block 5 lecture 8 action potentials Flashcards
what is an action potential?
rapid change in electrical charge across a plasma membrane
where do action potentials occur?
neurons muscle fibers and endocrine cells
what is the cell body of a neuron also called?
soma
what is the main input structure on a neuron?
dendrites
what is the output structure of a neuron
axon
what does myelination do?
provides insulation
what is the region between soma and axon called?
axon hilock
what may the signals be arriving at the synapse?
excitory or inhibitory
what are the signals called travelling in dendrites?
electrotonic potentials
when travelling in dendrites what is the response called and what does this mean?
graded response, response is proportional to the stimulus
what happens to the negative and positive electrotonic potential
they are summed in the soma
what does the excitation have to be above to get an action potential?
threshold
what kind of spread of action potential do you get down the axon?
non decramental
what is the membrane potential?
difference of electrical potential between the inside and outside of the cell
what voltage is the resting potential?
-70
what is the threshold potential? (value)
-55
what do ion channels do?
selectively transfer ions
what are the 3 types of ion channels in maintaining resting potential?
leak ion channels, voltage gated ion channels, ligand gates ion channels
what is the active tranport in an action potential?
sodium potassium pump
how does the sodium potassium pump work?
3 sodium and ATP binds to pump
hydrolysis of ATP phosphrylates the pump causing it to change in shape
this releases sodium ions and allows two potassium ions to bind
release of the phosphryl group releases potassium into the cystol
what are the three factors of resting potential?
low protein permeability
sodium potassium pump
high potassium permeability through leak channels
limitations of the nerst equation?
one ion
only considers valance and conc gradient
dosent consider permeability
what are the 4 stages of an action potential?
resting state
depolarizing phase
repolarising phase
undershoot
during the resting state what is happening?
-70mv, all voltage gated sodium and potassium channels closed
during the depolarization phase what is happening?
-55 threshold is reached, voltage gated sodium ion channels open
during the repolarization phase what is happening?
+40mv, voltage gated potassium ion channels open, sodium voltage gated channels close
during the undershoot what is happening?
-80mv, potassium channels slowly close
after the threshold what is the strength of the stimulus encoded by?
frequency of action potential
how is the action potential conducted in an unmyelinated axon?
sodium entry at axon hiloclk locally depolarises axon, adjacent axon depolarised
how is one way conduction of an action potential ensured?
sodium channels are inactivated due to the refractory period
how are action potentials conducted in a myelinated axon?
the myelin sheath prevents leakage, sodium and potassium channels are concentrated at the nodes of ranvier, saltatory conduction
what does the speed of conduction depend on?
diameter and myelination
what does the diameter change during action potential conduction?
larger axon faster conduction
what are C axons?
smaller than a micron and unmyelinated
what is MS?
autoimmune, T cells attack the myelin sheath
what is tetrodotoxin?
toxin produced by symbiotic bacteria in pufferfish that block s sodium channels
what do local anesthetic do?
block voltage gated sodium ion channels, prevent Adelta and C fibers which transmit pain
what are the types of local anesthetics?
esters: cocain
amides: lidocain
what can prolong local anesthetics?
vasoconstrictors
