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Human Anatomy & Phisiology - Jason > L19 Membrane Potential And Nervous Signals > Flashcards

L19 Membrane Potential And Nervous Signals Flashcards

1
Q

Where can neurons repair?

A
  • More successful in PNS than in CNS
  • Neuronal recovery only in axons damaged, not cell body
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2
Q

Why is recovery so limited in the CNS?

A
  • Higher density of axons in brain & spinal cord
  • Astrocytes & oligodendrocytes can block regrowth during repair
  • Microglia cant remove all cell debris from damaged area
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3
Q

Why is neuronal repair in the CNS prevented?

A
  • Improper removal of cell debris prevents recovery
  • Astrocytes proliferate to try and repair the axon
  • Oligodendrocytes reestablish connections with severed axon
  • These conflicting events prevent neuronal repair
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4
Q

What name do we give the process of tissue repair in the PNS?

A

Wallerian degeneration

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5
Q

What are the steps of Wallerian degeneration? in the PNS

A

1) Axon distal to injury degenerates (dies)
2) Macrophages clean up the area
3) Schwann cells proliferate to form a solid cord
4) Recovering axon fuses with long cord of schwann cells
5) Axon continues to grow inside the cord towards the distal cord

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6
Q

What are the nervous system pathologies?

A
  • Destruction of neurons = loss of sensory perception and motor control
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7
Q

What is demyelination?

A

Destruction of the myelin sheat in the CNS (oligodendrocytes) or PNS (Scwann cells)

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8
Q

What are examples of neuropathologies?

A

1) Heavy metal poisoning
2) Multiple sclerosis
3) Guillain-Barre syndrome

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9
Q

What does the neuropathology of heavy metal poisoning do to your nerves and neurons?

A

Slowing or disruption of nerve impulses by oxidative stress, denaturing proteins, and damaging organelles of neurons

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10
Q

What does the neuropathology of multiple sclerosis do to you?

A
  • Progressive autoimmune disease, causing myelin destruction
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11
Q

What does the neuropathology of Guillain-Barre syndrome do to you?

A

Temporary, virally-triggered autoimmune disease causing, myelin destruction

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12
Q

How is the membrane potential created?

A
  • The Na+/K+ ion pump moves sodium out and potassium into the cell, creating an electrochemical gradient.
  • Inside the membrane = negative because of ion pump & negatively charged proteins.
  • This difference is called the membrane potential.
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13
Q

What is a neuron at rest called?

A
  • Resting membrane potential (RMP)
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14
Q

What is the charge of the resting membrane potential and what is its value?

A
  • In neurons -70
  • Negatively charged at rest (in cytosol)
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15
Q

How do we establish the resting membrane potential?

A
  • With three membrane proteins
  • Na+/k+ Ion pump
  • NA+ leak channels
  • K+ leak channels
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16
Q

What does the Na+/k+ ion pump do?

A

Active transporter that pumps three Na+ out and two K+ in

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17
Q

What does the Na+ leak channels do?

A
  • Passive transporters
  • Always open
  • lets Na+ into the cell down its concentration gradient
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18
Q

What do K+ leak channels do?

A
  • Passive transporters
  • Always open
  • Let K+ out of cell down its concentration gradient
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19
Q

How can cells change the resting membrane potential?

A

By altering the permeability of the membrane to Na+ or K+

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20
Q

Why do cells alter the permeability of the membrane to Na+ or K+?

A
  • Perform exocytosis
  • Contract muscle cells
  • Send action potentials along neurons
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21
Q

How does the nervous system use membrane potential?

A
  • Sensory signals stimulate neurons by changing their membrane potential
  • Motor signals cause changes in membrane potential in effectors, causing muscle contraction or exocytosis of glandular cells
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22
Q

What are the different types of membrane channels?

A

1) Leak channels
2) Gated channels

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23
Q

How do leak channels control how ions move across the cell membrane?

A
  • Always open
  • Passively allowing ions to pass freely
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24
Q

Gated channels need to be stimulated to open. What are the type of gated channels?

A

1) Chemically gated channels
2) Mechanically gated channels
3) voltage gated channels

25
Q

How do chemically gated channels work?

A
  • Opened once molecule bounds
    Ex: neurostransmitters
26
Q

How do mechanically gated channels work?

A
  • Opened by physical forces
    Ex: Merkel cells, which sense ligh touch
27
Q

How do voltage gated channels work?

A
  • Opened when membrane potential reaches a certain value
28
Q

What is a move away from the resting membrane potential called?

A

Graded potential

29
Q

How do we define a graded potential?

A

A local chance in membrane potential

30
Q

How do we generate graded potentials?

A
  • By opening chemically or mechanically gated ion channels
  • Ions diffuse into or out, changing the resting membrane potential
  • In neurons, the str of the graded potential determines if it triggers an action potential
31
Q

In which cells can graded potentials occur?

A

All your cells, because they all generate a membrane potention

32
Q

A graded potential can cause something special in neurons what is it?

A
  • Neurons and muscle cells have EXCITABLE membranes
  • Graded potential can trigger an action potential, perpetuating electric signals along their membrane
33
Q

What special property causes a membrane to be excitable?

A

Voltage gated ion channels

34
Q

How is an action potential produced?

A
  • A graded potential strong enough (triggers the opening of voltage gated channels on the axon hilock)
35
Q

What happens if the graded potential was not strong enough?

A

change in the membrane potential does not reach axon hilock, therefore no action potential is produced

36
Q

What happens if a large change in the membrane potential occurs?

A

An action potential is produced

37
Q

What happens if a strong graded potential reaches the axon hilock?

A

voltage gated ion channels open

38
Q

What happens when volate gated ion channels open and the graded potential reaches the axon hilock and sends a aciton potential through the axon?

A
  • Channels open, causing voltage gated channels along the membrane to open
  • Perpetuates signal across the surface of the axon
39
Q

What is the threshhold of a graded potential to trigger an action potential?

A

-55mV

40
Q

What happens in a neuron at rest?

A
  • Membrane potential -70mV (maintained by ion pump and leak channels)
  • All voltage gated ion channels are closed
41
Q

What happens in a neuron that is stimulated?

A
  • graded potential occurs
  • if threshold -55mV reached at the axon hilock, VG Na+ channels open and neuron depolarizes
  • If not reached returns to resting membrane potential -70mV
42
Q

What happens in a neuron that is depolarizing

A
  • Na+ enters cell, causing more voltage gated channels to open on neighboring axolemma
  • causing depolarization signal to creep along the axon
  • Single patch, membrane potential increases from -55mV to zero and rises
  • this continues until it reaches +30mV
43
Q

What happens in a neuron with a membrane potential of +30mV

A
  • Voltage gated na+ channel inactivate
  • Voltage gated K+ channels open (slowly), but open fully at +30mV causing k+ to leave the cell
  • Repolarization occurs
44
Q

What happens in a neuron that is repolarizing back to resting membrane potential?

A
  • Inactivated VG Na+ channels close at -55mV
  • membrane potentials overshoots to -90mV
  • (-70 to -90 is called hyperpolarization)
  • VG K+ channels fully closed during hyperpolarization at -90mV
45
Q

How do we reach resting membrane potential when a neuron is hyperpolarized?

A

Na+/k+ ion pump

46
Q

How is RMP maintained?

A

Ion pump
leak channels
maintain membrane potential of -70mV

47
Q

How does a neuron get ready for the next action potentials?

A

when both voltage gated channels are closed

48
Q

How are action potentials prevented from moving backwards?

A

Voltage gated Na+ channels have 3 settings
1) Closed settings
2) open settings
3) inactivated

49
Q

What does the closed setting prevent in voltage gated Na+ channels?

A
  • ions from moving through the channel
50
Q

How do we open a closed setting in a voltage gated Na+ channel?

A

if the threshhold is reach, it will cause it them to open

51
Q

What does the open setting allow in voltage gated Na+ channels?

A
  • Ions to move through the channel DOWN their concentration gradient
  • Flow of Na+ causes depolarization
52
Q

What does the inactivated setting do in voltage gated Na+ channels?

A
  • Prevents ions from moving through the channel
  • Channel cannot be re-opened
  • Inactivation occurs at +30mV, while reseting to a closed position at -55mV (during repolarization)
53
Q

What settings to volated gated K+ channels have?

A

1) Open
2) Closed

54
Q

When does the closed setting happen in a voltage gated K+ channel

A
  • Neuron at rest
  • at the peak of hyperpolarization (approx -90mV)
55
Q

When does the open setting happen in voltage gated K+ channels?

A
  • When neuron depolarizes to +30mV
  • causing efflux of k+ repolarization and then hyperpolarization
56
Q

How does an action potential move along the membrane?

A

Down the axon in a wave of depolarization from the axon hilock

57
Q

What does the inactivation of voltage gated Na+ channels prevent?

A

A new signal from triggering a new action potential, this creates refractory periods

58
Q

How does the absolute refractory period occur? (ARP)

A
  • Channels are inactive and cannot open again until reset
  • No new action potential can occur during this time
59
Q

What is the relative refractory period? (RRP)?

A
  • During repolarization and hyperpolarization
  • Na+ channels are closed but can reopen if threshold is reached again
  • Membrane potential is lower than usual
  • Stronger stimulus is needed to trigger another action potential

Human Anatomy & Phisiology - Jason (6 decks)

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