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Lecture 12

Lecture 12 - Sensing The Environment

8 Pages
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Department
Biological Sciences
Course Code
BIOC32H3
Professor
Kenneth Welch

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Lecture 12
Chapter 7 Sensing the Environment
Section General Properties of Sensory Reception P. 216 230.
Section Mechanoreception Introduction through Insect Mechanoreceptors P. 238
240.
Sensory receptors
Each category of sensation is called a sensory modality
The features that characterize stimuli within a particular modality are qualities
Interoceptive (internal) receptors respond to signals from within the body and
communicate this information to the brain by pathways that typically are not
brought into consciousness
Proprioceptors monitor the positions of muscles and joints and other
interoceptive receptors monitor the chemical and thermal state of the body and its
orientation
3 types 2 are neurons = A and B
Where the neuron body is difference between A and B
Spike initiation zone sits on one side of the soma rather than the other difference
between A and B
In invertebrate sensory neurons using A
B = Long projection of dendrites etc. in verts. Touch receptors in B
C: the receptor cell itself is not a neuron
oChemical synapse
oWhen receptor current is generated, this results in synaptic vesicle release,
then inhibition of post synaptic membrane
oEx. A taste receptor is involved in sensory info but is NOT a neuron
Molecular mechanism
www.notesolution.com
Common themes work like muscarinic ACh receptors
ACh binds and conformational change and activation through either G-protein or
directly
Salt passive movement of Na+ ions; the saltier the more depol
Sour hyperpolarization
Taste receptors DO release synaptic vesicles but they are NOT neurons
Encoding stimulus intensity/duration
A depolarizing receptor potential spreads electrotonically from its site of origin in
the specialized receptor membrane to the spike-initiating zone in the axonal
membrane, which then generates APs
In other cases, the receptor cell forms a chemical synapse with a neuron in this
case, a depolarizing or hyperpolarizing receptor potential spreads electrotonically
from the sensory region of the receptor cell membrane to the presynaptic part of the
cell and modulates the release of a neurotransmitter
AP in different neurons all look the same so it isn`t encoded in the action potential
but is dependent on where the neuron is and where it goes to in the brain
Because APs are all-or-none, stimulus encoding within a single neuron can only be
done in AP freq. cant measure magnitude among different because they are all-or-
none
And the relationship b/w the strength of the stimulus, duration etc., and the
frequency of the APs differs depending on whether you are talking about tonic or
phasic
Can get additional ways about the sensory stimulus when you have more neurons
involved
Two general features are found in sensory receptor cells: 1. each kind is highly
selective for a specific kind of energy and 2. many receptors are exquisitely sensitive
to their selected modality because they are specialized to amplify that type of signal
The process by which receptor cells change stimulus energy into the energy of a
nerve impulse is called transduction
www.notesolution.com
Sensory receptors amplify the sensory signal: activation of receptor molecules in the
plasma membrane initiates a cascade of chemical reactions in the cell that
effectively amplifies the signal by many orders of magnitude
The final step in sensory receptor cells: opening or closing of ion channels, which
changes the amount of ionic current crossing the plasma membrane and directly or
indirectly modifies the number of APs sent to the CNS
Tonic sensory neurons
As long as you receive tonic sensory neurons, brain will maintain stimulus
Receptor adaptation does occur if stimulus intensity is maintained, AP frequency
decreases
Can see that the receptor potential goes down slightly but stimulus intensity
remains steady
Phasic sensory neurons
Action potentials decrease in frequency and stop RAPIDLY after stimulus has
reaches its
Change in stimulus but not duration = can be useful
Happens when a stimulus turns on and off
Tonic vs. phasic
Tonic can give us in terms of magnitude of a stimulus the frequency of AP should
be correlated to the intensity of the stimulus
Once that stimulus starts, frequency of APs should correlate to intensity of the
stimulus
Phasic encodes info about the rate of change of a stimulus
As the mechanical displacement goes from 0 to a new place, if it goes there slowly
while its changing well see lots of APs
www.notesolution.com

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Description
Lecture 12 Chapter 7 Sensing the Environment Section General Properties of Sensory Reception P. 216 230. Section Mechanoreception Introduction through Insect Mechanoreceptors P. 238 240. Sensory receptors Each category of sensation is called a sensory modality The features that characterize stimuli within a particular modality are qualities Interoceptive (internal) receptors respond to signals from within the body and communicate this information to the brain by pathways that typically are not brought into consciousness Proprioceptors monitor the positions of muscles and joints and other interoceptive receptors monitor the chemical and thermal state of the body and its orientation 3 types 2 are neurons = A and B Where the neuron body is difference between A and B Spike initiation zone sits on one side of the soma rather than the other difference between A and B In invertebrate sensory neurons using A B = Long projection of dendrites etc. in verts. Touch receptors in B C: the receptor cell itself is not a neuron o Chemical synapse o When receptor current is generated, this results in synaptic vesicle release, then inhibition of post synaptic membrane o Ex. A taste receptor is involved in sensory info but is NOT a neuron Molecular mechanism www.notesolution.com
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