Lecture 5 Flashcards by Anna Baldwin

The driving force for Na+ at resting of -65mV is _____mV

-127 mV

Vm - ENa+ = -65mv (+62)

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The driving force for K+ at resting of -65mV is _____mV

+15mV

Vm - EK+ = -65mV - (-80)

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If ENa+ = -127mV and EK+ = +15mV, this means resting potential is near (Ek+/Ena+) due to (low/high) conductance of (Na+/K+) leak channels.

EK+ ; high ; K+ leak channels.

K+ channels leave little room for it to leave at -65mV, so there is a LOW driving force.

BUT there is a HUGE want for Na+ to enter, yet at a low conductance.

Both have LOW conductance. ACTION POTENTIAL OCCURS

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Current equation (I) = _____ * ______ _______

conductance * driving force

Iion = gion * V

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T/F:

Na+ and K+ have the same driving force

NO. They are oppositely oriented.

This is why they are aligned, we see an action potential

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T/F:

One input to a neuron is enough to cause an action potential.

FALSE.

It receives thousands of input from presynaptic axons.

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Local potentials are (small/large) changes in somadendritic regions

SMALL

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Local potentials are (excitatory/inhibitory/both)

BOTH

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Hyperpolarization of the cell leads to an (EPSP/IPSP) since it is (easy/hard) to depolarize the neuron with it being (inhib/excit)atory

IPSP ; HARD ; INHIB

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A cell is hyperpolarized when (K+/NA+) bombards the cell with news, Cl- (wants to hear the hot goss/freaks out), and (stays in/moves out)

K+ bombards the inside, Cl- doesn’t want to listen, moves out

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When a cell is hyperpolarized, the inside becomes more (+/-)

NEGATIVE because K+ and CL- have just created a toxic friendship

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Depolarization of the cell leads to an (EPSP/IPSP) since it is (easy/hard) to depolarize the neuron with it being (inhib/excit)atory

EPSP ; easy ; excitatory

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A cell is DEpolarized when (K+/NA+) bombards the cell with news, Ca+ (loves Na+/can’t stand it), and (stays to listen/leaves the room)

Na+ ; Ca+ is so supportive of this ion they it will stand with it to the end

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When a cell is DEpolarized, the inside becomes more (+/-)

POSITIVE because Na+ and Ca- have such a lovely friendship

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With distance, an IPSP and EPSP will (dissipate/continue) together

Dissipate

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With (temporal/spatial) summation, the potentials occur at the same time in different locations, allowed to add up

Spatial

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Can IPSP subtract from EPSP?

YES

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With (temporal/spatial) summation, the potentials combine for a temporary time before the previous signal fades. Therefore, they try to build on each other ever so slightly.

Temporal

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Local potentials ______ with time

Dissipate

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Spatial Summation shows up (at the same time/repeatedly) to different locations

THE SAME TIME

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Temporal Summation shows up (at the same time/repeatedly) to different locations

REPEATEDLY

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An action potential is a rapid “____ ____ _____” increase in the membrane to +___mV followed by a rapid ___ back to resting

all or nothing ; +40mV ; fall

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When does action potential initiate at the axon?

the neuron is DEPOLARIZE to the threshold potential (~55mV)

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After action potential is initiated at the axon hillock, what does this result in? What phases of the action potential are these? (2)

opening of voltage gated Na+ channels in the axon hillock (40mv). Rising phase and peak

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After an action potential initiates at the axon hillock, the neuron increases to +40mv. What does this activate? What two phases of the action potential is this?

opening of voltage-gated K+ channels (returns membrane back to -65mv). Falling phase and discharge.

The action potential goes down the axon, resulting in what release?

Neurotransmitter release at the axon terminal

What are two ways we record action potentials?

1. electrode inside the cell 2. electrode placed extracellular near (group) cell

Subthreshold membrane potential oscillations do not result in what? And why?

Action potentials because they don't reach threshold

What determines an action potential?

Coincidence and summation of many stimulating inputs

Once membrane potential hits threshold, what happens?

the action potential is "all or nothing"

If threshold is met due to summed stimuli, what happens to voltage gated channels?

Na+ channels open and Na+ pours in, membrane potential briefly becomes positive

Why is action potential called all or nothing?

it fires completely when threshold is met, amplitude is almost always +40mv no matter how much strong the stimulus was

What can differ with action potentials in all or nothing?

firing frequency can increase with current amplitude (neuro. encoded)

Firing frequency of an action potential depends on what?

magnitude of depolarization

A neuron will fire what in action potential?

high spikes if depolarization is maintained and membrane manages above threshold

in action potential, encoding of stimulation intensity is what?

the spike frequency and train duration (the neuron screams)

Can a neuron fire again in absolute refractory period?

Can a neuron fire again in relative refractory period?

MAYBE but it's difficult to depolarize due to after-hyperpolarization

If injected current cannot depolarize the membrane to proper threshold, can an AP occur?

If injected current depolarizes the membrane to proper threshold, can an AP occur?

YES

The AP firing rate _____ as the depolarizing current ______

increase ; increase

With normal ion channel activity, absolute concentration of the ion in and out the cell changes/does not change substantially: (pick one)

DOES NOT CHANGE

How can you change absolute concentration of the ion?

in an experiment. just a few ions make a HUGE membrane potential difference

Hodgkin and Huxley used the ____ ____ to determine ionic permeability changes during the action potential:

voltage clamp

The voltage clamp is what system?

a feedback system

Hodgkin and Huxley observed what two currents?

oppositely-oriented and temporally separated

Hodgkin and Huxley showed that ____ ____ current is carried by ___ and outward by ____

early inward ; Na+ ; K+

Na+ produces an inward current due to what?

the inside is more positive ; cations flow IN and anions OUT so it's a downward current deflection (NEGATIVE PROCESS)

K+ produces an outward current due to what?

the inside is more negative ; anions flow IN and cations OUT so it's a upward current deflection (POSITIVE PROCESS)

Membrane potential (voltage) is _____ to current

OPPOSITE

Driving force for Na+ is greatest when Vm is at ______ potential and for K+ it is greatest at _____ potential

resting ; peak

Driving force equation is what?

Vm - Eion

What is the resting potential driving force for Na+?

-65mv at resting - (-62 for influx) = -127mv. Very negative resting but high EXTRAcellular Na+ since it wants to GO IN (and read)

What is the resting potential driving force for K+?

+40 mv at resting - (-80 for influx) = +120mv. Very positive resting but high INTRAcellular K+ since it wants to GO OUT! (party)

What is the calculation for current?

Iion = gion X Driving Force = gion x (Vm-Eion)

What drives rising and falling phases for Na+ and K+?

CURRENT

Driving force and current are ____ for Na+

negative (party POOPER)

Driving force and current are ____ for K+

positive (optimistic)

What is the current for any ion dependent on?

1. Conductance of ion-selective channel (high when open, low when closed... extrovert...) 2. Driving force (changes during AP)

What is the spike initiation zone?

Synaptic input at dendrites or soma which may depolarize the cell but CANNOT generate AP (low levels of Na+ channels in these cell parts. Not welcome)

If membrane potnetial reaches threshold at AP, it will initiate the what? (zone)

Spike Initiation

The spike initiation zone has high lvls of what?

Na+ and K+ voltage gated channels

What is an action potential?

abrupt depolarization of the membrane that rapidly spreads down the axon, allows neuron to communication with other parts of body

AP signal is like what at propagation?

Lit fuse

Why does the AP spread down the axon away from soma upon initiation?

the spread of axoplasmic Na+ to neighboring part axon, it depolarizes the threshold

Why does the AP signal back propagate?

the left is refractory, Na+ channels are already inactivated

Entry of positive charge during AP causes what?

the membrane ahead to depolarize and hit threshold

What three factors affect RATE of AP conduction?

1. thin axon (resists Na+ speed) 2. no saltatory conduction, internode myelin conduction 3. low resistance electrical shunt

What three factors affect AP conduction?

no voltage fated Na+ channels or mechanisms for AP in the internode (myelinated) regions.

Diverse firing patterns of neurons are due to what? (2 things)

1. type/combination of ion channels present 2. rate and pattern of info fired

Driving force for K+ = Vm-Eion when Vm = Eion gives a value of ____mV

0 gK = -80 (vM) - (-80 Ek (Eion)) = 0

If Vm = -80 (close to Ek), and there is high conductance for K+ with open channels, what is the driving force?

if Vm were more positive than -80mV (which is favorable for Ek), there will (not/always) be a K+ driving force and K+ is the (in/out)ward current if channels are open.

ALWAYS ; OUT

If driving force = 0, then there is no _______

current

If you increase external K+ experimentally, it (hyper/de)polarzies the cell *you need to think over the whole process for this one*

DEPOLARIZES K+ gives less of a difference between the outside and inside now. Therefore, you need LESS K+ ions to create a counterbalance so vM can be more positive. By increasing the K+ that goes out, you increase resting to be more positive. This changes Ek in the nerst equation, making Ek more positive as well. K+ will ALWAYS want to keep the cell this way. The cell is OVER threshold, causing Na+ to go on high alert and open so the cell can DEPOLARIZE, causing constant action potentials.

Lecture 5 Flashcards

Action Potential (76 cards)