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Year 2 MIS > Physiology of skeletal muscle contraction > Flashcards

Physiology of skeletal muscle contraction Flashcards

1
Q

The skeletal muscle is composed of lots of parts. What is the largest collection of?

1 - fascicles
2 - actin
3 - myofibrils
4 - sarcomeres

A

1 - fascicles

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2
Q

The skeletal muscle is composed of lots of fascicles wrapped tightly. What makes up the fascicles?

1 - sarcomeres
2 - actin
3 - myofibrils
4 - muscles fibres/cells

A

4 - muscles fibres/cells

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3
Q

The skeletal muscle is composed of lots of fascicles wrapped tightly, which is composed of bundles of muscle fibres/cells. What are muscle fibres/cells composed of?

1 - sarcomeres
2 - actin
3 - myofibrils
4 - muscles fibres/cells

A

3 - myofibrils

- rod like organelle of muscle cells composed of repeating sarcomere units

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4
Q

What are myofibrils that make up a skeletal muscle fibre/cell?

1 - sarcomeres
2 - actin
3 - myofibrils
4 - muscles fibres/cells

A

1 - sarcomeres

- composed of contractile proteins actin and myosin

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5
Q

Skeletal muscle is composed of lots of fascicles wrapped tightly, which is composed of bundles of muscle fibres/cells composed of myofibrils, which is made up of repeating units of sarcomeres. To ensure the skeletal muscle remains organised there are 3 layers. Label them using the labels below:

endomysium
perimysium
epimysium

A

1 - endomysium
2 - perimysium
3 - epimysium

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6
Q

Skeletal muscle is composed of lots of fascicles wrapped tightly, which is composed of bundles of muscle fibres/cells composed of myofibrils, which is made up of contractile proteins (actin and myosin) organised into repeating units of sarcomeres. To ensure the skeletal muscle remains organised there are 3 layers fibrocollagenous layers as we can see in the image below. Of the 3 layers: endomysium, perimysium and epimysium, which layer will blood vessels, nerves and lymphatic travel through?

A
  • endomysium
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7
Q

What is the cell membrane of a skeletal muscle fibre/cell called?

1 - cytoplasm
2 - sarcolemma
3 - cell membrane
4 - tubercles

A

2 - sarcolemma

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8
Q

The contractile proteins of the muscle are actin and myosin. When describing the anatomy of a sarcomere another term is used to describe these contractile proteins. What are actin and myosin also referred to as?

A
  • actin = think filaments

- myosin = thick filaments

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9
Q

In the image below we can see a sarcomere composed of contractile proteins. Using the labels below, match the descriptions to the labels in the image:

  • made of myomesin proteins, where the thick filaments attach
  • made of alpha actin proteins, where the thin filaments attach
  • only thin filaments are here and it appears light
  • only thick filaments are here and it appears dark
  • location where thin and thick filaments overlap
A
  • M line = made of myomesin proteins, where the thick filaments attach
  • Z line = made of alpha actin proteins, where the thin filaments attach
  • I band = only thin filaments are here and it appears light
  • H zone = only thick filaments are here and it appears dark
  • A band location where thin and thick filaments overlap
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10
Q

During a muscle contraction what happens to the following regions of a sarcomere?

  • A band (thick (myosin) filaments only)
  • I band (only thin filaments)
  • H zone (only thick filaments)
A
  • A band = remains constant
  • I band = shortens as there is more overlap between actin and myosin
  • H zone = shorten as there is more overlap between actin and myosin
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11
Q

What is myosin (thick filament) is composed of and what are the 3 key parts of the myosin structure?

A
  • composed of hundreds of myosin proteins

- each contain a tail, hinge and head

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12
Q

What is actin (thin filament) composed of?

A
  • balls of protein called G-actin which has active site for myosin (thick filament) binding
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13
Q

Actin is composed of balls of protein called G-actin which has active site for myosin (thick filament) binding. However, what 2 regulatory proteins are attached to actin to inhibit myosin from continually binding with actin?

1 - titin and tropomyosin
2 - troponin and titin
3 - titin and actin
4 - troponin and tropomyosin

A

4 - troponin and tropomyosin

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14
Q

The myosin (thick) filament contains 2 heads and in part of this is an ATPase. What must this ATPase do in order for the myosin head to cock backwards and what does this process allow the myosin head to do?

1 - bind actin
2 - bind another myosin
3 - release energy from an ATP molecule
4 - gain energy from an ADP molecule

A

3 - release energy from an ATP molecule

  • energy released in the from ATP forming ADP and phosphate
  • myosin head can bind with the active site on actin
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15
Q

The myosin (thick) filament contains 2 heads and in part of this is an ATPase. The ATPase must release energy from ATP, forming ADP and phosphate so that the myosin head can cock back into its high energy state and bind with the active site on actin. What is the binding called?

1 - antin-myosin binding
2- myosin-actin binding
3 - cross bridge formation

A

3 - cross bridge formation

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16
Q

Once we have cross bridge formation and myosin is bound to the active site of actin, what happens to the energy released from the myosin?

A
  • energy released is used to pull the actin along the myosin
  • this is called the power stroke and is a muscle contraction
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17
Q

Once the power stroke of a muscle contraction has been performed, how does the myosin head detach from the active site of the actin filament causing muscle relaxation?

A
  • ATP will bind to the ATPase on myosin

- as this occurs other myosin heads are binding for muscle contraction through power strokes

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18
Q

Actin is composed of balls of protein called G-actin which has active site for myosin binding. However, there are 2 regulatory proteins called troponin and tropomyosin that inhibit myosins ability to continually binding with actin. What cation is required to bind with troponin that is able to move troponin and tropomyosin away from the active site of actin and allow myosin to bind?

1 - Ca2+
2 - Na+
3 - K+
4 - Cl-

A

1 - Ca2+

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19
Q

Actin is composed of balls of protein called G-actin which has active site for myosin binding. However, there are 2 regulatory proteins called troponin and tropomyosin that inhibit myosins ability to continually binding with actin. Ca2+ is able to bind with troponin that is able to move troponin and tropomyosin away from the active site of actin and allow myosin to bind. What are the 3 subunits of troponin called?

A

1 - Troponin C (= Ca2+)
2 -Troponin I (Inhibitory subunit Troponin) allows myosin and F-actin interactions
3 -Tn T = Tropomyosin binding troponin

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20
Q

Actin is composed of balls of protein called G-actin which has active site for myosin binding. However, there are 2 regulatory proteins called troponin and tropomyosin that inhibit myosins ability to continually binding with actin. Ca2+ is able to bind with troponin that is able to move troponin and tropomyosin away from the active site of actin and allow myosin to bind. The 3 subunits of troponin are:

1 - Troponin C
2 -Troponin I
3 -Troponin T

What is the function of Troponin C?

A
  • binds Ca2+ causing a conformational change in tropomyosin

- exposes G-actin active site for myosin to bind forming cross bridging

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21
Q

Actin is composed of balls of protein called G-actin which has active site for myosin binding. However, there are 2 regulatory proteins called troponin and tropomyosin that inhibit myosins ability to continually binding with actin. Ca2+ is able to bind with troponin that is able to move troponin and tropomyosin away from the active site of actin and allow myosin to bind. The 3 subunits of troponin are:

1 - Troponin C
2 -Troponin I
3 -Troponin T

What is the function of Troponin I?

A
  • binds to tropomyosin
  • keeps G-actin active site of actin closed from myosin
  • think I for inhibition of muscle contraction
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22
Q

Actin is composed of balls of protein called G-actin which has active site for myosin binding. However, there are 2 regulatory proteins called troponin and tropomyosin that inhibit myosins ability to continually binding with actin. Ca2+ is able to bind with troponin that is able to move troponin and tropomyosin away from the active site of actin and allow myosin to bind. The 3 subunits of troponin are:

1 - Troponin C
2 -Troponin I
3 -Troponin T

What is the function of Troponin T?

A
  • binds to actin in thin myofilaments

- keeps the actin-tropomyosin complex in place

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23
Q

There is a large protein in skeletal muscle that spans the length of the Z band to the M line and stabilises the thick filament (myosin) and the sarcomere, ensuring it is not stretched too much. What is this protein called?

1 - fibril
2 - titin
3 - myosin
4 - actin

A

2 - titin

24
Q

There is a large protein in skeletal muscle that spans the length of the Z band to the M line and stabilises the thick filament (myosin) and the sarcomere called titin. What properties does this give the skeletal muscle?

A
  • stiffness and elasticity

- specifically the PEVK sequence of amino acids (seen in image below)

25
Q

Calcium is crucial to allow muscle contraction, through the binding to the Tn C (troponin binding Ca2+) subunit of troponin, where up to 4 Ca2+ ions are able to bind. Where is this Ca2+ released from within the muscle?

A
  • sarcoplasmic reticulum
26
Q

What is the relationship between Ca2+ levels and muscle contraction?

A
  • increased Ca2+ = increased muscle contraction due to actin:myosin binding
  • ATPase activity is therefore dependent on Ca2+
27
Q

There are 3 types of muscle fibres, what are they?

A

1 - Slow twitch muscle fibres (type I or red fibres)
2 - Fast twitch muscle fibres type IIa (Fast Oxidative-Glycolytic)
3 - Fast twitch muscle fibres type IIb (Fast Glycolytic)

28
Q

There are 3 types of muscle fibres:

1 - Slow twitch muscle fibres (type I or red fibres)
2 - Fast twitch muscle fibres type IIa (Fast Oxidative-Glycolytic)
3 - Fast twitch muscle fibres type IIb (Fast Glycolytic)

What gives slow twitch muscle fibres (type I or red fibres) their dark red colour?

A
  • high myoglobin content

- hold onto O2 for storage, important when O2 is low

29
Q

Slow twitch muscle fibres (type I or red fibres) are small fibres with a darker shade of red due to the high myoglobin content. Do these fibres have a good innervation and vascularisation?

A
  • high vascularisation

- allows high blood to deliver O2 to muscles

30
Q

Slow twitch muscle fibres (type I or red fibres) are small fibres with a darker shade of red due to the high myoglobin content. Do these fibres have a high or low mitochondrial number and do they fatigue easily?

A
  • high mitochondrial number = high aerobic respiration (32 ATP from glycolysis and TCA cycle)
  • slow muscle contraction, low fatigue, high endurance
31
Q

Slow twitch muscle fibres (type I or red fibres) are small fibres with a darker shade of red due to the high myoglobin content. These fibres tend to contract slowly. What is the key reason for this slow contraction?

A
  • smaller sarcoplasmic reticulum = less Ca2+

- lower Ca2+ ion concentration means less myoin-actin cross bridge formation

32
Q

Are slow or fast twitch fibres larger in size?

A
  • fast twitch
33
Q

Fast twitch muscle fibres are large fibres. These fibres tend to contract quickly. What is the key reason for this fast contraction?

1 - small SR and increased Ca2+ release
2 - large SR and reduced Ca2+ release
3 - large SR and increased Ca2+ release
4 - small SR and increased Ca2+ release

A

3 - large SR and increased Ca2+ release

- high Ca2+ ion concentration so fast actin:myosin binding

34
Q

Fast twitch muscle fibres are large fibres. These fibres tend to contract quickly due to large sarcoplasmic reticulum and high Ca2+ concentration. Do these muscle fibres have a high or low mitochondrial content and what effect does this have on the fatigue of the muscle?

A
  • low mitochondrial number
  • increased rate of glycolysis (2 ATP generated)
  • fast contraction but quickly fatigue
35
Q

Fast twitch fibres can be subdivided into:

1 - Fast twitch muscle fibres type IIa (Fast Oxidative-Glycolytic)
2 - Fast twitch muscle fibres type IIb (Fast Glycolytic)

Of the 2 which is larger and able to contract quicker?

A

2 - Fast twitch muscle fibres type IIb (Fast Glycolytic)

- BUT fatigues quickly due to low mitochondrial number meaning anaerobic respiration

36
Q

Fast twitch fibres can be subdivided into:

1 - Fast twitch muscle fibres type IIa (Fast Oxidative-Glycolytic)
2 - Fast twitch muscle fibres type IIb (Fast Glycolytic)

Of the 2 which is able to perform just aerobic and/or anaerobic respiration

A

1 - Fast twitch muscle fibres type IIa (Fast Oxidative-Glycolytic) = aerobic and anaerobic respiration
2 - Fast twitch muscle fibres type IIb (Fast Glycolytic) = anaerobic respiration

37
Q

How many ATP are generated in glycolysis and during the TCA cycle?

A
  • glycolysis = 2 ATP (type IIb fibres use this exclusively and type IIa can do this as well)
  • TCA cycle = 30 ATP (type I and IIa use this)
38
Q

What 2 molecules are required for glycolysis and what is formed as a result?

1 - lipids and glucose
2 - glucose and pyruvate
3 - glucose and protein
4 - lipids and protein

A

2 - glucose and pyruvate

- lactic acid is formed

39
Q

What is the role of creatine phosphate (CP) in muscle contraction?

1 - donates Po to ADP
2 - takes away a phosphate from ATP
3 - able to convert non-carbon molecules into ATP
4 - removes Po from ATP

Po = phosphate

A

1 - donates Po to ADP

  • once ATP is used for energy ADP and Po remain
  • CP donates a Po to ADP creating ATP
  • good but very short term
40
Q

Creatine phosphate is important for muscle contraction. It donates a phosphate molecule, where the phosphate can then bind to ADP and recycles to form ATP. What enzyme is required for this?

A
  • creatine kinase, also called creatine phosphokinase

- kinases add phosphates to things (ADP + phosphate = ATP)

41
Q

Once creatine phosphate has donated its phosphate group to generate ATP through combining phosphate with ADP, what happens to the creatine?

1 - gains the electrons release by ATP
2 - forms creatinine
3 - forms ADP
4 - becomes creatine kinase

A

2 - forms creatinine

- high levels of creatinine in blood indicates muscle breaking down in illness

42
Q

What is the definition of a motor unit?

A
  • where a neuron binds to a muscle
43
Q

In small and large muscles, generally do nerve fibres bind with a lot or a few skeletal muscle fibres?

A
  • small muscle fibres = nerve binds with a few muscle fibres

- large muscle fibres = nerve binds with 100s of muscle fibres

44
Q

What is the difference between a muscle twitch and muscle summation?

A
  • muscle twitch = a muscle fibre contraction

- muscle summation = muscle fibres contracting together

45
Q

Once acetylcholine binds with the post synapse at the neuromuscular junction and action potential is generated. This in-turn then binds to a specific receptor on the sarcolemma (membrane of muscle fibre) of the T-tubules of the skeletal muscle that is able to detect an action potential. What is this receptor called?

1 - phopshocreatine
2 - dihydropyridine (DHP) receptor (L-type Ca2+ channel receptor)
3 - G type Ca2+ channel

A

2 - dihydropyridine (DHP) receptor

- also known as an L-type Ca2+ channel receptor

46
Q

Once acetylcholine binds with the post synapse at the neuromuscular junction and action potential is generated. This in-turn then binds to a specific receptor on the sarcolemma (membrane of muscle fibre) of the T-tubules of the skeletal muscle that is able to detect an action potential called the dihydropyridine (DHP) receptor, also known as an L-type Ca2+ channel receptor. What receptor on the sarcoplasmic reticulum does the DHP receptor work with in order to release Ca2+ from the sarcoplasmic reticulum?

1 - phopshocreatine
2 - G type Ca2+ channel
3 - ryanodine receptor (RyR)

A
  • ryanodine receptor (RyR)
47
Q

What receptor is present on the sarcoplasmic reticulum that allows Ca2+ to recycled and re-enter the sarcoplasmic reticulum and what does encourage the muscle to do?

A
  • Sarcoplasmic Reticulum Ca2+ ATPase (SERCA)
  • encourages muscle relaxation
  • continuous muscle contract would be bad
48
Q

What is the relationship between sarcomere length and tension development?

A
  • shortest and longest sarcomere length = lower tension developed
  • middle sarcomere length = maximal tension generated
49
Q

Muscle twitches are when a muscle fibre contracts, and muscle summation is when muscle fibres contract together. What is the term used to describe continuous summation of muscle contractions, where the muscle acts as one unit and therefore allows you to generate maximal tension?

A
  • tetany/tetanisation
50
Q

What type of motor neuron communicates with skeletal muscle?

1 - beta motor neuron
2 - alpha motor neuron
3 - gamma motor neuron
4 - delta motor neuron

A

2 - alpha motor neuron

51
Q

What are the 2 types of receptors that are important for reflex generation?

A

1 - muscle spindles (proprioceptors)

2 - Golgi tendon organ (proprioceptors)

52
Q

When looking at intrafusal and extrafusal muscle fibres, which is located on the inside and outside of the muscle?

A
  • intrafusal = inside muscle contract only at the ends of the muscle
  • extrafusal = outside of muscle
53
Q

When looking at intrafusal (inside muscle) and extrafusal (outside of muscle) muscle fibres, which relates to muscle spindles and which relates to golgi tendon organ?

A
  • intrafusal (inside muscle) = muscle spindles

- extrafusal (outside of muscle) = golgi tendon organ as attached to the tendons

54
Q

Primary afferent nerve fibres Ia and Ib are used to detect changes in the golgi tendon organ and the muscle spindles. Which is associated with which?

A
  • primary afferent nerve fibres Ia = muscle spindles

- primary afferent nerve fibres Ib = golgi tendon organ

55
Q

When we stimulate the muscle spindles, like during a reflex test of the patellar tendon, what happens to the 1a fibres?

A
  • increased firing of action potential along 1a nerve fibre
  • 1a nerve fibre synapses with alpha motor neuron in anterior horn of spinal cord
  • activation of alpha motor neurons in extensor muscles causes knee to extend
  • this extension is a way of shortening the muscle spindles to protect the quadriceps
56
Q

When we stimulate the muscle spindles, like during a patella reflex, the following happens:

  • increased firing of action potential along 1a and IIa nerve fibre
  • 1a nerve fibre synapses alpha motor neuron in anterior horn of extensor muscles causing contraction
  • IIa nerve fibre synapse interneurons in anterior horn that inhibit alpha motor neurons of the flexor muscle
  • causes extension of the knee to try and shorten the stretched fibres caused by the patellar tendon tap
  • process is designed to limit over stretching

What is this whole process called?

1 - stretch reflex
2- golgi tendon reflex
3 - patella tendon response
4 - flexor reflex

A

1 - stretch reflex

57
Q

When we stimulate the golgi tendon organ, during muscular contraction of the biceps brachii for example, what happens to the 1b fibres?

A
  • tendon compresses during muscle contraction
  • compression causes increased firing of Ib afferent fibres in bicep
  • Ib afferent fibres from bicep brachii synapse with interneurons in anterior horn of spinal cord, that then inhibit alpha motor neurons of the biceps (relaxation)
  • Ib afferent fibres synapse with alpha motor neurons of triceps causing activation and contraction
  • results in relaxation of tendon being compressed
  • protective mechanism to stop you over contracting and rupturing the tendon

Year 2 MIS (48 decks)

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