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SF3: Cardiovascular, Respiratory and Musculoskeletal Systems > W2 Skeletal Muscle > Flashcards

W2 Skeletal Muscle Flashcards

1
Q

what are three functions of skeletal muscle?

A

any three of:
- move the body
- control body posture
- support and protect
- control orifice (voluntary control)
- participate in temperature regulation
- generate peristaltic movement

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2
Q

what are muscle fibers enveloped by?

A

a sheath of connective tissue

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3
Q

what bundles make up a muscle?

A

bundles of muscle fibers

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4
Q

what unit makes up muscle fibers?

A

myofibrils

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5
Q

what unit makes up myofibrils?

A

myofilaments

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6
Q

what unit makes up myofilaments?

A

sarcomeres

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7
Q

describe the structure of a sarcomere:

A

highly aligned, two Z-discs and and M-line containing myosin and actin filaments, Each muscle fibre has a light actin band (I-band) and a dark myosin band (A-band). The elastic fibre (Z-line) bisects each I-band, the thin filament is firmly anchored to the Z-line. The H-zone is the central part of the thick filament that is not overlapped by the thin.

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8
Q

what is myosin made up of and what are they centred by?

A

made up of several myosin molecules and centred between z-discs and m-lines by titin

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9
Q

what ensures uniformity in length of actin?

A

attachment to nebulin

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10
Q

what do T-tubules allow?

A

rapid conduction of AP

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11
Q

where are T-tubules found?

A

run through fibres either side of the z-discs

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12
Q

T-tubules are in close contact with what?

A

sarcoplasmic reticulum

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13
Q

what is a neuromuscular junction?

A

a synaptic connection between the terminal end of a motor nerve and a muscle, it is the site for the transmission of action potential from nerve to the muscle

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14
Q

describe the sliding filament theory:

A

during muscle contraction, myosin heads or cross-bridges come in close contact with the thin filaments of the actin bending the head towards the sarcomere, as a result the thin filaments are pulled towards the middle of the sarcomere, the Z-line attached to the actin filament is also pulled leading to the shortening of the sarcomere (the length of the bad remains constant as its original length but the I-band shortens and the H-zone disappears. this is caused by a serious of action potentials being reached in rapid succession

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15
Q

what is a cross bridge?

A

myosin heads binding to actin molecules

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16
Q

myosin have and ATP binding site which allows what?

A

hydrolysis of ATP (ATP -> ADP + P)

17
Q

what is a power stroke?

A

when calcium is released from sarcoplasmic reticulum allowing the myosin heads to bind and bend

18
Q

what happens following a power stroke?

A

ADP is released and myosin heads bind to another ATP molecule breaking the myosin/actin bond

19
Q

what controls the contractions of muscle?

A

tropomyosin and troponin by preventing the binding of myosin to actin in resting muscle

20
Q

what happens when an action potential arrives at the neuromuscular junction (NMJ)?

A
  1. calcium is released from sarcoplasmic reticulum
  2. the calcium then binds to troponin
  3. the tropomyosin changes position exposing the binding sites on the actin
  4. myosin heads bind and bend and the actin filament slides
  5. ATP binds to the myosin heads and breaks the bond to actin
  6. ATP is hydrolysed and the energy release straightens the myosin heads
  7. pumps in the sarcoplasmic reticulum pump calcium from cytosol back into the SR
  8. calcium dissociates from troponin
  9. tropomyosin blocks the myosin binding sites on actin
  10. the muscle relaxes
21
Q

what is rigor mortis and what causes it?

A

when the body becomes stiff after death, this is due to ATP production ceasing causing ion pumps to stop, calcium leaking into cytosol, calcium levels are not maintained, eventually calcium levels are high enough to cause binding of myosin heads that do not break free

22
Q

what is hypocalcaemia in ruminants and dogs respectively ?

A

paresis in ruminants and tetany in dogs

23
Q

calcium regulates the release of what in the synapse between motor neurones and muscle cells?

A

ACH

24
Q

low extracellular calcium depolarises all cells, what does this lead to in neurones?

A

spontaneous AP generation

25
Q

what happens to muscle contractions in dogs with hypocalcaemia?

A

involuntary contractions occur

26
Q

what happens to muscle contractions in ruminants with hypocalcaemia?

A

nothings, increased firing frequency does not lead to increased muscular activity as the NMJ is blocked

27
Q

what is used to make creatine phosphate?

A

some of the ATP produced by muscle fibres

28
Q

what catalyses ATP + creatine -> ADP + creatine phosphate?

A

catalysed by creatine kinase

29
Q

in resting muscles is creatine phosphate concentration higher or lower than ATP?

A

much higher

30
Q

as soon as contractions start, does the concentration of ATP increase or decrease?

A

decrease

31
Q

what three steps in energy metabolism is ATP essential for?

A
  1. energy for the power-stroke of the cross-bridges (from hydrolysis of ATP to ADP)
  2. ATP must bind to myosin heads in order to break their grip on actin
  3. energy released by hydrolysis of ATP is necessary for pumping calcium back into the sarcoplasmic reticulum
32
Q

describe the differences between location of skeletal, smooth and cardiac muscles:

A

skeletal - attached to bones
smooth - walls of hollow organs, blood vessels, eyes, glands and skin
cardiac - the heart

33
Q

describe the differences between function of skeletal, smooth and cardiac muscles:

A

skeletal - body movements
smooth - transport of food through GIT, emptying bladder, regulation of blood vessel diameter
cardiac - pumping of blood

34
Q

describe the differences between the calcium binding protein of skeletal, smooth and cardiac muscles:

A

skeletal - troponin
smooth - calmodulin
cardiac - troponin

35
Q

describe the differences between voluntary control of skeletal, smooth and cardiac muscles:

A

skeletal - yes
smooth - no
cardiac - no

36
Q

describe the differences between cell communication of skeletal, smooth and cardiac muscles:

A

skeletal - neuromuscular junctions
smooth - tight junctions
cardiac - gap junctions

SF3: Cardiovascular, Respiratory and Musculoskeletal Systems (15 decks)

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