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A&P 1 FAU > Lecture 9.2 main points > Flashcards

Lecture 9.2 main points Flashcards

1
Q

what must happen in order for electrical signals in motor neurons to be communicated to muscle

A

electrical signals (action potentials) from motor neurons must be transformed into chemical signals ( neurotransmitters)

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2
Q

where does the electrical signal in motor neurons communication to muscle

A

at the neuromuscular junction

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3
Q

as a result of the electrical signals, what do the chemicals cause in a muscle cell

A

chemical signals then stimulate electrical signals in sarcolemma of the muscle fiber ( if strong enough)
the electrical signal in the muscle fiber (action potential) then activate a series of events that leads to the shortening of the skeletal muscle fiber

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4
Q

what is the predominant theory of skeletal muscle contraction

A

sliding filament model of contraction

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5
Q

brief description of sliding filament model of contraction

A

interactions between thick and thin filaments of the sarcomere produce the contraction (shortening) of a skeletal muscle cell
-in a relaxed state, thin and thick filaments overlap slight
-during contraction thin filaments slide toward the M-line past the thick filaments (acting and myosin overlap more)

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6
Q

chemical gradients of certain ions are necessary for what

A

proper electrical, and contractile activity of skeletal muscle

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7
Q

three main ions in muscle cells. concentration at rest intracellular vs extracellular

A

intracellular [Ca] very low
intracellular [Na] very low
intracellular [K] high

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8
Q

what is the numeric value of intracellular charge at rest

A

-95 mV

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9
Q

what is the extracellular charge at rest

A

0 mV

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10
Q

what two events must occur for skeletal muscle to contract

A

activation and excitation-contraction coupling

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11
Q

how does activation occur and what must it generate

A

must be nervous system stimulation, must generate action potential in sarcolemma
happens at the neuromuscular junction

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12
Q

what does action potential (excitation) produce that is necessary for contraction

A

action potential propagated along sarcolemma
intracellular Ca levels must briefly rise leading to the onset of contraction

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13
Q

list the steps in sequence for phase 1 in which the motor neuron stimulates the muscle fiber (activation)

A

AP arrives at axon terminal at neuromuscular junction
Ach is released, binds to receptors on sarcolemma
Ion permeability of sarcolemma changes
Local change in membrane (depolarization) occurs
Local depolarization (end plate potential) ignites the AP in sarcolemma

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14
Q

list the steps in sequence for phase 2 in which excitation (action potential) - contraction coupling occurs

A

AP travels across the entire sarcolemma
AP travels along T tubules
SR releases Ca, Ca binds to troponin,
myosin binding sites on actin exposed
myosin heads bind to actin, contraction begins

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15
Q

what type of neuron connects to, and stimulates, a skeletal muscle cell, is it voluntary or involuntary

A

somatic motor neurons, voluntary

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16
Q

how do somatic motor neuron axons travel to skeletal muscle

A

travel via nerves (bundles of mostly neuron axons)

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17
Q

are somatic motor neuron axons branched or unbranched

A

may form several branches as it enters the whole muscle

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18
Q

each axon ending forms a neuromuscular junction with what

A

a single muscle fiber

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19
Q

events of the motor neuron at the NMJ (neuromuscular junction)

A
  1. action potential arrives at the axon terminal of motor neuron
  2. voltage gated Ca channels open. Ca enters the axon terminal moving it down its electrochemical gradient
  3. Ca entry causes Ach to be released by exocytosis
  4. Ach diffuses across the synaptic cleft and binds to its receptors on the sarcolemma
  5. Ach binding opens ion channels in the receptors that allow SIMULTANEOUS passage of Na INTO the muscle fiber and K OUT OF the muscle fiber
    more Na enters than K exits which produces a local charge in the membrane potential called the end plate potential
  6. Ach effects are terminated by its breakdown in the synaptic cleft by acetylcholinerase and diffusion away from the junction
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20
Q

at the NMJ do calcium channels open or close briefly

A

open briefly allowing calcium to enter the axon terminal

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21
Q

at the NMJ what ion moves through the channel and where does it go

A

calcium moves through the channel and goes into the cell

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22
Q

what is the purpose of calcium inside the axon terminal? What does it cause?

A

causes acetylcholine to be release by exocytosis

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23
Q

what is the neurotransmitter used for chemical communication between the motor neuron and skeletal muscle fiber

A

Ach (acetylcholine)

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24
Q

into what space is acetylcholine released

A

the synaptic cleft

25
Q

what Ach destroying enzyme waits in the synaptic cleft

A

acetylcholinesterase

26
Q

why is acetylcholinesterase important

A

breaks down Ach to acetate and choline
prevents continued muscle fiber contraction in the absence of addition stimulation

27
Q

as Ach makes it to the surface of the muscle cell at the NMJ what receptor does it bind to?

A

nicotinic acetylcholine receptor (nAchr)

28
Q

as Ach binds to nAchr does the ion channel open or close

A

open

29
Q

what two ions are allowed to pass through the post synaptic ion channel

A

sodium and potassium
sodium in, potassium out

30
Q

does Na or K flow through the channel in greater amounts in the post synaptic membrane

A

Na

31
Q

what effect does the ion flow have on the membrane charge of -95mV

A

makes it more positive, depolarization

32
Q

the change in sarcolemma membrane charge at the NMJ is called what

A

end plate potential

33
Q

is the end plate potential a local event or entire cell event

A

local, only happens at the NMJ not on the whole cell

34
Q

what is depolarization

A

when the membrane voltage gets closer to zero from its initial -95. Becomes less polar (different)

35
Q

what chemical directly affects the release of acetycholine

A

calcium

36
Q

term for critical value voltage that must be reached in order to illicit an action potential

A

threshold

37
Q

once threshold is reached, what ion channels open in large amounts

A

voltage gated sodium channels

38
Q

what do voltage gated sodium channels allow to pass

A

sodium into the cell

39
Q

what is the effect on the intracellular membrane voltage with the increasing flow of sodium into the cell

A

intracellular membrane voltage becomes more positive

40
Q

what phase of AP generation involves the opening of sodium channels called

A

depolarization phase

41
Q

what phase follows depolarization and what does it do for the electrical condition of the membrane voltage (intracellular)

A

repolarization, becomes less negative due to more potassium exiting than sodium entering

42
Q

during repolarization many voltage gated sodium channels begin to close, what channels begin to open

A

voltage gated K channels

43
Q

during repolarization, as sodium channels close, what happens to the amount of sodium flowing into the cell

A

decreases the influx of sodium

44
Q

during repolarization as potassium channels begin to open what happens to potassium flow outside of the cell

A

potassium flow more rapidly outside of the cell

45
Q

what is the effect of lessening sodium influx into the cell and increasing potassium efflux out of the cell, does the intracellular membrane voltage change?

A

intracellular membrane voltage becomes more negative

46
Q

what happens when potassium channels close

A

membrane potential is restored back to resting

47
Q

what cannot happen during the refractory period

A

another action potential cannot be stimulated

48
Q

what is the latent period

A

when E-C (excitation- contraction) coupling events occur, time between AP initiation and beginning of contraction

49
Q

certain voltage-sensitive proteins are found in the membrane of the T-Tubule, what is their name

A

DHP receptors

50
Q

what ion passes through DHP receptors

A

small amounts of calcium to flow into the sarcoplasm

51
Q

DHP receptors are connected to special protein channels called what

A

Ryanodine receptors

52
Q

where are ryanodine receptors found

A

in the terminal cisterns of the sarcoplasmic reticulum

53
Q

what is the function of ryanodine receptors

A

to release calcium from the sarcoplasmic reticulum into the sarcoplasm

54
Q

when stimulated by DHP receptors, ryanodine receptors allow what ion to pass through their channel

A

calcium

55
Q

where does the calcium flow when passed through ryanodine receptors

A

from the sarcoplasmic reticulum into the sarcoplasm

56
Q

how does the influx of calcium ions into the sarcoplasm affect sarcoplasmic Ca concentration

A

it increases

57
Q

excitation coupling events

A

single muscle AP causes brief activation of DHP receptors followed by activation of the ryanodine receptords allowing a brief release of calcium into the sarcoplasm. the DHP receptors deactivate therefore closing the Ryanodine receptors, ending the release of Ca into the sarcoplasm

58
Q

what happens if after the first AP there isn’t a subsequent

A

sarcoplasmic Ca will fall due to removal by SERCA pumps - pumping calcium back into the SR and sarcolemma ATPases that pump calcium out of the cell

A&P 1 FAU (15 decks)

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