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🟑 Neuroscience 🟑 > Nerve 2 > Flashcards

Nerve 2 Flashcards

1
Q

Describe the resting membrane potential

A

At rest :

Inside cell : negative
Outside cell: positive

Membrane potential about -70 mV

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2
Q

Nerve signals are transmitted by ___________________.

A

Action potentials

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3
Q

What are action potentials

A

Rapid changes in the membrane potential that spread rapidly along the nerve fiber membrane οΏΌ

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4
Q

What causes the changes in the membrane potential?

A

The movement of ions in and out of the cell

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5
Q

An action potential has three phases

A

Depolarization
Overshoot
Repolarization

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6
Q

What is meant by ion gating in axons?

A

We know that the changes in membrane potential are caused by changes in the net flow of ions through ion channels in the membrane.

These gates can open or close the ion channels in response to particular stimuli

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7
Q

When ion channels are closed , plasma membrane is _________ permeable to an ion.

A

Less

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8
Q

When ion channels are open , plasma membrane is _________ permeable to an ion.

A

More

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9
Q

At what reading is the resting state

A

-70 mV

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10
Q

What channel is closed during the resting state

A

Voltage-gated Na and K channels

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11
Q

Depolarization is characterized by what

A

Entry/infux of sodium (Na)

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12
Q

Steps of depolarization

A
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13
Q

During depolarization, we said the membrane potential depolarizes from -70 mV to +30 mV. Does the membrane potential reach more than +30mV?

A

NO because these voltage-gated Na channels open for a LIMITED time.

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14
Q

Describe the voltage-gated sodium channel during
- resting (-70 mV)
- activated (-70 to +35 mV)
- Inactivated (+35 to -70 mV)

A

Resting :
- activation gate: closed
- inactivation gate: open

Activated:
- activation gate: open
- inactivation gate: open

Inactivated:
- activation gate: open
- inactivation gate: closed

NOTE: the selectivity filter

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15
Q

Steps of repolarization

A
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16
Q

True or false
Voltage-gated sodium Na channel has 3 states

A

True

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17
Q

True or false
Voltage-gated potassium K+ channel has 3 states

A

False

2 states only (resting and slow activation)

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18
Q

What is afterhyperpolarization ?

What channels are closed or open?

A

More negative than resting membrane potential

Na channels are CLOSED
K channels are still OPEN

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19
Q

The length of time that Na and K channels stay open is ______________ of the strength of the depolarization stimulus

A

Independent

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20
Q

The change from -70 mV to +30 mV and back to -70 mV lasts only about ______ msec

A

3 msec

21
Q

The image of action potential on an oscilloscope screen looks like what shape?

A

Spike

NOTE: action potentials, therefore are called SPIKE POTENTIALS

22
Q

What is threshold?

A

The minimum stimulus required for generation of action potential

23
Q

Do the voltage-regulated gates open, when the depolarization is below threshold value?

A

NO, threshold must be reached in order to generate an action potential and open gates.

24
Q

What happens once the stimulus reaches threshold?

A

Action potential is produced

25
Q

Comment on the relationship between stimulus and response (action, potential generation)οΏΌ

A

Weak stimulus < threshold = no response

Strong stimulus > threshold = response

26
Q

Action potentials are all-or-none.

What does this mean ?

A

A stimulus normally either produces a full-sized action potential or fails to produce one.

The amplitude of action potential is constant, regardless of the strength of the stimulus ; therefore, a stronger stimulus cannot produce an action potential of greater amplitude.

27
Q

True or false

Stronger stimulus can produce an action potential of greater amplitude

A

False

The amplitude of action potential is constant, regardless of the strength of the stimulus

28
Q

How can the nerve transmit different strengths of stimuli ?

A

(See picture)

  1. Weak stimulus - no AP
  2. Strong stimulus - few AP
  3. Stronger stimulus - many AP
29
Q

When is the cell membrane refractory ?

A

When it is producing an action potential

30
Q

During refractory periods, the cell membrane is in either one of two situations. Explain

A

It is either :
- completely unable to fire an action potential
OR
- requires a much stronger stimulation than usual

31
Q

There are two types of refractory periods.

A

Absolute
Relative

32
Q

Absolute refractory period

A

The time during which the membrane cannot respond to any other stimulus NO MATTER HOW STRONG IT IS

Therefore, a SECOND action potential is NOT possible

33
Q

During absolute refractory period , a second action potential is not possible as the membrane cannot respond to any stimulus.

Why??

A

Large fraction of Na channels are inactivated = cannot be reopened until the membrane is repolarized

β€œBall and chain” effect

34
Q

Explain the β€œball and chain” action during absolute refractory period

A

First we know that the :

  • Na voltage-gated ion channel is closed at resting membrane potential, and it opens in response to a threshold level of depolarization where ions required for action potential diffuse.

SO…
After a brief period, the channel is inactivated by the β€œball and chain” portion of a polypeptide chain.
This inactivation ends after a fixed period when the ball leaves the mouth of the channel. Hence, no action potential is produced/ no response to any stimuli.

35
Q

Relative refractory period

A

The time during which an axon can be stimulated with sufficiently very strong stimulus.
So, the cell CAN fire a second action potential, BUT a stimulus stronger than normal is required.

36
Q

Why are we able to fire an action potential with a strong stimulus during the relative refractory period BUT not during the absolute refractory period ?

A

Because during the relative refractory period:
- some Na channels are still inactivated
- enough Na channels in the closed state
- K+ channels are open

37
Q

Explain the local ionic disturbance at the end of an action potential.

A

The Na+/K+ pump reset the chemical equilibrium at the end of the action potential by pumping 3 Na+ out of the cell and 2K+ in the cell, restoring the resting ionic distribution.

38
Q

Explain the conduction of action potential in an UNMYELINATED axon

A
39
Q

Conduction of action potential in a MYELINATED axon

A
40
Q

Myelin sheath provides ______________ for the axon , preventing the movement of Na and K+ through the membrane

A

Insulation

41
Q

The myelin sheath has interruptions called

A

Nodes of Ranvier

42
Q

Na+ channels are __________________________ at the nodes but they are almost _____________ in the regions of axon membranes between the nodes

A

Highly concentrated
Absent

43
Q

What is meant by Saltatory conduction

Can it occur in unmyelinated axons?

A

Action potential only occurs at nodes of Ranvier
(Saltatory conduction describes the way an electrical impulse skips from node to node down the full length of an axon)

NO, only in myelinated axons

44
Q

Compare the conduction rate of myelinated vs unmyelinated axons

A

Myelinated : fast (100 m/sec )

Unmyelinated: slow (1 m/sec)

45
Q

What is the relationship between conduction velocity and nerve diameters?

A

As the diameter DECREASES, the conduction velocity DECREASES.

Therefore, the relationship is DIRECTLY PROPORTIONAL

46
Q

True or false

Multiple sclerosis (MS) is a demyelinating autoimmune disease.

What occurs in multiple sclerosis??

A

True

  • Myelin is destroyed by immune cells
  • Slow or no transmission of action potential
  • Difficulty in performing routine tasks
47
Q

What are local anesthetics?

A

Drugs that REVERSIBLY bind to Na+ channels in the axon membrane, preventing these channels from opening ( NO DEPOLARIZATION)

  • Block the ability of sensory axons to produce action potentials
  • Reduce membrane excitability = nerve impulses fail to pass along the anesthetized nerves
48
Q

Examples of local anesthetics

A

Lidocaine
Procaine

🟑 Neuroscience 🟑 (3 decks)

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