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Unit 5 > 11/24/2014 Medical Physiology Excitation-Contraction Coupling Eric Olson > Flashcards

11/24/2014 Medical Physiology Excitation-Contraction Coupling Eric Olson Flashcards

1
Q

A motor action potential travels along a ___ to the ___ at the neuromuscular junction

A

motoneuron; motor endplate

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2
Q

The nerve endings secrete ___ which acts on a local area of the sarcolemma to open numerous acetylcholine-gated ion channels

A

acetylcholine

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3
Q

The muscle action potential propagates down ___ membranes into the interior of the muscle fiber to the ___, where it causes release of calcium ions that have been sequestered in the ___

A

the T-tubule (transverse tubule)
triad junction
longitudinal sarcoplasmic reticulum

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4
Q

The calcium ions are pumped back into the sarcoplasmic reticulum by the ___ located in the sarcoplasmic reticulum membrane, thus reducing the concentration of calcium in the sarcoplasm, and allowing the muscle fiber to relax

A

Ca-ATPase ion pump

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5
Q

Lengthening of the muscle is achieved by contraction of an ___

A

antagonistic muscle

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6
Q

What is an important difference between the events at the neuromuscular junction and the events during excitation-contraction coupling in skeletal muscle?

A

neuromuscular junction –> neuronal action potential

excitation-contraction coupling –> motor action potential

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7
Q

Acetylcholine binds the ___ receptors embedded in the ___ plasma membrane (at the motor endplate)

A

acetylcholine; muscle

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8
Q

The Acetylcholine receptors open, allowing ___ to rush into the muscle cell and depolarize the motor endplate, producing a change in the ___

A

sodium (Na+); endplate potential

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9
Q

Some ___ can also come out of the cells through the open acetylcholine receptor

A

potassium (K+)

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10
Q

The depolarized endplate potential causes nearby voltage-gated ___ in the ___ plasma membrane to open leading to the initiation of a ___ action potential that propagates down the length of the muscle fiber

A

sodium channels; muscle; muscle

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11
Q

___ quickly inactivates the released ___

A

acetylcholinesterase; acetylcholine

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12
Q

What is myasthenia gravis?

A

Disorder of excitation-contraction coupling caused by an autoimmune response to acetylcholine receptors

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13
Q

What exactly happens in MG at the cellular level?

A

Antibodies block or reduce the number of nicotinic acetylcholine receptors at the neuromuscular junction, resulting in muscle fatigability

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14
Q

Describe the diagnostic test for MG

A

Edrophonium test:

  • edrophonium chloride (cholinesterase inhibitor) increases acetylcholine at the neuromuscular junction
  • administered intravenously, it will temporarily relieve symptoms of muscle weakness, including diplopia (double vision), in myasthenia gravis
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15
Q

What are some other disorders of EC coupling?

A

Motor neuron –> ALS

Nerve –> Demyelinating disease e.g. Guillain-Barre Syndrome

Muscle –> muscular dystrophy

Sarcomere –> malignant hyperthermia

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16
Q

Calcium movements during contraction and relaxation in skeletal muscle (1):

The muscle action potential (AP) ___ the sarcolemma (the muscle fibers plasma membrane), including the ___.

A

depolarizes; transverse t-tubules;

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17
Q

Calcium movements during contraction and relaxation in skeletal muscle (2):

The skeletal muscle action potential is ___ dependent and ___.

A

sodium (Na+); brief (~2 msec)

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18
Q

Calcium movements during contraction and relaxation in skeletal muscle (3):

Depolarization of the T-tubules opens ___ channels (ryanodine receptors) in the sarcoplasmic reticulum (SR), releasing Ca++ i into the ___ and raising sarcoplasmic (cytosolic ) calcium [Ca++] from 10-7 M to 10-5 M.

A

calcium; sarcoplasm

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19
Q

What does it mean that the sodium dependent action potential triggered by Acetylcholine release at the neuromuscular junction triggers the release of calcium from an internal store (the SR) inside the muscle cell (muscle fiber)?

A

That skeletal muscle can contract in the absence of extracellular calcium

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20
Q

Calcium allows ___ to interact with ___, thus resulting in the development of tension

A

actin; myosin cross-bridges

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21
Q

What happens after a brief time interval, and if there are no other action potentials?

A

Calcium is actively transported back into the SR by a calcium ATPase ion pump, resulting in relaxation

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22
Q

Some calcium is bound to ___ in the SR

A

calsequestrin

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23
Q

The cycling of calcium is ___ in skeletal muscle

A

intracellular

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24
Q

Describe the T-tubule

A

invagination of the muscle cells plasma membrane (the sarcolemma)

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25
Q

Do Na+-dependent action potentials traveling on the surface of the muscle also travel down into the T-tubule?

A

Yes

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26
Q

Describe terminal cisternae

A

Physically attached to the T-tubule through the direct coupling of L-type calcium channels embedded in the T-tubule membrane to the Ryanodine receptors embedded in the membrane of the sarcoplasmic reticulum

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27
Q

Depolarization of the ___ membrane induces a change in the structure of the DHP receptor (an ___ channel) , which in turn opens a calcium channel gate in the ___ receptor in the sarcoplasmic reticulum membrane causing calcium release into the sarcoplasm (cytosoplasm) and triggering ___

A

t-tubule; L-type calcium; ryanodine; sarcomere contraction

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28
Q

What is ryanodine?

A

Plant alkaloid that binds to and opens SR calcium release channels (ryanodine receptors) at nanomolar concentration

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29
Q

Higher concentration of ryanodine (micromolar) ___ ryanodine receptors

A

closes

30
Q

Define Calcium Induced Calcium Release (CICR)

A

Process by which the sarcoplasmic reticulum releases its calcium store rapidly through ryanodine receptors release

31
Q

How is skeletal muscle contraction terminated?

A

By the removal of calcium from the sarcoplasm (cytoplasm)

32
Q

What does the major mechanism for calcium removal involve?

A

The sarcoplasmic reticulum calcium ATPase (SERCA)

33
Q

How does SERCA work?

A

It uses the energy of ATP hydrolysis to pump calcium back into the sarcoplasmic reticulum where it can be bound by calcium binding proteins Calreticulin and Calsequestrin

34
Q

Why does skeletal muscle not require calcium influx from outside the cell (myofiber) to contract?

A

Because the calcium needed for contraction is released from, and then returned to the sarcoplasmic reticulum

35
Q

Are there other mechanisms of calcium removal from the sarcoplasm that do extrude calcium into the extracellular fluid (outside the cell)?

A

Yes –>2

  • plasma membrane calcium ATPase (PMCA)
  • pumps 1 calcium ion out of the cell at the expense of 1 ATP molecule (using ATP hydrolysis)
  • Sodium Calcium eXchanger (NCX)
  • lets 3 sodium ions into the cell (down the Na+ gradient) to remove 1 calcium ion from the cell
36
Q

Temporal relation between skeletal action potential, Ca and tension during a twitch:

The ___-dependent action potential (

A

sodium; calcium

37
Q

Define summation

A

Increase in muscle tension from successive action potentials

38
Q

Define tetanus

A

Maintained contraction in response to repetitive stimulation

39
Q

If a tetanus oscillates, it is called ___ tetanus while a tetanus without oscillations is called ___ tetanus

A

unfused; fused

40
Q

A single action potential produces a ___, where tension rises and then returns to baseline. However, the functional refractory period (FRP) of the AP is much ___ than the contraction time. This means that high frequency APs cause contractions that can ___. At very high frequency APs this leads to ___

A

twitch; shorter; summate; fused tetanus

41
Q

The strength of contraction of skeletal muscle is graded by:

A

(1) rate coding or frequency of stimulation

(2) recruitment of additional motor units dependent

42
Q

Define treppe

A

Steady increase in tension in successive twitches

43
Q

What can produce treppe?

A

Repeated stimulation of the muscle at low frequency

44
Q

Why is treppe NOT summation?

A

Because each twitch relaxes to zero tension before the next twitch initiates

45
Q

In treppe successive twitches show ___ peak tension, in a step-wise fashion

A

greater

46
Q

Treppe means stairs or steps in what language?

A

German

47
Q

Why does treppe occur?

A

Because Ca++ released from previous twitches exceeds Ca++ reuptake and this results in an increase in Ca++ concentration

48
Q

What does treppe result in?

A

An increase in the number of cross-bridges that form in the following contractions

49
Q

Define motor unit

A

Somatic motor neuron and all the muscle fibers (myofibers) it innervates

50
Q

A single ___ will innervate multiple muscle fibers BUT a single ___ is innervated by only one neuron

A

neuron; skeletal muscle fiber

51
Q

Generally large motor units are found in ___ twitch muscle (Type II) while small motor units are found in ___ twitch (Type I) muscle

A

fast; slow

52
Q

Are all of the innervated muscle fibers simultaneously stimulated to contract with all-or- none twitches when a motor unit is activated?

A

Yes

53
Q

Motor units are recruited according to the ___

A

Size Principle

54
Q

___ motor units are recruited after ___motor units as ___ force is required

A

Large; small; more

55
Q

What happens when requirements for force are low, but control demands are high?

A

The ability to recruit only a few muscle fibers gives the possibility of fine control

56
Q

The force generated when skeletal muscle is stimulated is related to:

A
  • the size of the motor units stimulated
  • the number of motor units activated
  • the frequency of stimulation of the muscle fibers
57
Q

___ is used to fuel the crossbridge cycle and to maintain ionic gradients

A

ATP

58
Q

How does phosphocreatine act as a source of energy available to skeletal muscle?

A

Can rapidly transfer a high energy phosphate to ADP regenerating, but supply will last for 5-8 seconds of muscle activity

59
Q

How does glycogen act as a source of energy available to skeletal muscle?

A

Glycogen stored in muscle is rapidly broken down to glucose, that is either metabolized anaerobically (in the absence of oxygen) to produce ATP

60
Q

___ metabolism produces ATP ___, but is an inefficient process and produces ___

A

Anaerobic; rapidly; lactic acid

61
Q

___ metabolism of glucose is ___, but is comparatively efficient and can provide sustained ATP

A

Aerobic; slow

62
Q

Can oxidative metabolism of lipids (fatty acids) and proteins (amino acids) provide extended supplies of ATP for muscle contraction?

A

Yes

63
Q

What produces muscle pain (burn)?

A

Lactic acid build up and accumulation when heavy muscle activity and low oxygen lead cause the muscle to rely on anaerobic glycolysis to produce ATP

64
Q

What is the name of pain/burn caused by accumulation of lactic acid in heart muscle fiber?

A

Angina

65
Q

What is Delayed Onset Muscle Soreness (DOMS)?

A

Occurs in the days following intense muscle use and associated with muscle damage, and possibly and inflammatory response

*not correlated with lactic acid levels in muscle

66
Q

Define Muscle Fatigue

A
  • decline in muscle tension as a result of previous contractile activity
  • decreased shortening velocity
  • slower rate of relaxation
67
Q

What causes muscle fatigue?

A

Buildup of lactic acid and of inorganic phosphates (from phosphocreatine breakdown)

*NOT due to low ATP since a fatigued muscle still has quite high concentration of ATP

68
Q

Fatigue may in fact be an adaptation to prevent ___ that will result from very low ATP level

A

rigor

69
Q

Low ATP favors ___ actin myosin complexes, ___ calcium levels in the sarcoplasm, and therefore ___

A

stable; high; rigor

70
Q

What causes high frequency fatigue accompanying high intensity, short duration exercise?

A

Failure in the conduction of action potential in the T tubule

*recovery is rapid

71
Q

What causes low frequency fatigue seen with low intensity, long duration exercise?

A

Build up of lactic acid and phosphates which may change the conformation of muscle proteins

*recovery is slow

Unit 5 (36 decks)

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