CBIO 2200 1nd Edition Lecture 22 Outline of Last Lecture I. Visceral ReflexesII. Functional OrganizationIII. The Enteric Nervous SystemIV. Neurotransmitters and Their ReceptorsOutline of Current Lecture I. Sensory ReceptorsII. General SensesIII. Special SensesCurrent LectureChapter 16: Sense OrgansI. Sensory Receptorsa. Properties and types of sensory receptorsi. Sensory receptor: specialized structure for detecting a stimulus1. Bare nerve endings – general senses2. True sense organs – e.g. eye (doesn’t do anything except see)ii. General properties1. Transduction2. Receptor potentiala. Strong receptor potential  action potential3. Sensation – created by the action potential4. Sensory receptors transmit four kinds of information:a. Modality – i. Labeled line code theory – says all action potentialsare identical; the pathways are labeled some way These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.so brain can tell where action potentials are comingfromii. Tells you which sense perceived stimulus (e.g. whether it was heard or seen)b. Location i. Receptive field – the portion of an area (usually skin) that is innervated by a neuron1. Some are large and some are very small2. With large receptive fields, it is difficult to tell where stimulus is coming from in that areaii. Two-point touch discrimination – when two pricks in same large receptive field, it feels like there was just one prick; if two pricks are given at small receptive field, you can more accurately feel the two separate pricks (the pins will hit two separate receptive fields)c. Intensity – encoded by:i. Which fibers are sending the signalsii. How many fibers are sending the signalsiii. How fast are these fibers sending the signalsd. Duration – change in firing frequency over timei. Sensory adaptation – the longer a stimulus is present, the firing of the neuron gets slower and slowerii. Phasic receptors – gives information about smell (for example) something that adapts over time (eventually you won’t smell or be aware the odor as much)iii. Tonic receptors – a stimulus that makes neurons continue to fire at the same rate over time (e.g. balance, blood pressure); usually senses that give information about body positionII. General Sensesa. Simple in structureb. Distributed all over body c. Divided into:i. Somatic sensory receptors1. From skin, muscles, and jointsii. Visceral sensory receptors1. From visceraiii. Injured tissues release chemicals that stimulate pain fibers1. Bradykinin: most potent pain stimulus known2. Histamine, prostaglandin, and serotonind. Types:i. Pain – something we avoid1. Discomfort caused by tissue injurya. Lost in diabetes mellitus  diabetic neuropathy2. Nociceptors – two types providing different pain sensationsa. Fast pain travels myelinated fibers at 12-30m/sb. Slow pain travels unmyelinated fibers at .5-2 m/s3. Analgesics a. Exogenous opioids (opium, morphine, and heroin receptors in the brain)b. Endogenous opioids (opium-like substances)i. Enkaphalinsii. Endorphinsiii. Dynorphins 4. Referred pain – pain in viscera often mistakenly thought to come from the skina. Heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1 and T5 (why you feel painin arm during heart attack)ii. Heatiii. Coldiv. Touchv. Texturevi. Ticklevii. Stretchviii. PressureIII. Special Sensesa. Taste (gustation)i. The tongue has four types of lingual papillae1. Filiform papillae – no taste buds2. Foliate papillae – very few taste buds3. Fungiform papillae4. Vallate (circumvallate) papillaeii. All taste buds look alike1. Taste (gustatory) cellsa. Have gustatory microvilli – sensation of taste2. Basal cells – stem cells of taste bud; replace taste cells every 7-10 days3. Supporting cellsiii. Taste is influenced by food texture (mouthfeel), aroma, temperature, and appearance iv. Hot pepper – taste sensation that we get is stimulation of free nerve endings in mouth, not through taste hairs ( how we perceive hot peppers)v. Actions of major tastants1. Two basic mechanisms of action:a. Activate a second messenger systemb. Directly depolarize cellsvi. To be tasted, molecules must dissolve in saliva and flood taste pore1. Five primary sensationsa. Saltyb. Sweet – carbohydrates c. Sour – citric acidd. Bitter – alkaloidse. Umami – amino acids vii. Projection pathway for taste1. Facial nerve (CN VII) – anterior two-thirds of tongue2. Glossopharyngeal nerve (CN IX) – posterior 1/3 of tongue3. Vagus nerve – pharynx, epiglottis, and palateviii. All fibers reach solitary nucleus in medulla oblongata ix. From there, signals sent to hypothalamus and amygdala 1. Thalamus relays signals to insula and postcentral gyrus of cerebrum b. Hearing and equilibriumi. Hearing – made from vibrating air moleculesii. Equilibriumiii. Vestibulocochlear nerve (CN VIII)iv. Both senses reside in the inner earv. Three sections:1. Outer2. Middlea. Tympanic membrane (eardrum)b. Tympanic cavity i. Contains auditory ossicles c. Auditory (Eustachian) tubed. Otitis media3. Inner a. Located in temporal boneb. Bony labyrinthc. Membranous labyrinth – fleshy tubes lining bony labyrinthi. Filled with endolymphii. Floating in perilymph vi. Deafness can be a problem with conduction or neural stimulation1. Conductive deafness – conditions interfere with transmission of vibrations to inner ear2. Sensoneural (nerve) deafness – death of hair cells or any nervous system elements concerned with