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Exam 1 > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

Exam 1, FOM 1, Lecture 20

1
Q

What is the basic contractile unit of skeletal muscle?

A

motor unit

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2
Q

What is the function of a motor unit?

A

all fibers are innervated by a single motor unit

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3
Q

What stimulates a skeletal muscle contraction?

A

motor neuron

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4
Q

What is excitation-coupling?

A

the series of events from electrical stimulation of the muscle to contraction and force generation

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5
Q

What neurotransmitter is released into the neuromuscular junction?

A

acetylcholine

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6
Q

How does the ACh binding to its receptor on the muscle cell lead to the firing of an action potential?

A

it depolarizes the muscle plasma membrane past the threshold to fire an action potential

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7
Q

How is the action potential propagated through the muscle?

A

it is carried over the surface of the muscle and goes into the T-tubule system

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8
Q

What channels open when an action membrane is initiated along a motor neuron?

A

voltage-gated calcium channels

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9
Q

The opening of voltage-gated calcium channels initiates the release of what neurotransmitter?

A

acetylcholine

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10
Q

When the endplate potential reaches threshold, what channels will open?

A

voltage-gated sodium channels

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11
Q

What type of channel serves as a voltage sensor as the action potential propagates along the sarcolemma and t-tubules?

A

L-type calcium channel

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12
Q

A conformational change in what channel results in the calcium release from the sarcoplasmic reticulum?

A

L-type calcium channel with ryanodine receptor

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13
Q

What enzyme pumps calcium back into the sarcoplasmic reticulum?

A

Ca-ATPases

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14
Q

What molecule in the sarcomere does calcium bind to?

A

troponin-C

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15
Q

What are the steps that allow the binding of calcium to troponin C to lead to actin-myosin cross-bridge cycling?

A
  • Calcium binds to troponin-C
  • Conformational shift in troponin-T
  • Conformational shift in tropomyosin
  • Exposes active site on F-actin
  • Initiates actin-myosin cross-bridge cycling
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16
Q

Binding of what to the myosin head decreases affinity of myosin for actin resulting in
detachment of the head.

A

ATP

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17
Q

What is a twitch?

A

A single action potential leads to a spike in Ca2+ that

initiates a small contractile force

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18
Q

What is tetanus?

A

Repeated stimulation of muscle before it has time to relax
Leading to sustained increases in
Ca2+ and sustained force generation

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19
Q

What is temporal summation?

A

multiple subthreshold EPSPs from one neuron occur close enough in time to combine and trigger an action potential

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20
Q

What is an Isometric contraction?

A

a contraction that

generates force with no shortening

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21
Q

What is a Isotonic contraction?

A

shortening against

constant force

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22
Q

What is the Length-passive force relationship a result of?

A

elastic nature of cell

membrane and connective tissue

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23
Q

What is the Length-active force relationship a result of?

A

arrangement of actin and myosin

molecules in the sarcomere

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24
Q

What is the optimal length of a muscle?

A

Initial muscle length

that, leads to maximal force generation

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25
Q

What is the optimal length of a muscle a result of?

A

optimal organization of a muscle

26
Q

What influences the force generate during isometric condition of a muscle?

A

– number of cells stimulated
– frequency of stimulation
– Length of muscle before stimulation

27
Q

What is the relationship between force and velocity?

A

Changes in the initial length
of the muscle shift the curve and isometric point but
do not alter the Vmax

28
Q

What impacts the difference in velocity at any given afterload?

A

number of crossbridges taking part in contraction

29
Q

What decides the number of crossbridges taking part in contraction?

A

preload

30
Q

What is Vmax dependent on?

A

how fast a single

crossbridge can cycle unimpeded

31
Q

What is Vmax a result of?

A

molecular characteristics

of myosin ATPase

32
Q

What is the relationship between calcium and force?

A

direct

33
Q

How is force graded in a muscle?

A

Recruitment of more motor units

Alternating stimulation of adjacent motor units

34
Q

How does Poliomyelitis impact muscles?

A

destruction of motor nerve fibers which leads to atrophy of the affected muscle

35
Q

How do polio patients regain muscle strength and recover from paralysis?

A

some remaining

fibers will sprout new extensions that innervate other muscle fibers–resulting in larger than normal motor units

36
Q

What are macromotor units?

A

larger than

normal motor units

37
Q

How do macromotor units impact fine motor control?

A

results in loss of fine motor control

38
Q

What three characteristics impact muscle size?

A
  • genetics
  • testosterone
  • training
39
Q

What is hypertrophy?

A

increase in muscle fiber diameter

40
Q

How do myofibrils change in hypertrophic muscle??

A

increased number

41
Q

How do mitochondria change in hypertrophic muscle??

A

increased number and size

42
Q

How does ATP content change in hypertrophic muscle??

A

40% increase

43
Q

How does glycogen content change in hypertrophic muscle??

A

up to 100% increase in storage

44
Q

How does triglyceride content change in hypertrophic muscle??

A

up to 75% increase in storage

45
Q

How do enzymes change in hypertrophic muscle??

A

increase

46
Q

How are atrophied muscles treated?

A

Resistance training
Electrical stimulation
Selective androgen receptor stimulation

47
Q

How is passive force generated in a muscle?

A

produced by titin, that spans the half-sarcomere, connecting the A-band to the I-bands

48
Q

If the muscle is lengthened, what force increases?

A

passive force

49
Q

If the muscle is shortened, what force increases?

A

active force

50
Q

What is active force and how is it generated?

A

the rise in force observed on activation of a muscle and is associated with cross-bridge interactions between myosin and actin

51
Q

What are the steps for contracting smooth muscle?

A 
• Increased Intracellular Calcium
• Calmodulin-calcium 
binding protein 
• Myosin Light Chain Kinase
• Myosin Phosphatase
• Latch State
52
Q

How can the Vmax be shifted up or down for smooth or cardiac muscle?

A

stimulation of the sympathetic and parasympathetic system

53
Q

How many nuclei do skeletal muscle cells have?

A

multiple near sarcolemma

54
Q

How many nuclei do smooth muscle cells have?

A

single, centrally located

55
Q

How many nuclei do cardiac muscle cells have?

A

single, centrally located

56
Q

Where are filaments found in skeletal and cardiac muscle?

A

in sarcomeres

57
Q

Where are filaments found in smooth muscle?

A

scattered throughout sarcoplasm

58
Q

What is the energy source of skeletal muscle?

A

aerobic metabolism usually

glycolysis during peak activity

59
Q

What is the energy source of smooth muscle?

A

aerobic metabolism

60
Q

What is the energy source of cardiac muscle?

A

aerobic metabolism

usually lipid or carb substrates

61
Q

What is optimal preload?

A

initial stretching of the cardiac myocytes (muscle cells) prior to contraction

62
Q

How can changes in optimal length affect velocity of contraction?

A

force of a muscle contraction declines with increasing velocity

Exam 1 (8 decks)

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