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BIOSCI 107 > Muscles 1 > Flashcards

Muscles 1 Flashcards

1
Q

Describe skeletal muscle (6)

A
  • Striated
  • Voluntary*
  • Single long, wide, cylindrical cells
  • Multiple nuclei*
  • Attached to bones by tendons
  • Responsible for movement
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2
Q

Describe cardiac muscle (6)

A
  • Striated
  • Branched*
  • Involuntary
  • 1 (sometimes 3) nuclei*
  • Lots of mitochondria*
  • All cells electrically connected via intercalated discs (gap junctions and desmosomes)*
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3
Q

What is voluntary control?

A

Under control of somatic nervous system (only skeletal)

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4
Q

What is involuntary control?

A

Under control of autonomic nervous system (cardiac, smooth)

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5
Q

What is a motor unit?

What is the other way cells can be connected in tissue?

A
  • A group of muscle cells innervated by a single neuron

- Direct cellular contacts

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6
Q

What are actins? (2)

A
  • Globular proteins that form THIN filaments

- Have accessory proteins (troponin, tropomyosin)

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7
Q

What is troponin? (2)

A
  • Regulatory accessory protein on actin

- Has Ca binding site = allows movement to start

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8
Q

What is tropomyosin? (2)

A
  • Regulatory accessory protein on actin

- Regulates myosin head binding to actin

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9
Q

What are myosins? (3)

A
  • THICK filaments
  • 2 subunits: globular head, tail (forms double helix)
  • Head is enzyme that breaks down ATP
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10
Q

Describe calcium in muscle processes (3)

A
  • Increase in Ca levels is ‘on switch’ for contraction
  • Interacts with troponin (in actin regulated muscles), calmodulin (in myosin regulated muscles)
  • Comes from inside cell stores (SR) and outside cell
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11
Q

How does the cross-bridge cycle work? (4 steps)

A

Calcium binds to troponin causing it to change shape, tropomyosin reveals actin binding sites

  1. Myosin head binds actin and forms cross-bridge (must be activated by ATP hydrolyses)
  2. Power stroke: ADP is released and myosin slides actin towards centre
  3. Cross-bridge detachment: ATP binds to myosin causing it to detach
  4. ATP hydrolysed, reactivate myosin head
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12
Q

Describe a muscle contraction

What happens to the sarcomere?

A
  • Caused by single AP
  • Activates of cross-bridge cycle
  • Sarcomere contracts and thin filaments are pulled over thick
  • Z-discs pulled towards M-line, I-band and H-zone narrow, A bands don’t change
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13
Q

What is the length-tension relationship? (2)

A
  • Ability to develop tension depends on initial strength

- Overlap determines cross bridges attached during isometric form

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14
Q

What is passive tension?

A

Elastic elements stretched out and want to return to shape

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15
Q

What are the components of a skeletal muscle cell? (4)

A
  • Sarcomere made up of fibrils surrounded by sarcolemma
  • Fibrils made up of thick/thin filaments
  • SR
  • T-tubules
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16
Q

What is the sarcoplasmic reticulum? (3)

A
  • Extensive network of membrane-bound compartment surrounding fibril
  • Calcium store
  • Skeletal > cardiac > smooth
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17
Q

What are the t-tubules? (4)

A
  • On surface of sarcolemma
  • Interior of tubules is exterior of cell (tubules are continuous with sarcolemma)
  • Receives AP
  • Between A and I bands for skeletal / at Z lines for cardiac / not present in smooth
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18
Q

What is a triad?

What is the function of the arrangement?

A
  • 2 bulges of SR (terminal cisternae) against 1 t-tubule

- Close so t-tubule can signal SR easily (to open calcium stores)

19
Q

What are the components of the sarcomere in skeletal muscle? (5)

A
  • M line: thick filaments linked by accessory proteins
  • H zone: thick only
  • A band: all of thick, some thin
  • I band: thin only
  • Z disk: boundary of sarcomere - attachment site for thin
20
Q

In the length-tension relationship of skeletal muscle…

What happens when muscle is stretched out? (4)

A

> 2.2um

  • Less overlap between filaments
  • Myosin can’t grab onto actin = reduced number of cross-bridges
  • Less tension as active forces decline
21
Q

In the length-tension relationship of skeletal muscle…

What happens when the muscle length is half or more? (3)

A

< 2.0um

  • Filaments collide and interfere = reduces force developed
  • Myosin heads can’t effectively grab onto actin (and move towards M line)
22
Q

In the length-tension relationship of skeletal muscle…
What is maximal force/normal working range of the muscle?
What is total tension?

A
  • 2.0-2.2um

- Total tension: sum of active tension, dependent on sarcomere length and passive tension

23
Q

What does isometric mean?

A

Contracted but not shortened

24
Q

What does isotonic mean?

A

Muscle shortened (L-T relo can’t be measured)

25
Q

What is the neuromuscular junction?

A

Where the axon terminals of motor neuron meet the motor end plate on a skeletal muscle fibre

26
Q

Describe muscle contraction at the neuromuscular junction in skeletal muscle (7 steps)

A
  1. AP travels to motor neuron axon terminal
  2. VG Ca+ channels open and Ca+ diffuses into terminal
  3. Ca+ causes synaptic vessels to release ACh via exocytosis
  4. ACh diffuses across synaptic cleft and binds to ACh receptors (contain LG cation channels)
  5. LG cation channels open
  6. Na+ enter and K+ exit muscle fibre (causes depolarisation)
  7. Threshold reached and AP propagates sarcolemma and t-tubules
    (stops when ACh removed from cleft; diffusion or ACh enzyme)
27
Q

Describe excitation-contraction coupling in skeletal muscle (3)

A
  • Voltage sensor in t-tubule is directly linked to Ca+ release channel in SR
  • When AP reaches t-tubule the sensor opens the channel so Ca+ can flow out of SR
  • Contraction ends when Ca is pumped back into SR via Ca2+ATPase pump (troponin moves back over binding site)
28
Q

What is the role of creatine phosphate in muscle metabolism? (3)

A
  • For <15s it can act as an ATP store
  • Creatine phosphate + ADP = creatine + ATP
  • ANaerobic (no O2)
29
Q

What is anaerobic glycolysis in terms of muscle metabolism? (2)

A
  • Short exercise 10-30s (fast, inefficient)

- Build up of lactate and H+ limit to 120s

30
Q

Describe aerobic metabolism (3)

A
  • Efficient but slow (produces a lot)
  • Requires O2 - need good blood supply
  • Postural and endurance
31
Q

What is a type 1 muscle fibre? (5)

A
  • Slow twitch (posture, walking)
  • Aerobic
  • Small
  • High mitochondria/myoglobin/blood supply
  • Low glycolytic capacity
32
Q

What is a type 2b muscle fibre? (5)

A
  • Fast twitch (jumping, weights)
  • Anaerobic glycolysis
  • Large
  • Low mitochondria/myoglobin/blood supply
  • High glycolytic capacity
33
Q

What affects regulation of force? (2)

A
  • RATE of stimulation of individual motor units

- NUMBER of motor units recruited

34
Q

What is temporal summation?

regulation of force

A

Increased FREQUENCY of stimulation (AP) during contraction

  • Rapid stimulation = sustained contraction
  • Less/slow = more, stronger contractions
35
Q

Describe recruitment of motor units

regulation of force

A

Amount of force developed determines the number of motor units recruited

  • Heavy = more
  • Increases VOLTAGE
36
Q

What is different about the contraction of cardiac muscle? (3)

A
  • Longer AP and contraction
  • AP has plateau phase due to Ca current
  • Contract:relax = 1:3 (refil) a premature contraction will be small due to less refil
37
Q

What is the process of contraction in cardiac muscle? (3 steps)

A
  1. Rapid depolarisation (Na moves into cell quickly)
  2. Plateau phase (opening of slow VG Ca channels)
  3. Repolarisation (K channel open, inward channels close)
38
Q

What are the features of the t-tubule and SR in cardiac muscle? (4)

A
  • T-tubules on Z discs
  • Less extensive SR
  • LTCC (L-type Ca channel) on t-tubule (reason for plateau) = Ca source
  • RyR receptors on SR, associated with Ca channel (Ca binds RyR to release Ca)
39
Q

Describe the initiation of the heart beat at the SA node (2)

A
  • Electrical activity starts at SA node then spreads throughout cells
  • Pacemaker cells are ‘leaky’ because they let Na into the cell so the RMP naturally increases to threshold
40
Q

What regulates the frequency of of the heart beat? (nerve, neurotransmitter, effect)
(2)

A
  • PARAsympathetic (vagus) nerves release ACh and DECREASE depolarisation/heart rate
  • SYMpathetic nerves release noradrenaline and INcrease depolarisation/heart rate
41
Q

Describe the calcium cycle in cardiac cells compared to that of skeletal muscle (4)

A
  • AP spreads sarcolemma to t-tubules and triggers L-type Ca+ channels to open = AP plateau and lets Ca+ into cell
  • There’s always Ca+ pumped out through Na/Ca exchanger (gradient established by Na/K)
  • Ca+ binds to RyR and opens SR Ca+ channel to flood cell
  • “Calcium induced calcium release”
    = contraction occurs
42
Q

Describe the location and structure of smooth muscle (9)

A

Airways, bladder, reproductive, blood vessels, eyes, gut

  • Spindle shaped
  • Single nucleus
  • Visceral arrangement (sheet) = single unit / multiunit smooth muscle tissue (isolated, need more nerves)
  • No t-tubules (caveolae instead)
  • Dense bodies (act like Z lines)
  • Gap junctions
  • Intermediate filaments (still have thick and thin)
  • Poorly developed SR
43
Q

Explain how smooth muscle contraction is initiated (4)

A
  • VG Ca channels (few Na channels)
  • Ca binds to CALMODULIN (not troponin)
  • Which activates MLCK(inase)
  • Which acts on myosin heads
44
Q

Describe how smooth muscle contractile force may be modulated (3)

A
  • Relaxes when myosin light chain phosphotase dephosphorylates it
  • Ca-ATPase reduces intracellular Ca
  • Contraction is enzyme regulated (slow but efficient)

BIOSCI 107 (14 decks)

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