Bi 121 Lab Week 9: THE SPECIAL SENSES The special senses include smell, taste, vision, hearing, and balance. In this laboratory exercise, we will look at many of the structures that provide for these senses. OLFACTION Obj 1 Identify these structures associated with olfaction. Models: skull, brain, skull with olfactory nerves [M p569-570 Fig 15.21] olfactory bulb, olfactory nerve (=cranial nerve I), olfactory foramina, olfactory epithelium Obj 2 Identify these structures associated with taste. models: torsos, sagittally sectioned heads slides: taste bud [M p571-572, Fig 15.23] tongue papillae, taste buds (slide only) THE EYES AND VISION Obj 3 Identify the following parts of the eye and categorize them as extrinsic and intrinsic structures. models: eyes [M:p548-556 Fig15.1-8, 19] (Structures marked with an * are those you will not be expected to find on the sheep eye in Obj 4). Please be aware that not all structures are visible on all models.
Extrinsic structures extrinsic eye muscles, lacrimal gland*, lacrimal sac*, conjunctiva*, optic nerve(=cranial nerve II), optic chiasma* Intrinsic structures layers of the eyeball: 1.fibrous layer: sclera, cornea 2.vascular layer: choroid, ciliary body, iris, 3.sensory layer: retina, optic disk, macula lutea*, fovea centralis*, rods* and cones* other structures: lens, suspensory ligaments, anterior cavity(filled with aqueous humor), posterior cavity(filled with vitreous body/humor), pupil, canal of Schlemm (= scleral venous sinus)* Draw and label the structures of the eyeball. Obj 4 Identify the following parts of the eye and categorize them as extrinsic and intrinsic structures. models: eyes specimens: preserved sheep eyeballs [M:p548-556 Fig15.1-8, 19] After identifying the following structures on the models, identify them on the eyeball specimen: 1. Clear off the fat on the posterior surface to expose the extrinsic eye muscles and optic nerve. 2. Poke a hole into the eyeball ¼ inch posterior to the edge of the cornea and then cut around the eyeball so that you can lift off the anterior part with the lens, iris, etc.
Extrinsic structures extrinsic eye muscles, optic nerve(=cranial nerve II) Intrinsic structures layers of the eyeball: 1.fibrous layer: sclera, cornea 2.vascular layer: choroid, ciliary body, iris, 3.sensory layer: retina, optic disk, other structures: lens, suspensory ligaments, anterior cavity(filled with aqueous humor), posterior cavity(filled with vitreous body/humor), pupil Draw and label the structures of the sheep eyeball. Obj 5 Test your vision for colorblindness using the provided charts. [M:p562-563] Obj 6 Demonstrate the blind spot in your vision. Explain what causes the blind spot. blind spot card [M:p553, Fig:15.4, 6, 7]
Cover one eye. Hold the blind spot card so the 'cross' is lateral and the 'dot' is medial. Fix your vision on the dot and then move the card slowly toward your open eye. The cross should disappear from view. Explain why the cross disappears. Obj 7 Identify the chart used to test for astigmatism. Test your vision for astigmatism. astigmatism 'chart' [M:p559] Remove your glasses/contacts. Hold the chart where you can see the lines fairly clearly (It is best to use a chart larger than the example given above. Assess whether any set of lines appears darker/clearer than the others; note their position. Rotate the card and reassess. Explain what structural alteration in the eyeball results in astigmatism. Why do the lines appear darker/clearer?
THE EARS, HEARING AND BALANCE The ear is used for the senses of hearing and balance (dynamic and static equilibrium). It can be divided into three regions: External ear Middle ear Inner ear Obj 8 Identify the following parts of the ear and categorize them as parts of the external ear, middle ear and inner ear. models: ears, cochlea specimen: ossicles [M:p574-581 Fig15.25-28] External ear auricle (= pinna), external auditory meatus (=external ear canal) Middle ear eardrum=tympanic membrane, cavity of middle ear, ear ossicles(malleus=hammer, incus=anvil, stapes=stirrup), oval window Inner ear cochlea(round window, tectorial membrane, basilar membrane, hair cells, cochlear duct), vestibule, semicircular canals, vestibulocochlear nerve=cranial nerve VIII Other structures Eustachian tube = auditory tube = pharyngotympanic tube Obj 9 Explain which special sense occurs in each structure of the ear. Hearing: cochlea Dynamic equilibrium: semicircular canals Static equilibrium: vestibule