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Biol 331 > Membrane Potentials > Flashcards

Membrane Potentials Flashcards

1
Q

What is a neuron (nerve cells)

What are most neurons found in

A

A specialized cell that is used for communication with other cells in the form of electrical impulses (that a formed by changes in ion gradients)

Most neuron are part of the central nervous system and peripheral nervous system (brain and spinal cord)

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2
Q

What is a neuron composed of

A

Dendrites

Axons

Terminal knobs

Myelin sheaths

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3
Q

What are dendrites

A

They are the parts of the neuron than branch out from the neuron body and receive information (from other neurons)

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4
Q

What are axons

A

The long end of the nerve cell that extends from the body to the terminal knobs

It conducts outgoing information

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5
Q

What are terminal knobs

A

Thing where the impulses are transmitted to the target cells

One neuron can have many terminals knobs that interact with many different cells

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6
Q

What is the myelin sheath

A

It’s a lipid rich membrane that wraps around most vertebrate axons

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7
Q

All cells have a ___

A

Membrane potential/ membrane voltage

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8
Q

What is a membrane potential/voltage

A

The difference in charge across a membrane

The outside of the cell has different charge than the inside of the cell

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9
Q

What is the resting potential

A

The potential of the membrane when a nerve cell is in an unexcited state (not stimulated)

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10
Q

What is the axon membrane voltage diffence between the inside of the membrane and the outside

If just outside?

A

The voltage is -70

0 because there’s no charge difference

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11
Q

What is the voltage of the inside of the cell compared to the outside

A

-70

Means the cell in more Negative on inside

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12
Q

What is the resting potential of a neuron

A

-70mV

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13
Q

What contributes to the difference in charge across the membrane?

A
  1. The sodium potassium pump in the membrane pumps 3 sodium ions out of the cell per every 2 k+ going in. Creating a gradient and making the voltage more negative

This means that overall more positive charges are going out of the cell, making the outside more +

  1. The k+ ions have the most permeability in a resting nerve cell

they flow out of the cell through potassium leak channels (following their concentration gradient)
This cause more postive charges on the outside of the cell

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14
Q

How is equilibrium reached if more postive is outside the nerve cell membrane than the outside

A

the concentration gradient favours k+ going out

The electrical gradient favours the k+ going in

So a balance between k in and k out occurs so overall voltage doesn’t change much from -70

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15
Q

What is an action potential

A

It is the changes in the axons membrane potential after a stimulus (poke, heat) is introduced

The basic for neural communication

Includes depolarization and repolarization and takes 5ms in a squids axon

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16
Q

What are the step of what happens for an action potential

A

Resting potential

Depolarization

Repolarization

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17
Q

What is the resting potential part of action potentials

A

The k plus is leaving the cell through the leak channel, the inside of the membrane is more negative than outside

The membrane is not very permeable to sodium or potassium through the sodium or potassium gates (gates are closed)

18
Q

What is depolarization

A

The electrical potential/voltage difference across the membrane decreases

meaning the inside of the membrane is more postive like the outside, and the voltage is less negative

19
Q

How does depolarization happen

What happened if there a larger stimulus

A

In response to the stimulus, sodium channels In The cell membrane open and the sodium diffuses into the cell through a voltage gated na Channel

The inside of the cell has become more postive

If larger stimulus more sodium in the cell

If lower stimulus less sodium into cell and depolarization doesn’t happen

20
Q

What is the threshold value to depolarization to happen and what happens after

A

Enough na has to come in so that the membrane potential goes from -70 to -50mV

Once this happens, the voltage gated sodium channels open and wayyy more sodium comes into the cell to make the potential go to +40mV

The sodium channel close spontaneously after 1ms

21
Q

What happens to the permeability of NA and K during depolarization

A

The na is wayyyy more permeable then the k+

22
Q

What happens during repolarization

A

Want more negative on inside of the cell to get more negative voltage

After the depolarization occurs, this triggers the the voltage gated K channels of open and the sodium’s channels close

This makes it so that more + is now LEAVING the cell and creating the polarity. This causes the membrane potential to go to -80mV

Because the membrane potential becomes very largely NEGATIVE now due to charge difference (more negative on inside) the voltage gated potassium channels CLOSE

23
Q

What happens to the permeability of potassium and NA during repolarization

A

The K is initially very high permeable and sodium is low

Then after a while the K get lower and the na gets lower

24
Q

What is hyperpolarization

A

The potassium channels are slow to close so the potential over shoots and goes to -80 during repolarization

25
Q

During the action potential how is the voltage and na and k concentration gradients affected

A

The voltage gradient changes but the concentration gradients are barley affected

26
Q

How does the action potential travel down the axon

A

Through a nerve impulse

the action potential is sent along the neuron by the triggering of action potentials in adjacent portions of the membrane

27
Q

What are the two way a nerve impulse can happen

A

Continuous conduction

Saltatory conduction

28
Q

what is continuous conduction

A

Happens in unmyleinated axons (with no myelin sheet)

The flow of current during the action potential will make the membrane region next to where the action potential is happening to become depolarized

The action potential that was induced along the axon doesnt lose its intensity but

The part of the membrane that previously had the action potential is in a refractory period where the sodium channels can’t reopen to move the action potential backwards.

29
Q

What happens in a saltatory conduction

A

Happens myelinated axons where the nerve impulses are 20x faster than in unmyelinated because

The myelin (lipid rich) prevents ions from passing across the membrane

This means the the na and k channels are found in or near unmyelinated region of the axon called nodes of ranvier.

The action potential at this NODE induced action potential at another NODE (faster propagation of the action potential down the axon)

30
Q

Can nerve impulses be amplified

A

No

31
Q

What determines the direction of the nerve impulse down the axon

A

The refractory period

32
Q

What is a synapse

A

The junction (interaction) of a neurons terminal knob with its target cell

33
Q

What is a pre synaptic cell

A

The neuron that conducts the impulse (action potential) towards a synapse

34
Q

What is the synaptic cleft

A

The space separating the neuron from the target cell

35
Q

What is the postsynaptic cell

A

The cell that takes in the impulse

36
Q

What is the synaptic vesicles

A

The things that store neurotransmitters in the terminal knobs of the axons

37
Q

What are neurotransmitters

A

The chemical that’s released from the synaptic vesicles and binds to the postsynaptic cell

38
Q

What happens after the nerve impulse is propragted along the axon and goes to the terminal knob

A

The impulse causes depolarization to happen in the knob which leads to the voltage gated calcium channels to open in the presynatic cell (knob)

This leads to calcium diffusing into the presynatpic cell since initially ca concentration was low in the cell

39
Q

After the ca goes into the presynaptic cell after the nerve impulse what happens

A

The influx of ca into the presynaptic cell triggers the synaptic vesicles to fuse with the plasma membrane of the presynaptic cell

This releases the neurotransmitters (acetylcholine) in the synaptic vesicle to the recipient cells and allows them to bind to the ligand gated ion channels or the postsynaptic cells membrane

40
Q

After the neurotransmitters are binded to the ligand gated ion channels on the postsynaptic cell what 2 things can happen

A

Excitatory effect: The neurotransmitters cause an influx of na (+) ion into the postsynaptic cell which depolarizes the cell and bring it to form action potential/nerve impulse

Inhibitory effect : negative ions (cl) are influx instead and do hyperpolarization where action potential less likely to happen

41
Q

What stops the postsynaptic cell from continually being stimulated once neurotransmitters have entered the synaptic cleft

A

The neurotransmitters have a short half-life

enzymes destroy them in the synaptic cleft

Or they are taken back up into the presynaptic cell by transporters in the presynaptic cell

Biol 331 (18 decks)

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