Electrical properties of Membranes: Neurons 3 Flashcards Preview

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Flashcards in Electrical properties of Membranes: Neurons 3 Deck (50):

What does refractory mean?

unable to respond


Which domain has a refractory period to a 2nd depolarization for a short time?

the axonal domain


Why is there a refractory period in the axonal domain?

because of inactivation of the voltage gate Na+ channels
there is a population of Na+ channels in the membrane that function independently of each other


What are the two refractory periods?

absolute refractory period
relative refractory period


What is the absolute refractory period?

the time from the peak of action potential depolarization through the repolarization phase

2nd depolarization cannot be generated no matter what


Why does the absolute refractory period occurs?

because of the majority of the Na+ channels in that patch of membrane is in the inactive form


What is the relative refractory period?

refers to period of time when the incoming of a greater than normal intensity may produce a smaller than normal action potential


Why does the absolute refractory period occurs?

because of the majority of the Na+ channels in that patch of membrane is in the inactive form


How large of a stimulus is needed and when, is dependent on what factor?

how close the 2nd stimulus is to the the first action potential.
the closer the stimulus is to the initial action potential the larger the stimulus needs to be to generate a small action potential


Why is a larger stimulus needed the closer the 2nd stimulus is to the 1st action potential?

because most of the Na+ channels are still in the inactive state


What passively spreads the the wave of depolarization?

inside + atrcted to the inside - on adjacent membrane
outside - attracted to outside +


Where is the largest wave of voltage deflection?

at the initial point
voltage deflection decreases as it moves away from the initial point
the amplitude of voltage deflection also decreases


Why does the voltage deflection and amplitude of the voltage deflection decrease as it moves away from the initial point?

some leaks out/away until it is no different from the resting potential
this decay happens in all cells


Why doesnt the action potential in excitable cell decay?

Because a new action potential is generated at a new point in the membrane. if a threshold is reached


What depolarizes the adjacent patch of membrane?

the spread of the initial polarization polarizes the adjacent patch of membrane
if depolarization >/= threshold Na+ channels open in that patch inducing a new action potential


which way will the action potential move if it was generated in the middle of the axon?

in both directions


Which way would the action potential move if it was generated at the axon hillock?

only move toward the axon
because the bod and dendrites do not have voltage gated channels to generate an action potential


What is constant and maximal all along the length of the axon?

the amplitude (level of depolarization) of the action potential
you cannot increase stimulus to get a higher action potential


when is it you don't get the maximal action potential?

only in the refractory period


What induces the opening of all the voltage gated Na+ channels in a certain patch of membrane?

the depolarizing of that patch of membrane only


when is it you don't get the maximal action potential?

only in the refractory period


What is a synapses?

specialized site for the transmission transmission of information between neurons


What is the presynaptic cell?

Neuron transmitting the signal


what is the post-synaptic cell?

Neuron/target receiving the signal


what is the post-synaptic cell?

Neuron/target receiving the signal


what is a synapse?

Where the postsynaptic and presynaptic abut each other


What is the pre and post synaptic cells separated by?

synaptic cleft


What is the purpose of the neurotransmitter?

the electrical signal cannot jump the synaptic cleft
the electrical signal induces the release of chemical signals (neurotransmitters) from the presynaptic axon terminus


Where are the neurotransmitter stored?

synaptic vesicles within the cytoplasm of the axon terminus in the presynaptic neuron


What does an incoming action potential do to the axon terminus?

depolarizes the membrane at the axon terminus
this opens voltage gated Ca2+ channels


How large is the electrochemical gradient for CA2+ on the outside of the cell?

1000x greater than the inside.
Tis is a strong driving force of Ca2+ to the inside of cell


What is the purpose of Ca2+?

it acts as a intracellular 2nd messenger and induces exocytosis of synaptic vesicles containing NTs


How are the NTs released?

vesicles fuse with axon terminus membrane
NTs are released
NTs diffuse across the synaptic cleft
Binds to receptors on the dendrites of post synaptic cells


Why do enzyme within the synaptic cleft degrade NTs?

to prevent them from being taken up by the presynaptic cell and repackaged


Why are degrading of NT important?

as long as it is present it will stimulate the post synaptic cell


Where does the conversion of the chemical signal back into an electrical signal happens?

in the post synaptic cell


What does the binding of the NT do on the postsynaptic cell?

it opens up non voltage gated ion channels


What are the receptors on the dendrites?

usually ligand gated or G protein linked receptors with an ion channel as a target for the G protein


What is the movement of ions in/out of the postsynaptic dendrite/ cell body change?

The membrane potential
tis depends on what type of NT and receptor
every time a neurotransmitter binds it produce a small change in membrane potential


Why doesn't the initial change of membrane potential does not induce an action potential in the dendrites/soma?

dendrites/soma do not contain voltage gated channels


What will produce an action potential of the axon hillock of the post-synaptic neuron?

Multiple incoming NTs will lead to an action potential at the axon hillock
if enough NTs input is received change in membrane potential is passively moved along the membrane to the axon hillock


Where is the site of action potential initiation?

axon hillock


What are post synaptic potentials?

when a NT induces its own small, graded voltage deflection along dendritic and cell body membranes


What are the types of post synaptic potentials?

Excitatory postsynaptic potentials (EPSPs)
Inhibitory post synaptic potentials (IPSPs)


What are Excitatory post synaptic potentials (EPSPs)?

always depolarizations usually due to the influx of Na+ or Ca+
spread along membrane to axon hillock no action potential generated


What are Inhibitory post synaptic potentials (IPSPs)?

always hyper polarizations due to efflux of K+ or influx of Cl-


What do PSPs do not do that APs do?

they decay with distance
PSPs can summate with multiple PSPs and be =/> threshold to create a action potential


What is a temporal summation of a PSP?

frequent stimulation of the same patch before it goes back to the resting potential


What is spatial summation?

different PSP are created near each other and they can sum up to greater than resting potential


Why does temporal and spatial summations occur?

Because any patch can receive PSPs aver space and time

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