BSC2086 A&P II Final Exam Study Guide – Lesson 2 1 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 tissues of the eye • Regulates the amount of light entering eye • Secretes & reabsorbs aqueous humor that circulates within 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 retinaBSC2086 A&P II Final Exam Study Guide – Lesson 2 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 spotBSC2086 A&P II Final Exam Study Guide – Lesson 2 3 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 • Lens 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 Image reversal Visual Acuity: Clarity of vision • Normal = 20/20 Astigmatism: Condition where light passing through cornea and lens is not refracted properly • Visual image is distortedBSC2086 A&P II Final Exam Study Guide – Lesson 2 4 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 segmentBSC2086 A&P II Final Exam Study Guide – Lesson 2 5 • 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 o Optic Radiation: Bundle of projection fibers linking lateral geniculate with visual cortex From combined field of vision; arrive at visual cortex of opposite occipital lobe • Left half of field of vision right occipital lobe • Right half of field of vision left occipital lobe • Field of VisionBSC2086 A&P II Final Exam Study Guide – Lesson 2 6 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 membrane o Encloses & protects three (3) auditory ossicles: 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 window • Internal Ear o Contains fluid called endolymph o Bony Labyrinth: Surrounds and
View Full Document
Unlocking...