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Physiology Block 5 > Propagation And Tranimssion Of Action Potentials > Flashcards

Propagation And Tranimssion Of Action Potentials Flashcards

1
Q

What happens to depolarization as distance from stimulus increases?

A

Decay rapidly

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2
Q

Distance between axon hillock and synapse

A

Long

  • can be meters long
  • AP has to maintain strength to elicit response
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3
Q

Single APs

A

Usually not sufficient to carry info along a neuron

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4
Q

What kind of feed back is AP propagation?

A

Positive

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5
Q

AP propagation

A

Initial AP begets new APs in adjacent membrane

-bi direction if able, physiologically in one direction

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6
Q

Each new AP in propagation

A

Is full strength and follows the same steps and propagates itself

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7
Q

What allows for full strength APs to travel along length of neuron?

A

Each new AP is full strength and follows the same steps and propagates itself

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8
Q

Speed at which APs are conducted away from initiation site

A

Conduction velocity

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9
Q

What is conduction velocity dependent upon

A

Time and length constants

-how quickly you change charge across membrane

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10
Q

How fast membrane can depolarize to 63% of max AP voltage

A

How far depolarization travels before falling below 63% of max

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11
Q

Smaller time constant (t)

A

Faster depolarization, faster conduction

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12
Q

What does the time constant depend on (Rm)

A

Number of open channels (resistance)

-more open channels, lower resistance, more ion flow, faster depolarization

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13
Q

What is the second thing that the time constant depends on? (Cm)

A

How well the membrane holds charge (capacitance)

-less charge in membrane, more is transferred inside, faster depolarization

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14
Q

What allows depolarization to travel further?

A

High resistance, less open channels fewer ions leaking out, depolarization can travel further

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15
Q

How easy current can flow inside the cell

A

Internal resistance (Ri)

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16
Q

What is a better conductor than the membrane?

A

Cytoplasm

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17
Q

_____ nerves have more cytoplasm than thinner nerves (better conduction)

A

Thicker

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18
Q

Increasing diameter does what to Ri

A

Lowers by increasing area of cytoplasm to membrane

-higher length constant means further/faster conduction

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19
Q

____ nerves conduct impulses faster than smaller nerves

A

Thick

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20
Q

What limits the size of nerves?

A

Anatomical constraints

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21
Q

Which of the following set of conditions would give you the most rapid conduction?

A
  • low time constant

- high length constant

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22
Q

Layers of glial cells wrapped around axon

A

Myelination

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23
Q

What are the cells that myelinated in the CNS

A

Oligodendrocytes

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24
Q

What are the cells that myelinated in the PNS

A

Schwann

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25
Myelin distribution in axons
Evenly distributed along axon with small spaces between
26
What are the small spaces between the myelination
Node of ranvier
27
What does myelin do for the axons?
Insulates the axon to make AP 'jump' between nodes
28
What is it called when the AC jumps between the nodes of ranvier
Saltatory conduction
29
Myelin wraps around axon and doesn't allow any ______ in the area it surrounds
Ion flux
30
What does myelin do the Rm (membrane resistance) under the sheath?
Increases it to increase the length constant
31
Rm (membrane resistance at the nodes
Allows for ion channels to be enriched, so decreases Rm at node to decrease time constant
32
Myelin essential does what to the nerve
Shortens it
33
Which nerve is likely the most heavily myelinated?
Motor neuron because its long distance and needs to be quick (reflexes)
34
What are some examples of demyelination diseases?
- MS (central) - Guilin-Barre syndrome (peripheral) - Diabetic Neuropathy (peripheral) Usually autoimmune
35
Because myelin makes nerves fast, they control __________- receptors
Skeletal muscle and pain/touch receptors
36
Los of myelin decreases ____ to a point where APs might not be propagated
Length constant | -low number of ion channels under sheath. When destroyed are unable to depolarize
37
What does loss of myelin cause?
Muscle weakness, loss of coordination, loss of sensation, paralysis, death
38
Site of communication fro one cell (usually a neuron) to another
Synapse
39
Electrical synapse
Gap junctions (not that common)
40
Chemical synapse
Most common
41
Direct connections between cells which allows ions to flow between (easiest)
Electrical synapse
42
What type of synapse creates a syncytium?
Electrical synapses
43
What is the purpose of the gap junctions in electrical synapses?
Connexons make holes in neighboring membranes
44
Examples of electrical synapses
Heart, smooth muscle, bladder, where coordinated contraction is required
45
Is there integration in electrical synapse?
No
46
Speed of electrical synapses
Fast
47
Information is transported via chemicals across the synaptic cleft in a unidirectional flow
Chemical synapse
48
What alters the membrane potential on the post synaptic cell
neurotransmitters released from presynaptic cell by the AP
49
What do neurotransmitters do once released
Bind to receptors on post synapse
50
Speed of chemical synapse
Slow
51
Is there integration in a chemical synapse?
Yes
52
Synaptic transmission
- propagation of AP - release of neurotransmitter - binding of neurotransmitter to receptors - effect on post synaptic cell
53
Propagation of AP
AP is propgated down the axon of the pre synaptic nerve
54
Release of neurotransmitter
- When AP reaches the terminal, voltage gated calcium channels *VGCC) open - Ca2+ enters, causes the release of NT into the synaptic cleft
55
What happens when the AP reaches the terminal?
Voltage gated calcium channels (VGCC) open
56
Binding of neurotransmitter to receptors
- NT diffuse across the cleft from pre to post synaptic cell | - bind to receptors on post synaptic cell membrane
57
Effect on post synaptic cell of NT
- binding of NT to receptor alters membrane potential - depolarize - excitatory- more likely for AP to fire (Na+, Ca+) - hyperpolarize - inhibitory - less likely for AP to fire (K+, Cl)
58
Predict the effect of calcium ionosphere on NT release
More NT is released because voltage gated calcium channels open in the terminal bouton
59
Predict the effect of hypocalcemia on NT release
Less NT release
60
Action of NT at the neuromuscular junction
- AP travels down motor neuron, open VGCC, allow influx of Ca+ - Ca2+ causes release of Ach - Ach binds to nicotinic receptors (nAchr) on post synaptic cell - nAchr are Na+ channels-leads to EPP(Na goes in, hypopolarization, AP) - if enough open, depolarization reaches threshold. New AP in the muscle causes contraction
61
What is Ach broken down by?
Acetylcholine esterase (AchE)
62
What does acetylcholine get broken down into?
Choline and acetate
63
_____ is taken up by pre and used to regenerate Ach for next transmission
Choline
64
Once Ach is no longer bound
EPPs stop, APs stop and contraction stops
65
Altering the NMJ
Done therapeutically for anesthesia or treating diseases. Can be fatal
66
Predict the mechanism of action of neostigmine
Inhibits acetylcholine esterase (allows Ach to accumulate in synapse)
67
What are some chemicals that affect NMJ?
- Botulinum toxin-Botox - Curare-arrow poison - Neostigmine -AchE inhibitor - hemicholinium-blocks choline reabsoroption - no Ach
68
How does botulinum toxin (Botox) affect NMJ?
Blocks release of Ach- paralysis - locally, no wrinkles on your forehead. - systemically, paralyzed respiratory muscle, dead
69
How does curare (poison arrow) affect NMJ?
Blocks Ach receptors-paralysis | -no medicinal use, paralyzed respiratory muscle, dead
70
How does neostigmine affect NMJ?
AchE inhibitor-prolongs time Ach stays in cleft, increases contractions -used in myasthenia gravis and to reverse paralytic anesthesia
71
What are some uses of disruption of the NMJ?
- potent chemical ware fare | - pesticides (organophosphates)

Physiology Block 5 (8 decks)

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