Action Potentials and Synaptic Transmission Flashcards
what are key factors of AP
Self-propagating biochemical disturbance that generates an electric field or dipole
Successive APs can only be triggered following a brief recovery period, and finally
Absolute and relative refractory periods
All-or-none response
Naturally travel only in one (forward) direction
Describe an action potential generation
a neuron is depolarized to threshold
sodium ion channels open in response to changes in membrane potential (changes in voltage) (voltage gated ion channels)
since more positively charged sodium ions are outside the cell and inside the cell is more negative, opening of the channel allows sodium to rush in due to influence of diffusion and electrostatic forces
influx depolarizes the cell causing more voltage sodium channels to open leading to more depolarization (rising phase of an action potential)
potassium channels open and allow it to rush out along with potassium leak channels
signal moves down axon
what is the rising phase of an AP
the rapid change in membrane potential
when the influx of sodium causes depolarization in turn causing more voltage gated sodium ion channels to open leading to more depolarization
how does an ap come to an end?
once neuron membrane potential reaches its peak, voltage gated sodium channels begin closing
potassium moving out of a cell through potassium gated ion channels and leak channels helps repolarize the cell (back to resting membrane potential)
sodium potassium pump also helps to restore mp
how does an AP move down an axon
once depolarization occurs at one segment causes voltage gated sodium ion channels to open regenerating the ap in the next segment of the axon
lipid rich material that wraps around axons making propagation of ap down the axon faster and more efficient
myelin
How does myelin help propagations of ap go faster?
prevents current from leaking out of the axon
increases speed of propagation interruped by nodes of Ranvier (gaps in myelin)
these nodes are rich in voltage gated sodium channels causing inrushing of sodium and regeneration of AP (happens at each node) propelling the AP down the axon
saltatory conduction
regeneration of ap at nodes of ranvier and slowing at the myelinated regions between them (internodes) causes AP to appear as if its jumping down the axon
what is meant by all or none of an AP
refractory period makes rate of ap firing related to intensity of stimulation
AP don’t vary in size based on intensity of a stimulus, they either fire or they don’t
when they fire they’re consistent amplitude/size
more intense stimuli will cause ______ frequency firing of AP
more
why does a more intense stimuli will cause more frequency firing of AP?
they’re able to overcome relative refractory period in neurons
what happens after a RP depolarizes a receptor
connected axon can generate an AP
or after a receptor send NT across a synapse, the post-synaptic neuron will be triggered and if it is EXCITED postsynaptic potential (EPSP), the voltage change from the EPSP will start the AP
what are ligand-gated channels
alter their permeability as a function of the binding of chemicals/ligands to specific receptors as in the binding of a neurotransmitter to a post-synaptic cell
protein channel that allows an ion to pass through the membrane in response to the binding of a chemical messenger, like a neurotransmitter
what are mechanically or thermally gated channels
mechanically - open and close in response to mechanical vibration or pressure, such as sound waves or the pressure of touch
thermally - activated by temperature, voltage, pH, lipids, and agonists. usally calcium or magnesium channels
how long to voltage gated ion channels open for
10 milliseconds
where does voltage gated channel open at?
axon hillock
depolarization activates what
voltage gated potassium channels
gives rising phase
depolarization, influx of sodium
gives falling phase
repolarize, potassium leaving the cell
which channel stays open longer
potassium causing a prolonged outward K+ current
what is resting potential in mv
-70