Lecture 18

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University of Toronto St. George
Cell and Systems Biology
Melanie Woodin

CSB332H1S L18; March. 21, 2012 Amplification of Rec Signals Sensory Systems  Sensory signals greatly amplified at level of rec  Ex. Fish electrorecs can detect electrical fields of a few nanovolts/cm2 Sensory Processing o smaller than field that would be produced if two wires connected  Sensory signals go 1 to thal (relay station) to either pole of a flashlight battery would be dipped into either   Msgs travel to primary sensory areas in cortex (dif area for each end of Atlantic! sense)   "higher" regions of brain for “processing”. Relationship between Receptor Potential Amplitude and Stretch o Processing involves determining what signals are coming in from Figure 19.2 other parts of brain, + incorporating prior learning, overall goals,  red = stretch amt & general state of arousal, motivation  as increase stretch, amplitude of rec pot  Not a reflex increases o 2 ary & tertiary areas  relationship not linear o Output regulated by motoneurons  Many sensory recs have a non-linear relationship w sensory stimuli o Advantage = ability to provide amplitude coding over wide- range of stimulus intensities o  More pts in the 0.2mV range  Have maximum response Transduction of Mechanical Stimuli  Very high levels of stimulus intensity  rec pots saturate – can’t increase in amplitude anymore  If stimulus maintained  rec pot adapts to lower level  Short recs – sensory recs located on sensory cells that have rec pots that spread passively from sensory region to synaptic region o Adaptation can occur quickly or slowly o Ex. cells w short axons, often epithelial  Slowly adapting recs encode stimulus duration o No axons, no APs o Want to know how intensity changes over period of time o Responds during stimulus duration  Short recs release neurotransmitter tonically; depolarization increass Rapidly adapting recs are specialized to detect changes in stimulus or hyperpolarization decreases rate of release o Fire when intensity changes  Good to have mix of both  Cat muscle spindle sensory region.  Each muscle fiber wrapped by nerve terminals in spiral fashion.   Large amt of sensory input from each muscle fibre  Calibration bar 10 mm.  Chua & Hunt.  Long recs – rec pots give rise to trains of APs whose duration & freq code info about duration & intensity of stimulus Sensory Receptors  Sensory recs define limits of sensitivity & determine range of stimuli  Cell body located in a ganglion that can be detected  Sensory input travels along neurite (not classic shape)  Specialized to respond to 1 type of stimulus energy – the adequate Transduction of Mechanical Stimuli stimulus  Transduction of mechanical stimuli occurs in sensory cells of skin, o Ex. photorecs respond to photons  Stimulus transduced to electrical signal termed a rec pot muscles, joints, internal organs o Stimulus energy  rec pot  Receptive endings of sensory cells sense stimulus intensity & timing  encode it into a rec pot (similar to a postsynaptic pot)  CNS recognizes type of stimulus signal & its position by: o Can be depolarizing or hyperpolarizing 1. Its anatomical location of rec  As stimulus intensity ↑  rec pot ↑ in amplitude o 2. The nature of its sensory ending o Ex. larger stretch o & where projects to in CNS o Not always linear relationship  Harder for short recs to reach threshold to get into CNS  100, 000 olfactory rec neurons w axons project from nasal epithelia to olfactory bulb
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