1/10/2013. Topic 16: Sensory Organs. How do receptors work?

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1 Topic 6: Sensory Organs How do sensory receptors work? Cutaneous receptors Prorioceptors Chemoreceptors Electroreceptors Lateral line system Auditory receptors Photoreceptors How do receptors work? nerve endings cells Can be simple Can be elaborate Receive a stimulus when stimulated (phasic receptors) Initiate an in a sensory neuron Liem et al. Fig. 2-6; Chandrashekar et al Cutaneous Receptors Meissner s Corpuscle What are? Pain Free neuron ending Superficial are Deep are Merkel Disk Monitor tension in muscles, tendons, joints Postural feedback Dealing with gravity Intrafusal inside sheath Extrafusal Passively stretched as muscle stretches Unlaminated adapt Laminated adapt What does this mean? Pacinian Corpuscle Ruffini Ending Liem et al. Fig. 2-6 Liem et al. Fig. 2-7

2 Chemoreceptors What sorts of signals are received by chemoreceptors? What organs/structures have evolved to receive these cues? How does olfaction work? Cilia increase receptive area Axons directly to olfactory N. Odorants in mucus Bind to receptor molecules in cell membrane Depolarization R Stephenson Liem et al. Fig. 2- How does olfaction work? What is the Organ? Fishes Incurrent naris Excurrent naris Tetrapods Naris Choana Water/Air Jacobsen s organ Odorants and pheromones Most tetrapods Not birds, apes, bats Lepidosaurs with long tongues Liem et al. Fig. 2-2; Liem et al. Fig. 2-4; J Hillenius

3 How does gustation work? _ Rely on mucus and aqueous solution of flavors Some fishes All over body, especially barbels Most tetrapods In buccal cavity Facial, glossopharyngeal, vagus nerve inputs What cranial nerve numbers are these? How does gustation work? Flavors Support for model Sour Across-fiber model rejected Sweet Liem et al. Fig. 2-5; Chandrashekar et al Chandrashekar et al. 2006; library.thinkquest.org Electroreception Evolved in vertebrates, lost in bony fishes and tetrapods Sensitive to temperature, salinity, electric currents Navigation Earth s magnetic field Hunting can detect electrical currents from prey muscles/heart Jelly acts as capacitor What is the lateral line system? Series of canals Fishes, larval amphibians _: Water movement/ disturbance Low frequency vibes Innervated by series of cranial lateral line nerves Liem et al. Fig. 2- Liem et al. Fig. 2-0 ; How does the lateral line system work? organs Receptors: hair cells & project into gelatinous cupula Deformation of cilia initiates action potential Afferent lateralis neuron is excitory Efferent lateralis neuron is inhibitory Suppresses background noise How does the lateral line system work? Sensory output is directional Deformation of stereocilia first Excitation Deformation of kinocilium first _ Inhibition Liem et al. Fig. 2-8 Vertebrate Life, Fig. 8-0

4 Endolymph Perilymph Ciliated sensory structures Receptors very similar to lateral line system Hair cells with cilia Deformation of cilia by movement of fluid Endolymph Produces action potential Now hair cells are much more internalized Which cranial nerve carries these signals? Anterior vertical semicircular duct Posterior vertical SD Horizontal SC Cristae Utricular macula Lagena Cochlea Lagenar macula Structure in Pearson Education Liem et al. Fig. 2-5 Fish. Sacculus & Utriculus 2. Semicircular ducts 3. Lagena 4. Basilar papilla 5. Cochlea,2,3 Transfer of vibrations to sacculus:. 2. Columella 3. A 2,B Lizard Sacculus Vibratory structures Semicircular ducts Lagena Basilar papilla Cochlea A. Swim bladder B. Tympanum 3 Human Liem et al. Fig 2-6 (modified) Liem et al. Fig. 2-7, 2-9, 2-22 How is sound sensed in human hearing? What types of photoreceptors do vertebrates have? Vibrations travel: Hit tympanum Transferred to Malleus Incus Stapes Perilymph of scala vestibuli Perilymph of scala tympani Basilar membrane Hair cells of Organ of Corti Action potential Vertebrates have two types of eyes Median parietal eye Paired image-forming eyes Both form as evaginations of the Liem et al. Fig Photo PJB 2

5 How have median parietal eyes evolved? How do the paired image-forming eyes work? Deep to skull in fishes, mammals Superficial in amphibians, lizards Lamprey Layers of eye fibrous vascular sensory Linked to circadian rhythm and photocycle Melatonin secretion Tuatara has retina Ammocoete & lizards can detect light and dark Mammal Lizard Frog Light passes through: Conjuntiva single cell thick Cornea Anterior chamber with aqueous humor Lens Vitreous body Pineal gland in mammals Retina Fovea & Optic disk Liem et al. Fig Liem et al. Fig Anableps simplex How is light sensed by the retina? Receptors: & Photoreceptive pigments: opsins Change conformation, releasing energy & initiating action potential Rods have single pigment: Rhodopsin 3 cone types: Red, green, blue Neurons overlie rods & cones Eye movements to compensate for shadowing Air vs. Water refracts light Water is similar density to the cornea Eyes are tuned to focus on the retina in water or air Liem et al. Fig. 2-24, 2-26 Liem et al. Fig. 2-29; Photo PJB Air vs. Water Cornea is divided into dorsal and ventral Retina is also divided Allows simultaneous focusing in both media Liem et al. Fig