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UAB BY 116 - Afferent Senses
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By 116 1st Edition Lecture 10 Outline of Last Lecture II. Signal IntensityCell to cell communicationNeurotransmitter signalsPost-synaptic EventsPleotropic propertiesOutline of Current LectureIII. Afferent SensoryAll senses have the following physiologyAfferent pathwaysSomatic Sensory systemVisceral SensesSpecial SensesCurrent LectureIII. Afferent SensoryAll Senses have the following physiology Stimulation- Nerve energy Transduction- conversion to electrical signal Relay- physical route to the CNSProcessing- Interpretive value Alter Behavior- whole point of sensory system, dependent on environment for nutrientsAfferent pathways Receptive field is the size of the area of the field that the stimulus is detected by the 1st order neuron – PNS sense organ to CNSnever see more distance in receptive field than in the somatosensory, the smallest, most fine receptive field is in the special sensesinteraction region concerning nerve energy (what was the stimulus that was detected- typically only one stimulus), specificity, sensitivity and intensity2nd order neuron= CNS relay to thalamus1st order neuron synapses on and activates the 2nd order neuronEPSPs determine what tract the sensory information will travel onimportant is what happens at this synapse, sometimes it triggers motor behaviorcomplex reflex is initiated at second order neuron and travels all the way up to the brain speed by which we get to 2nd order neuron is very important, have presynaptic and postsynaptic neurons that effect it greatlyThese 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.3rd order- Thalamus to the primary processor Thalamus is great sensory relay system determines what parts of the brain will interpret this informationDetermines crude and fine detail here, perceptual threshold and modified behaviorPrimary Line of neuron must code for type, location, intensity (strength) and duration (how longstimulus is present)Somatic Sensory system- conscious, integument of body Receptive field: on body surface with free and capsulated receptors- (mainly skin- has 3 nerve endings that are inflamed or corpuscular that are pressurized)Synapses in the spinal chord- this is important for the immediate pain responsemostly phasic- there are some tonicStimuli- touch, pressure, temperature, Itch-pain (picked up by hair), nosiceptor (tells us about injury) proprioreception (deep underlying muscles)Stimuli modality Mechanical distortionfree nerve endings around hair- protectiveCorpuscles- pressurized- deep pressureSpindle Fibers – MusclesNoxious distortionFree nerve endings called nociceptors- respond to dead skin, also respond greatly to the immune chemical prostoglandin that is activated by phagocytes that activate the enzyme COXenzyme. Most pain medications are made to inhibit the COX enzyme like NSAID (non-steroidal anti-inflammatory drugs), analgesicThermal distortionCorpuscles – hot and cold receptorsHot are deep in tissue (want warm receptors deep to monitor the warmness in blood closely, so need to be deep)Cold are near surface (because the environment will make you cold, and we need to know this quickly because being too cold is more important to us than being too hot) 1st order neuron from skin and muscles enters the dorsal horn of the spinal cord via the dorsal root In dorsal root all senses are grouped together, but as it moves to dorsal horn, they are regrouped with information.How they get in is grouped by anatomical information and how they leave the spinal cord, they are regrouped by physiological informationOn lateral spinal chord (dorsal columns)= tracts for muscles and skin, that are named by where the information is goinggracillis and cuneatus are named for the nucleus that they are going to in the medullaname tells you destination (start of name indicates origin, end of the name is insertion)Spinal thalamic tracts (anterolateral system)= pain and temperature ascend from posterior horns to thalamuspain and temperature are also connected to lower neuron to quickly react when they synapse inspinal chordmotor neuron can be activated directly by the pain- why it is important that they synapse in the spinal chord as a defensive mechanism CNS routing and final processor post-central gyrus= primary somatosensory cortexsensory homunculus- most sensitive areas= are hands, feet, face, genitals (more likely to discriminate stimulus)least sensitive= dorsal body (can’t discriminate stimulus)Visceral senses- subconsciousReceptive field- soft organs and muscles (free/encapsulated receptors)Routing goes through Vagus nerve (largest branched nerve in body, mixed sensory and motor) and Spinal chord Vagus nerve (wandering nerve), very important- sends mechanical distortion through out the body, particularly stretch receptors for mechanical distortionMostly tonic, some phasic Stimuli: stretch, pressure, temperature, pain, proprioreception, blood chemistry (nutrient, gasesand osmolarity)Core temperature: maintaining blood tempStretch receptors (baroreceptors) in blood vessels: ascending aorta and in the internal carotid arteryThermal- core, heart and sensitive more to loss of heat than gainVagus nerve synapses on more anterior side of medulla before ascending to the thalamus – vastmajority of information is processed in brainstem where we are not aware of itThings we monitor in bodyGases- CO2 and O2 – more about CO2 than oxygen, also monitor salt, nutrient receptors, glucose, etc.Visceral pain – in soft organs called referred pain because not routed through Vagus nerve and rather the spinal cord (synapse on second order neurons in spinal chord and it is referred to a surface area)Gall stones- crystallized cholesterol and the pain is referred to the upper arm, very sharp pain Appendix- referred pain higher and more central than actual area, in to the belly button area- often mistaken for stomach acheHeart attack- referred pain is like a knife between the shoulder blades- called angina- type of referred pain that advances, and on occasion moves to jaw line and behind the ears or can be felt in either armKidney stones- experience flank pain in the uretersreferred pain- referred to the surface, never weaker than a localized pain, but is diffuse or difficult to describe and locateSpecial senses- conscious and subconscious – have specialized senses of transduction for vision, taste, hearing and smellSense organs


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