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PCS > Muscle Unit > Flashcards

Muscle Unit Flashcards

To do well on this exam

1
Q

In the context for the big themes of physiology, what role does muscle often have?

A

It often is an effector

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2
Q

What is the general function of skeletal muscle?

A

It is generally involved in voluntary movement, it is connected via tendons, in contractions the bones can be pulled closer together.

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3
Q

Muscle cells are represented through long _____, ____ extend throughout the cell which helps withsupplying the cell with all the materials it needs

A

long fibers, nuclei

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4
Q

Skeletal muscle fibers only contract in response to a __________ The axon of an individual motor neuron branches and makes synapses on multiple muscle fibers.

A

Motor neuron

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5
Q

Although the axon of an individual motor neuron branches and makes synapses on multiple muscle fibers, each muscle fiber is only directly controlled by ____ motor neuron.

A

one

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6
Q

What is a motor unit?

A

A motor neuron, and the muscle fibers it controls together

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7
Q

Outline the general structure of the physical contractile units within a muscle

A
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8
Q

Which physical feature(s) are set up to allow for contraction/shortening

A

Both the H zone and the I band can shorten

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9
Q

The thick filaments contain the ____

A

myosin cross bridges (actin binding sites, ATP binding sites)

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10
Q

The thin filaments contain the ____

A

Troponin, tropomyosin, actin, myosin binding sites

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11
Q

_____ at rest is preventing myosin from binding to actin

A

tropomyosin

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12
Q

myofibrils

A

are cylindrical structures in muscle fibers containing contractile proteins; they themselves are composed of repeating units called sarcomeres

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13
Q

what are t tubules

A

t tubules are extensions of the plasma membrane that dive into the muscle fibers themselves

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14
Q

what is the sarcoplasmic reticulum

A

specialized endoplasmic reticulum

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15
Q

what is the “first step” in getting a muscle to contract?

A

The motor neuron needs to fire an action potential

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16
Q

Describe the “steps” of the action potential

A

1) motor neuron action potential occurs
2) Ca 2+ enters voltage gated channels
3) Acetylcholine release
4) Acetylcholine binding opens ion channels
5) Na+ entry and K+ exit
6) propagated action potential in muscle plasma membrane

17
Q

describe the relationship between the muscle fiber action potential and muscle contraction

A

there is a slight delay between the action potential and the muscle contraction

18
Q

Describe the steps involved in a muscle contraction from the end of the action potential to the beginning of the contraction

A

Action potential propagates along muscle fiber membrane and into T-tubules
DHP receptor is a voltage-gated Ca 2+ channel that physically interacts with a Ca 2+ channel in sarcoplasmic reticulum called a ryanodine receptor.
When action potential arrives, the DHP receptor senses voltage change, undergoing its own conformational change that opens the ryanodine receptor.
Ca2+ enters cytoplasm from sarcoplasmic reticulum
Ca2+ binds to troponin, which causes tropomyosin to shift and uncover myosin binding sites on actin
1) Cross bridge binds to actin
2) Cross-bridge moves
3) ATP binds to myosin, causing cross-bridge to detach
4) Hydrolysis of ATP energizes cross-bridge
Ca 2+ ATPase pumps Ca2+ back into sarcoplasmic reticulum, removing free Ca2+ available to bind troponin
Tropomyosin blocks myosin binding sites on actin again

19
Q

now, describe the steps involved in a muscle contraction from the initiation of the action potential

A

1) motor neuron action potential occurs
2) Ca 2+ enters voltage gated channels
3) Acetylcholine release
4) Acetylcholine binding opens ion channels
5) Na+ entry and K+ exit
6) propagated action potential in muscle plasma membrane

then ….
Action potential propagates along muscle fiber membrane and into T-tubules
DHP receptor is a voltage-gated Ca 2+ channel that physically interacts with a Ca 2+ channel in sarcoplasmic reticulum called a ryanodine receptor.
When action potential arrives, the DHP receptor senses voltage change, undergoing its own conformational change that opens the ryanodine receptor.
Ca2+ enters cytoplasm from sarcoplasmic reticulum
Ca2+ binds to troponin, which causes tropomyosin to shift and uncover myosin binding sites on actin
1) Cross bridge binds to actin
2) Cross-bridge moves
3) ATP binds to myosin, causing cross-bridge to detach
4) Hydrolysis of ATP energizes cross-bridge
Ca 2+ ATPase pumps Ca2+ back into sarcoplasmic reticulum, removing free Ca2+ available to bind troponin
Tropomyosin blocks myosin binding sites on actin again

20
Q

Trace the movement of ATP through steps 1-4 of the figure 9.12 cycle

A

Initially, ADP + Pi are bound to the energized cross-bridge. After the cross bridge binds to the actin, the ADP + Pi leave the cross bridge head. ATP rebinding to Myosin catalyzes ATP hydrolysis, which re-energized the cross-bridge.

21
Q

What maintains the smoothness of the contraction

A

All of the myosin heads do not bind to the actin at once

22
Q

Describe the role of ATP in skeletal muscle function

A
  • ATP detaches cross bridges
    Provided energy via ATPases:
    Ca 2+ ATPase
    Myosin ATPase
    NaK+ ATPase
23
Q

What makes the most sense as an explanation for why increasing frequency of stimulation leads to an increased force generated by a muscle fiber/motor unit?

A

A higher proportion of myosin cross bridges can bind actin simultaneously.

24
Q

All motor units (and muscle fibers…)

A

Are distinguishable by type (slow fibers, fast fatigue-resistant fibers, fast fatiguable fibers), such that a single motor unit will share the same type of fiber.

25
Q

Rank the motor units by how fast they fatigue

A

1) Fast fatiguable fibers = fast glycolytic fibers
2) Fast fatigue-resistant fibers = fast oxidative fibers
3) Slow fibers = slow oxidative fibers

26
Q

What kind of muscle fibers are recruited first?

A

Slow fibers are recruited first, fast fatiguable fibers are recruited last. Fiber types are mixed throughout the muscle.

27
Q

Rank the muscle fibers in terms of diameter size, from SMALLEST to LARGEST

A

1) slow fibers = slow oxidative fibers
2) fast fatigue resistant fibers = fast oxidative fibers
3) fast fatiguable fibers = fast glycolytic fibers

28
Q

Slow fibers:
- Primary ATP source
- Mitochondria
- Capillaries
- Myoglobin content
- Glycolytic Enzyme activity
- Glycogen content

A
  • oxidative phosphorylation
  • high
  • high
  • many
  • low
  • low
29
Q

Fast fatigue-resistant fibers:
- Primary ATP source
- Mitochondria
- Capillaries
- Myoglobin content
- Glycolytic Enzyme Activity
- Glycogen content

A
  • oxidative phosphorylation
  • intermediate
  • many
  • high
  • medium
  • medium
30
Q

Fast fatiguable fibers
- Primary ATP source
- Mitochondria
- Capillaries
- Myoglobin content
- Glycolytic Enzyme Activity
- Glycogen content

A
  • glycolysis
  • low
  • low
  • low
  • high
  • high
31
Q

Skeletal muscle
- description
- voluntary?
- striated appearance?
- actin-myosin based contraction
- electrical synapses
- role of neural input

A
  • the general format we’ve been studying
  • yes
  • yes
    -yes
  • no
  • required for contraction
32
Q

Smooth muscle
- description
- voluntary?
- striated appearance?
- actin-myosin based contraction
- electrical synapses
- role of neural input

A
  • typically surround hollow areas, regulate movement through space. smooth muscle found in the blood vessel, urinary tract, GI tract, iris
  • no
  • no
  • yes
  • some
  • neural and hormonal input not required, but can module muscle activity
33
Q

Cardiac muscle
- description
- voluntary?
- striated appearance?
- actin-myosin based contraction
- electrical synapses
- role of neural input

A
  • only found in the heart, contractions generate blood flow, coordinated
  • no
  • yes
  • yes
  • yes
  • neural and hormonal input not required, but can modulate muscle activity

PCS (4 decks)

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