BIO 251 1nd Edition Lecture 7 Outline of Last Lecture I Neural basis of speech behaviors II Memory III Glial cells IV Nourishment of blood brain barrier V Spinal cord Outline of Current Lecture I Introduction a Perceiving reality b Perception II Receptor Physiology a Sensitivity of receptors to stimuli i Transduction ii Types of receptors b Responses to receptors structure c Adoption of receptors to stimulus d Fate of info transmitted by receptors III Taste and smell a Description 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 b Taste c Taste sensations d Smell IV How caffeine works Current Lecture Introduction o Review organization of whole nervous system Fig 7 1 Afferent division sends info from body to CNS o Definitions Visceral afferent is subconscious info sent from internal viscera to CNS E g concentration of CO2 in blood chemoreceptors E g blood pressure baroreceptors Afferent input that does not reach level of conscious awareness is called sensory info pathway is called a sensory afferent Somatosensory system Body surface sensations E g skin muscles joints inner ear limb position Special senses Vision Touch Hearing Taste Smell o Perceiving reality We can perceive Sound Color Shape Texture Smells Tastes Temp We can not perceive Magnetic fields birds can Light polarization birds can Radio waves X rays Humans are limited in even perceptions we do have Cant hear high frequencies that dogs can Some features of stimuli are accented or ignored during precortical processing Cerebral cortex further manipulates data to complete the picture 10 1 Perceptions do not replicate reality Perception o Eyewitness identification evidence is the leading cause of wrongful criminal conviction in the US Of more than 200 people exonerated by way of DNA evidence in the US over 75 were wrongfully convicted on basis of erroneous eyewitness identification evidence Receptor Physiology Sensitivity of receptors to stimuli o Transduction Receptor functions by converting stimulus energy to an action potential AP Conversion of stimulus energy to an AP accomplished by receptors o A receptor is specialized for specific stimuli Eyes see but don t hear If you are hit in eye hitting mechanical stimulus you see stars o Types of receptors 10 1 Photoreceptors vision Thermoreceptors Warmth Cold Mechoreceptors Osmoreceptors ECF osmolarity Baroreceptors blood pressure Hair cells sound balance Chemoreceptors Taste smell blood oxygen blood pH Nociceptors pain o Compound sensations also occur E g wet mechano thermo Responses of receptors structure o Two types of receptor structure 10 2 Separate cell Produces a receptor potential which is a graded potential Most senses are like this Modified ending of afferent neuron Produces a generator potential which is a type of graded potential Olfactory is only special sense like this o When receptor stimulated either type results in Non selective opening of all small ion channels Net influx of Ca and or Na ions Which causes a membrane depolarization Graded potential not an action potential so bigger stimulus bigger change in potential o Conversion of receptor and generator potentials into Aps Modified ending of efferent neuron 10 2a Local current flow occurs from end of efferent neuron to axon of same efferent neuron Causes opening of Na channels If threshold is reached in axon AP occurs Separate cell 10 2b Separate receptor cell stimulated which opens Ca channels Influx of Ca causes release of chemical messenger Messenger binds to protein receptor on membrane of affront axon Causes Na channels to open on affront axon If enough Na channels open threshold is reached AP occurs o Stronger the stimulus higher frequency of AP that occur in affront neuron 10 7 o As more receptors are activated more AP are produced 10 8 Adoption of receptors to stimulus 10 3 o Slow adapting tonic receptors Don t adapt to stimuli Continue to produce AP as stimuli continue E g muscle stretch receptors o Fast adapting phasic receptors Rapidly adapt to stimuli Stop producing AP even though stimuli continue E g body surface tactile receptors once you put on shirt you are no longer aware of it being on Fate of info transmitted by receptors 10 6 o Receptor causes AP in efferent neuron first order neuron o Affront AP reaching spinal cord either Becomes part of reflex arc See topic 6 Or is relayed toward brain by interferon second order neuron Second order synapses with 3rd order in thalamus Third order transmits info to cerebral cortex where sensory perception occurs Taste and smell Description o Receptors and chemoreceptors Receptor binds specific chemical generates neural signal o Stimulation of taste and smell receptors can cause pleasurable or objectionable sensations o Important in finding good food avoiding toxins finding mates Taste o Taste buds 10 52 are modified by epithelial cells 10K taste buds in mouth mostly in tongue Each taste bud has a single opening Consists of about 50 receptor cells Each receptor has binding sites that selectively bind chemicals Binding a chemical causes Depolarization of receptor membrane Can imitate AP in affront neurons with which they synapse o Taste receptors has lifespan of 10 days Taste sensations fig on website Sour Caused by acids H H blocks K channels which reduces K leaking out of cell which depolarizes membrane When membrane depolarizes Ca channels open and Ca enters cell Entry of Ca causes release of neurotransmitter which bind to taste affront and can cause AP in taste affront Sweet Glucose or related sugar bind receptor Activates a G protein system that involves several enzymes Ultimately result in blocking K channels which reduces K leaking out of cell which depolarizes membrane When membrane depolarizes Ca channels open and Ca enters cell Entry of Ca causes release of neurotransmitter which bind to taste afferents and can cause AP in taste afferents Bitter Many chemicals bind to bitter receptors caffeine nicotine morphine strychnine Bitter moles Blocks K channels which reduces K leaking out of cell which repolarizes membrane When membrane depolarizes Ca channels open and Ca enters cell Entry of Ca causes release of neurotransmitter some bitter taste buds use G protein system as described for sweet which causes release of neurotransmitter which bind to taste afferents and can cause AP in taste afferents How caffeine works o Adenosine the building block of