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Physiology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

Sarcolemma

A

Cell membrane of a muscle fiber

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2
Q

Sarcoplasm

A

Cytoplasm of a muscle cell

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3
Q

Myofibril

A

Highly organized bundles of contractile and elastic proteins that carry out the work of contraction

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4
Q

Sarcoplasmic Reticulum

A

A form of modified ER that wraps around each myofibril like a piece of lace. It concentrates and sequesters calcium ions with help of calcium ATPase

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5
Q

Transverse tubules

A

Aka t-tubules. Extensions of the cell membrane that associate with the ends of the SR

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6
Q

Ends of SR are called

A

Terminal cisternae

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7
Q

Thin filaments

A

Made up of microfilament actin (protein) which makes up muscle fiber, one actin is globular protein. Multiple G actin molecules polymerize to form long chains or filaments.
The “rope”

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8
Q

Thick filaments

A

Made from motor protein called myosin (2 polypeptide tail, hinged heads. Ability to create movement.
Arranged so that the myosin heads are clustered at end of the filament and the central region of the filament is a bundle of myosin tails
Attached to M line
“ hands on rope”

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9
Q

What is sarcomere

A
  • The contractile unit of myofibril.
  • Consists of a repeat pattern of light and dark bands which are thick and thin filaments
  • Contains 2 Z disks, I band, A band, H zone and M line
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10
Q

A band

A
  • Anisotropic band because It’s scatters light unevenly
  • Darkest band, encompasses entire length of thick filament
  • On the outer edges of the a band contains thick and thin filaments overlapping
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11
Q

H zone

A

Central region of the a band is lighter than the outer edges of theA band because the H zone is occupied by thick filaments only
• Tails of thick filaments contained here

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12
Q

M Line

A

The middle of the sarcomere attachment site for the thick filaments

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13
Q

Z disks

A

Attachment site of Actin and the ends of one sarcomere

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14
Q

I band

A

Lightest band found adjacent to each Z disk, represent a portion of the sarcomere that has just thin filaments

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15
Q

What is the role of troponin

A

It regulates the on and off positioning of tropomyosin

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16
Q

What is the role of TROPOMYOSIN

A

It allows for the “off” relaxed and “on” contracted states of sarcomere

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17
Q

How does troponin regulate contraction

A

When calcium levels increase in cytosol, Calcium binds to TN, This pulls tropomyosin away from Actin’s myosin binding site.
When calcium concentrations decrease, Calcium unbinds from troponin, allowing tropomyosin to cover actin’s myosin binding sites

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18
Q

Which receptor are involved in the initiation of contraction and where are they located

A

Nicotinic Cholinergic receptors

On the motor and plate

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19
Q

Receptors on the motor end plate combine with what neurotransmitter

A

ACh

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20
Q

After ACh combines with receptor at the motor and plate which channels open

A

Sodium and potassium Channels open

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21
Q

What net ion change takes place in order to depolarizes the cell to initiate contraction?
What does this create

A

Na+ entry

End plate potential

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22
Q

EPP is the same as what and where does it spread to

A

An action potential

Across sarcolemma into t- tubules

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23
Q

What receptor is located in the T tubules

A

DHP (dihydropyridine) receptors

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24
Q

What kind of receptor is DHP and once activated what do they do

A

Voltage sensitive

Open Ca channels on SR

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25
Q

How does a muscle fiber end contraction

A

Calcium must be removed from the cytosol.

The SR pumps calcium ions back into its lumen using a calcium ATPase

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26
Q

How much ATP does aerobic metabolism create with one glucose

A

30

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27
Q

How much ATP does anaerobic metabolism yield for one glucose

A

Two ATP

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28
Q

What is muscle fatigue

A

The inability to sustain a contraction even when signaled

29
Q

What are 4 factors that are believed to contribute to muscle fatigue

A

Lack of ACH

Glycogen depletion

Reduction in calcium release

Increased Pi production of CaPO4

Loss of K++

30
Q

Why do H+ and in organic phosphate accumulate during exercise

A

H+ accumulat as a result of ATP hydrolysis

Pi accumulates when ATP and phosphocreatine are used for energy in muscle fiber

31
Q

What is the role of myoglobin in skeletal muscle

A

It has a high affinity for oxygen this allows it to act as a transfer molecule bringing oxygen more rapidly to the interior of fibers

32
Q

Which fiber type has a most MYOGLOBIN

A

Oxidative fibers have the most because they rely on oxidative phosphorylation for ATP

( type I and type IIA)

33
Q

What is the role of creatine phosphate (phosphocreatine)in muscle

A

It is a backup energy source for muscle. it is high energy phosphate bonds are created from creatine and ATP at rest. Anaerobic

34
Q

How can muscles become condition to be more fatigued resistance

A

Muscle fibers have plasticity and can shift their type depending on their activity. Fast twitch type to a muscle fibers are glycolytic but become more oxidative with endurance training. Endurance training increases capillaries and mitochondria in muscle cells. The more oxidative the muscle type the less fatigue resistant.

35
Q

What is asynchronous recruitment

A

This is a sustained contraction used by the nervous system to avoid fatigue. It’s the alternation of active motor units where some motor units rest between contractions preventing fatigue.

36
Q

Why do long and short sarcomere develop less tension the sacromere at optimal length

A

Long sacromere barely overlap & form few cross bridges and don’t generate much force

Short sarcomere overlap too much at the beginning, they move a short distance, this prevents cross bridge formation andd dereased tension

Optimal Is when the sarcomere are slightly overlapped–>numerous cross bridges between thick and thin filaments

37
Q

What is the relationship between tension and cross bridges

A

The amount if ension is directly proportional to the amount of cross bridges formed between thick and thin filaments

38
Q

What is temporal summation in muscle fiber

A

If the interval of time between action potentials is shortened then the muscle fiber does not have enough time to relax completely between both stimuli, this results in a more forceful contraction

39
Q

What is a motor unit

A

This consists of a somatic motor neuron and the group of muscle fibers that function together controlled by this neuron

40
Q

Muscles responsible for fine movements will have more or fewer muscle fibers in its motor units

A

Fewer

41
Q

Are the types of muscle fibers in a single motor unit the same or different fiber types

A

Same

42
Q

What is motor unit recruitment and how does it take place

A

It is the force of contraction and skeletal muscle increase by recruiting additional motor units. And weak stimulus activates neurons with low threshold. As stimulus increases additional motor neurons with higher thresholds are activated

43
Q

Single unit smooth muscle

A

The cells are electrically connected by gap junctions and they contract as a coordinated unit

44
Q

Multi unit smooth muscle

A

The cells are not linked electrically and each muscle cell functions independently

45
Q

How are the arrangement of contractile fibers in smooth muscle different from those in skeletal muscle

A

Smooth muscle contractile fibers are not arranged in sacromeres and they lack the distinct banding patterns of striated muscle.

46
Q

What type of summation is motor unit recruitment in smooth muscle

A

Temporal summation, Like that of neurons and graded potential

47
Q

Explain the events of excitation contraction coupling in and smooth muscle

A
  1. No action potential
  2. Signal is sent from autonomic motor neuron
  3. This activates an increase in calcium in cytosol from ECF and SR
  4. Calcium binds to CALMODULIN
  5. This activates the enzyme MLCK, This phosphorylates myosin light protein chains and increase myosin ATP ase activity
  6. Active myosin cross bridges slide along actin and create muscle tension
48
Q

What is the role of MLCK/MLCP ratio in smooth muscle contraction

A

Less contraction = MLCP dominates MLCK, Ca++ is desensitized, decreasing myosin ATPase activity

More contraction = signal molecules decreased MLCP activity, MLCK dominates, Ca++ more sensitive

49
Q

What are the 2 sources of calcium in the smooth muscle

A

SR and ECF

50
Q

How do calcium levels and smooth muscle cell become elevated

A
  1. Voltage gated calcium channels open in response to depolarization
  2. Ligand gated calcium channels also known as receptor operated calcium channels (ROCC)
  3. Stretch activated channels
  4. SR–>RYR –>calcium induced calcium release (CICR) or IP3–>SR
  5. When SR Ca depleted, ST1M1 sends msg to cell membrane to allow more Ca into cell
51
Q

How is smooth muscle relaxation different from skeletal muscle relaxation

A

Smooth muscle can stay contracted and it doesn’t fatigue, it consumes minimal ATP

52
Q

The membrane of the t-Tubules contains receptor that are sensitive to

A

Voltage

53
Q

Multiple globular molecules polymerize to form long chains or filaments

A

Actin

54
Q

What connects thick filaments to thin filaments that span the space between myosin and actin molecules

A

Cross bridges

55
Q

Straighted muscles are so called because of the repeating pattern of light and dark bands. One repeating unit of the banding pattern is called a

A

Sarcomere

56
Q

The tension generated in a skeletal muscle fiber is directly proportional to the number of

A

Active cross bridges formed

57
Q

Each myosin head has a binding site for

A

Actin and ATP

58
Q

The hydrolysis of ATP causes myosin to immediately

A

Rotate into a position cocked to bind to actin

59
Q

The binding of ACh to its receptor at the neuromuscular Junction causes the opening of a

A

Channel for both sodium and potassium

60
Q

The relaxation of skeletal muscle relies on the activity of what which decreases cytoplasmic calcium concentration

A

CaATPase

61
Q

Within a single fiber the tension developed during a twitch depends upon the

A

Length of the sarcomere prior to contraction

62
Q

A motor unit consists of

A

One neuron and all the skeletal muscle fibers it controls

63
Q

Which fibers generate more force

A

Fast twitch fibers

64
Q

Which fibers fatigue sooner

A

Fast twitch fibers

65
Q

The nervous system avoids muscle fatigue during submaximal contraction by

A

Asynchronous recruitment

66
Q

Smooth muscle cells do not have which proteins

A

Troponin

67
Q

Which is not a property of single unit smooth muscles

A. Smooth muscle cells are connected by gap junctions
B. Their contraction occurs in a coordinated manner
C. Electrical responses travel directly between cells
D. Only some of this smooth muscle cells are associated with autonomic neuron axon terminals
E. Each cell functions independently of its neighbor

A

D.. Only some of this smooth muscle cells are associated with autonomic neuron axon terminals

68
Q

What are comparisons of cardiac monocytes to other muscle cell types

A
  1. Like smooth muscle cells some cardiac cells have peacemaker potentials
  2. Like some smooth muscle cells cardiac cells are electrically coupled
  3. Like skeletal muscle cells actin and myosin are organized into sarcomere
  4. Like smooth muscle cells cardiac muscles are under hormonal control
69
Q

What is Titan

A

A very large protein that is positioned at the ends of the thick filaments and extend to the Z disks. It is a Spring like protein that coils up with contraction and then recoils to push the Z disks apart with relaxation

Physiology (9 decks)

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