BSC 2086 1st Edition Lecture 3 Outline of Last Lecture I. Major Sensory PathwaysII. Somatic Motor PathwaysIII. OlfactionIV. Gustation Outline of Current Lecture I. Accessory Structures of the Eye II. Visual Physiology III. Structures of the Ear Current LectureI. Accessory Structures of the Eye a. Palpebrae i. Eyelidsii. Blinking causes lubrication of the eyeiii. Tarsal Glands: keep eyelids from sticking together by secreting lipid-rich fluidb. Superficial Epitheliumi. Lacrimal caruncle: thick secretions which are to blame for the gritty residues in eye after sleepingii. Conjunctiva1. Palpebral conjunctiva: covers inner surface of eyelids2. Ocular conjunctiva: covers outer surface of eye3. Pinkeye or conjunctivitis is caused by inflammation c. Lacrimal apparatusi. In charge of tearsii. Lacrimal gland = tear gland1. Secretions contain an antibacterial enzyme called lysozyme which kills bacteria in eye d. Tearsi. Lacrimal puncta lacrimal canaliculi lacrimal sac nasolacrimal duct inferior meatus of noseii. All collect in lacrimal lake at medial canthus e. Eyeball i. Large posterior cavity 1. Filled with thick jelly known as vitreous humora. Vitreous body is a gel that supports the retina and stabilizes the eye b. Diabetic retinopathyi. Due to blockage of normal vessels, abnormal blood vessel growth, and blood leakage into cavityii. Acuity decreases due to death of photoreceptors ii. Small anterior cavity1. Filled with a more liquid substance known as aqueous humor a. Goes through wall of anterior chamber into scleral venous sinus and then goes back into blood circulationb. Intraocular pressure: helps keep eye shapei. Glaucoma: aqueous humor drainage decreases, therefore increasing pressure which presses on optic nerve 1. Peripheral vision affected 2. Anterior chamber before iris, from cornea to iris3. Posterior chamber after iris, between iris, ciliary body and lensf. Three Layers of the Eye i. Outer fibrous layer1. Cornea: anterior transparent region2. Sclera: white part of the eye3. Corneal limbus: between cornea and scleraii. Vascular Layer (uvea)1. Iris: changes diameter of pupil through sympathetic and parasympathetic stimulation a. Uses papillary muscles2. Ciliary body: controls shape and position of lens a. Ciliary processes and ciliary muscle attach to suspensory ligaments of the lens3. Choroid: made of blood vessels that deliver oxygen and nutrients to the retina iii. Inner Layer1. Pigmented part (outer)a. Prevents rebounding of light by absorbing it as it passes through neural part 2. Neural part (inner) retina a. Has visual receptors and their associated neuronsb. Photoreceptors:i. Rods: provide black-and-white or gray-scale vision1. Used at nighttimeii. Cones: color vision1. Clustered in the fovea c. Bipolar cells i. Allow for synapse between photoreceptors and ganglion cells ii. Light goes through ganglion cells and bipolar cells before hitting photoreceptors d. Horizontal cellsi. Between photoreceptors and bipolar cells ii. Alter sensitivity to light of retinae. Amacrine cellsi. Between bipolar cells and ganglion cells ii. Alter sensitivity to light of retinaf. Optic disci. Origin of optic nerveii. Blind spot 1. Scotomas: abnormal blind spots a. Compression of optic disc, damage to visual pathway or photoreceptors g. Lens i. Focuses light entering eye1. Light refraction is the bending of light caused by the cornea and the lens 2. Astigmatism: light not refracted properly a. Distortion of visual image 3. Accommodation issues: a. Emmetropia: normal visionb. Myopia: nearsightednessc. Hyperopia: farsightednessi. Presbyopia: develops with age ii. Lens fibers1. Cells with no nuclei or organelles located in interior of lens2. Crystallins: provide clarity and focus poweriii. Cataract: lens loses transparency1. Senile cataract is the most common type caused by aging II. Visual Physiologya. Rods and Cones Anatomyi. Rods: Very sensitive, respond to almost any energy photonii. Cones: Ranges of sensitivity iii. Outer segment:1. Visual (photo) pigments: synthesized from vitamin Aa. Light absorption occurs here b. Retinitis pigmentosa: mutation in visual pigmenti. Causes blindnessii. Most common inherited visual problemiv. Inner segment: connected by a stalk to outer segmentb. Color visioni. Red, green, and blue conesii. Color blindness: inability to detect certain colors1. Cones either missing or cant produce pigments to absorb light at that frequencyiii. Nyctalopia: night blindness1. Vitamin A deficiency can be prevented by increasing vitamin A intakec. Visual pathwaysi. Photoreceptors visual cortexii. Messages cross synapse connecting photoreceptor to bipolar cell and synapse connecting bipolar cell to ganglion cell before it goes to braind. Central Processing of visual informationi. Ganglion cell axons meet at the optic discii. Enter wall of the eye iii. As optic nerve (II) they go towards diencephaloniv. Two optic nerves, one being for each eye, reach diencephalon at the opticchiasmv. Half of the fibers go to the contralateral lateral geniculate nucleusvi. Half go to the ipsilateral side e. Visual datai. Optic radiation: fibers linking lateral geniculate and visual cortex ii. Left occipital lobe receives information from right visual fieldiii. Right occipital lobe receives information from left visual field f. Depth perception: achieved by comparing relative position of items between right-eye and left-eye imagesg. Circadian rhythm: tied to day-night cycle i. Fibers from lateral geniculate nucleus go to hypothalamus III. Structures of the Eara. External Eari. Auricle: surrounds entrance and protects opening of external acoustic meatus ii. External acoustic meatus: separates external ear from middle ear1. Ends at the eardrum (tympanic membrane) 2. Ceruminous glands: secrete waxa. Keeps foreign substances out of tympanic membraneb. Slows growth of microorganismsb. Middle Ear (tympanic cavity)i. Auditory tube: allows equalization of pressures on both sides of tympanicmembrane1. Allows for communication with nasopharynxii. Three auditory ossicles:1. Malleus (hammer)2. Incus (anvil)3. Stapes (stirrup)4. Function: conduct vibrations in ear iii. Vibration of tympanic membrane1. Translates sound waves to mechanical movements 2. Ossicles and tympanum protected from loud noises by:a. Tensor tympani muscle: stiffens membrane so ossicles wont vibrate so muchb. Stapedius muscle: wont stimulate cochlea as much therefore reducing movement of stapes at oval
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