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BIO 172 prof. Wells > Chapter 12 [ EXAM #1 ] > Flashcards

Chapter 12 [ EXAM #1 ] Flashcards

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1
Q

action potentials (3)

A

To get electrical signal from dendrites and cell body to axon terminal

Rapid change in membrane potential that once starts moves along length of excitable membrane without loss of strength: “all or none” (-60mV does not work)
- Neurons and muscle cells

Voltage gated Na+ channels (VGSCs) open at axon’s initial segment

  • Depolarizes and triggers more to open
  • Action potential is nerve impulse: domino effect along membrane
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2
Q

threshold (4)

A

Depolarization of membrane to certain level: threshold (~60mV in neurons)

Result of local graded potentials produced by >1 stimuli

Locally summed at axon hillock

Spreads to initial segment

  • VGSCs in initial segment open
  • Chain reaction along membrane
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3
Q

threshold all-or-none principle (3)

A

Triggered when threshold reached -55mV: graded potentials result of stimuli added together

or not (subthreshold): only produces graded potential below threshold -55mV

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4
Q

Action Potential Generation (the 4 steps)

A
  1. ) Depolarization to threshold (-60mV)
  2. ) Rapid Depolarization: Activation of VGSCs (Na+ channels)
  3. ) Repolarization: Inactivation of VGSCs and activation of K+ channels (Kv)
  4. ) Hyperpolarization and return to normal resting potential and permeability
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5
Q

Channels involved in action potential generation

A

voltage gated Na+ (VGSCs) and K+ (Kv) channels

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6
Q

At resting potential, what channels are open?

A

Only leak channels are open at this phase

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7
Q

1.) Depolarization to threshold (-60mV)

A

local currents, graded potential summation at axon hillock

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8
Q

2.) Rapid Depolarization (3)

A

Activation of VGSCs (Na+ channels)

At threshold Na+ channel activation gates open, influx of Na+ occurs, opens more Na+ channels (up to +30mV)

Positive feedback loop

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9
Q

Is sodium positive or negative charge?

A

positive

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10
Q

3.) Repolarization (4)

A

Inactivation of VGSCs (close) and activation of K+ channels (open) (Kv)

Occurs at +30mV

Kv channels open slowly

K+ flows out of neuron

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11
Q
  1. Hyperpolarization (6)
A

return to normal

Kv channels begin to close at RMP (~ 70mV)

Kv finish closing slowly (~90 mV)

returns to rest (AP is over)

Na+/K+ ATPase works to restore ion concentrations

Na+ channels reset (ready)

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12
Q

Define refractory period

A

time between action potential start until normal resting potential regained

2nd action potential can not form in response to normal threshold stimulus

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13
Q

Absolute refractory period

A

Can not respond to any further stimulation

Maximum VGSCs open or inactivated

K+ flow-opposing force

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14
Q

Relative refractory period

A

Can produce another action potential in response to larger-than-normal stimuli….why?

Some VGSCs have returned to resting state

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15
Q

Propagation of action potentials

A

Propagation: message passed along axon by repeating same events over and over (open voltage-gated channels etc.)

Can be continuous or saltatory

From point of generation (axon hillock and initial segment) to axon terminal action potential keeps its strength

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16
Q

Where does continuous propagation occur

A

unmyelinated axons

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17
Q

is continuous propagation fast or slow

A

slow (2mph)

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18
Q

how does continuous propagation operate?

A

local Na+ current opens VGSCs in next axon segment

every axon segment affected

message is “retold” over and over until it reaches synapse

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19
Q

why can’t continuous propagation travel backward?

A

refractory periods

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20
Q

where does saltatory propagation occur?

A

myelinated axons of PNS and CNS

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21
Q

is saltatory propagation fast or slow?

A

fast (250 mph)

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22
Q

does saltatory propagation require more or less ATP than continuous propagation?

A

saltatory propagation uses less ATP than saltatory propagation

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23
Q

how does saltatory propagation operate?

A

local currents skip internodes, depolarize nodes of Ranvier

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24
Q

how does axon diameter affect absolute refractory period?

A

smaller axon diameter = longer abs. refract. period

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25
Q

what prevents continuous propagation in saltatory propagation?

A

myelin wrapped around axons = greater resistance to ion flow (few VGSCs)

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26
Q

what are type A nerve fibers?

A

largest

myelinated

urgent 250mph

somatic sensory and motor fibers

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27
Q

what are type B and C nerve fibers?

A

smallest

myelinated and unmyelinated

slow 2mph

visceral sensory and motor fibers serving organs

some somatic pain

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28
Q

what are synapses

A

non-direct cell-to-cell attachment

most neuron-neuron and all neuron-cell

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29
Q

where does NT travel in the context of post- and pre-synapse?

A

from the pre-synaptic cell to the post-synaptic

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30
Q

what is the chemical called that is released from the pre-synaptic cell?

A

neurotransmitter

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31
Q

what is an excitatory neurotransmitter?

A

depolarization results

promotes action potential

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32
Q

what is an inhibitory neurotransmitter?

A

hyperpolarization results

opposed action potential

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33
Q

what is the function of synaptic vesicles?

A

to store neurotransmitters

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34
Q

what is a cholinergic synapse?

A

a synapse that releases acetylcholine (ACh)

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35
Q

where can you find cholinergic synapses?

A

NMJ

neuron-neuron in PNS

parasympathetic neuromuscular and neuroglandular synapses

brain

36
Q

what are the four steps occurring in a cholinergic synapse?

A

AP arrives and depolarizes at synaptic terminal

Ca2+ enters synaptic terminal, triggering exocytosis of ACh

ACh binds to receptors and depolarizes the postsynaptic membrane

ACh removed by AChE

37
Q

what is synaptic delay

A

time between arrival of action potential and post-synapic effect

reflects time of Ca2+ influx and NT release

less synapses = short synaptic delay

more synapses = more synaptic delay

38
Q

what does Ca2+ do?

A

causes release of vesicles that release ACh

39
Q

what is synaptic fatigue? what does it depend on?

A

NT cannot recycle fast enough to meet demands

depends on RER production in cell body and axoplasmic transport

40
Q

where is norepinephrine released?

A

adrenergic synapses

CNS & sympathetic nerves

41
Q

what is the role of norepinephrine?

A

excitatory and deploarizing effect

42
Q

where is dopamine found?

A

CNS

43
Q

what is the role of dopamine?

A

excitatory or inhibitory depending on the synapse

44
Q

is dopamine depleted or increased in Parkinson’s?

A

depleted

45
Q

is dopamine depleted or increased with cocaine usage?

A

increased

46
Q

where is serotonin found?

A

CNS

47
Q

what is the function of serotonin?

A

alters emotional states (e.g. chronic depression)

effects depend on receptors

48
Q

what is substance P?

A

pain

49
Q

what is the function of amino acid based peptide NTs?

A

substance P and pain nerves

50
Q

what is the function of opioids?

A

endorphins and pain reduction

51
Q

what is the function of neuromodulators?

A

affect pre- and post-synaptic cells

rate of NT synthesis

52
Q

what are the direct effects NTs have on membrane potential?

A

NT binds chemically to gated ion channel, channel opens

Ionotropic: alters ion flow through membrane

fast effect compared to indirect

53
Q

what is Ionotropic? is it a direct or indirect effect on membrane potential?

A

direct effect

alters ion flow through membrane

54
Q

what are the indirect effects NTs have on membrane potential?

A

NT bind to membrane proteins linked to G-proteins

Metabotropic: NT receptor coupled to G protein

slow effect compared to direct

55
Q

function of G protein?

A

triggers intracellular signaling cascade, turns on enzymes, etc.

56
Q

can the same NT be excitatory at some synapses and inhibitory at others?

A

yes

57
Q

how does lipid soluble gas enter the cell?

A

diffusion

58
Q

what does lipid soluble gas bind to?

A

enzymes in cytosol

59
Q

what is the role of lipid soluble gas?

A

it’s the second messenger production that affects post-synaptic cell activity

60
Q

what are the two gases at certain brain synapses?

A

NO and CO

61
Q

how many stimulus is needed for action potential formation?

A

> 1

62
Q

what determines form of action potential?

A

sum of all stimuli

63
Q

role of axon hillock

A

integrates (sums) stimuli, determines effect on initial segment

64
Q

what are the two types of summation?

A

temporal summation

spatial summation

65
Q

define temporal summation

A

summation of stimuli that occur at same synapse but at different times

66
Q

if a second stimulus arrives before the effects of the first has worn off, it is called…

A

temporal summation

67
Q

does temporal summation result in more or less NT released by presynaptic terminal?

A

more NT

68
Q

do graded depolarizations (or hyperpolarizations) increase or decrease in temporal summation?

A

increase

69
Q

define spatial summation

A

summation of stimuli at multiple synapses at same time

70
Q

what two things does the amount of depolarization depend on in spatial summation?

A

number of synapses active at same time

how far away from axon hillock the synapse is

71
Q

define postsynaptic potentials (PSP)

A

graded potentials develop in postsynaptic membrane when NT binds

72
Q

define excitatory PSP (EPSP)

A

NT causes membrane depolarization

Na+ flows in

makes more neg

73
Q

define inhibitory PSP (IPSP)

A

NT causes hyperpolarization

makes more positive

74
Q

define facilitation

A

a neuron whose membrane potential shifts closer to threshold

75
Q

if EPSPs > IPSPs, but below threshold what is the result

A

no AP

76
Q

if EPSPs > IPSPs and reaches threshold what is the result

A

AP produced

77
Q

rates of action potentials are limited by what two things?

A

refractory periods and NT availability

78
Q

what determines how the message is interpreted in action potentials?

A

frequency

79
Q

define neuronal pools

A

connected neurons in CNS responsible for a specific function

80
Q

define neural circuit

A

wiring patterns of synaptic connection in neuronal pools

81
Q

what is a diverging circuit?

A

one neuron synapses on many post-synaptic cells

amplifies signal

tree-effect

one brain neuron stimulating many muscle fibers

82
Q

what is converging circuit?

A

several neurons synapse of one post-synaptic

effective stimulation or inhibition

primarily sensory

83
Q

what is reverberating circuit

A

branches from later neurons to former ones

recycles impulses

prolongs response to stimulus

short term memory, normal breathing

84
Q

what is serial processing?

A

info relayed in stepwise manner from one neuron to another

straight line, single file

spine reflexes, sensory to brain

85
Q

what is parallel processing

A

divergence

several neurons process info at same time side by side

BIO 172 prof. Wells (23 decks)

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