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Human Form & Function > Muscle Physiology > Flashcards

Muscle Physiology Flashcards

1
Q

skeletal muscle cells

A

Voluntary

attached to bones or skin

very long, cylindrical

multinucleated

not self stimulated

no rhythmic contractions

fatigues easily

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2
Q

cardiac muscle cells

A

involuntary

branching

only in heart

self stimulated

striated

does not fatigue

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3
Q

cardiac muscles are… (characteristics)

A

striated
elongated
branched cells (linked via intercalated disks)

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4
Q

desmosomes (cardiac muscle cells)

A

specialized cell junctions along intercalated disks between cells “spot welds”

withstand high mechanical stress from myocardial beating

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5
Q

gap junctions (cardiac muscle cells)

A

provide electrical conduction that enables intercalated cells to beat as a single conductive unit (syncytium)

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6
Q

what enters cytoplasm from both the sarcoplasmic reticulum stores and extracellular sources

A

Calcium

  • L-type calcium channel enables Ca2+-induced calcium release
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7
Q

autorhythmicity

A

intrinsic pacemaker cells (cardiac muscle cells)

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8
Q

What type of respiration do cardiac muscle cells primarily use?

A

aerobic respiration

able to moderately resist fatigue (large mitochondria)

high myoglobin content for O2 storage

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9
Q

cardiac myocytes don’t _____ but are …

A

don’t fatigue easily BUT they are very sensitive to ischemia/hypoxia

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10
Q

smooth muscle cell’s shape and nucleus?

A

spindle-shaped and mononucleated

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11
Q

T/F: smooth muscle cells form sheets on the walls of hollow organs and some blood vessels

A

TRUE

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12
Q

smooth muscle cells: voluntary or involuntary control?

A

involuntary control

slow, rhythmic (wave-like) contractions

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13
Q

T/F: smooth muscles cells are striated

A

FALSE:

smooth muscle cells are NOT striated (not organized into sarcomeres)

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14
Q

smooth muscle cell organization

A

thin (actin) fibers are attached to the cell wall and to dense bodies in the cytoplasm between myosin bundles

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15
Q

smooth muscle cell activation causes what?

A

When activated, thin actin fibers slide over the myosin bundles causing shortening of the cell walls

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16
Q

smooth muscle cells contracted vs contracted state

A

crumples up when contracted

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17
Q

motor unit

A

the functional unit of skeletal muscle

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18
Q

a motor unit is composed of…

A

composed of an alpha motor neuron and all the muscle fibers (myofibrils) it innervates

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19
Q

alpha motor neuron axon characteristics

A

synapse with up to thousands of muscle fibers BUT each muscle fiber is connected to only ONE alpha motor neuron

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20
Q

motor unit recruitment

A

the process by which more and more motor units are put into action

the greater the number/size of the motor units recruited, the more powerful the contraction

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21
Q

sarcomere

A

a structural unit of myofibril in striated muscle

gives Striated Muscle its “striped” appearance

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22
Q

sarcomere is composed of…

A

myosin (thick)
actin (thin)

both protein filaments

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23
Q

arrangement of sarcomere

A
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24
Q

sarcomere: what does the z-disk do?

A

anchor for actin filaments

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25
Q

sarcomere: what is the I-band?

A

space between A-bands containing only actin and z-disk

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26
Q

sarcomere: what is the H-zone?

A

forms the center (lightest part) of the A-band

contains myosin filaments only

shortens during contraction

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27
Q

sarcomere: M-line

A

middle/midline of the H-zone and the A-band

accessory proteins anchor myosin to M-line

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28
Q

sarcomere: A-band

A

darker, thicker band containing both myosin and actin

length does not change during contraction

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29
Q

sarcomere: titins

A

elastic filaments that anchor myosin to z-discs (springs)

30
Q

what sarcomere components shorten during muscle contraction?

A

I-band
H-zone

A-band does NOT shorten

31
Q

sliding filament theory

A

During contraction, the heads of each thick (myosin) filament form a cross-bridge with adjacent thin (actin) filaments.

During excitation-contraction coupling, the actin filaments slide toward the M-line (center) shortening the sarcomere

32
Q

sliding filament theory is a ______- dependent process

A

ATP-dependent process

33
Q

T/F: during muscle contraction, the length of the actin and myosin filaments shorten

A

FALSE: the length of the filaments do not shorten

the I-band and H-band shorten *actin and myosin are pulled together

34
Q

excitation-contraction coupling

A

Physiological conversion of electrical stimuli (action potential (APs )) to mechanical responses (contraction) at the neuromuscular junction

35
Q

6 steps of excitation-contraction coupling

A
36
Q

cross-bridge formation

A
37
Q

during relaxation is cytoplasmic Ca2+ low or high?

A

low Ca2+ in relaxation

38
Q

during muscle relaxation (low Ca2+), what blocks the myosin binding site on actin?

A

tropomyosin block binding site on actin (prevents contraction)

39
Q

during muscle contraction (high Ca2+), what is activated?

A

troponin is activated by Ca2+

troponin pulls tropomyosin off the actin’s myosin binding site

myosin head is able to bind to actin and contract muscle

40
Q

what does high Ca2+ concentration do?

A

The higher the Ca2+ concentration, the greater the # of tropomyosin molecules moved to expose myosin binding sites

41
Q

cross-bridge cycle

A
42
Q

cross bridge cyle can continue as long as…

A
  1. muscle is activated
  2. ATP is available
  3. the physical limit of shortening the sarcomere has not been reached
43
Q

Main events of Skeletal muscle contraction

A
44
Q

sarcomere length-tension relationship

A

The lower limit of contractile ability (75% of resting length)

Optimal operating length (80-120%)
—— muscle is slightly stretched with a slight overlap between myofibrils.

The maximum limit the sarcomere can stretch (170%).

45
Q

3 energy sources for muscle contraction

A

creatine phosphate
glycogenolysis/anaerobic resp
aerobic resp

46
Q

muscle contraction: creatine phosphate

A

direct phosphorylation

energy source: CP

oxygen use: none

produces 1 ATP per CP

47
Q

muscle twitch

A

response of a muscle to a single action potential on its motor neuron

48
Q

muscle twitch threshold

A

minimum voltage necessary to produce contraction

a single brief stimulus at that voltage produces a quick all or nothing cycle of contraction & relaxation (i.e., a twitch)

49
Q

phases of muscle twitch

A

latent period
contraction phase
relaxation phase
refractory period

50
Q

multiple motor unit summation

A

“Recruitment”

Increasing the strength of the stimulus at a constant frequency to recruit additional motor units and thereby increase the tension developed

51
Q

tetanus

A

prolonged contraction without relaxation of muscles

NOT sustainable –> fatigue

52
Q

unfused (incomplete) tetanus

A

“staircase effect”/treppe

wave summating at a frequency sufficient to produce periods of incomplete relaxation between contractions

53
Q

wave summation

A

“temporal summation”

Increasing frequency of a stimulus held at a constant intensity

54
Q

to shorten the muscle and move the object, the tension generated by the
muscle must ______ the load from the object

A

to shorten the muscle and move the object, the tension generated by the muscle must EXCEED the load from the object

55
Q

tension vs load (muscle physiology)

A

tension: the force exerted on an object by a contracting muscle

load: the force exerted on the muscle by an object

56
Q

isometric contraction

A

load exceeds the tension (muscle doesn’t shorten)

57
Q

isotonic contraction

A

the tension (force) generated by the muscle is greater than the load (muscle shortens)

58
Q

fractionation

A

All motor units in a muscle do not need to activate

However, the more motor units activated, or the larger the motor units recruited, the greater the tension (i.e., force) achievable by the muscle

59
Q

Henneman’s “Size Principle”

A

Motor unit recruitment depends on the demand (i.e., load).

Motor units are recruited in the order of the size of the motor unit based on the force needed

60
Q

Size Principle: under increasing load

A

motor units are recruited from smallest to largest

Type I (slow) motor units are recruited first for light exercise then Type IIa (fast) then Type IIb (slow)

Type I (slow)
Type IIa (fast)
Type IIb (slow)

61
Q

slow vs fast twitch muscle fibers

A

slow (Type I)
Fast (Type II)

62
Q

reflex arc

A

a neural pathway that controls a reflex (muscle phys)

63
Q

somatic

A

skeletal muscle

64
Q

autonomic

A

smooth and cardiac muscle

65
Q

6 basic components of reflex arcs

A

sensory receptor
sensory (afferent) neuron
integration center (CNS)
interneuron
motor (efferent neuron)
effector (muscle)

66
Q

example of monosynaptic reflex

A

Knee jerk (stretch reflex)

stimulus: muscle stretch
result: contraction of stretched muscle

67
Q

example of a disynaptic reflex

A

golgi (deep) tendon reflex

stimulus: muscle contraction
result: relaxation of muscle

68
Q

what type of muscle

A
69
Q
A
70
Q

rigor mortis

A

If cellular energy stores are depleted (as happens after death) the cross bridges cannot
detach due to lack of ATP and the cycle stops in the attached state. This produces
stiffness of the muscle known as “rigor.”

Human Form & Function (36 decks)

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