity and the pharynx Explain to other members of your lab group what fluid is caused to vibrate when the foot of the stapes at the oval window vibrates

INTRODUCTION: ****************************************************************************************************

INTRODUCTION: **************************************************************************************************** BIOLOGY 211: HUMAN ANATOMY & PHYSIOLOGY **************************************************************************************************** EYES AND VISION ****************************************************************************************************