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SU17: Physiology > Neuromuscular Junction > Flashcards

Neuromuscular Junction Flashcards

1
Q

T/F: Most skeletal muscle cells have multiple nmj’s on the surface membrane.

A

FALSE

just one

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2
Q

T/F: The nmj is a synapse.

A

TRUE

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3
Q

Describe the events of the nerve part at the nmj.

A
  1. Action potential travels to NMJ
  2. Ca enters nerve through voltage-gated channels
  3. Acetylcholine releases into synapse
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4
Q

Describe the events of the muscle part of the NMJ.

A
  1. Acetylcholine binds to and opens ion channels
  2. Na+ enters muscle cell through ion channels
  3. Current develops as entering Na+ is shuttled out
  4. Action potentials flows through muscle plasma membrane
  5. Acetylcholine degradation
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5
Q

Na+ enters the sarcolemma via _______ regulated channels and is shuttled out through _______ regulated channels.

A

Chemically; voltage

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6
Q

T/F: The endplate potential in muscle cells is an all-or-none amplitude.

A

FALSE

it is a graded potential

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7
Q

T/F: Miniature endplate potentials are spontaneous releases of ACh.

A

TRUE

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8
Q

What is the function of Acetylcholinesterase?

A

Found on the motor endplate to breakdown ACh

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9
Q

What are the breakdown products of ACh?

A

Acetate and choline

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10
Q

How does curare inhibit the NMJ?

A

Binds to ACh receptor so ACh cannot bind.

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11
Q

Which toxin blocks ACh release to cause flaccid paralysis?

A

Botulinum

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12
Q

How do some organophosphates effect the NMJ?

A

Block AChE action. Initially spastic followed by flaccid paralysis

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13
Q

What is the difference between the action potential and the end plate potential?

A

AP = much stronger and in the nerve

EPP = in muscle cell

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14
Q

Where is acetylcholinesterase found?

A

In the motor end plate

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15
Q

What are the levels of organization for a skeletal muscle cell?

A

Whole muscle -> Fascicle -> Muscle fiber (cell) -> myofibril -> sarcomere -> filament -> protein

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16
Q

What makes up a thin filament?

A

Two intertwined chains of actin molecules wrapped in tropomyosin and troponin

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17
Q

What makes up the thick filaments?

A

Myosin

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18
Q

What makes up the sarcomere?

A

Thick filaments, thin filaments, and z-lines

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19
Q

T/F: Thick filaments make a triangle around the thin filaments.

A

TRUE

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20
Q

Describe the role of Ca in muscle contraction.

A
  1. Ca enters the cell into lateral sac
  2. Ca leaves lateral sac and binds to troponin
  3. Binding removes inhibiting tropomyosin to allow actin and myosin to incorporate
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21
Q

What molecule binds Ca in the lateral sac?

A

Calsequestrin

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22
Q

What makes up the sarcoplasmic reticulum?

A

Lateral sacs and fenestrated colar

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23
Q

The ________ of the sarcoplasmic reticulum takes up Ca to cause relaxation.

A

Fenestrated colar

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24
Q

What does the binding of Ca to troponin do?

A

Moves tropomyosin so that actin can bind to myosin cross-bridge

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25
Q

Do the filaments change length as the muscles contract and relax?

A

NO; they slide

26
Q

T/F: The amount of force generated is proportional to the number of cross-bridges attached to actin.

A

TRUE

27
Q

What are the three sources of ATP production in a muscle cell?

A
  1. Glucose from blood
  2. Oxygen from blood
  3. Creatine phosphate
28
Q

What determines the velocity at which a muscle contracts?

A

Rate of cross-bridge cycling

29
Q

What is the determining factor of the amount of force a muscle cell can generate?

A

Arrangement and length of thick and thin filaments

30
Q

T/F: A muscle can shorten at a higher velocity with a lighter load.

A

TRUE

31
Q

What is a motor unit?

A

A single motor neuron and all the fibers it innervates

32
Q

What three factors differentiate muscle fibers?

A
  1. Structural
  2. Biochemical
  3. Physiological
33
Q

What is the difference between fast and slow fibers?

A

Slow has…

  1. smaller NMJs
  2. smaller diameter
  3. different protein isoforms
  4. resistant to fatigue
34
Q

Slow fibers are type __ fibers.

A

Type 1

35
Q

T/F: Type IIA fibers tend to be smaller than type IIB fibers.

A

True

36
Q

T/F: Cardiac muscle cells are larger than skeletal muscle cells.

A

FALSE

Skeletal are larger

37
Q

________ are the regions between discs in cardiac muscles that transmit a signal from one to the other.

A

Gap junctions

38
Q

What types of synapses are involved with cardiac muscles?

A

Electrical

39
Q

T/F: Action potentials in the heart are much quicker than skeletal muscles.

A

FALSE

Skeletal APs are quick

40
Q

In which type of cell (cardiac or skeletal) does muscle contraction begin after the AP is complete.

A

Skeletal

41
Q

The _______ period in the cardiac action potential is very long preventing a tetanic contraction.

A

refractory

42
Q

T/F: Calcium induced calcium release is involved with cardiac muscle cell activation.

A

TRUE

43
Q

What mechanism of Ca removal in cardiac muscle cells does not consume ATP directly?

A

Na/Ca exchanger (secondary active transport)

44
Q

What are the sources of Ca for cardiac muscle cell activation?

A
  1. Interstitial space

2. SR

45
Q

What are the methods of Ca removal for cardiac muscle cell relaxation?

A
  1. Uptake by SR
  2. Sarcolemma Ca ATPase
  3. Na/Ca exchanger
46
Q

What type of muscle cell is the smallest?

A

Smooth muscle

47
Q

What major molecule is not expressed in smooth muscle?

A

Troponin

48
Q

In smooth muscle cells the thin filaments are attached to ______.

A

Dense bodies

49
Q

All neuronal control of smooth muscle cells is from ______ nervous system.

A

Autonomic

50
Q

Why do smooth muscles have a wide range of varying lengths over which force can be generated?

A

Allows organs to change in volume

51
Q

T/F: There is virtually no fatigue in smooth muscle.

A

TRUE

52
Q

How does calcium work to contract smooth muscle sarcomeres?

A
  1. Binds to calmodulin
  2. Ca-calmodulin activates MLCK (myosin light chain kinase)
  3. Ca-calmodulin-MLCK contracts myosin (overcomes phosphatase inhibition)
53
Q

What are the sources of Ca for smooth muscles?

A

Extracellular fluid and some from SR

54
Q

T/F: There are NMJs in smooth muscle.

A

FALSE

55
Q

What are four factors that can control smooth muscle activation?

A
  1. Spontaneous AP
  2. Motor neurons
  3. Hormones
  4. Local factors (pH, O2 level, etc.)
56
Q

How is Ca removed from the smooth muscle fiber?

A
  1. Ca pump in sarcolemma
  2. Na/Ca exchanger
  3. SR
57
Q

What are the two types of smooth muscle?

A
  1. Single-unit: gap junctions, spontaneous, pacemaker cells for innervation (intestines)
  2. Multi-unit: each cell independently activated, not spontaneous, few gap junctions (large arteries and airways)
58
Q

Describe the differences in smooth and skeletal muscle activation.

A

Both use Ca

Smooth: Ca binds to several molecules which eventually phosphorylate myosin cross-bridges so they bind to actin

Skeletal: Ca binds to troponin moving tropomyosin and allowing myosin to bind to actin

59
Q

The ____ receptor is in the transverse tubule (cell membrane) and the ____ receptor is in the sarcoplasmic reticulum.

A

DHP; Ryanodine

60
Q

T/F: During muscle contraction the thick filament gets closer to the z line.

A

TRUE

61
Q

T/F: The H band and I band are both reduced during muscle shortening.

A

TRUE

62
Q

Which band is unchanged during muscle contraction?

A

A band

SU17: Physiology (9 decks)

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