BIO 012 Lecture Notes - Lecture 12: Membrane Potential, Ligand-Gated Ion Channel, Sensory System
12 Jun 2018
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Chapter 46 10/12/17
46.1 How Do Sensory Receptor Cells Convert Stimuli into Action Potentials?
Stimuli (light, sound, touch, temperature) – physical entity of the world around you
Sensation – turning a stimulus into an action potential
Perception – interpreting sensations
Sensory receptor cells usually simply called sensors or receptors, transduce physical and chemical stimuli
such as light and sound waves, pressure, and odorant and taste molecules into neural signals. These
signals are then transmitted to the central nervous system for processing and interpretation. The first
steps of this process of sensory transduction is a change in the membrane potential of the receptor cell in
response to a specific type of stimulus.
Receptor potentials – graded potential in sensory cells caused by environmental stimulus. These
potentials also cause changes in the membrane potential of a receptor cell in response to a stimulus.
- The receptor potential may trigger action potentials in the receptor cell
- The receptor potential may cause the receptor cell to release neurotransmitters that can induce
a postsynaptic neuron to generate action potentials.
Strength of stimuli – affected by number of action potentials
- To get more action potentials; more neurons have to be fired or one neuron can fire more often.
Every action potential created by a graded potential looks the same because it is all or none.
Ex: Bats sensing echolocation, fish sensing bugs out of water and shooting them with water
Sensory transduction involves changes in membrane potentials.
- They usually begin with a receptor protein that opens of closes ion channels in response to a
specific stimulus such as heat, light, chemicals, mechanical force, or electric fields.
Sensory receptor proteins act on ion channels
- These proteins respond to stimuli by directly or indirectly opening or closing ion channels in the
sensory channels in the sensory cell, leading either to an action potential or to the release of
neurotransmitter.
o These proteins are either ionotropic or metabotropic.
- Electrosensors most likely do not have receptor proteins but they are grouped with the ionotropic
receptors.
- Metabotropic sensory receptor proteins influence ion channels indirectly through G proteins and
second messengers.
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Sensory receptors can be activated fast or slow
- Fast: Ionotropic receptors - stimuli directly affects ion channels. Neurotransmitter binding to an
ionotropic receptor causes a direct change in ion movement across the plasma membrane of the
postsynaptic cell. These proteins enable fast, short lived responses. Responds to stimuli is quick
o Pressure – sensitive cation channel →Membrane changes shape because of pressure
– mechanical gate
o Temperature sensitive cation channel
o Voltage gated Ca2+ channel → voltage change can open the gate
- Slowly: Metabotropic receptors - stimuli indirectly affects ion channels. They induce signaling
cascades in the postsynaptic cell that secondarily lead to changes in ion channels. Responds to
stimuli slowly
o When a molecule attaches to proteins (receptors) on the membrane, the proteins
change shape, and things in the cell are affected until finally the channels open.
o Proteins in the retina change shape based on light hitting them
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“esory Receptors ca Adapt fast or slow to a stiuli
- Adaptation → gradually diminishing activity in response to a maintained, repeated, or
sustained stimuli. An animal can ignore background or unchanging conditions while
remaining sensitive to changes and new info.
o Ex: walk into a bathroom, smells bad, after a while you do’t id the sell
- Some sensory cells adapt very little or very slowly; examples are some types of pain receptors
and the mechanoreceptors that control balance.
Phasic vs. Tonic Receptors
- Phasic receptors are fast-adapting
o Ex: slight touch →high five, or slight temperature change → in the shower, smell →
smelly room
- Tonic Receptors are slow adapting
o Ex: pain → throbbing pain sometimes you may not pay attention to but it will be hard
to go away simply, vision → visual system
Sensation depends on which neurons receive action potentials from sensory cells.
- All sensory cells process info in the form of action potentials. But the sensations we perceive
– heat, pressure, light, etc. – differ because the messages from different kinds of sensory cells
arrive at different places in the CNS.
- Some sensory receptor cells are assembled with other types of cells into sensory organs, such
as eyes, ears, and noses, that enhance the ability of sensory cells to collect, filter, and amplify
stimuli.
- Sensory systems include the sensory cells, their associated organs, and the neural networks
that process the info.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Stimuli (light, sound, touch, temperature) physical entity of the world around you. Sensation turning a stimulus into an action potential. Sensory receptor cells usually simply called sensors or receptors, transduce physical and chemical stimuli such as light and sound waves, pressure, and odorant and taste molecules into neural signals. These signals are then transmitted to the central nervous system for processing and interpretation. The first steps of this process of sensory transduction is a change in the membrane potential of the receptor cell in response to a specific type of stimulus. Receptor potentials graded potential in sensory cells caused by environmental stimulus. These potentials also cause changes in the membrane potential of a receptor cell in response to a stimulus. The receptor potential may trigger action potentials in the receptor cell. The receptor potential may cause the receptor cell to release neurotransmitters that can induce a postsynaptic neuron to generate action potentials.
