CBIO 2200 1nd Edition Lecture 22 Outline of Last Lecture I Visceral Reflexes II Functional Organization III The Enteric Nervous System IV Neurotransmitters and Their Receptors Outline of Current Lecture I Sensory Receptors II General Senses III Special Senses Current Lecture Chapter 16 Sense Organs I Sensory Receptors a Properties and types of sensory receptors i Sensory receptor specialized structure for detecting a stimulus 1 Bare nerve endings general senses 2 True sense organs e g eye doesn t do anything except see ii General properties 1 Transduction 2 Receptor potential a Strong receptor potential action potential 3 Sensation created by the action potential 4 Sensory receptors transmit four kinds of information a Modality i Labeled line code theory says all action potentials are 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 coming from ii 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 neuron 1 Some are large and some are very small 2 With large receptive fields it is difficult to tell where stimulus is coming from in that area ii 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 signals ii How many fibers are sending the signals iii How fast are these fibers sending the signals d Duration change in firing frequency over time i Sensory adaptation the longer a stimulus is present the firing of the neuron gets slower and slower ii 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 position II General Senses a Simple in structure b Distributed all over body c Divided into i Somatic sensory receptors 1 From skin muscles and joints ii Visceral sensory receptors 1 From viscera III iii Injured tissues release chemicals that stimulate pain fibers 1 Bradykinin most potent pain stimulus known 2 Histamine prostaglandin and serotonin d Types i Pain something we avoid 1 Discomfort caused by tissue injury a Lost in diabetes mellitus diabetic neuropathy 2 Nociceptors two types providing different pain sensations a Fast pain travels myelinated fibers at 12 30m s b Slow pain travels unmyelinated fibers at 5 2 m s 3 Analgesics a Exogenous opioids opium morphine and heroin receptors in the brain b Endogenous opioids opium like substances i Enkaphalins ii Endorphins iii Dynorphins 4 Referred pain pain in viscera often mistakenly thought to come from the skin a Heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1 and T5 why you feel pain in arm during heart attack ii Heat iii Cold iv Touch v Texture vi Tickle vii Stretch viii Pressure Special Senses a Taste gustation i The tongue has four types of lingual papillae 1 Filiform papillae no taste buds 2 Foliate papillae very few taste buds 3 Fungiform papillae 4 Vallate circumvallate papillae ii All taste buds look alike 1 Taste gustatory cells a Have gustatory microvilli sensation of taste 2 Basal cells stem cells of taste bud replace taste cells every 7 10 days 3 Supporting cells iii 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 tastants 1 Two basic mechanisms of action a Activate a second messenger system b Directly depolarize cells vi To be tasted molecules must dissolve in saliva and flood taste pore 1 Five primary sensations a Salty b Sweet carbohydrates c Sour citric acid d Bitter alkaloids e Umami amino acids vii Projection pathway for taste 1 Facial nerve CN VII anterior two thirds of tongue 2 Glossopharyngeal nerve CN IX posterior 1 3 of tongue 3 Vagus nerve pharynx epiglottis and palate viii 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 equilibrium i Hearing made from vibrating air molecules ii Equilibrium iii Vestibulocochlear nerve CN VIII iv Both senses reside in the inner ear v Three sections 1 Outer 2 Middle a Tympanic membrane eardrum b Tympanic cavity i Contains auditory ossicles c Auditory Eustachian tube d Otitis media 3 Inner a Located in temporal bone b Bony labyrinth c Membranous labyrinth fleshy tubes lining bony labyrinth i Filled with endolymph ii Floating in perilymph vi Deafness can be a problem with conduction or neural stimulation 1 Conductive deafness conditions interfere with transmission of vibrations to inner ear 2 Sensoneural nerve deafness death of hair cells or any nervous system elements concerned with hearing