BSC2086 A P II Final Exam Study Guide Lesson 2 Lesson 2 Special Senses Special Senses There are five 5 special senses o Olfaction Smell o Gustation Taste o Vision Sight o Equilibrium Balance o Hearing The Eye Three 3 layers of the eye o Fibrous Layer outer Cornea Transparent anterior region Sclera White of the eye Cornal Limbus Border between cornea and sclera o Vascular Layer Uvea intermediate Functions Provides route for blood vessels lymphatics that supply Regulates the amount of light entering eye Secretes reabsorbs aqueous humor that circulates within tissues of the eye chambers of eye Controls shape of lens essential to focusing Components Iris Contains pupillary muscles o Sympathetic AND parasympathetic innervation change the diameter of the pupil o Sympathetic stimulates pupillary dilator pupils get bigger dilate o Parasympathetic stimulates pupillary constrictor pupils get smaller constrict Ciliary Body Contains ciliary processes ciliary muscle that attaches to suspensory ligaments of lens o Control lens position and shape Choroid Delivers oxygen nutrients to retina 1 BSC2086 A P II Final Exam Study Guide Lesson 2 o Inner Layer deep Pigmented Part outer layer Absorbs light that passes through neural part Prevents rebounding of light Neural Part Retina inner layer Contains visual receptors and associated neurons Photoreceptors o Rods Don t discriminate light colors highly sensitive to light Used in low light nighttime o Cones Provide color vision Densely clustered in fovea at center of macula Horizontal amacrine cells alter sensitivity of the retina Optic Disc Circular region just medial to fovea where the optic nerve originates o Blind spot 2 BSC2086 A P II Final Exam Study Guide Lesson 2 o Scotomas Abnormal blind spot located in areas other than optic disc May be caused by Compression of optic disc Damage to photoreceptors Damage to visual pathway Chambers of the eye o Vitreous Chamber large posterior cavity Vitreous Humor Body Gelatinous mass that helps stabilize the eye shape supports the retina Diabetic Retinopathy Caused by blockage of normal blood vessels growth of abnormal blood vessels in retina blood leakage into cavity Acuity decreases as photoreceptors die Develops in many with diabetes mellitus o Anterior Cavity smaller Divided into Anterior Chamber Extends from cornea to iris Posterior Chamber Between iris ciliary body and lens iris lens Aqueous Humor Fluid circulates within the eye Diffuses through walls of anterior chamber into scleral venous sinus canal of Schlemm then re enters blood circulation Intraocular Pressure Fluid pressure in aqueous humor Helps retain eye shape Glaucoma Decreased aqueous humor drainage increases pressure pressing on optic nerve o Peripheral vision affected first o Lens Fibers Cells in interior of lens No nuclei or organelles Filled with crystallins provide clarity focusing power to lens o Cataract Lens loses its transparency Senile Caract Lens loses transparency as a natural consequence of aging most common type o Light Refraction Bending of light caused by cornea and lens Shape of lens changes to focus image on retina Visual Acuity Clarity of vision Normal 20 20 Image reversal Astigmatism Condition where light passing through cornea and lens is not refracted properly Visual image is distorted Lens 3 BSC2086 A P II Final Exam Study Guide Lesson 2 Visual Physiology Anatomy of Rods Cones o Outer Segment with membranous discs Visual Photo Pigments Where light energy absorption occurs Synthesized from vitamin A Retinitis Pigmentosa Caused by mutation in visual pigment causes cell death blindness o Most common inherited visual problem o Inner Segment Narrow stalk connects outer segment to inner segment 4 BSC2086 A P II Final Exam Study Guide Lesson 2 Color Vision Integration of information from red green and blue cones o Colorblindness Inability to detect certain colors Cones might be missing OR present but unable to produce visual pigments to absorb light at that frequency o Nyctalopia Night blindness Results from vitamin A deficiency Visual Pathways o Begin at photoreceptors end at visual cortex of cerebral hemispheres o Message crosses two 2 synapses before it heads toward brain Photoreceptor bipolar cell Bipolar cell ganglion cell Central Processing of Visual Information o Axons from ganglion cells converge on optic disc o Penetrate wall of eye o Proceed toward diencephalon as optic nerve cranial nerve II o Two optic nerves one for each eye reach diencephalon at optic chiasm o Half the fibers travel to the contralateral geniculate nucleus half to ipsilateral side Visual Data visual cortex occipital lobe Field of Vision o Optic Radiation Bundle of projection fibers linking lateral geniculate with From combined field of vision arrive at visual cortex of opposite Left half of field of vision right occipital lobe Right half of field of vision left occipital lobe 5 BSC2086 A P II Final Exam Study Guide Lesson 2 o Depth Perception Obtained by comparing relative positions of objects between left eye and right eye images Circadian Rhythm Tied to day night cycle affects other metabolic processes o Some fibers from lateral geniculate nucleus goes to hypothalamus The Ear Middle Ear Tympanic Cavity o Communicates with nasopharynx via auditory tube Permits equalization of pressures on either side of tympanic o Encloses protects three 3 auditory ossicles membrane Malleus hammer Incus anvil Stapes stirrup o Vibration of tympanic membrane converts arriving sound waves into mechanical movements Auditory ossicles conduct vibrations to inner ear Tympanum ossicles protected from loud noise by Tensor Tympani Muscle Stiffens tympanic membrane Stapedius Muscle Reduces movement of stapes at oval Internal Ear window o Contains fluid called endolymph o Bony Labyrinth Surrounds and protects membranous labyrinth 6 BSC2086 A P II Final Exam Study Guide Lesson 2 o Subdivided into Vestibule Encloses saccule utricle Receptors provide sensations of gravity linear acceleration Semicircular Canals Contain semicircular ducts Receptors stimulated by rotation of head Cochlea Contains cochlear duct elongated portion of membranous labyrinth Cochlea has two 2 windows o Round Window Thin membranous partition that separates perilymph from air spaces of middle ear o Oval Window Connects to baste of stapes Cochlear duct receptors provide sense of hearing o Auditory Ossicles Convert pressure fluctuation in air into much greater pressure fluctuations in perilymph of cochlea
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