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Human Physiology > Skeletal muscle > Flashcards

Skeletal muscle Flashcards

1
Q

What are the 2 common functions on muscle

A
  • generate motion
  • generate force
    (also generate heat to maintain homeostasis)
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2
Q

What are the 3 types of muscle and the function

A

Skeletal: attached to bone and control body movement
Cardiac: heart and move blood around
Smooth: internal organs and movement of substances in, out and around body

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3
Q

What type of muscles are striated? Why?

A

skeletal and cardiac muscle

because of alternated light and dark bands

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4
Q

What is unique about skeletal muscles?

A

contract only in response to a sign from somatic motor neuron. Hormones do not directly affect contraction

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5
Q

Describe the structure of skeletal, cardiac and smooth muscle

A

Skeletal: large fibres, multinucleated, striated
Cardiac: fibres, branched and uninucleated. Intercalated junctions connect cells.
Smooth: small fibres with no striations

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6
Q

Explain the extrinsic control and modulation of smooth and cardiac muscle

A

extrinsic control: autonomic innervation

modulation: endocrine system (hormones)

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7
Q

What do tendons do?

A

made of collagen, they attach skeletal muscle to bone

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8
Q

What is the origin and insertion of skeletal muscle?

A

Origin: attached end closest to stationary bone.
Insertion: mobile attachment

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9
Q

How much can an independent myosin move actin per 1 ATP?

A

5 to 10 nm per ATP molecule

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10
Q

What defines the speed of muscle shortening?

A

Defined by how fast each sarcomere shortens in the muscle. If each sarcomere shorten by 10%, the whole muscle shorten by 10%

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11
Q

What is a sarcomere?

A

Contractile unit of the muscle. All or nothing action

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12
Q

Define the term tension, twitch and sarcomere

A

Tension: force generated by contraction
Twitch: single contraction/relaxation cycle of a muscle fibre.
Sarcomere: the contractile unit of muscle

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13
Q

What determinate force generation in skeletal muscle?

A
  1. number of sarcomeres in parallel
  2. number of myofibrils in parallel
  3. muscle fibres in parallel
  4. more/bigger muscles
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14
Q

What is a motor unit? And what is particular about them?

A

Motor neuron innervating a muscle fibre (or more). Muscle fibre innervated by 1 motor neuron must be of the same type.

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15
Q

What is the source of Ca+ in the muscle?

A

Sarcoplasmic reticulum

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16
Q

What is the latent period?

A

When the muscle is preparing to contract.

  1. Creation of muscle action potential
  2. Release of Ca++ from sarcoplasmic reticulum
  3. Diffusion of Ca++ to filaments
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17
Q

What action potential happens first in the process of muscle twitch?

A

Motor neuron action potential and then muscle fibre action potential during the latent period

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18
Q

Name and describe the 3 phases of muscle twitch

A
  1. Latent phase: muscle preparing to contract
  2. Contraction: maximum tension
  3. Relaxation: calcium being released
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19
Q

What does maximum tension depends on?

A
  1. Sarcomere length at the beginning of the contraction

2. Frequency of action potential (how many times is the neuron firing)

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20
Q

What does Speed of contraction activation depend on?

A

Depend on myosin isoform in the muscle.

different myosis act and interact in different ways

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21
Q

What determinates the contraction duration in a muscle single muscle twitch?

A
  1. Speed of Ca+ being pumped back in the sarcoplasmic reticulum
  2. The resistance of the muscle to fatigue
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22
Q

What is the relationship between the length and tension of the sarcomere?

A

Sarcomere was to be at an optimal resting length of 2.0 um to perform muscle twitch. Optimal length allows the formation of the maximum n of bridges between myosin and actin filaments without overlapping

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23
Q

What is the relationship between action potential frequency and tension?

A

If the frequency of action potential is low (not often). The muscle fibres have time to relax between stimuli.
If the frequency is high, the muscle does have time to relax with increases force of the contraction. (summation)

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24
Q

What is summation? And what causes it?

A

Tension in muscle fibres, increase with each action potential due to muscles not relaxing completely

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25
Q

What is tetanus? (muscle twitch)

A

State of maximum contraction (no relaxation) caused by high-frequency motorneuron stimulation that causes partial or complete fused twitches.
Can be voluntary.

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26
Q

DIfferent between summation, partial and complete fused twitch.

A

Summation: stimuli close together but muscles can still relax fully.
Partially fused twitch: muscles relax partially
Complete fused twitch: muscles do not relax, there is steady short tension

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27
Q

What determinates fatigue?

A

CNS: psychological effect, protective reflexes
PNS: neuromuscular junction, excitation and contraction coupling, Ca+ signal

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28
Q

What are the 3 types of human muscle fibres?

A

Type 1: slow-twitch red
Type 2A: fast-twitch red
Type 2B: fast-twitch white (faster speed of activation)

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29
Q

Compare characteristics of fast and slow-twitch muscles.

A 
Fatigue resistance:
- type 1: high
- type 2A: intermediate
- type 2B: low
Myoglobin
- type 1: high (red colour)
- type 2a: high (red)
- type 2b: low (white colour)
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30
Q

Difference between fast and slow-twitch fibres?

A

Slow: gross movement. Calves.
Smaller, darker (myoglobin). Need more blood supply so more capillaries and more mitochondria.
Fast: fine movement found in the eye.
Larger diameter, pale and easily fatigued.

31
Q

How does the nervous system avoid fatigue in sustained contractions?

A

Asynchronous recruitment.

Motor neurons take turns to maintain tension

32
Q

What does cardiac and smooth muscle contract in response to?

A

Autonomic nervous system or spontaneously

33
Q

Is skeletal muscle directly influenced by the endocrine system?

A

No. Nut cardiac and smooth muscles are.

34
Q

What is the difference between a ligament and a tendon?

A

Ligament: bone to bone
Tendon: muscle to bone

35
Q

Describe the components of a muscle fiber.

A

Tendon, muscle, connective tissue, nerves, blood vessels, muscle fiber bundle (fascicle) myofibrils

36
Q

What is the diameter of muscle fibers?

A

approx 100 um / 1 mm

37
Q

What is the outer membrane of muscle fibres?

A

Sarcolema

38
Q

What is a myofibril?

A

Bundles of contractile proteins made of sarcomeres

39
Q

What is the function of nebulin?

A

Align actin filaments by attaching to Z disk

40
Q

What is the function of titin (connectin)?

A
  1. Provide elasticity by returning stretched muscles resting length.
  2. Stabilizes position of filaments
41
Q

What are the contractile components of muscle fibers?

A

Myosin and Actin

42
Q

What are the regulatory proteins of muscle fibers?

A

tropomyosin and troponin

43
Q

What is the function of the heavy chain in myosin?

A

Motor domain that binds ATP to create movement

44
Q

What is the difference between G-actin and F-actin?

A

G-actin: globular actin, form of individual actin

F-actin: polymer of G-actin

45
Q

How many states does cross bridging between actin and myosin have?

A

2, relaxed and contracting

46
Q

What is a Z disk?

A

End of the sarcomere

47
Q

What is the A band and H zone?

A

A band is the location in which myosin and actin overlap .

H zone is the location in which myosin and actin do not overlap during contraction but overlap during contraction.

48
Q

Name the different bands and zones in a picture of a sarcomere.

A
49
Q

What happens to the length of thin and thick filaments when the muscle contract?

A

Length stays the same. Muscle is shortened due to filament sliding on each other.

50
Q

What are the component of troponin complex and what are the functions?

A

Troponin T: binds tropomyosin.
Troponin I: binds actin
Troponin C: binds Ca++

51
Q

Where is troponin complex found?

A

Around the thin filament

52
Q

What is the process of troponin regulation?

A

Toponin C binds to Ca++ causing conformation change that causes myosin head to be exposed

53
Q

What is the Sarcoplasmic recticulum?

A

specialized smooth endoplasmic recticulum with no ribosomes. is the source of Ca++ for contraction

54
Q

Describe the process of filament sliding.

A
  1. Initiates with rigor state with tight binding between thin and thick filaments.
  2. ATP binds to myosin head leading to a conformation change that dissociates the myosin head to the actin filament.
  3. ATP is hydrolysed to ADP and inorganic Pi.
  4. Inorganic Pi release cause another conformation change that results in relaxed state (90’).
  5. ADP is also released returning the myosin head and actin filament to rigor state
55
Q

What is the degree difference between rigor and relaxed state?

A

Rigor state, there is a tight binding between myosin head and actin. Cross bridge at 45’

Relaxed state: weak binding with a cross bridge at 90’

56
Q

What does the release of inorganic Pi result in?

A

Myosin head pushing actin filament towards the M line resulting in a relaxed binding state of 90’ degrees.

57
Q

Are muscles found in relaxed or rigor state?

A

Muscle are found at relaxed state. There is a lot of ATP around

58
Q

Why are T tubules important?

A

They allow action potential to reach interior fibres. Without T tubules, action potential would have to be propagated through sarcoplasm which would delay the response time

59
Q

What are the components of myofibrils?

A

Subunit of muscle fibres.

Made of actin, myosin, troponin, tropomyosin, titin and nebulin

60
Q

What is another name for the heavy chain of myosin?

A

Heavy chain: myosin ATPase

61
Q

What is excitation-contraction coupling?

A

Process in which muscle action potential initiates Ca signals that activate a contraction-relaxation cycle.

62
Q

What is the function of tropomyosin?

A

Partially cover actin-myosin binding site on the actin filament in resting position preventing myosin from binding to actin.
There is still weak binding between actin and myosin

63
Q

What is DHP?

A

An action potential receptor found in T-Tubule linked to Ca++ release channels in sarcoplasmic reticulum

64
Q

What is phosphocreatine?

A

High energy molecule made from ATP and creatine. During exercise, Pi group is transferred to ADP by creatine kinase.

65
Q

What is recruitment?

A

INcreasing the force of contraction by recruiting additional motor units

66
Q

Whatis asynchronous recruitment?

A

Constant tension due to modulation of firing rate to allow motor units to take turns

67
Q

How is the force of contraction increased?

A

By recruiting more motor units

68
Q

What is the difference between how contraction force is varied between single-unit and multi-unit smooth muscle cells?

A

Single-unit increase force by increasing the amount of Ca++ that enter the cell.
Multi-unit: increases force by recruiting more muscle fibers.

69
Q

What is the difference in receptor location in smooth and skeletal muscle?

A

SK: motor endplates (specific receptor location)
SM: receptors found on the surface of the cell. Neurotransmitters are released and they have to find their way to a receptor.

70
Q

What is the difference in Ca++ response between smooth and skeletal muscle?

A

SK: Ca++ bind to troponin to initiate contraction
SM: Ca++ initiates MLCK and activates ATPase.

71
Q

What is different between SK and SM myosin?

A

SM myosin is longer and has myosin heads along the entire length of the filament

72
Q

What does the phosphorylation and dephosphorylation of MLK do?

A

Control contraction and relaxation of in smooth muscle

73
Q

What controls the contraction state of smooth muscle?

A

The ration between MLCK and MLCP

Human Physiology (2 decks)

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