BSC 2086 1st Edition Lecture 3 Outline of Last Lecture I Major Sensory Pathways II Somatic Motor Pathways III Olfaction IV Gustation Outline of Current Lecture I Accessory Structures of the Eye II Visual Physiology III Structures of the Ear Current Lecture I Accessory Structures of the Eye a Palpebrae i Eyelids ii Blinking causes lubrication of the eye iii Tarsal Glands keep eyelids from sticking together by secreting lipid rich fluid b Superficial Epithelium i Lacrimal caruncle thick secretions which are to blame for the gritty residues in eye after sleeping ii Conjunctiva 1 Palpebral conjunctiva covers inner surface of eyelids 2 Ocular conjunctiva covers outer surface of eye 3 Pinkeye or conjunctivitis is caused by inflammation c Lacrimal apparatus i In charge of tears ii Lacrimal gland tear gland 1 Secretions contain an antibacterial enzyme called lysozyme which kills bacteria in eye d Tears i Lacrimal puncta lacrimal canaliculi lacrimal sac nasolacrimal duct inferior meatus of nose ii All collect in lacrimal lake at medial canthus e Eyeball i Large posterior cavity 1 Filled with thick jelly known as vitreous humor a Vitreous body is a gel that supports the retina and stabilizes the eye b Diabetic retinopathy i Due to blockage of normal vessels abnormal blood vessel growth and blood leakage into cavity ii Acuity decreases due to death of photoreceptors ii Small anterior cavity 1 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 circulation b Intraocular pressure helps keep eye shape i 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 iris 3 Posterior chamber after iris between iris ciliary body and lens f Three Layers of the Eye i Outer fibrous layer 1 Cornea anterior transparent region 2 Sclera white part of the eye 3 Corneal limbus between cornea and sclera ii Vascular Layer uvea 1 Iris changes diameter of pupil through sympathetic and parasympathetic stimulation a Uses papillary muscles 2 Ciliary body controls shape and position of lens a Ciliary processes and ciliary muscle attach to suspensory ligaments of the lens 3 Choroid made of blood vessels that deliver oxygen and nutrients to the retina iii Inner Layer 1 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 neurons b Photoreceptors i Rods provide black and white or gray scale vision 1 Used at nighttime ii Cones color vision 1 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 cells i Between photoreceptors and bipolar cells ii Alter sensitivity to light of retina e Amacrine cells i Between bipolar cells and ganglion cells ii Alter sensitivity to light of retina f Optic disc i Origin of optic nerve ii Blind spot 1 Scotomas abnormal blind spots a Compression of optic disc damage to visual pathway or photoreceptors II g Lens i Focuses light entering eye 1 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 vision b Myopia nearsightedness c Hyperopia farsightedness i Presbyopia develops with age ii Lens fibers 1 Cells with no nuclei or organelles located in interior of lens 2 Crystallins provide clarity and focus power iii Cataract lens loses transparency 1 Senile cataract is the most common type caused by aging Visual Physiology a Rods and Cones Anatomy i Rods Very sensitive respond to almost any energy photon ii Cones Ranges of sensitivity iii Outer segment 1 Visual photo pigments synthesized from vitamin A III a Light absorption occurs here b Retinitis pigmentosa mutation in visual pigment i Causes blindness ii Most common inherited visual problem iv Inner segment connected by a stalk to outer segment b Color vision i Red green and blue cones ii Color blindness inability to detect certain colors 1 Cones either missing or cant produce pigments to absorb light at that frequency iii Nyctalopia night blindness 1 Vitamin A deficiency can be prevented by increasing vitamin A intake c Visual pathways i Photoreceptors visual cortex ii Messages cross synapse connecting photoreceptor to bipolar cell and synapse connecting bipolar cell to ganglion cell before it goes to brain d Central Processing of visual information i Ganglion cell axons meet at the optic disc ii Enter wall of the eye iii As optic nerve II they go towards diencephalon iv Two optic nerves one being for each eye reach diencephalon at the optic chiasm v Half of the fibers go to the contralateral lateral geniculate nucleus vi Half go to the ipsilateral side e Visual data i Optic radiation fibers linking lateral geniculate and visual cortex ii Left occipital lobe receives information from right visual field iii 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 images g Circadian rhythm tied to day night cycle i Fibers from lateral geniculate nucleus go to hypothalamus Structures of the Ear a External Ear i Auricle surrounds entrance and protects opening of external acoustic meatus ii External acoustic meatus separates external ear from middle ear 1 Ends at the eardrum tympanic membrane 2 Ceruminous glands secrete wax a Keeps foreign substances out of tympanic membrane b Slows growth of microorganisms b Middle Ear tympanic cavity i Auditory tube allows equalization of pressures on both sides of tympanic membrane 1 Allows for communication with nasopharynx ii Three auditory ossicles 1 Malleus hammer 2 Incus anvil 3 Stapes stirrup 4 Function conduct vibrations in ear iii Vibration of tympanic membrane 1 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 much b Stapedius muscle wont stimulate cochlea as much therefore reducing movement of stapes at oval window c Internal Ear i Contains endolymph fluid ii Membranous labyrinth is surrounded and protected by bony labyrinth iii Subdivisions include 1 Vestibule
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