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BSCI 1511 > Muscle > Flashcards

Muscle Flashcards

1
Q

What is the general purpose of skeletal muscle?

A

To move the bones in the body.

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2
Q

What is a skeletal muscle?

A

A skeletal muscle is a bundle of long muscle fibers.

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3
Q

What is each muscle fiber?

A

A long, multinucleated muscle cell that contains several myofibrils.

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4
Q

What is each myofibril composed of?

A

Repeating section called sarcomeres. Sarcomeres line up in adjacent myofibrils, giving skeletal muscle its striated appearance.

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5
Q

What are the two parts of the sarcomere, and how do they interact?

A

The two parts are thick and thin filaments. They work by sliding past one another during contraction.

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6
Q

What are thin filaments made of?

A

Two coiled strands of actin.

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7
Q

Where are thin filaments anchored?

A

They are anchored at the Z-lines–the sarcomere edge.

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8
Q

What are thick filaments made of?

A

Staggered arrays of myosin.

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9
Q

Where are thick filaments anchored?

A

They are anchored at the M-line–the sarcomere middle.

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10
Q

What powers filament movement?

A

ATP.

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11
Q

How do the length of the contracting muscle and filaments change during contraction?

A

Although the contracting muscle shortens, the filaments remain the same length.

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12
Q

During rest, how are the thin and thick filaments oriented?

A

They partially overlap.

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13
Q

What is the M-line?

A

The middle of the sarcomere.

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14
Q

How does the length of the contracting muscle and filaments change during contraction?

A

Although the contracting muscle shortens, the filaments remain the same length. The more they overlap during contraction, the shorter the sarcomere will be.

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15
Q

Describe the low-energy configuration of the sliding-filament model of muscle contraction.

A

The myosin head is bound to ATP, meaning it is in its low-energy configuration. It is not bound to the actin thin filament.

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16
Q

What happens after the low-energy configuration in the sliding-filament model?

A

The myosin head hydrolyzes ATP to ADP and P and is in its high-energy configuration. It is still not bound to the actin thin filament.

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17
Q

What happens after the myosin head hydrolyzes ATP to ADP and P?

A

The myosin head binds to actin, forming a cross-bridge with the thin filament.

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18
Q

What happens after the myosin head binds to actin?

A

The cross-bridge couples the release of ADP and P to a power stroke that slides the thin filament along the myosin and returns the myosin head to a low-energy state.

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19
Q

How is a new cycle of muscle contraction begun?

A

Through the binding of a new molecule of ATP that releases the myosin head from actin.

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20
Q

What are tropomyosin and the troponin complex bound to?

A

They are bound to the actin strands of thin filaments.

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21
Q

At rest, how is tropomyosin positioned?

A

At rest, tropomyosin covers the myosin binding site.

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22
Q

What signals the muscle cell to release calcium into the cytosol?

A

A motor neuron that forms a synapse with a muscle cell.

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23
Q

What happens after calcium is released into the cytosol of a muscle cell?

A

Calcium binds to the troponin complex, which shifts the position of tropomyosin, exposing the myosin binding sites in actin. Myosin then binds the actin filaments and contraction begins.

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24
Q

How does the body stimulate the contraction of a muscle?

A

It causes a motor neuron to release acetylcholine at a synapse with the muscle cell.

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25
Q

After acetylcholine is released at a synapse with a muscle cell, what happens?

A

Acetylcholine binds a ligand-gated ion channel on the surface of the muscle that allows the muscle to depolarize, and the action potential moves along the membrane.

26
Q

What are T-tubules, and what do they do?

A

They are a kind of invagination of the plasma membrane that allows the action potential to go deep into the myofibers so that it can affect all the myofibrils within the myofiber.

27
Q

What happens as an action potential moves along the membrane of a myofiber?

A

It leads the sarcoplasmic reticulum to release calcium into the cytosol, causing the myofibril to contract.

28
Q

What is the sarcoplasmic reticulum?

A

The ER of muscle.

29
Q

How is a contraction stopped quickly?

A

The cell has ATP pumps that take the calcium and bring it back into the sarcoplasmic reticulum to be reused when another action potential comes along.

30
Q

What happens when calcium is removed from the cytosol of a muscle cell?

A

If removed, that swings tropomyosin back over the myosin binding sites, stopping any filaments from sliding; no power stroke occurs.

31
Q

How does the contraction of an individual muscle fiber differ from the contraction of a whole muscle?

A

The contraction of an individual muscle fiber is a brief all-or-none twitch. Contraction of a whole muscle is graded.

32
Q

What are the two nervous controls of graded muscle contractions?

A
  1. Varying the number of muscle fibers that contract.
  2. Varying the rate at which muscle fibers are stimulated.
33
Q

What makes up a motor unit?

A

A motor unit consists of one motor neuron and the muscle fibers it controls.

34
Q

When a motor neuron produces an action potential, how do the muscle fibers in its motor unit respond?

A

All the muscle fibers in its motor unit contract as a group.

35
Q

What does the strength of contraction depend on?

A

The number of muscle fibers the motor unit controls.

36
Q

What is the synaptic relationship between motor neurons and muscle fibers?

A

Each branched motor neuron may synapse with many muscle fibers, but each muscle fiber is controlled by only one motor neuron.

37
Q

What is the relationship between recruitment (activation of motor neurons) and tension?

A

As more motor neurons are activated (recruitment), the force (tension) developed by a muscle increases.

38
Q

Give an example of summation in muscle contraction.

A

If a second action potential arrives before relaxation, the two add and result in greater tension.

39
Q

What causes tetanus?

A

Action potentials that arrive too frequently result in tetanus. This means that the muscle contracts to completion. An example is a cramp.

40
Q

What causes fatigue?

A

Prolonged contraction can result in fatigue because 1) ATP is depleted and 2) ion gradients dissipate.

41
Q

How does the speed with which fast-twitch fibers develop tension compare to that of slow-twitch fibers?

A

Fast-twitch fibers develop tension two to three times faster than slow-twitch fibres.

42
Q

How long does a muscle twitch in a slow-twitch fiber last compared to in a fast-twitch fiber? Why?

A

It lasts five times longer. This is because cytosolic calcium lingers longer in a slow-twitch fiber.

43
Q

What is the major source of ATP for slow-twitch fibers?

A

Aerobic respiration.

44
Q

What is the major source of ATP for fast-twitch fibers?

A

Usually, via glycolysis (anaerobic respiration). This makes them fast.

45
Q

How does the number of mitochondria compare in slow-twitch and fast-twitch fibers?

A

Slow-twitch fibers have many while glycolytic fast-twitch fibers have only a few.

46
Q

How does the myoglobin content of slow-twitch fibers compare to that of fast-twitch fibers?

A

The content is high in slow-twitch fibers and low in glycolytic fast-twitch fibers.

47
Q

What is red meat?

A

Muscle that is oxidative; the red color comes from the myoglobin.

48
Q

What is white meat?

A

Muscle that is glycolytic (fast-twitch fiber).

49
Q

What are the key characteristics of skeletal muscle?

A
  1. Attaches to bones
  2. Striated
  3. Voluntary; controlled by motor neurons
50
Q

What are the key characteristics of cardiac muscle?

A
  1. Found in the heart
  2. Striated and branched
  3. Involuntary–nervous input is not required
  4. Cells are electrically connected by intercalating discs
51
Q

What are the key characteristics of smooth muscle?

A
  1. Found in the walls of hollow organs: GI tract, blood vessels
  2. Not striated–actin and myosin are not regularly arrayed
  3. Involuntary–controlled by the autonomic nervous system or without nervous input.
52
Q

How do the skeleton and skeletal muscles work together to move the body?

A

Movement occurs by contracting muscle connected to two parts of the skeleton. Usually, to move a body part back and forth, two muscles attached to the same section of the skeleton sequentially contract.

53
Q

How is fluid held in hydrostatic skeletons?

A

Fluid is held under pressure in a closed body compartment.

54
Q

How is movement achieved with a hydrostatic skeleton?

A

Movement occurs by changing the shape of the fluid-filled compartments.

55
Q

What type of organisms have hydrostatic skeletons?

A

Cnidarians, flatworms, nematodes, and annelids.

56
Q

How are muscles attached in organisms with an exoskeleton?

A

The exoskeleton is an outer body shell, and muscles attach to this outer covering.

57
Q

How does the exoskeleton differ between arthropods and bivalves?

A

In arthropods, the exoskeleton is joined, made of chitin, and called the cuticle. In bivalves, it is made of calcium carbonate and called a shell.

58
Q

What is an endoskeleton?

A

An internal skeleton buried within soft tissues. In humans it is composed of cartilage and bone.

59
Q

What is the purpose of tendons?

A

To attach muscle to bone.

60
Q

What is the purpose of ligaments?

A

To hold bones together at a joint.

BSCI 1511 (32 decks)

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