APK 2105C Lecture Notes - Lecture 24: Axon Hillock, Membrane Potential, Ion

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Chapter 7, Lecture 3
Neurons
Electrical signaling = changing Vm
o Leak channels help establish the resting Vm
o Gated channels can be signaled to open or close in order to change the Vm
Voltage gated channels
Change in membrane potential that triggers it
Ligand gated channels
Chemical messenger binds to membrane receptor to trigger it
Fast ligand gated channels open
o Acts as receptor and channel
Slow ligand gated channels open AND close
May be specific to ions or just specific to charges (ex: cation
channel, anion channel)
As ion channels are signaled to open, permeability to that ion is
increased—drives the Vm closer to that ion’s Ex
Even though it gets closer, it will NEVER fully reach that ion’s Ex
Describing changes in Vm
o The plasma membrane is polarized at rest
There is a difference in voltage across the membrane
o Depolarization = less negative, may become positive
Open to positive ions
o Repolarization = more negative, less positive
o Hyperpolarization = more negative than resting Vm
Graded potentials = small, decremental changes in Vm that occur when ion channels are
signaled to open or close
o Needed to generate an action potential
o Stronger stimulus = strong depolarization
o Weaker stimulus = weaker potential change
o There is time between stimulus and potential change
o Decremental = as potential travels along plasma membrane, it decreases in
amplitude
Unique to graded potentials
Change in Vm decreases as it moves away from the stimulus site
Axon hillock accumulates the depolarization across the whole cell
Says “can I generate enough positivity to create an action
potential?”
Sum up all the activity
o Can be hyperpolarizing or depolarizing
Hyperpolarizing
Vm = more negative
Inhibitory graded potential = more difficult for the action potential
to be generated
Also decrementally travels to the axon hillock
Depolarizing
Vm = less negative
Becomes more positive
o Open channel to let more positives in
o Close channel to keep more positives inside
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