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BIOL1008 > Muscles > Flashcards

Muscles Flashcards

1
Q

How many muscles are there in the body

A

Approx 640 muscles

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2
Q

What is the strongest muscle?

A

The masseter (i.e. jaw)

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3
Q

What is the largest muscle?

A

The gluteus maximus

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4
Q

What is the smallest muscle

A

Stapedius muscle

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5
Q

What are the main roles of muscles

A

Allow for movement of the body, bones, food, blood and fluids

Responsible for energy metabolism and storage (glycolysis)

Thermoregulation (creates body heat)

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6
Q

What are the four basic properties of muscle

A

Contractility
Excitability
Extensibility
Elasticity

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7
Q

What is contractility

A

Ability of muscle to shorten with a force. It requires energy and relaxes passively

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8
Q

What is excitability

A

Capacity of muscle to respond to stimulation (nerves) - electrical stimulation

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9
Q

What is extensibility

A

Muscle can be stretched to its normal resting rate and beyond to a limited degree

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10
Q

What is elasticity

A

Muscles return or recoil to resting position when relaxed

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11
Q

What % of body mass is skeletal muscle for men compared to women

A

men = 40%

women = 30%

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12
Q

Does muscle mass decrease with agr

A

Yes it decreases, leading to sacropenia (involuntary loss of skeletal muscle) and ultimately loss of physical capacity

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13
Q

How do muscles function (basic)

A

They function by performing opposing actions (agonist and antagonist)

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14
Q

What does the agonist do

A

Agonist causes movement

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15
Q

What does the antagonist do

A

Antagonist provides opposite movement to agonist

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16
Q

What are the 3 different types of muscles

A

Skeletal

Cardiac (myocardium)

Smooth

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17
Q

What is skeletal muscle

A

Muscle attached to skeleton - its responsible for voluntary movement

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18
Q

What is cardiac muscle?

A

Forms the heart, which is also responsible for pumping blood, and it is ultimately an involuntary movement

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19
Q

What is smooth muscle?

A

Located in tissues and is responsible for controlling diameter of structures and peristalsis (involuntary constriction and relaxation of muscles, causing wave like movement that pushes contents forward in the gut)

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20
Q

Explain the structure of muscle fibers (in terms of ascending size)

A

Sarcomeres –> myofibril –> muscle fibre –> muscle bundle –> muscle

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21
Q

What are sarcomeres made up of?

A

Made up of actin and myosin filaments

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22
Q

What are actin filaments

A

These are the thin contractile filaments compared to myosin

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23
Q

What are myosin filaments

A

These are the thick contractile filaments compared to actin

24
Q

Explain the process of muscle contraction

A

1) ATP bound myosin is in the relaxed position

2) When ATP is dephosphorylated to ADP + Pi (inorganic phosphate), it is positioned to form a cross bridge. Tropomyosin inhibits/blocks binding sites on actin and prevents cross bridge formation

3) Electrical excitation of the muscle cell releases calcium from the sarcoplasmic reticulum. Calcium binds to troponin and moves the tropomyosin out of the way to allow cross bridge formation

4) Power stroke: Release of phosphate bound to the myosin head - myosin head moves along the actin filament

5) At the end of excitation, calcium pumps back into SR allowing tropomyosin to block myosin binding again, and ATP is bound again

25
Q

What is tropomyosin

A

ropomyosin is the guard mechanism that prevents a skeletal muscle from contracting irregularly or on its own. Tropomyosin is a protein filament used to create a barrier between actin and myosin protein filaments and prevent the skeletal muscle from contracting.

26
Q

What is troponin

A

Troponin (Tn) is the sarcomeric Ca2+ regulator for striated (skeletal and cardiac) muscle contraction. On binding Ca2+ Tn transmits information via structural changes throughout the actin-tropomyosin filaments, activating myosin ATPase activity and muscle contraction.

27
Q

What is the myosin head

A

In addition to binding actin, the myosin heads bind and hydrolyze ATP, which provides the energy to drive filament sliding.

28
Q

What are the two different muscle fiber types

A

Type 1 and Type 2

29
Q

What are type 1 muscle fiber types

A

They are also called slow twitch and red muscle fibers. They contract slowly, but are slow to fatigue.

It uses aerobic (slower) metabolism to generate large amounts of ATP - adapted to deliver O2 to the mitochondria

Fibers are red due to the myoglobin content which transports O2 to the area

30
Q

WHat are type 2 muscle fiber types

A

They are also called fast twitch or white muscle fibers

They contract quickly and are fast to fatigue. They use anaerobic (faster) metabolism to generate less ATP - not adapted to deliver O2 to mitochondria

31
Q

WHat are the two types of white muscle fiber

A

Type 2A and type 2B

32
Q

What does type 2A and type 2B muscles do

A

Type IIA fibers have high myosin ATPase activity (pH 9.4), are fast twitch, have high oxidative and glycolytic capacity, and are relatively resistant to fatigue. Type IIB fibers have high myosin ATPase activity (pH 9.4), are fast twitch, have low oxidative and high glycolytic capacity, and fatigue rapidly.

33
Q

What are the characteristics of smooth muscles

A

Single shaped cells without striations

Single central nucleus

Contracts more slowly with less power than skeletal muscle

34
Q

What are the two types of contractions in smooth muscles

A

Phasic - rapid

Tonic - slower, maintain tension longer

35
Q

Where are smooth muscles formed

A

Walls of organs, vessels

Respiratory tract

Eye - dilation constriction of pupil

Skin

kidneys

36
Q

What is the process of smooth muscle contractions

A

1) Ca2+ influx into cell from SR and extracellular sources via L type Ca2+ channels

2) Ca2+ binds calmodulin in sarcoplasm

3) Ca2+-/calmodulin activates MLCK which phosphorylates head of myosin filament (ATP) - cross bridge formation

4) No influx - relaxation

Overall. There is increase in cytosolic Calcium. Calcium ions bind to calmodulin in cytosol. Calcium calmodulin complex binds to myosin light chain kinase. This kinase uses ATP to phosphorylate myosin cross bridges. Phosphorylated myosin cross bridges bind to actin filaments. The cross bridge cycle produces tension and shortening

37
Q

What are the differences between smooth and skeletal muscle contraction?

A

Ca2+ binds to calmodulin in cytosol in smooth muscle contraction vs binding to troponin on thin filaments in skeletal muscle

MLCK phosphorylation of myosin cross bdirge

Smooth muscle contraction is 100-1000 times slower than skeletal - allows smooth muscle to maintain prolonged tonic contraction while consuming little ATP and O2

Stimulus for smooth muscle contraction can be varied - stretch, neural (automatic NS), hormonal, skeletal-innervation(somatic NS)

38
Q

What is a motor unit

A

It is one motor neuron which supplies a group of muscle cells

39
Q

What are the features of small motor units

A

Innervate less muscle fibers

Generate less tension

Enable fine control

Fatigue resistant

I.e. eye movements

40
Q

What are the features of large motor units

A

Generate more tension

Fatigues more quickly

41
Q

What are slow motor units

A

Typically help with type 1 fibers - sustained contraction

42
Q

What are fast motor units

A

Typically help with type 2 fibers - large rapid forces

43
Q

How can an increase in force be generated

A

By activating more motor units simultaneously

44
Q

What is the overall tension produced in a skeletal muscle a function of?

A

The frequency of neural stimulation and the number of motor units

45
Q

What are the two types of smooth muscle cells?

A

Single unit and multi unit

46
Q

What are single unit smooth muscle cells

A

All cells function collectively and simultaneously as a single unit (unitary) i.e. abdomen or bladder

47
Q

What are multi unit smooth muscle cells

A

All cells cannot function collectively and instead work independently

48
Q

What are the 3 periods to muscle tension

A

Latent period, contraction period and relaxation period

49
Q

What is the latent period

A

Action potential is being propagated along the membrane and Ca2+ ions are released from the sarcoplasmic reticulum

50
Q

What is the contraction period

A

Period of cross bridge formation

51
Q

What is the relaxation period

A

When Ca2+ is pumped back into SR and cross bridge cycling stops

52
Q

Describe the muscle tension across the periods of muscle tension

A

During latent and contraction period it is increasing, and peaks right at the end of the contraction period. Then, during the relaxation period, the muscle tension decreases

53
Q

What is a muscle twitch

A

It is a single contraction from one action potential from a motor neuron

54
Q

What is the idea of summation in muscle tension

A

If a muscle cell is stimulated while a previous twitch is still occurring, the second twitch will be stronger.

The second stimulus releases more Ca2+ ions and allows more cross bridge formations

55
Q

What is a tetanic contraction

A

It is a sustained muscle contraction evoked by a motor nerve emitting action potentials at a very high rate

56
Q

What is the sarcoplasmic reticulum

A

The sarcoplasmic reticulum (SR) is a specialized form of the endoplasmic reticulum of muscle cells, dedicated to calcium ion (Ca2+) handling, necessary for muscle contraction and relaxation.

BIOL1008 (17 decks)

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