Chapter 16 Sense Organs Sensory receptor any structure specialized to detect stimulus Sense organ enhanced receptor nervous tissue other tissues Transduction conversion of one form of energy to another to nerve signals Receptor potential local action potentials brain sensation although some are filtered Types of information Modality type of stimulus Labeled line code pathway from sensory cell to the brain is labeled to identify its origin brain interpret what modality the signal represents Location is encoded by which nerve fibers are issuing signals to the brain Receptive field Intensity based on the firing frequencies number of nerve fibers recruited type sensitive or less sensitive Duration changes in the firing frequency Sensory adaptation Phasic receptors burst when first stimulated quickly adapt Some would fire again when stimulus ceases smell hair movement Tonic receptors adapt more slowly proprioceptors slowest Classification BY Modality thermo t photo light nociceptors pain chemo odor taste mechano touch stretch etc hearing balance Origin exteroceptors external vision etc intero internal proprio position of body parts Distribution in the body special in the head general all the others Chemical Senses Olfaction smell Structure Olfactory mucosa Olfactory cells neurons with olfactory hairs nonmotile cilia with binding cites supporting cells epithelial basal stem cells Hairs are embedded in mucus with odorant binding proteins for hydrophobic odorants Each olfactory cell has only one receptor type binds only one odorant ligand channels Olfactory axons meet mitral and tufted cells in glomeruli Each glomeruli is dedicated to a particular type of odor Olfactory tracts primary olfactory cortex and limbic system emotional response Gustation taste action of chemicals dissolved in saliva on the taste buds Lingual papillae Filiform tiny spikes without taste buds Most abundant Texture Foliate weakly developed most degenerate by 2 3 years Fungiform 3 taste buds each Widely distributed concentrated on tip and sides of tongue Vallate large 250 taste buds each Humand have only 7 12 of them Taste buds structure Lemonshaped groups of epithelial taste cells with taste hairs supporting cells and basal cells stem cells Physiology Salty metal ions Na K penetrate into the cell and depolarize it directly Sour acids H penetrate into the cell and depolarize it directly Sweet sugars Bitter alkaloids stimulate taste cells by binding to receptors on the membrane surface activate Umami glutamate G proteins and second messenger systems within the cell That either causes Ca channels to open or cell releases Ca from intracellular stores triggers exocytosis neurotransmitters are released action potentials are sent to the brain Nerves 7 Facial 9 Glossopharyngeal 10 Vagus to gustatory nuclei in medulla thalamus primary gustatory cortex Hearing Sound audible vibration of molecules Molecules collide with the eardrum and make it vibrate Outer ear auricle pinna external acoustic meatus auditory canal gueard hairs ceruminous glands Middle ear tympanic membrane auditory tube auditory ossicles malleus tensor tympani muscle incas stapes stapedius muscle Oval window Inner ear Bony labyrinth lined by membranous labyrinth with perilymph between Endolymph is inside the membranous labyrinth Vestibule equilibrium organ and cochlea the organ of hearing Cochlea three fluid filled chambers scala vestibuli scala tympani both filled with perilymph cochlear duct with vestibular membrane on top and basilar membrane on bottom Filled with endolymph Within the cochlear duct spiral organ acoustic organ Epithelial hair cells with stereocilia each stereocilia has a K channel and supporting cells Tectorial membrane 1 row of inner hair cells what we hear 3 rows of outer HC adjust the response of cochlea for precision Cochlear nerve meets vestibular nerve vestibulocochlear nerve 8 medulla midbrain auditory cortex Summary Equilibrium 1 Sound waves strike the tympanic membrane and cause it to vibrate 2 The malleus the incus and the stapes vibrate 3 The foot plate of the stapes vibrates in the oval window 4 The perilymph in the scala vestibuli vibrates 5 The vestibular membrane vibrates 6 The endolymph vibrates 7 Displacement of the basilar membrane 8 Movement of the basilar membrane detected by hair cells of the spiral organ 9 Vibrations transferes to the perilymph of the scala tympani 10 Vibrations are transferred and dampenes by the round window Vestibular apparatus three semecircular ducts succule anterior chamber utricle posterior Static equilibrium and linear acceleration saccule utricle Maccula horizontal in utriculi vertical in sacculi Hair cells have 60 stereocilia and one true cilium kinocolium Tips are embedded in otolithic membrane Angular acceleration semicircular ducts Ducts are filled with endolymph all connected to utricle Ampulla dilated sac at end Within ampulla crista ampullaris hair cells with stereocilia and kinocilium embedded in cupula Vision Accessory structures Eyebrows Eyelids palpebrae Tarsal plate with tarsal glands oil Eyelashes Conjuctiva mucous membrane Highly vascular Lacrimal apparatus lacrimal gland and ducts Lacrimal punctum lacrimal canal lacrimal sac nasolacrimal duct Extrinsic muscles superior inferior lateral medial rectus Superior oblique along medial wall trochlea superolateral aspect of the eyeball Inferior oblique originates at medial wall inferolateral aspect of the eyeball Anatomy Tunics Fibrous sclera and cornea Vascular choroid ciliary body iris pupil Nervous retina beginning of optic nerve Optical components Aqueous humor secreted by the ciliary body posterior chamber anterior chamber scleral venous sinus bloodvessel Lens suspended by suspensory ligament attached to the ciliary body Vitreous humor Neural components Retina attached to the rest of the eye at the optic disc blind spot and ora serrata Macula lutea with fovea centralis most detailed images Sensory transduction in the retina Photoreceptor cells they are not neurons but related to the ependymal cells of the brain Rods night scotopic vision monochromatic vision gray None in fovea Visual pigment rhodopsin protein opsin vitamin A derivative retinal Cones day photopic vision trichromatic vision color Mostly in fovea Photopsin can absord different wavelengths of light Bipolar cells first order neurons Ganglion cells second order neurons Their axons form the optic nerve Some absorb light directly