neuron function part 3 Flashcards
Why were giant squid axons used to study?
easily visible to naked eye
not present in mammals
cable properties of axons:
each area of axon consists of an electrical circit what are the three resistors?
extracellular fluid
membrane
intracellular
What does a capacitor do?
stores electrical charge
two conducting materials (ICF and ECF)
insulating layers (phospholipids)
Action potentials travel long distances:
what are 4 characteristics?
all of non all have the same value
self propagating, an AP triggers the next ap in adjacent area of membrane without degredation
electrotonic current spreads along membrane
regenerative cycle
ion entry–> electrotonic current spread–> triggering AP
Cable properties of axons:
axons behave like what?
electrical current
ions moving through voltage gated channels cause current across membrane
current spreads electrotonically along axon
some current leaks out of axon and flows backwards along outside of axon, completing circuit
what are the two ways to increase speed in axons?
myelination and increase diameter of axon
axonal conduction is a combonation of what?
electrotonic current flow and ions flowing though voltage gated channels during AP
Electrotonic current flows faster than what?
opening of voltage gated channels
Electrotonic current flow decrease when?
over distance
what are the disadvantages of larger axons?
take up a lot of space
limits the number of neurons that can be packed into nevouse system
large volume of cytoplasm makes them expensive to produce and maintain
myelin enables rapid conduction in compact space
how does myelin increase conduction speed?
increase membrane resistance- insulator decrease current loss through leak channels increasing the length constant
decreased membrane capacitance- increased thickness of insulating layer reduces capacitance, decreasing the time constant
high length constant and low time constant increase conduction speed
nodes of ranvier are needed to boost depolarization
what are the Node of ranvier for?
areas of exposed axonal membrane between myelin where na channels are concentrated to help boost depolarization
what are internodes?
the myelinated region
what are saltatory conduction?
Ap’s leap from one node to another in very rapid conduction
aps occur at the nodes of ranvier and electrotonic current spreads through the internode
unidirectional signals
action potentials start at the axon hillock and travel towards the axon terminal
down stream na channels are in the absolute refractory period
this prevents retrograde transmission and summation of AP’s
