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L13 - Afferent Nervous System - Pain - Taste - Smell


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Sensory Receptors - Sensation
*connect to environment, stimulus activates receptor
*transduction converstion stimulus into physiological signal
*brain interprets the physiolgical signal
*change receptor in some way
*each receptor binds to one stimulus vest
*brain always assumes stimulus is "normal"
*conscious senses - 5 senses
*unconscious senses - position in space, BP, temp
Types of Receptors
*parts of cells-no dendrites, modified receptor structures
*many produce AP's, many do not(produce receptor potentials)
Types of receptors
*physical chang either opens ion channel, or alters protein or smaller molecule
*touch, hair cell in ears, photo receptors, beroreceports
Types of receptors
*taste, smell
*chemical must bind to receptor-ion channel
*pain receptor -chemical/phys receptors
Receptor Potentials
*generator potential
*local potential, graded potential
*all receptor cells-short-only RP
*in long-receptor potential-AP
Receptor Potentials
*in short cells, the RP causes release proportional to stimulus
*in long-# pf AP proportional to stimulus size
Receptor Potentials
-Frequency Dependence
*to reach CNS-some afferent neuron must fire APs-brain interprets # of APs as size of stimulus
*decrease in # of APs despite a prolonged stimulus
-phasic receptors
*adapt over time-rate is variable
*many also have off response
*touch-very fast
*pain, BP-adapt more slowly
-tonic receptors
*do not adapt
*most tonic receptorts-truck muscles-posture
sensory specificity
*brain interprets all stimuli as normal
*both stimulus and its site of action
*survival value, protection from harm
*anticipation of pain activates pain areas of cortex
-fast pain
*sharp, localized, passes quickly
*uses unmyelinated fibers-NT is substance P
-Substance P
*ALWAYS associated with slow pain
*unique to pain pathway synapses
*treatable with strongest analgesics. dont wait forever to start treatment
-Opioid Receptors
*bind natural analgesics and outside analgesics-morphine
*open ion channels-> change membrane potential
Chemical Senses
*molecular binding to receptors
*flavor:comb. of taste and smell
*molecules must dissolved in saliva
*molecules must reach taste buds in order to be tasted
Taste Buds
*receptors of taste pore
*tight junction ring cells at taste pore
*epithilial cells-> basal cells-> receptor cells~(10 days)
-Neural Tracts
*taste info
*thalamus-parietal lobe-"what youre eating"
*limbic system-"like it"
-Taste receptors
*acid/sour-H+ ions
*bitter-quinine-(+) charge. (most sensitive, good detecting poisions)
*umami-glutomate(amino acids)
*receptors top of nasal cavity
*>1000 distinct smell receptors. >1% of human genome
Olfactory Receptors
*covered with mucus-water soluble
*smelled-must be volatile enough to float to top
*hydrophilic enough to dissolve in mucus
*receptor-dendrites->replace every few weeks
Olfactory Adaptation
*receptor tonic
*adaptation in CNS-brain can control what you detect
*adaptation to one cell doesnt affect other smells
*signal goes cortex(what) limbic system(like)

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