APK 2105C Lecture Notes - Lecture 24: Axon Hillock, Membrane Potential, Ion
5 Jun 2018
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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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