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Physiology > Smooth Muscles & Muscle Metabolism > Flashcards

Smooth Muscles & Muscle Metabolism Flashcards

1
Q

composed of small fibers that are usually 1 to 5 micrometers in diameter and only 20 to 500 micrometers in length.

A

smooth muscle

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2
Q

In contrast to skeletal muscle fibers
are as much as 30 times greater in diameter and hundreds of times as long.

A

smooth muscle

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3
Q

has thick and thin filaments that are not arranged in sarcomeres; therefore, they
appear homogeneous rather than striated

A

smooth muscle

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4
Q

Most important, essentially the same attractive forces between myosin and actin filaments cause contraction in smooth muscle as in skeletal muscle, but the___________ is different

A

internal physical arrangement of smooth muscle fibers

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5
Q

is present in the iris, ciliary muscle of the lens, and vas deferens, arrector pili muscle
- behaves as separate motor units

Each fiber can contract independently of the others
and the control is exerted mainly by nerve signals

A

Multi-unit smooth muscle

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6
Q

has little or no electrical coupling between cells.

is densely innervated; contraction is controlled by neural innervation (e.g., autonomic
nervous system)

A

Multi-unit smooth muscle

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7
Q

In contrast, a major share of control
of unitary smooth muscle is exerted by ____________

A

non-nervous stimuli

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8
Q

unitary smooth muscle, syncytial
smooth muscle, and visceral smooth muscle

A

Single-unit smooth muscle

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9
Q

Muscle fibers contract together as a single unit

Cell membranes of adjacent fibers are connected
electrically by gap junctions

A

Single-unit smooth muscle

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10
Q

is spontaneously active (exhibits slow waves) and exhibits “pacemaker”
- which is modulated by hormones and neurotransmitters.

■ has a high degree of electrical coupling between cells and, therefore, permits coordinated contraction of the organ (e.g., bladder).

A

Unitary (single-unit) smooth muscle

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11
Q

is the most common type and is present in the uterus, gastrointestinal tract, ureter, and
bladder.

biliary tract, ureter , fallopian tube, blood vessels

A

Single-unit smooth muscle (unitary smooth muscle, syncytial smooth muscle, and visceral smooth muscle)

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12
Q

has properties of both multi-unit and single-unit smooth muscle

A

vascular smooth muscle

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13
Q

Smooth muscle does not have the same striated arrangement of actin and myosin filaments.

A

Actin filaments attach to dense bodies

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14
Q

Dense bodies are dispersed in linking one dense body to another or attached to the cell membrane and form bonds with dense bodies of adjacent cells allowing______

A

force to be transmitted from one cell to another

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15
Q

have similar functions to Z
disks in skeletal muscle.

A

Dense bodies

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16
Q

are interspersed among actin filaments.

its filaments have a diameter that is more
than twice as large as that of the actin filaments.

A

Myosin filaments

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17
Q

consist of actin filaments radiating from 2 dense bodies; these filaments overlap a single myosin filament that is located midway between the dense bodies.

A

Contractile units

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18
Q

Most smooth muscle contractions are prolonged __________ones that sometimes last hours or even days.

A

tonic

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19
Q
  1. Slow cycling of the cross-bridges
  2. Low energy requirement
  3. Slow onset of contraction and relaxation
  4. Increased maximum force of contraction
  5. “Latch Mechanism”
A

MUSCLE CONTRACTION

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20
Q

smooth muscle contracts 50-100
milliseconds after it is excited.

It has a long total contraction time of about ________, which is 30x stronger than skeletal muscle

A

1-3 seconds

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21
Q

Increased force of contraction is postulated to
resolve due to the long period of attachment of the _____

A

myosin cross bridges to the actin filaments.

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22
Q

Skeletal muscles have a useful distance contraction of only ¼-⅓ of its resting length, whereas smooth muscles often contract more than __________ of its stretch length.

A

⅔

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23
Q

facilitates prolonged holding contractions; muscle can maintain its full force of contraction even when there is reduction in the degree of activation from the initial level

A

“Latch Mechanism”

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24
Q

can maintain prolonged tonic contraction for hours with use of relatively low energy levels

A

“Latch Mechanism”

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25
Q

Calcium ions combine with ___________ to cause activation of myosin kinase and phosphorylation of the myosin head.

A

Calmodulin (Counterpart of Troponin)

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26
Q

The calcium ions bind with calmodulin; the
calmodulin-calcium complex then joins with and
activates ______________

A

myosin kinase (phosphorylating enzyme)

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27
Q

One of the light chains of each___________ becomes phosphorylated in
response to myosin kinase

A

myosin head (regulatory chain)

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28
Q

When the “regulatory chain” is phosphorylated, the
HEAD has the capability of binding with the actin
filament, causing _________

A

muscle contraction

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29
Q

is required for cessation of contraction

A

Myosin Phosphatase

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30
Q

Once ________ falls below a critical level, processes automatically reverse except for phosphorylation of the myosin head.

A

calcium ion concentration

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31
Q

Reversal of this step requires ___________, which splits the phosphate from the regulatory chain
— relaxation then occurs

A

myosin phosphatase

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32
Q

neuromuscular junctions of the highly structured
type found on skeletal muscle fibers are not present in smooth muscles

due to the presence of:

A
  1. Diffuse junctions formed by the autonomic fibers
  2. Varicosities on the axon terminals distributed along the axis (loaded with transmitter substance) (- axon do not have typical branching)
  3. Contact junctions in the multi unit of smooth
    muscles (similar to neuromuscular junction)
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33
Q

Neurotransmitters _________ & ____________ can have
excitatory or inhibitory effects at the smooth muscle neuromuscular junction

A

acetylcholine and norepinephrine

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34
Q

○ Secreted by the autonomic neurons that innervate the smooth muscles

○ Subs are never secreted at the same time

A

acetylcholine and norepinephrine

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35
Q

excitatory transmitter for smooth
muscle fibers in some organs but inhibitory in others

A

Acetylcholine

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36
Q

would inhibit some excitatory
actions of the acetylcholine

A

Norepinephrine

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37
Q

depends of the smooth muscle and the momentary condition of the muscle

is usually about -50 to -60 millivolts, or about 30
millivolts less negative than in skeletal muscle

A

RMP (Resting membrane potential)

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38
Q

Action Potentials occur in single-unit smooth muscle, such as visceral smooth muscle, in a manner similar to that of skeletal muscle, occurs in 2 forms:

A
  1. Spike potentials
  2. Action potentials with plateaus
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39
Q

—occurs in most types of
single unit smooth muscle and can be
elicited by electrical stimulation, stretch or
the action of hormone/ transmitter subs,
spontaneous generation from muscle fiber

A

Spike potentials

40
Q

onset is similar of the spike, however
depolarization is delayed for about several
100 milliseconds

A

Action potentials with plateaus

41
Q

accounts for the prolonged
period of contraction in the
uterus, ureter, and some types of
vascular smooth muscles

A

Action potentials with plateaus

42
Q

are required for generating smooth muscle action potentials

○ Movement of Ca ions to the interior of the fiber is mainly responsible for the action potential

A

Calcium Ions

43
Q

_______ in single unit smooth muscle can lead to generation of action potentials

A

Slow-wave potentials

44
Q

are slow oscillations in membrane
potentials.

is not an action potential , but can LEAD or can CAUSE an action potential —> making muscle contract

A

Slow waves

45
Q

Causes of slow waves:

A
  1. The oscillation of sodium pump activity
    which causes membrane potential to
    become more negative (sodium is
    pumped rapidly) and less negative (sodium
    is pumped slowly)
  2. The conductance of the ion channel may
    increase & decrease rhythmically
46
Q

sodium is pumped rapidly

A

membrane potential become more negative

47
Q

Action potential can be initiated when the potential of a slow wave raises above the threshold ___________

A

-35 millivolts

48
Q

__________are often generated when
visceral (Single-Unit) smooth muscle is stretched

A

Spontaneous Action Potentials

49
Q

Spontaneous action potentials result from a combination of the normal SLOW WAVE potentials in addition to a decrease in the negativity of the
membrane potential caused by the ____________

A

stretch (self-stimulus)

50
Q

The response to stretch allows the GI wall when excessively stretched, to ______________ thereby resisting the stretch

A

contract rhythmically

51
Q

______________ in blood vessels occurs in response
to local tissue factors

A

Smooth Muscle Relaxation

52
Q

is required for local control of blood flow

A

Vasodilatory response

53
Q

Many circulating ________in the body affect smooth muscle
contraction to some degree

A

hormones

54
Q

A hormone causes contraction when the muscle cell membrane contains ____________ for the
respective hormone

A

excitatory receptors

55
Q

Conversely, the hormone causes relaxation if the membrane contains _________________

A

inhibitory receptors

56
Q

Fibers are stimulated by certain:

A

neurotransmitters
(acetylcholine & norepinephrine),

hormones, or

autorhythmic signals (eg in the GIT system to move food along)

57
Q

Action Potentials are transmitted via

A

gap junction

58
Q
  • Walls of arteries and veins
    ○ Walls of Hollow organs
    ○ Walls of airway to the lungs
    ○ (Arrector pili) Muscles that attach to hair follicles

○ Muscles that adjust pupil diameter
○ Muscles that adjust focus of the lens in the eye

A

smooth mucles

59
Q

Layers of Smooth Muscle (2) oriented at right angles to each other:

A

○ Longitudinal layer — causes organ dilation & shortening

○ Circular layer — causes organ constriction & elongation

60
Q

in skeletal muscle cell, which has neuromuscular junction, in smooth muscle cells you
see these _________

A

varicosities

61
Q

in skeletal muscle you have somatic nerve fibers, in smooth muscle -

A

autonomic nerve fibers

62
Q

series of neurotransmitter-filled bulges

an axon courses through smooth muscle, loosely forming motor units ([link]).

releases neurotransmitters into the synaptic cleft.

A

varicosities

63
Q

With sympathetic innervation,
usually the neurotransmitter is ________

A

norepinephrine

64
Q

parasympathetic innervation, generally the
neurotransmitter will be _________.

A

acetylcholine

65
Q

Contains both thick filaments and thin filaments
- Not arranged in orderly sarcomeres
- Arranged diagonally
- No regular pattern of overlap - not striated

A

SMOOTH MUSCLE TISSUE

66
Q

_________in the sarcolemma instead of T tubules

A

Caveolae

67
Q

why smooth muscles are not striated?

A

thick filaments and thin filaments are not arranged in orderly sarcomeres

No regular pattern of overlap

68
Q

__________in the sarcolemma instead of T tubules

A

Caveolae

69
Q

not may SR in smooth muscle tissue so most of the calcium will come out from _____________

A

extracellular fluid

70
Q

instead of Z disks, it has _______

A

dense bodies

71
Q

functions same as Z disks,

During contraction the filaments pull on the _________ causing a shortening of the muscle fiber

A

dense bodies

72
Q

protein used to bind calcium in the cytosol (instead of troponin)

then activates myosin kinase, which
phosphorylates myosin head

A

Calmodulin

73
Q

During contraction, the __________ do get pulled closer to each other

A

dense bodies

74
Q

There is an ion channel that allows calcium inside.

Remember, most of your calcium will come from the _________, but some will still come from the SR

A

extracellular fluid

75
Q

calcium makes its way into the ______

A

cytosol

76
Q

calcium becomes available, __________ will
activate

A

calmodulin

77
Q

This activated calmodulin can then activate __________.

and they can then catalyze the transfer of this phosphate from ATP onto myosin

A

myosin light chain kinases

78
Q

the activated kinase enzymes catalyze transfer of phosphate to myosin, activating the

A

myosin ATPases

79
Q

Starts slower and lasts much longer than skeletal
muscle contraction

A

SMOOTH MUSCLE TISSUE - physiology

80
Q

Prolonged presence of calcium in the cell provides for a state of continued ___

A

partial contraction

81
Q

calcium moves slowly out of the muscle fiber, delaying _________

A

relaxation

82
Q

delay relaxation is important in ___________ where a steady pressure is maintained on the contents of the tract

A

Gastrointestinal tract

83
Q

delay relaxation is important in the _________ which maintain a
steady pressure on blood

A

walls of blood vessels

84
Q

Smooth muscle fibers contract or relax in response to:

A
  • Action potentials
  • Stretching
  • Hormones
  • Changes in pH, oxygen and carbon dioxide levels
  • Temperature
85
Q

Action potentials is from the ________

unlike skeletal system that uses somatic nervous system

A

autonomic nervous system

86
Q

cold temperature can cause muscle contractions

A

true

87
Q

Pupil constriction due to increased light energy is an example of

A

action potential

88
Q

Food in digestive tract stretches intestinal walls
initiating peristalsis

A

stretching

89
Q

_________ causes relaxation of smooth muscle in the air-ways and in some blood vessel walls

A

Epinephrine

90
Q

______________of the cell membrane opens voltage-gated Ca2+ channels and Ca2+ flows
into the cell down its electrochemical gradient, increasing the intracellular [Ca2+].

A

Depolarization

91
Q

Hormones and neurotransmitters may open ligand-gated Ca2+channels in the cell membrane.

They also directly release Ca2+ from the SR through_______

A

inositol 1,4,5-triphosphate
(IP3)-gated Ca2+ channels

92
Q

Ca2+ binds to calmodulin.

The Ca2+–calmodulin complex binds to and activates myosin light-chain kinase.

When activated, myosin light-chain kinase phosphorylates myosin and allows it to bind to actin, thus initiating cross-bridge cycling.

The amount of tension produced is proportional to the intracellular Ca2+ concentration.

A

A decrease in intracellular [Ca2+] produces relaxation

93
Q

Upstroke of action potential in skeletal muscle and smooth muscle is Inward Na+ current

in cardiac muscle:

A

Inward Ca2+ current (SA node)

Inward Na+ current (atria,
ventricles, Purkinje fibers)

94
Q

Plateau in skeletal muscle and smooth muscle is NO (absent)

in cardiac muscle:

A

No (SA node)

Yes (atria, ventricles, Purkinje
fibers; due to inward Ca2+ current)

95
Q

Duration of action potential in skeletal muscle is 1msec

smooth muscle is 10msec

cardiac muscle:

A

150 msec (SA node, atria)
250–300 msec (ventricles and
Purkinje fibers)

96
Q

Excitation–contraction
coupling in smooth muscle:

A

Action potential opens
voltage-gated Ca2+
channels in cell membrane

Hormones and transmitters
open IP3– gated Ca2+
channels in SR

97
Q

Molecular basis for
contraction

A

Ca2+–calmodulin ↑ myosin light-chain kinase

Physiology (11 decks)

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