Special Senses and Eyeball Dissection

Module 09 Lab Worksheet: Special Senses and Eyeball Dissection INTRODUCTION This week’s lab will focus on the special senses of vision, hearing, balance, smell and taste. OBJECTIVES Objectives for this week’s lab include: 1) Identify the anatomical components of the special senses, 2) Identify the anatomical structures of the eye through dissection, and 3) Analyze the function of the special senses. OVERVIEW The special senses consist of vision, taste, smell, hearing and equilibrium. Compared to the general senses (touch sensation, pain, temperature, pressure) that are widespread throughout the body, the special senses are localized to the head region of the body and contain highly complex nerve receptors. Nearly 70% of our sensory receptors are found in the eye and just about half of our cerebral cortex is dedicate to visual processing. Technically, there are three layers to the eye: Fibrous layer (outer layer which includes the sclera), vascular layer (middle layer that includes the choroid and iris) and the inner layer (which includes the retina). The major components of the eye include the: Cornea, iris, pupil, vitreous humor and the retina. The retina contains two types of photoreceptor cells: Rods, which are responsible for dimly light/black & white vision and cones, which are responsible for color vision. In a very simplistic sense, incoming light is refracted (bent) by the cornea, lens and vitreous humor to be focused on a specific spot of the retina. The photoreceptor cells of the retina will convert light energy into an electrical impulse that is transmitted to the occipital lobe via the optic nerve. The eye can have imbalances with the refraction of the light on the retina, producing vision that is labeled ‘near-sightedness’ or ‘far-sightedness’ and leading to the need for corrective eyewear. Both the sense of taste and smell are classified as a chemical sense because they contain chemoreceptors, which are receptors that bind molecules to initiate their sense perception. For the sense of taste, mastication of food releases molecules that bind to sensory nerves found within our tastes buds. A human has roughly 10,000 taste buds that are housed within these tiny projections called papillae. Once the taste cell (gustatory epithelial cell) binds a molecule, it initiates an action potential that is sent to various locations of the cerebrum creating the sense of taste. The sense of smell utilizes the same method. Odor molecules, known as odorants, enter the nose and bind to the olfactory cells, which are connected to the olfactory bulb.Upon binding an odorant, the olfactory cells will generate an action potential that is projected to various regions in the cerebrum and stimulates our sense of smell. The sense of hearing and equilibrium is housed within the inner ear. The cochlea, vestibule, and semicircular canals are the major structures involved. The cochlea is a small, spiral shaped boney chamber that houses the spiral organ, which ultimately allows for the sense of hearing. The spiral organ contains hair cells that move in accordance to air vibrations sensed by the tympanic membrane and generate an action potential that is sent to the temporal lobe for the sense of hearing. The vestibule contains the saccule and utricle while the semicircular canals contain the ampullas. These structures contain sensory hair cells that move in accordance to the movement of head creating the sense of acceleration, de-acceleration, head position and rotational movements of the head. MATERIALS 1. Models of the eye and ear 2. Tuning fork 3. Starbursts™ candy 4. Eyeball specimen 5. Dissection tray and kit PRE-LAB EVALUATION QUESTIONS The pre-lab evaluation questions must be answered prior to lab and demonstrated to your lab instructor. You must read through the assigned chapter readings, lab introduction, objectives, overview and procedure to answer these questions. Please cite your work for any reference source you utilize in answering these questions. 1. As light passes through the eye, describe the three major structures and their function that light passes through before reaching the retina. 2. Compare and contrast the function of rods and cones. What role does the fovea centralis have in vision? Describe the blind spot of the eye and how we adjust for it? 3. Describe how our ability to taste is connected to our sense of smell. 4. In your own words, briefly describe how the tympanic membrane, ear ossicles and the spiral organ work together to create the sense of hearing.  5. Compare and contrast the two types of hearing loss.  Part 01 Procedure: Anatomy of Eye and Ear 1. Utilizing the eye and ear models set up in lab and the terms listed below, identify and label the anatomical structures of the eye and ear: (choroid, cochlea, cochlear nerve, cornea, ear ossicles, eustachian tube, iris, lens, optic disc, optic nerve, pupil, retina, sclera, semicircular canals, tympanic membrane, vestibular nerve, vestibule, vitreous humor) A) B) C) D) E) F) G) H) I) J) K) L) M) N) O) P) Q) R) Part 02 Procedure: Hearing Test- Rinne and Weber  1. The Rinne and Webber hearing tests are used to differentiate from sensorineural and conductive hearing loss.  2. Perform the Rinne hearing test first which compares air and bone conduction hearing for both ears: 1. Gently strike a 512 Hz tuning fork on the heel of your hand and place the tuning fork on the patient’s left mastoid process. Record the time when you start the test. 2. Have the patient inform you when sound is no longer heard. Quickly record the time. 3. Immediately move the tuning fork from the mastoid to a position right outside of the external auditory meatus and start recording the time. 4. Have the patient inform you when the sound is no longer heard. 5. Record your results below: LEFT EAR Bone Conduction (mastoid) Hearing Time: _________________ Air Conduction Hearing Time: _________________ RIGHT EAR Bone Conduction (mastoid) Hearing Time: _________________ Air Conduction Hearing Time: _________________ Possible Results: 1. Normal Hearing: Patient will hear air conduction sound about twice as long as bone conduction 2. Conductive Hearing Loss: Patient will have bone conduction hearing longer or just as equal to air conduction hearing in the affected ear 3. Sensorineural Hearing Loss: Patient will still hear air conduction hearing longer than bone conduction hearing in the affected ear but dramatically less than found in normal hearing.  4. Perform the Weber hearing test which helps distinguish between conductive and sensorineural hearing loss: 1. Gently strike a 512 Hz tuning fork on the heel of your hand and place the tuning fork on the mid-sagittal suture on the top of the head. 2. Ask the patient if the sound is heard equally in both ears or if it is louder on one side. 3. Record your results below: Hearing the same in both hears Hearing louder in the right ear Hearing louder in the left ear Possible Results: 1. Normal Hearing: Patient will hear sound equally in both ears 2. Conductive Hearing Loss: Patient will hear sound louder in ear with conductive hearing loss. To demonstrate this, plug one of your ears (simulating conductive hearing loss) and repeat the test. 3. Sensorineural Hearing Loss: Patient will hear sound louder in ear without sensorineural hearing loss 4. Utilization of both tests will help differentiate between conductive and sensorineural hearing loss within the patient. Please be able to diagnose sensorineural and conductive hearing loss with results from these tests. Part 03 Procedure: Taste and Smell Test 1. The sense of taste is about 80% due to our sense of smell. This may not seem right but think about when you have been sick and congested in the nasal region. Your smell is obviously diminished and so is your taste; that’s why foods taste bland to someone who has nasal congestion. We are going to test this concept utilizingStarbursts™ candy. If you have any allergies, concerns or issues with consumingStarbursts™ candy, please refrain from completing this section. 2. Locate the three bags labeled 1, 2, and 3. Each bag contains a specific flavor of Starbursts™ candy; lemon, orange or strawberry. You will test your lab partner’s ability to taste with his/her nose open and closed. 3. Test your lab partner’s taste ability: With your lab partner’s EYES CLOSED, randomly chose one of the three flavors ofStarbursts™ candy, unwrap it and hand it to him/her. Do not inform him/her of the flavor. Have your lab partner chew theStarbursts™ candy and determine the flavor. Record the flavor they think they are eating and record the results in the chart below in the appropriate row and column. Once finished, complete the same procedure for the other twoStarbursts™ candy flavors. 4. Next, you will complete the same procedure as above but with your lab partner’s EYES CLOSED and NOSE PLUGGED. Record the results below: Flavor Type Flavor Guessed w/Eyes Closed Flavor Guessed w/Eyes Closed & Nose Plugged Flavor: Lemon Flavor: Orange Flavor: Strawberry Part 04 Procedure: Eyeball Specimen Dissection 1. Utilizing the “Rasmussen Dissection Guide – Eye Unit”, follow the instructions, protocol and diagrams under: Eyeball Specimen Dissection.  2. When completed with the dissection, dispose of the eyeball specimen in the appropriate location as instructed by your lab instructor along with clean your lab dissection materials and disinfect your lab workstation. Part 05 Procedure: Mini Case Studies 1. Utilizing the case studies handed out in the lab session, please determine and describe the type of hearing loss presented in each case: Case Study A: Case Study B: Case Study C:  POST-LAB EVALUATION QUESTIONS The post lab evaluation questions must be completed prior to your submission of the lab. Answers for these questions will be derived from the lab protocol, the weekly concepts associated with the lab and possibly research content from the book and/or online resources. Please cite your work for any reference source you utilize in answering these questions. 1. Describe two specific features that you found interesting with the eyeball dissection. What was beneficial for you with this dissection? 2. Compare and contrast the cause, treatments and complication of myopia and hyperopia. How does an astigmatism influence these conditions? What is the importance of the light being refracted on the retina? 3. Compare and contrast how glaucoma and cataracts disrupt vision. 4. Vertigo and tinnitus are both conditions of the inner ear. How do they differ from symptoms, causation (what is causing the condition) and treatments? 5. As we age, hearing loss progresses but not equally in all individuals. What are some factors that can cause or lead to an accelerated rate of hearing loss? Why is permanent hearing loss permanent? What treatments are available for individuals with hearing loss? Are there any pros and cons to them?