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Term I: Histology > Muscle III > Flashcards

Muscle III Flashcards

1
Q

What makes up the motor unit of a skeletal muscle?

A

Nerve, neuromuscular junction, and muscle itself

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2
Q

What controls which and how many of our motor units contract?

A

CNS

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3
Q

What determines the fiber type of a muscle?

A

The innervating nerve

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4
Q

What are the two types of skeletal fiber types?

A

Type I (red) and Type 2 (white)

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5
Q

Describe Type I skeletal fiber.

A
  • Oxidative metabolism
  • Lots of myoglobin and mitochondria
  • Sustained, protracted force generation
  • Slow
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6
Q

Describe Type 2A skeletal fiber.

A
  • Moderately oxidative
  • Mixed aerobic and anaerobic
  • Intermediate speed
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7
Q

Describe type 2B skeletal fiber.

A
  • Very glycolytic (anaerobic)

- Fast, but unsustained force generation

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8
Q

Describe muscle bioenergetics of skeletal muscle.

A
  • Bursts of activity separated by periods of rest (glycolysis THEN aerobic metabolism)
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9
Q

What does skeletal muscle release after an immediate burst of activity?

A

Creatine phosphate

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10
Q

Describe bioenergetics of cardiac muscle.

A

Continuous work demand w/ periods of increased demand (aerobic metabolism), no rest and relentless contraction

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11
Q

What is preferred fuel of cardiac muscle?

A

Fatty acids

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12
Q

Which type of muscle has the most mitochondria?

A

Cardiac muscle

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13
Q

Describe bioenergetics of smooth muscle.

A

Slow, sustained activity and low energy consumption, mitochondria very scattered

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14
Q

Which muscle type exhibits latching?

A

Smooth muscle

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15
Q

What is a maternally inherited defect of the mitochondria and which muscles does it usually involve?

A

Mitochondrionapathies - skeletal and cardiac

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16
Q

What is the plateau in cardiac skeletal muscle AP due to?

A

Voltage gated Ca2+ channels

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17
Q

What causes the force of the cardiac myofiber contraction to increase?

A

Increase of cytoplasmic Ca concentration

18
Q

What is isometric contraction?

A

No change in muscle length

19
Q

What is preload?

A

Isometric tension generation at a preset length

20
Q

What is passive tension?

A

Tension developed by simply stretching a muscle to different lengths

21
Q

What is active tension?

A

The active force developed during cross-bridge cycling

22
Q

What is total tension?

A

Sum of active and passive tension

23
Q

When does maximal active tension occur?

A

When the overlap of actin and myosin is maximal

24
Q

Is maximal tension achieved with the shortest or longest sarcomere?

A

Shortest

25
Q

Why is isometric tension not really ever = 0, even when there is no actin/myosin overlap?

A

Titin elasticity and the reticular collagen and basal lamina in endomysium create some tension (the passive tension)

26
Q

Why does isometric tension plateau at the H zone?

A

There are no cross bridges

27
Q

Why does isometric tension drop as actin myofilaments cross M line?

A

Steric hindrance of cross bridges by double overlap of actin and polarity dichotomy

28
Q

Why does sarcomere have a minimum length it can shorten to?

A

The rigid platform of the myosin hits the Z lines.

29
Q

What is the afterload?

A

Force against which the muscle contracts

30
Q

What kind of relationship do the velocity of shortening and the afterload have?

A

Inverse - as afterload increases, velocity of shortening decreases

31
Q

When does Vmax occur?

A

Zero loading

32
Q

What happens when afterload exceeds force generation?

A

Velocity of shortening = 0

33
Q

Describe preload and afterload in cardiac contraction.

A

If preload is optimized, it can improve cardiac contraction. If afterload is high (pressure against which heart pumps is high), can have reduced velocity of contraction.

34
Q

What is unitary smooth muscle? Give examples.

A

Smooth muscle cells connected by gap junctions that act as one due to electrical coupling. Involves spontaneous, slow waves of depolarization. Ex: GI tract, uterus, ureter, bladder

35
Q

What is multiunit smooth muscle? Give examples.

A

No gap junction coupling, myofibers function individually so that each myofiber is innervated by autonomic nerve fibers. There is strong neural control involved. Ex: Iris, ciliary muscle of lens, vas deferns

36
Q

Describe regeneration in skeletal muscle.

A

Lmtd due to few stem cells (satellite cells).

Hypertrophy occurs in response to exercise.

37
Q

What is hypertrophy?

A

Enlargement of existing cells

38
Q

What is hyperplasia?

A

Generation of new cells

39
Q

Describe regeneration in cardiac muscle.

A

No regeneration b/c no stem cells.

Hypertrophy can occur in response to exercise and afterload (hi BP)

40
Q

Describe regeneration in smooth muscle.

A

Unlimited regeneration.
Hypertrophy can occur in uterus during pregnancy.
Hyperplasia can occur in breast glandular epithelium during pregnancy.

Term I: Histology (15 decks)

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