Lecture 7 Action Potentials Flashcards
K channels
4 subunits
Channel pore loop forms
Selectively permeable to K ions
Scorpion toxins
Block potassium channel opening
Mckinnon
x-ray crystal structures
Mutations of specific k channels
inherited neurological disorders
Importance of external K regulation concentration
Restin membrane potential is close to K because it is mostly permeable to K
Increase extracellular K depolarizes membrane
BBB, Potassium spatial buffer by astrocytes
Mechanisms regulating the external potassium concentration
Ligang-gate channels
Open in response to binding of specific chemical (ligand) to specific receptors (neurotransmitters and receptors)
Voltage-gated channels
Open in response to changes in voltage across membrane
Neurotransmitter binds to
receptor opening chanel
Graded (local) potentials
small local changes in potential of neurons plasma membrane
Depolarization
Cation enter cytosol, making membrane potential less negative, membrane potential approaches 0 mV
Hyperpolarization
Cation exit cytosol or anion enter
Membrane potential become more negative
Repolarization
Cell returns to resting MP
Anion enter cell, cations enter cytosol
Change in MP depends on
Length of stimuli
number of ion channels open
types of ion channels open
Reversible
when stimulus stops, neuron quickly returns to resting potential
decremental
current is lost across membrane
useful for short-distance signaling only
Actionpotentials
uniforms, rapid depolarization and repolarization of the MP
AP generated
trigger zones (axolemma, axon hillock, initial segment of axon)
Voltage gated channels
responsible for AP
Types of VG channels
VG sodium ion channel
VG potassium ion channel
Resting state
channels are closed; no potassium ions are able to cross plasma membrane
Activated state
Channels are open; potassium ions are able to flow down concentration gradient
VGSC resting potential
inactivation gate is open and activation gate is closed
No sodium ions are able to move
VGSC activated state
voltage change opens activation gate
VGSC inactivated state
inactivation gate is closed and activation gate is open
Channel no longer allows sodium ions to move through; once AP is over channel returns to resting
VGSC structure
4 domains, each has 6 transmembrane helices S1-6, pore loop
S4 transmembrane
contains positively charged amino acids groups
changes conformation moving towards extracellular surface opening pore
AP depolarization
membrane potential rises towards 0; then becomes positive briefly
AP repolarization
MP returns to negative value
AP hyperpolarization
MP temporarily becomes more negative than resting MP
AP steps write out fully
resting potential
Rising phase
overshoot
falling phase
undershoot
Absolute refractory period
time from opening of Na channels until inactivation gate is closed
enforces one-way transmission
Relative refractory period
follows absolute period
Most Na channels have returned to their resting state
Some K channels still open