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Biology 1 > Lecture 16- How do muscles contract? > Flashcards

Lecture 16- How do muscles contract? Flashcards

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1
Q

What does the skeleton and muscles make up?

A

The musculoskeletal system

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2
Q

What are embryonic muscle cells called?

A

Myoblasts

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3
Q

What are muscle fibres?

A

Multinucleate muscle cells

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4
Q

What do muscles consist of?

A

Muscle fibres bundled together by connective tissue

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5
Q

What does a single muscle fiber consist of?

A

Many nucleus
Plasma membrane (sarcolemma)
Mitochondria
Myofibrils

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6
Q

Muscle contraction is the result of interactions between which two contractile proteins?

A

Actin- thin filaments

Myosin- thick filaments

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7
Q

What are myofibrils?

A

Bundles of actin and myosin filaments

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8
Q

What are myosin filaments held in place by?

A

Titin

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9
Q

What are the repeating units that make up a myofibril called?

A

Sacromeres

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10
Q

What does titin connect to?

A

The full length of the sarcomere, from Z to Z line

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11
Q

Where does resistance to stretch come from in relaxed muscle?

A

Titin

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12
Q

What is anchored to the Z line, other than titin?

A

Actin

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13
Q

What is the A band?

A

The band that contains all of the myosin filaments

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14
Q

What is in the H zone?

A

Region where the actin and myosin does not overlap (myosin side)

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15
Q

What is in the I zone?

A

Region of actin where myosin does not overlap

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16
Q

What is the M band?

A

Contains a protein to help hold the myosin filaments in their regular arrangements

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17
Q

What happens when muscles contract to the sarcomeres?

A

They shorten

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18
Q

What happens to the H and I zone when muscles contract?

A

They shorten

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19
Q

What happens to the z lines as a muscle contracts?

A

Move towards the A band (A band is where they overlap)

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20
Q

What is the name of the theory of muscle contraction called?

A

Sliding filament theory

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21
Q

What causes filaments to slide?

A

Actin-myosin interactions

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22
Q

How is muscle contraction initiated?

A

Action potential from a motor neuron at the neuromuscular junction

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23
Q

What is a motor unit?

A

All the muscle fibers activated by one motor neuron

24
Q

How does actin-myosin interactions cause muscles to slide past each other?

A

Myosin heads bind to specific sites on actin molecules to form cross bridges
Myosin changes conformation, actin filament slides 5-10 nm

25
Q

What may one muscle have?

A

Multiple motor units

26
Q

How is strength of muscle contraction increased?

A
  • Increased rate of firing of motor neuron

- More motor neurons firing

27
Q

What does a myosin filament consist of?

A

Myosin molecules which consist of a linear polypeptide chain and a globular head

28
Q

What does an actin filament consist of?

A

Actin monomer, tropomyosin, troponin

29
Q

What does it mean that muscle cells are excitable?

A

The plasma membrane can conduct action potentials

30
Q

What molecule is released at the motor neuron to open ion channels in the motor end plate?

A

Acetylcholine- a neurotransmitter

31
Q

How do action potentials travel deep within muscle fibers?

A

T tubules

32
Q

What are T tubules?

A

Transverse tubules

Descend into the sarcoplasm (muscle fiber cytoplasm)

33
Q

What do T tubules run close to?

A

Sacroplasmic reticulum

34
Q

What is in the sarcoplasmic reticulum?

A

A high concentration of Ca2+ at rest

Ca2+ pumps

35
Q

What happens when an action potential reaches the receptor proteins?

A

The Ca2+ channels open, calcium ions flow out of sarcoplasmic reticulum, triggers actin-myosin interactions

36
Q

What is troponin?

A

A protein with three sub units: one binds actin, one binds myosin, one binds Ca2+

37
Q

What does tropomyosin do at rest?

A

Blocks binding sites on actin

38
Q

What happens to troponin when Ca2+ is released?

A

They bind, conformation of troponin change

39
Q

What happens once troponin has bound to Ca2+?

A

Tropomyosin and troponin bind, tropomyosin twists to expose actins active site

40
Q

How does contraction of a muscle stop?

A

Ca2+ pumps remove Ca2+ from the sarcoplasm, contraction stops

41
Q

How is cardiac muscle similar and different to skeletal muscle?

A

Also striated
Cells are smaller and only have one nucleus
Cells branch and interdigitate to withstand high pressures

42
Q

What provides mechanical adhesions between cardiac muscle cells?

A

Intercalated discs

43
Q

What initiates coordinated heart contractions?

A

Pacemaker, conducting cells

44
Q

What does it mean that the heart is myogenic?

A

It generates the heartbeat its self

45
Q

How else is heart rate determined?

A

The autonomic nervous system

46
Q

How do cardiac muscles contract?

A

DHP proteins in T tubules are Ca channels
ryanodine receptors are ion gated calcium channels, sensitive to calcium ions

Action potential causes Ca2+ to flow into sarcoplasm from T tubules, increase opens ca channels in sarcoplasmic reticulum, initiates contraction

47
Q

TL;DR, how do cardiac muscles contract?

A

Ca2+- induced Ca2+ release

48
Q

How are smooth muscle cells arranged?

A

In sheets, electrical contact is via gap junctions- action potential in one cell spreads to others in sheet

49
Q

What happens when smooth muscles are stretched?

A

Cells depolarise and fire action potentials to start contraction

50
Q

How does smooth muscle contract?

A

Ca2+ influx to sarcopasm stimulated by hormones, stretching or action potentials
Ca2+ binds to calmodulin- activates myosin kinase which phosphorylates myosin heads- bind and release actin

51
Q

Explain how the hypothesis that stretch and parasympathetic stimulation induce contraction in gut smooth muscle can be tested experimentally.

A

Incubate a strip of smooth muscle in a saline bath

Measure action potentials and force of contraction.

52
Q

Explain the method of this experiment.

A

The muscle is anchored to a device which applies a stretch force
An electrode detects membrane and action potentials which is recorded
In experiment 2, acetylcholine or norepinephrine is dripped on

53
Q

What are the results of this experiment?

A

Stretching depolarises the membrane which causes action potentials which activates contractile membrane
Neurotransmitters alter membrane resting potential to alter rate at which action potentials are fired

54
Q

What is the minimum unit of skeletal contraction?

A

A twitch

55
Q

What factors determine the force generated by an entire muscle?

A
  • Number of activated motor units

- Frequency of firing of motor units

Biology 1 (16 decks)

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