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Physiology Intro > Lecture 2 NS Physio / APs > Flashcards

Lecture 2 NS Physio / APs Flashcards

0
Q

Describe the concentrations of sodium and potassium inside and outside the neuronal cell membrane

A

Na+ is higher outside the cell 140mM
K+ is higher inside the cell 140mM
Na+ 15 mM inside
K+ is 5mM outside

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1
Q

All neurons have different electrical properties resulting from
A)
B)

A

A) differences in ion concentration across the cell membrane
B)special permeability characteristics of the plasma membrane to ions

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2
Q

How are the concentration differences MAINTAINED across the neuronal cell membrane?

A

Na+ K+ ATPase pump located on the cell membrane

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3
Q

What is the permeability of the neuronal plasma membrane to ions due to?

A

The presence of ion channels located in the membrane.

The ions follow the rules of diffusion aka; Na+ will move IN and K+ will move out

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4
Q

Describe non-gated ion channels in relation to the neuronal membrane.

A

Always in the open position

Higher number of K* channels than Na+

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5
Q

At rest is the neuronal membrane more permeable to k+ or Na+ ?

A

K+

There is more non-gated channels

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6
Q

What are gated ion channels?

And the 3 types ?

A

Not involved at rest.
Require stimulation to open. Opening to stimulus defines the type of gate:
Voltage gated
Chemical gated - binding of nT of a hormone
Mechanical gated - temperature changes

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7
Q

What is potential difference ?

A

The DIFFERENCE in charge across a cell membrane. If the inside is -70. That means the inside of the cell is 70 mV more negative than the outside of the cell.

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8
Q

Resting membrane potential is

A

-70mV potential difference

Inside is 70 times more negative than out

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9
Q

Describe the Na+ / K+ ATPase pump

A

Uses 1 ATP to pump 3 Na+ out and 2K+ in. It maintains RMP.
Moves ions against gradient.
Only slightly contributes to RMP

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10
Q

3 reasons the resting membrane potential is maintained

A

1) Na+ k+ ATPase pump
2) the high amount of nongated K+ channels
3) the negatively charged organic molecules inside a cell

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11
Q

How does the higher preponderance of non gated K+ channels help maintain RMP?

A

The membrane is more permeable to K+ than Na+ at rest.

K+ diffuses out I the cell down it’s gradient making the inside more negative.

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12
Q

How does large negatively charged molecules in the cell help maintain RMP?

A

Too large to leave cell and carry a negative charge

So when K+ leaves the inside is more negative

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13
Q

When the cell becomes more negative toward RMP what begins to happen?

A

Diffusion of K out slows
Na+ diffusion in increases
At some point they stabilize so that the net movement of charge is 0 and the RMP is -70mv

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14
Q

When is the net movement of charge 0 in a neuron?

A

When resting membrane potential is reached.

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15
Q

What is a polarized membrane ?

A

An unequal distribution of charge
Just means not balanced
This unequal distribution of charge is also known as A POTENTIAL DIFFERENCE

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16
Q

There are only 2 types of cells that are electrically excitable, what are they?

A

Muscle and nerve cells

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17
Q

What does an electrically excitable cell entail?

A

They are able to produce departures from the resting membrane potential. Called an ACTION POTENTIAL.

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18
Q

What is an action potential ?

A

an impulse

A large change in membrane potential that propagates along an axon with no change in intensity.

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19
Q

Action potentials are produced in response to stimuli which are

A

Changes in internal or external environment of the body

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20
Q

What Is a graded potential ?

A

Small change in membrane potential usually on the dendrite or cell body
Causes ions to move - travel passively a short distance.
Short lived UNLESS the grades potential is large enough to reach threshold potential .. Then an action potential will occur.

21
Q

True or false the larger the stimulus the larger the graded potential?

A

True

22
Q

What kind of transport is involved in the ions when a graded potential occurs?

A

Passive

Creating a flow of electrical current

23
Q

Graded potentials can occur two different ways what are they?

A

Depolarization.
And
hyperpolarization

24
Q

What is depolarization

Give an example

A

The resting membrane potential is becoming less polar . In a cell whose RMP is -70mV .. A depolarization would be if a stimulus occurred that changed it’s mV to 65mV

25
Q

Describe hyperpolarization and give an example

A

This occurs when the stimulus makes the cell more polar. In the case of a cell with RMP of -70 mV a hyperpolarization would cause the cell to become more negative ie, -80mV

26
Q

Depolarization and hyperpolarization make use of which chanels?

A

gated ion channels

27
Q

Graded potentials are given different names for different areas, what are they?

A

Receptor potential or generator potential - sensory receptor excited

Post synaptic potential - when stimulus is a nT released by another neuron

28
Q

Repolarization is

A

Return to resting membrane potential

29
Q

Summation (of graded potential)

A

If the first graded potential is still present when the second stimulus happens the resulting graded potential will be larger than the first

30
Q

Why are graded potentials important ?

A

Because if the GP is large enough than AP will occur

31
Q

What potential difference must be reached at axon hillock for an AP to occur ?

A

-55mV @ axon hillock

32
Q

Where does an action potential begin?

Along what does it propagate ?

A

Axon hillock (trigger zone) or dendrites of UNIPOLAR neurons

Axon

33
Q

Why are graded potentials short distance signals ?

A

Current is lost through leaky plasma membrane, the voltage declines with distance from the stimulus ie voltage is decremental

34
Q

Sequence of events of action potential

A

1) -70mv - graded potential occurs, if reaches -55mv then the action potential takes place which is steps 2, 3, and 4.
2) depolarization - +30mv
3) repolarization
4) hyperpolarization , below -70mv

35
Q

Describe the depolarization of action potential

A

MUST BE ABOVE THRESHOLD (-55)
Voltage gated Na+ channels open
Na+ rushes in cell depolarizing it
The inside of the cell becomes positively charged to +30mV

36
Q

Describe the repolarization phase of action potential

A

The Na+ channels become inactivated as the cell becomes more polar again
The voltage gated channels for k+ also open and that allows K+ to exit the cell.- making cell more negative.
Approaches RMP again

37
Q

Describe what happens during hyperpolarization and after

A

As K+ rapidly leaves the cell via the voltage gated channels there is a period where the cell is more negative than RMP = hyperpolarization
The gated channels then close their gates and RMP is re-established via diffusion / Na+ K+ ATPase pump

38
Q

During what stage of action potential is K+ most permeable?

A

Repolarization
The Na+ gates have become inactivated once +30 has been reached and the cell wants to become more negative quickly so K+ gates open and it rushes out.

39
Q

What is the absolute refractory period ?

A

The period in which an action potential is not possible even by the largest stimuli

40
Q

Why does an absolute refractory period occur ?

A

1) because the Na+ channels are still open (depolarization)

2) Na+ channels inactivated (cannot open until membrane potential passes resting membrane potential)

41
Q

What is the relative refractory period ?

A

The period when an action potential can be generate but requires a stimulus larger than normal.
After the membrane potential passes resting membrane potential on the way to hyperpolarization the Na+ gates are able to be reopened. The k+ channels are open and therefore leaving the cell ; hyperpolarized, so now a greater than normal stimulus is needed to reach threshold.

42
Q

What is the all or none principal ?

A

Action potentials are all or nothing.
-55 must be reached or AP will not occur
All APs look the same.
If a stimulus is very strong the AP will not be different
A weak stimulus will not generate AP because it’s below threshold

43
Q

What types of gated channels ate associated with graded potentials… With action potentials ?

A

Chemical and mechanical for gated

Voltage for AP

44
Q

Describe what happens when an action potential propagates:

Depolarization during the action potential:

A

Positive charge moves toward more negative charge on adjacent membrane. The depolarization is large enough and gets another action potential .

45
Q

Why do action potentials move in only one direction ?

A

Because the preceding membrane is still in refractory period.

46
Q

The rate of action potential is dependant on a couple things, what are they ?

A

1) fiber diameter

2) myelination

47
Q

If a fiber undergoing action potential is large, do you think the speed of propagation would be faster or slower ? Why?

A

Faster
There is less resistance to current
Aka; less stuff in the way

48
Q

Would the speed of propagation be Slower in a myelinated fiber or an unmyelinated one?

A

Slower in the unmyelinated

49
Q

Where does the action potential occur on myelinated fibers?

What is a name for myelinated fiber conduction ?

A

Nodes of Ranvier

Saltatory conduction

50
Q

Where does action potential occur in an unmyelinated fiber?

What’s a name for this kind of conduction ?

A

All along the length of the fiber
This is called continuous conduction
Slower

Physiology Intro (10 decks)

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