Muscle Physiology 2 Flashcards Preview

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Flashcards in Muscle Physiology 2 Deck (83):
1

Induces an upregulation in 1) mitochondrial number and function, 2) ATP and phosphocreatine content, 3) enhanced levels of intramuscular glycogen stores, and 4) an increase in intramuscular triglyceride levels

Exercise

2

Muscle fibers express type β2 adrenoceptors. Acute adrenergic stimulation causes an

Increase in forceful contraction of Type 2b fibers

Decrease in force develops in Type 1 fibers

3

Chronic stimulation of the skeletal muscle adrenoreceptor system via a β2 agonist (ex: albuterol) exerts and

Anabolic effect

4

Controls various aspects of muscle metabolism by controlling SERCA

-upregulates rate of contraction and relaxation but does NOT increase contractile force

Thyroid hormone

5

The effects of thyroid hormone are most profound in

Type 1 muscle

6

Although the rate of contraction-relaxation is augmented by thyroid hormone, the overall efficiency of energy turnover is

Decreased

7

Age associated loss in muscle mass

Sarcopenia

8

The process of sarcopenia actually begins sometime around age 30 years, after which muscle loss can approach

3-8% per decade

9

Decrease proteogenesis and the rate of amino acid transport and inhibit IGF-1 expression

Glucocorticoids (ex: prednisone and dexamethasone)

10

A transcription factor required for satellite cell differentiation into myofibers

-inhibited by glucocorticoids

Myogenin

11

Functions as an endocrine organ

Muscle

12

Aerobic and anaerobic muscle work is correlated with the secretion of growth factors and immune mediators from muscle fibers, collectively known as

Myokines

13

Can modulate muscle hypertrophy and myogenesis

Myokines

14

Consists of 1) a motor neuron and relatively few muscle fibers and/or 2) numerous motor neurons innervating single and/or small groups of muscle fibers.

One motor unit in muscles mediating fine control (i.e. hands)

15

These small diameter fibers are extremely well vascularized (hence the bright red appearance), and can effectively utilize oxidative metabolism for energy

Type 1 muscle fibers

16

Type 1 muscle fibers contain an abundance of

Myoglobin and mitochondria

17

Function as a hybrid between type 1 and type 2b fibers

Type 2a fibers

18

Are relatively large in diameter, this giving them a greater potential for force of contraction

Fast fibers

19

Fast fibers have a relatively low complement of mitochondira, but an extensive

SR

20

What are the two types of efferent neurons that innervate skeletal muscle fibers?

α and ƴ motor neurons

21

Mediate essentially all of the voluntary contractile responses of skeletal muscle

α neurons

22

Smaller, slower neurons that innervate the intrafusal muscle fibers within the muscle spindles

ƴ neurons

23

Contain sensory receptors that are designed to detect changes in muscle length and the rate of change of length

Muscle spindles

24

Intrafusal fibers run in parallel to the force generating extrafusal fibers. The intrafusal fiber ends are innervated by

Type II afferent fibers and ƴ motor neurons

25

The ends (chain) of intrafusal fibers can be stimulated to contract in response to

ƴ motor neuron activity

26

In contrast, the central portion of intrafusal fibers (bag) can not contract but is sensitive to

Stretch

27

Have receptors that encircle the center of the intrafusal fibers

-Impulses are continually being transmitted via
these sensory neurons to the spinal cord

Type 1a afferent neurons

28

Stretch and/or an increase in the rate of stretch can up-regulate the number and frequency of APs transmitted by

Type 1a afferent neurons

29

During muscle contraction, the bag region of
muscle spindles initially go slack, and type II and Ia activity is suppressed. If sustained contraction is required, descending (motor) tracts stimulate

ƴ motor neuron activity

30

ƴ motor neurons then stimulate contraction of the

Intrafusal muscle ends

31

Contraction of the fiber ends causes stretch within the
center (bag) portion of intrafusal fibers, and this stretch reactivates

Type 1a afferent activity

32

What happens when the limit of contraction/re-stretch of intrafusal fibers is reached?

Isotonic muscle contraction ceases

33

Continuously provides the CNS with information about muscle length and rate of change in length in order to allow and sustain the full range of skeletal muscle contraction

The muscle spindle

34

Located in musculotendon junctions where they serve as an early warning system to the CNS that muscle tension has suddenly increased

-serve as a protective mechanism against muscle tear

Golgi tendon organs (GTOs)

35

If load (due to passive stretch or active contraction) causes an increase in tension in the muscle, the activity of GTOs is up-regulated, and there is an increase in the frequency of

Type 1b action potentials

36

Activation of type 1b muscle fibers stimulates

Decrease in muscle tension

37

Stimulate inhibitory interneurons and antagonistic muscles

Type 1b afferents

38

Defined as a reversible decrease in contractile force in
response to an increase in stimulation frequency or duration

Muscle fatigue

39

Force generation is especially restrained due to a breakdown in pCr, attributing to an insufficient rate of ADP phosphorylation and the accumulation of

Inorganic phosphate

40

What are the differences between smooth and skeletal muscle cells?

Smooth muscle cells:
1.) are smaller
2.) have 1 central nucleus
3.) unstriated
4.) small SR
5.) high actin to myosin ratio (15:1)

41

Smooth muscles have many dense bodies, some of which are attached to the cell membrane. Dense bodies serve the same function as

Skeletal Z-discs

42

Connected by gap junctions which allow innervation of only a few muscle fibers to result in excitation of all muscle fibers in a region

Visceral smooth muscle

43

Visceral smooth muscle acts as a

Single unit

44

What contains more vascular smooth muscle, arteries or veins?

Arteries

45

The contraction and relaxation of vascular smooth muscle (i.e. vascular smooth muscle tone) is under the
control of the

Sympathetic nervous system

46

Contraction of smooth muscle occurs by a

-similar to skeletal muscle

Sliding filament mechanism

47

Because actin filaments are attached to dense bodies within the cell membrane, fiber shortening pulls the cell membrane inward causing the muscle cell to appear

Crinkled

48

With smooth muscle, as with skeletal muscle, the contractile system is activated by an increase in

Sarcoplasmic Ca2+

49

In smooth muscle, Ca2+ is obtained from extracellular sources following cell depolarization and activation of

Voltage-gated Ca2+ channels

50

Can each activate Ca2+ channels in the SR membrane through which SR stores of Ca2+ enter the sarcoplasm in smooth muscle cells

Ca2+-induced Ca2+ release and/or IP3-mediated signal transduction

51

In smooth muscles, when sarcoplasmic Ca2+ concentrations are sufficiently elevated, Ca2+ binds the calcium sensor known as

Calmodulin

52

The Ca2+/Calmodulin complex then activates

Myosin light chain kinase (MLCK)

53

Activation of MLCK causes phosphorylation of myosins, which gives them a very high affinity for

Actin

54

Dephosphorylates myosin in smooth muscle cells, resulting in the cessation of contration

MLCK phosphatase

55

Prolonged in comparison to skeletal muscle contraction

Smooth muscle contraction

56

In order to accomplish these relatively long duration contractions, smooth muscle utilizes

Oxidative metabolism

57

Slow, sustained contraction is caused by slow cycling of the

Myosin crossbridges

58

In smooth muscle cells, contraction requires very little

ATP

59

MLCK phosphatase is activated, crossbridge cycling ceases, and muscle relaxation occurs when

Ca2+/Calmodulin levels fall

60

In contrast to skeletal muscle, smooth muscle can shorten from 50% to 75% of its relaxed length
without altering the overlapping of

Myosin and actin filaments

61

As opposed to the linear contraction of skeletal muscle, smooth muscle can contract upon itself in

Multiple dimensions

62

In smooth muscle, stretch of the smooth muscle fibers results in Ca2+ inflix, which activates the

Contractile system (increases active tension)

63

The elastic properties of smooth muscle aids in the process of

-allows for an alleviation in pressure, which follows an increase in volume
-especially advantageous to hollow organs

Stress relaxation

64

What is Laplace's Law?

P = T/r

where,

P = pressure
T = tension
r = radius

65

The concept of stress relaxation is especially important in the

-less important in vascular tissues

Bladder

66

ANS post ganglionic neurons have axons which have swollen areas called

-in close proximity to the smooth muscles they innervate

Varicosities

67

Function as diffuse neuromuscular junctions

Variscosities

68

Have vesicles containing the neurotransmitter, ACh (parasympathetic nervous system), or norepinephrine (sympathetic nervous system)

Variscosities

69

There are different types of action potentials that can be generated by smooth muscle. The main type of potential is called a

Slow wave potential

70

Not action potentials, but are rhythmic, subthreshold, pacemaker-type changes in membrane depolarization and repolarization

Slow wave potentials

71

The depolarization phase of a slow wave is induced by the opening of Ca2+ channels. These Ca2+ channels can be

Ligand- or voltage-gated

72

Slow waves set what is known as the

Basal electrical rythm of the gut

73

Smooth muscle potential which is similar to skeletal muscle APs.

-Depolarization is mediated by activation of Ca2+ and/or Na+ chanels

Spike potential

74

Both outward IK+ and ICa2+ can be involved in repolarization of

Spike potentials

75

100-1000 msec slower than spike potentials due to delayed repolarization.

-Like spike potentials, depolarization is mediated by inward ICa2+ and/or INa+

Plateau potentials

76

In a plateau potential, depolarization is followed by a transient repolarization phase, which is dependent on

Outward IK+

77

An example of a tissue that utilizes both spike potentials and plateau potentials

Myometrium

78

Ion flux is different in

Smooth muscle than in skeletal

79

In smooth muscle, the RMP is

-50 to -60 mV

80

In smooth muscle, the threshold potential is

-30 to -35 mV

81

Stimulation of smooth muscle increases Na+ influx, this in turn initiates

Membrane depolarization

82

The depolarization phase of a spike potential is due
predominantly to

Ca2+ influx

83

Participates not only in the depolarization phase of the AP in smooth muscle, but also in the initiation of smooth muscle contraction

Ca2+

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