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Lecture 18

CSB332H1 Lecture Notes - Lecture 18: Olfactory Bulb, Muscle Spindle, Myocyte


Department
Cell and Systems Biology
Course Code
CSB332H1
Professor
Melanie Woodin
Lecture
18

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CSB332H1S L18; March. 21, 2012
Sensory Systems
Sensory Processing
Sensory signals go 1st to thal (relay station)
Msgs travel to primary sensory areas in cortex (dif area for each
sense)
"higher" regions of brain for “processing”.
o Processing involves determining what signals are coming in from
other parts of brain, + incorporating prior learning, overall goals,
& general state of arousal, motivation
Not a reflex
o 2ndary & tertiary areas
o Output regulated by motoneurons
Short recs sensory recs located on sensory cells that have rec pots
that spread passively from sensory region to synaptic region
o Ex. cells w short axons, often epithelial
o No axons, no APs
Short recs release neurotransmitter tonically; depolarization increases
or hyperpolarization decreases rate of release
Long recs rec pots give rise to trains of APs whose duration & freq
code info about duration & intensity of stimulus
Cell body located in a ganglion
Sensory input travels along neurite (not classic shape)
Transduction of Mechanical Stimuli
Transduction of mechanical stimuli occurs in sensory cells of skin,
muscles, joints, internal organs
Receptive endings of sensory cells sense stimulus intensity & timing
encode it into a rec pot (similar to a postsynaptic pot)
o Can be depolarizing or hyperpolarizing
As stimulus intensity rec pot in amplitude
o Ex. larger stretch
o Not always linear relationship
Amplification of Rec Signals
Sensory signals greatly amplified at level of rec
Ex. Fish electrorecs can detect electrical fields of a few nanovolts/cm2
o smaller than field that would be produced if two wires connected
to either pole of a flashlight battery would be dipped into either
end of Atlantic!
Relationship between Receptor Potential Amplitude and Stretch
Figure 19.2
red = stretch amt
as increase stretch, amplitude of rec pot
increases
relationship not linear
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
o Adaptation can occur quickly or slowly
Slowly adapting recs encode stimulus duration
o Want to know how intensity changes over period of time
o Responds during stimulus duration
Rapidly adapting recs are specialized to detect changes in stimulus
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.
Sensory Receptors
Sensory recs define limits of sensitivity & determine range of stimuli
that can be detected
Specialized to respond to 1 type of stimulus energy the adequate
stimulus
o Ex. photorecs respond to photons
Stimulus transduced to electrical signal termed a rec pot
o Stimulus energy rec pot
CNS recognizes type of stimulus signal & its position by:
1. Its anatomical location of rec
o
2. The nature of its sensory ending
o & where projects to in CNS
Harder for short recs to reach threshold to get into CNS
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