Action Potential Flashcards
of cell types in the CNS
80-100 billion neurons in the adult brain
Each neuron connects to about how many others
1000-thus 100 trillion connections
Neurons function
Transmission, storage, and processing of info; communicate mainly via chemical synapses
Glia
supporting cells, now known to be involved in processing and signaling
Astrocytes
Supply nutrients, buffer substances (pH), communicate, insulation, form CNS scarring
Damage repair of brain
Astrocytes
Oligodendrocytes
Form myelin sheaths around axons in the CNS
Microglia
Macrophage system of CNS
Ependymal cells
line ventricles (fluid filled)
Gray matter
neuron and glial cell bodies
White matter
myelinated axons
Soma
Cell body
Dendrites
Receive signals to the body
dendritic spine
Form synapses/connections-mushroom shaped
Axon hillock
important in signaling
Axon lenght
very long-can be myelinated too
Axon terminal
Vesicles filled with NTs to be sent to the next neuron in the chain
Impulse conduction main two categores
graded
graded potentials
local changes-change in Amplitude based on distance from the signal
Nearby –> strong effect
Far –> weaker effect (smaller Amplitude)
Max distance graded potentials and go and how they move
transduction of these is passive, and can go a max of 5mm
Variable Amplitude
Of passive conduction-goes down with distance
Action potentials
a way to send a signal very long distances (30ft in a whale :P) without having it decline
ALL OR NOTHING PHENOMONUM`
Which cells do APs happen in
Cells which are excitable (neurons, muscles, heart)
Threshold potential
Membrane potential at which you would fire an action potential. happens when the sodium conductance is greater than the potassium conduction.
Active propagation-
Energy to keep the action potential going is stored along the axon. -Like rows of dominoes.
Potential energy energy stored in dominoes and you are tipping them over and they will keep going.
Energy far from the site is the same as the energy close to the site. AMPLITUDE IS CONSTANT OVER THE DISTANCE!
How is action potential energy stored
as resting membrane potential
Na+ channel opens when
if the threshold is reached they open –> membrane highly depolarizes
Inactivation of Na+ channel? How long?
Seperate from channel opening.
It is like a
flap at the end of the channel and prevents sodium from moving even if channel is open.
Have to reset
it so that it can be activated again. aka REPOLARIZE TO OPEN Open rapidly.
K+ delated rectifier-what does that mean
They open slow and close slow (stay open longer)
Rate at which Na and K channels open
Na open fast and close fast
Resting membrane level is at
-60mV
Threshold of AP
All or nothing-Starts here! Sodium is greater than K conductance here
Rising phase
Na Channels opening and depolarized up to zero
Overshoot
After 0 the potential becomes hyperpolarized to near +25mV
Period of Repolarization
K channels open and Na channels inactivate
Peak
Na channels maximally opened (not all are open but the most than can be at once are)
After hyperpolarization
K conductance returns to the point of normal leak rate
Gk vs Gk at rest
gK > Gk at rest
What happens to stop depolarization
inactivation flap closes
Refractory period
Axon is resistant to firing another action potential, right after one has been fired. Need time to rest
Absolute Refractory period
Cannot fire another action potential-system has to reset first and the Na channel is inactive
Relative refractory period
Threshold here is higher than at rest-still high levels of K conductance –> threshold you need to reach is more +++ and the amplitude will be less
A wave of what follows the action potential (behind it)
in unmyelinated axons—passive depolarization which is very fast and said to be in refractory- this keeps the action potential propagating in one direction.
Passive depolarization happens in which kind of neurons
myelinated
How AP is propagated in a myelinated axon
oligodendrocytes will insulate more of the cell membrane (CNS)
what myelinates axons in the PNS
Schwann cells
Nodes of Ranvier
interruptions of myelin on the myelinated axon which the AP jumps across (Saltatory conduction)–high Na channel concentration here
Concentration of Na channels at nodes of ranvier
high concentration Na channels here
At the nodes what kind of conduction happens?
Passive, thus passive is very fast
Myelinated axons conduction V
225mph
Unmyelinated axons conduction V
225mph
Effect of axon size on speed of conduction
larger the axon the faster it is—–want large myelinated axons
