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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 orless 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: BYModality – 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 SensesOlfaction (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 cellThat either causes Ca channels to open, or cell releases Ca from intracellular stores → triggers exocytosis → neurotransmitters are released – action potentials are sent to the brainNerves: 7 - Facial9 - Glossopharyngeal10 - Vagus → to gustatory nuclei in medulla → thalamus → primary gustatory cortexHearingSound – 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 hear3 rows of outer HC → adjust the response of cochlea (for precision).Cochlear nerve meets vestibular nerve → vestibulocochlear nerve (8) → medulla → midbrain → → auditory cortexSummary: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 window4. The perilymph in the scala vestibuli vibrates5. The vestibular membrane vibrates6. The endolymph vibrates7. Displacement of the basilar membrane8. Movement of the basilar membrane detected by hair cells of the spiral organ9. Vibrations transferes to the perilymph of the scala tympani10. Vibrations are transferred and dampenes by the round window.EquilibriumVestibular 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.VisionAccessory structures:EyebrowsEyelids (palpebrae). Tarsal plate with tarsal glands (oil). EyelashesConjuctiva – mucous membrane. Highly vascular.Lacrimal apparatus – lacrimal gland, and ducts. Lacrimal punctum → lacrimal canal → lacrimal sac → nasolacrimal ductExtrinsic 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 corneaVascular – 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

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