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Neurophysiology > Action Potentials and Synaptic Transmission > Flashcards

Action Potentials and Synaptic Transmission Flashcards

1
Q

What is Ohm’s Law?

A

Rate of FLOW of charges across a membrane = current

I=V/R (current=voltage/resistance

charge, difference of charges across membrane, voltage, permeability

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2
Q

When is Ohm’s law most useful?

A

UNEQUAL distribution of charges VERY close on either side of membrane

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3
Q

Nernst potential

A

Membrane potential is which in/out movement of an ion is balanced/equal. EQUILIBRIUM

DIFFUSIONAL force/ energy gradient

NOT FLOW OR RESISTANCE

VOLTAGE across a membrane that is PERMEABLE to X given ratio of X in:out

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4
Q

At rest, neurons typically have a membrane potential of _______ which is close to the Nernst potential for ______ which is ________.

A

-75mV, K+, -90mV

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5
Q

At rest, which ion channels are the only ones open? What are they known as?

A

K+, leak channels

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6
Q

What does the membrane potential of any cell depend on?

A

relative permeability of the membrane to each ion AND the concentration of the ion on either side of membrane

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7
Q

What does it mean if the membrane potential is close to the Nernst potential of a particular ion?

A

That it is more permeable to that ion

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8
Q

What is the modified form of the Nernst equation, considering more than 1 ion involved? More accurate.

A

The Goldman Field equation

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9
Q

Why is the membrane potential of a neuron close to, but not the same, as the equilibrium (Nernst) potential for K+?

A

Because of the presence of other ions and the activity of ion pumps that contribute to the overall resting membrane potential.

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10
Q

Membrane potential depends on 2 things for each ion. Name them.

A

1.) permeability
2.) concentration gradients

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11
Q

Membranes are poorly permeable to what kind of particles? What does the membrane need for these particles?

A

charged, channels

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12
Q

What is a channel?

A

pores in the membrane that allow movements of an ion

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13
Q

Are channels selective to few ions which the same charge, or open to many ions with different charges?

A

few ions, same charge

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14
Q

Can membrane permeability change very quickly?

A

yes

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15
Q

What dictates how channels change their open/closed states?

A

What they are “built” to detect

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16
Q

What are the different types of channels/their stimuli? (4)

A

1.) voltage-gated
2.) stretch/mechanical deformation- mechanoreceptors/osmoreceptors
3.) intracellular messengers
4.) extracellular messengers -ionotropic receptors (ligand binds to a receptor which is also a channel, binding opens channel and allows ion to cross membrane

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17
Q

Which 3 parts of the neuron are involved in the action potential?

A

axon, axon hillocks, synaptic terminal

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18
Q

What kind of channel does an action potential require?

A

sodium voltage-gated
SOMETIMES calcium voltage-gated

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19
Q

What kind of feedback do action potentials rely on?

A

positive

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20
Q

Action potentials always result in a membrane voltage change that is the same size or gradually increasing in size?

A

same size

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21
Q

Action potentials occur very quickly/or relatively slowly? The membrane becomes more positive/negative?

A

Very quickly, positive (miliseconds!)

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22
Q

What helps to quickly terminate the action potential?

A

K+ VGC

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23
Q

For Na+/K+ ATPase channel, Na+ go in or out? How many? K+?

A

3 Na+ out, 2 K+ in

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24
Q

K+ concentrations are high inside/outside, so it diffuses in/out? This is why we need the pump

A

out

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25
Q

Step 1 is the _____ ________ _________

A

resting membrane potential

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26
Q

What is step 2?

A

depolarization

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27
Q

What does is depolarization activated by?

A

The inside of the membrane becoming more positive

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28
Q

What is the membrane potential that activates Na + VGC to open and Na+ to enter the cell?

A

~-55mV

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29
Q

What channels open in response to depolarization of the cell membrane?

A

Na+ VGC

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30
Q

How do Na+ initiate and propagate action potentials ?

A

By allowing rapid influx of sodium ions

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31
Q

When do K+ VGC open?

A

In response to depolarization but typically with slight delay

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32
Q

What is the role of K+ VGC?

A

contribute to REPOLARIZATION and RESTORATION of resting membrane potential by allowing efflux of potassium ions

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33
Q

What is the period called after an action potential has begun, when a second action potential cannot be triggered for about 1-2 msec, no matter how large the stimulus?

A

absolute refractory period- time required for the Na+ channel gates to reset to their resting positions

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34
Q

Why is absolute refractory period important?

A

so that action potentials moving from trigger zone to axon terminal cannon overlap and cannot travel backward

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35
Q

What’s happening in the relative refractory period?

A

some but not all Na+ have reset and K+ channels are still open.

Na+ that have not quite returned to their resting position CAN BE REOPENED by a stronger-than-normal graded potential.

36
Q

What limits the rate at which signals can be transmitted down a neuron?

A

refractory periods

37
Q

What are depolarizations or hyperpolarizations whose strength is directly proportional to the strength of triggering event. They lose strength through cell.

A

graded potential

38
Q

_____________ made a neuron more likely to fire an action potential. ______________ make a neuron less likely to do so.

A

depolarizing graded potentials
hyderpolarizing graded potentials

39
Q

Which is faster, activation gate or inactivation gate?

A

activation

40
Q

What initiates an action potential?

A

depolarization

41
Q

Difference in fiber size/ speed of impulse?

A

A fibers=largest/fastest/myelinated (touch, pressure, position, heat, cold) final common pathway (12-130 m/sec)

B fibers=medium/medium speed/Non-myelinated15m/sec)
viscera to brain/SC, autonomic efferents to auto. ganglia

C fibers= smallest, non-myelinated (.5-2m/sec) pain, touch, pressure, heat, cold from skin, pain impulses from viscera, efferents to heart/smooth muscle/glands

42
Q

In a chemical synapse, which neuron releases a neurotransmitter?

A

presynaptic

43
Q

In a chemical synapse, where are the receptors?

A

post-synaptic cell membrane

44
Q

What transport mechanism is used in chemical synapses for NT to cross the synaptic cleft from pre-synaptic to post-synaptic membrane?

A

diffusion

45
Q

Where is synapse located? What expresses the receptor for NT?

A

between a dendritic spine or an axon terminal
dendritic spine

46
Q

NT vesicles are synthesized and packaged where? Transported down the axon via what?

What is this called??

A

rER and Golgi
microtubules
fast axonal transport

47
Q

Where are NT synthesized?

A

cytosol of presynaptic terminal

48
Q

How are the NTs transported into the viscle?

A

proton pump

49
Q

In the presynaptic terminal cytoskeleton, vesicles bind to ______ and are transported to release sites aka _________ close to synapse

A

actin, active zone

50
Q

Which type of channels are used in NT release?

A

calcium VGC which leads to release and diffusion across synaptic cleft

51
Q

What does the entry of calcium trigger?

A

exocytosis of synaptic vesicle contents

52
Q

5 steps of neurotransmitter release

A

1.) AP depolarizes axon terminal
2.) depolarization opens Ca2+ VGC and Ca2+ enters the cell.
3.) Ca2+ triggers exocytosis of synaptic vesicle contents
4.) NT diffuses across syn. cleft and binds with receptors of the postsyn. cell.
5.) NT binding initiates response in the postsyn. cell.

53
Q

Key players in vesicle release?

A

v-SNARES, t-SNARES, complexin, synaptotagmin

54
Q

v-SNARES are attached to what? What do they do?

A

vesicles, they “force” the vesicles to fuse with the presynaptic membrane and dock with t-SNARES

55
Q

What type of protein is synaptobrevin?

A

v-SNARE

56
Q

What protein complex is attached to the pre-synaptic membrane and “grabs” the v-SNARE?

A

t-SNARE (target)

57
Q

What are 2 t-SNARES?

A

syntaxin and SNAP-25

58
Q

Which molecule prevents premature release after v-SNARE and t-SNARES engage?

A

complexin

59
Q

Name the calcium-binding protein that “knocks” complexin off the v-SNARE/t-SNARE complex

A

synaptotagmin

60
Q

What does the toxin released by Clostridium botulinum do?

A

impairs assembly and function of v-SNARES and t-SNARES

61
Q

What does Botox A bind to?

A

SNAP-25 (v-SNARE)

62
Q

Which enzymes degrades acetylcholine to acetate and choline?

A

acetylcholinesterase

63
Q

Once NTs are degraded, what reabsorbs them? Where are they then diffused out?

A

astrocytes and presynaptic terminal. Out of cleft and carried by blood

64
Q

What is the result of NTs causing cation channels to open?

A

depolarization for sodium and calcium
hyperpolarization for potasium

65
Q

What is the result of NTs causing anion channels opening?

A

hyperpolarization

66
Q

Many NTs cause what kind of effect? (ex. G-protein)

A

intracellular cascade of second messengers. Can open/close for longer periods of time. Change kinase activity, and gene expression

67
Q

What do ionotropic receptors do?

A

open an ion channel when they bind to their ligand

68
Q

Which type of receptor binds to the NT glutamate which causes Na+ and Ca2+ channel to open

A

NMDA receptor

69
Q

Which receptor binds to acetylcholine, causing Na+ channels to open?

A

Nicotinic acetylcholine receptor

70
Q

Which receptors bind to GABA and glycine causing Cl- channels to open?

A

GABA(a) and glycine receptors

71
Q

Most ____________ receptors are linked to G-protein signaling.

A

metabotropic receptors

72
Q

What is the NT of the neuromuscular junction and expressed through the brain?

A

acetylcholine

73
Q

What is the most important inhibitory NT of the “intracranial” CNS?

A

GABA

74
Q

What is the most important inhibitory NT of the spinal cord?

A

glycine

75
Q

What is are the most common excitatory NT of the CNS?

A

glutamate

76
Q

NMDA receptors are very important for what?

A

learning and memory

77
Q

Which NT has autonomic NS functions, cortical and limbic system roles

A

norepinephrine

78
Q

If NT binds to an inhibitory receptor what happens? excitatory?

A

hyperpolarization (membrane becomes more negative)
depolarization (membrane becomes more positive)

79
Q

What brings about graded potentials in the dendrites and cell bodies?

A

graded potentials

80
Q

Graded potential is any change in membrane potential that DOES NOT result in what?

A

action potential

Include changes in membrane potential that are below the threshold for an action potential or occur in areas of the cell that do not have Na+ VGCs

81
Q

Which lasts longer, graded or action potential?

A

graded

82
Q

If multiple graded potentials add up in a “staircase” fashion over time, this is called what?

A

temporal summation

83
Q

What does it take for graded potentials to initiate an action potential in a Na+ VGC?

A

The net result of all EPSPs and IPSPs are integrated and the axon hillock and if it brings the hillock to threshold, an AP (or string of APs) will fire

84
Q

What kind of receptors can have very long-lasting effects including protein synthesis and long-lasting intracellular signals?

A

metabotropic

85
Q
A

Neurophysiology (9 decks)

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