BIPN 100 Lecture Notes - Lecture 5: Schwann Cell, Cardiac Muscle, Oligodendrocyte
26 Jun 2018
School
Department
Course
Professor
BIPN100 Lecture 5 Notes 4/11/18
- Phases of the action potential: size of action potential is constant
oNeuron starts at resting membrane potential at -70 mV
oWhen graded potential reaches axon hillock and reaches
threshold of depolarization, activates action potential
oVoltage-gated Na+ channels activate (activation gates open)
through depolarization, increasing Na+ permeability and Na+
moves into cell down its electrochemical gradient. This makes
the cell more positive, causing the membrane potential to
increase
oOnce the cell reaches +40 mV, the inactivation gate of the
voltage-gated Na+ channels blocks the channel so Na+ can no
longer cross into the cell (time dependent, not voltage
dependent). This occurs at the peak of the action potential.
Activation gate closes and Inactivation gate opens once
repolarization occurs (goes back to original position)
oVoltage-gated K+ channels start activating at -55 mV due to
depolarization, however, they are slow compared to Na+ channels. They
only have one gate, so it takes longer for enough channels to open for K+
movement. This allows the repolarization stage as K+ exits the cell. K+
continues to leave cell until it reaches its equilibrium potential of -90 mV,
causing hyperpolarization. Slowly deactivate as channels close
oNa+ slowly enter cell through leaking and cell returns to resting ion
permeability and resting membrane potential
- Regenerative propagation of action potentials
opropagates without losing its strength
ograded potential reaches axon hillock. If above threshold,
action potential occurs
odepolarization from graded potential activates voltage-gated
Na+ channels. Na+ enters cells and locally propagates signal
by activating the next patch of Na+ channels. Depolarization
continues to occur, continually activating the neighboring
Na+ channels, so no strength is lost
opropagation doesn’t go back to the cell body because of the
refractory period
orefractory period: time where you cannot generate another
action potential if you stimulate the neuron. Voltage-gated
K+ channels active and K+ exits cell to prevent backflow of
action potential, as depolarization cannot occur
absolute refractory period: cannot stimulate action
potential no matter how large the stimulus is because Na+ channels are inactivated;
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
This occurs at the peak of the action potential. Activation gate closes and inactivation gate opens once repolarization occurs (goes back to original position: voltage-gated k+ channels start activating at -55 mv due to depolarization, however, they are slow compared to na+ channels. They only have one gate, so it takes longer for enough channels to open for k+ movement. This allows the repolarization stage as k+ exits the cell. K+ continues to leave cell until it reaches its equilibrium potential of -90 mv, causing hyperpolarization. Slowly deactivate as channels close: na+ slowly enter cell through leaking and cell returns to resting ion permeability and resting membrane potential. Regenerative propagation of action potentials: propagates without losing its strength, graded potential reaches axon hillock. If above threshold, action potential occurs: depolarization from graded potential activates voltage-gated. Na+ enters cells and locally propagates signal by activating the next patch of na+ channels. Depolarization continues to occur, continually activating the neighboring.
