This is a comprehensive and detailed note on Chapter 44; sensory systems for Biol 105.
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44.1 Sensory Receptor Cells Convert Stimuli into Action Potentials
Sensory receptor cells (sensors or receptors) transduce physical and
chemical stimuli into neural signals
Sensory transduction begins with a receptor protein that opens or closes
ion channels in the membrane, changing the membrane potential (receptor
potential)
Sensory receptor proteins respond to stimuli by directly or indirectly opening
or closing ion channels
The receptors may be ion channels themselves (thermoreceptors and
mechanoreceptors)
2+
Electroreceptors respond to depolarization by opening voltage-gated Ca
2+
channels, and the Ca triggers neurotransmitter release
Chemoreceptors and photoreceptors influence ion channels indirectly by
activating G proteins and second messengers
Some sensory receptor cells are organized with other cells in sensory
organs, such as eyes and ears.
Sensory systems include sensory cells, associated structures, and neural
networks that process the information.
Sensory adaptation: diminishing response to repeated stimulation.
, o Enables animals to ignore background conditions but remain sensitive
to changing or new stimuli
44.2 Chemoreceptors Respond to Specific Molecules
Chemoreceptors: receptor proteins that bind to specific molecules, their
ligands
o Responsible for taste and smell
o Also monitor the internal environment, such as CO levels in blood
2
Olfaction: sense of smell
o Olfactory receptors are neurons in the nasal cavity
o The dendrites extend as olfactory cilia on the surface of the nasal
epithelium.
o The axons extend through holes in the overlying bone and into the
olfactory bulb in the brain
Odorant: molecule that binds to a specific olfactory receptor protein on the
cilia of olfactory receptor neurons (ORNs).
o Odorant binding to a receptor activates a G protein, which activates
the second messenger cAMP .
o cAMP binds to cation channels in ORN’s membrane, causing an influx
of Na and generating an action potential.
Pheromones: chemical signals used to communicate among individuals of
the same species.
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