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MSK > Muscle Physiology - Cardiac and Smooth > Flashcards

Muscle Physiology - Cardiac and Smooth Flashcards

1
Q

Cardiac Myocytes

  • Length
  • Thickness
  • Nucleation
  • Shape
A
  • Short
  • Thick
  • Mono or bi nucleated
  • Branched
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2
Q

Is cardiac muscle striated?

A

Yes

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3
Q

Does cardiac muscle have a sarcomere? Is it the same kind of sarcomere as skeletal muscle?

A

Yes
Yes

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4
Q

Cardiac myoctes are attached end to end by […] which appear as particularly dark cross-striations in cardiac muscle.

A

Intercalated discs

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5
Q

What structure is indicated by the arrows?

A

Intercalated discs

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6
Q

Are myocytes individually innervated?

A

No - they have gap junctions at the intercalated discs that allow for functional connection between myocytes that causes them to function as a single cell.

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7
Q

What structures are shown by the labeled arrows?

A

1 - Transverse intercalated discs

2 - Longitudinal intercalated discs

3 - Z-line of sarcomere

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8
Q

What structures are present in the transverse vs. longitudinal intercalated discs?

A

Transverse = fasica adherens (anchor for thin filaments as well as cell-cell junction) and desmosomes

Longitudinal = desmosomes and gap junctions

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9
Q

What kind of muscle is shown and how can you tell?

A

Cardiac muscle due to presence of intercalated discs and many mitochondria that run parallel and between myofibrils

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10
Q
A
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11
Q

How do t-tubules of heart muscle compare to those of skeletal muscle?

A

They are larger in diameter

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12
Q

Describe how an electrical action potential leads to cardiac muscle contraction.

A
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13
Q

Describe how calcium balance is restored after muscle contraction.

A

Calcium is pumpedback into SR via active transport. It is also pumped out of the cell to extracellular environment via sodium/calcium pump (calcium out, sodium in) and the sodium balance is then restored by a sodium potassium pump.

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14
Q
A
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15
Q

Because individual cardiac myoctes are not innervated by distinct nerves, how can you generate more force for cardiac contraction?

A

The amount of calcium that enters from the extracellular environment dictates how much calcium will be released from the SR intracellulary and thus determines the force of contraction

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16
Q

Smooth Muscle

  • Shape
  • Nucleation
A
  • Fusiform
  • Mono-nucleated
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17
Q

Does smooth muscle have gap junctions?

A

Yes

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18
Q

Is smooth muscle striated?

A

No - the actin and myosin are arranged in a different manner

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19
Q

Describe how contraction occurs in smooth muscle.

A

It occurs via actin and myosin crossbridge formation but there is no myofibril organization. Actin filaments are attached to dense bodies throughout the cell and along the membrane. The dense bodies then attach the cytoskeleton to the external lamina and thus to other smooth muscle cells.

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20
Q
A
21
Q

What type of muscle has the most variation in function?

A

Smooth

22
Q

What type of muscle is shown?

A

Visceral smooth muscle, it acts as a single unit due to gap junctions present in tissue

23
Q

What type of muscle is shown?

A

Multi-unit smooth muscle, these act more independently

24
Q

Explain this image.

A

This image shows the innervation of multiunit (left) and visceral smooth muscle (right).

With multiunit, multiple axons synapse with individual smooth muscle cells and release neurotransmitters which leads to increased calcium and contraction.

With visceral, a single axon can synapse on multiple smooth muscle cells and the response can be propogated due to the presence of gap junctions in the cells.

Both types of smooth muscle cells are able to be acted upon by hormones in the blood.

25
Q

What types of signals are able to cause stimulation/excitation of smooth muscle?

A
  • Neuronal (electrical)
  • Spontaneous
  • Stretch (myogenic)
  • Hormonal
  • Environmental (increased CO2 and decreased O2 during exercise is sensed by smooth muscle in capillaries and leads to vasodilation in response)
26
Q

Describe the process of contraction of smooth muscle.

A
  • Contraction is dependent on rise in intracellular Ca2+, can come from outside of the cell or intracellular stores or both
  • There is no troponin
  • Calmodulin activation leads to changes in myosin filament leading to cross bridge cycle
27
Q

Describe the process of smooth muscle relaxation.

A
28
Q

Describe the arrangement of actin and myosin in smooth muscle.

A
29
Q

Why is smooth muscle more efficient than skeletal muscle?

A

Because its ATPase activity is slower so there is a decreased energy requirement and thus increased efficiency

30
Q

What is the relationship between length of a muscle fiber and tension?

A

Each muscle has a certain optimal range of length associated with it such that it functions best when it is not stretched beyond that range or contracted below that range. If stretched too much, there may be poor overlap between the myosin heads and the actin filaments, leading to poor tension. If contracted too much, there would be maximal overlap but that may produce sub-maximal force.

31
Q

What is unique about the length-tension relationship of skeletal muscle?

A

It exhibits a much longer dynamic functional range of the sarcomere when compared to other types

32
Q

What is unique about the length-tension relationship of cardiac muscle?

A

It exhibits a much higher passive tension

33
Q

What is unique to about the length-tension relationship of smooth muscle?

A

It can adjust its length-tension relationship

34
Q

What is the Frank-Starling Mechanism?

A

Increased stretch on the muscle allows for greater force development

35
Q

What is an isotonic contraction?

A

Shortening or lengthening of a muscle against a fixed load

36
Q

What is an isometric contraction?

A

When the muscle contracts but does not move the joint (i.e just holding a dumbell with your arm at 90 degrees).

37
Q

What is a concentric contraction?

A

When the muscle shortens during contraction

38
Q

What is an eccentric conctraction?

A

When the muscle lengthens during contraction

39
Q
A
40
Q

Muscle Spindle

  • What does it detect?
  • Where are they located?
  • How many intrafusal fibers do they have?
  • Do they have actin and myosin?
  • What are they innervated by?
A
  • Static and dynamic changes in muscle length
  • Distributed throughout muscles
  • 3-12
  • No - their centers do not have these filaments and do not contract; instead function solely as sensory receptor
  • Gamma motor neurons
41
Q

What are the 2 types of intrafusal fibers?

A
  1. Nuclear bags - detect rate of change in length (dynamic), innervated bby type 1a sensory afferent neurons
  2. Nuclear chains - detect static changes in length, innervated by type 2 sensory afferents
42
Q

Explain how muscle spindles work to sense changes in length.

A

Stretching a muscle also stretches the muscle spindle, thereby increasing its length. It stimulates its gamma motor neurons, which can stimulate alpha motor neurons in spine to cause contraction of muscle.

43
Q

True or false: alpha motor neurons and gamma motor neurons are co-activated.

A

True - this is necessary so that muscle spindle can continue to sense changes in length during muscle contraction

44
Q
A
45
Q

What is the golgi tendon organ?

A

A group of type 1b afferent fibers wrapped around collagen bundles in tendons that detects tension in the tendon either by static stretch of the tendon or by contraction of the muscle

46
Q

Explain what is happening to the golgi tendon organ during the knee reflex.

A

Tension in GTO of quads causes 1b afferent firing and inhibition of alpha motor neuron to quads and activation of alpha motor neuron to hamstrings (antagonist)

47
Q

What is an exercise associated muscle cramp?

A

Sudden, spasmodic and painful involuntary contraction of a muscle where action potentials are firing at abnormally high rates. These typically occur in single multi-joint muscles when the muscle is contracting in a shortened state.

48
Q

What are the 2 theories for the cause of exercise associated muscle cramps?

A
  1. Electrolyte depletion and dehydration
  2. Altered neuromuscular control (muscle fatigue causes abnormal activity in muscle spindle and golgi tendon organ such that there is an imbalance between excitatory impulses from spindle and inhibitory impulses from golgi tendon and during fatigue there is increased feedback from muscle spindle but not GT so there is an excess of excitatory signals and unwanted contraction)

MSK (38 decks)

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