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Physio > Exam 1 - Muscle Physiology > Flashcards

Exam 1 - Muscle Physiology Flashcards

1
Q

describe the following:

  • A band
  • Z line/disk
  • I band
  • H zone
  • M line
A

A: region w/ thick filaments
Z: attaches to thin filaments in both directions
I: region w/ only thin filaments and Z disk
H: central region where thin don’t overlap with thick
M: attaches to thick filaments in both directions

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2
Q

what is the basic contractile unit?

A

sarcomere

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3
Q

what is the sliding filament hypothesis?

A

neither the thick nor thin filaments change in length during contraction -> shortening occurs b/c thick and thin filaments slide past each other, increasing region of overlap

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4
Q

composition of thick and thin filaments

A

thick: myosin
thin: actin, tropomyosin, troponin

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5
Q

function of tropomyosin

A

covers the myosin binding site on actin until Ca2+ binds to troponin C, which then moves tropomyosin off of the binding site -> initiate contraction

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6
Q

function of troponin I, T, and C

A

I: inhibits interaction of actin and myosin (covers binding site)
T: attaches tropomyosin to troponin complex
C: Ca2+-binding protein

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7
Q

describe the SR

A
  • intracellular sack surrounding myofibrils
  • not continuous w/ plasma membrane
  • [Ca2+] higher inside SR than rest of cell
  • SERCA (Ca2+ ATPase pump) accumulates Ca2+ inside SR using energy from ATP
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8
Q

describe T-tubules

A
  • period infoldings of plasma membrane

- provide a path for events related to plasma membrane depolarization to reach interior of the cell

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9
Q

describe the areas where T-tubules come close to the SR

A

voltage activated Ca2+ channels in T-tubule (dihydropyridine receptors) are linked to Ca-induced Ca-release channels in SR (ryanodine receptors)

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10
Q

describe the steps of excitation-contraction in skeletal muscle

A
  1. AP in muscle membrane propagated to T-tubules by
    spread of local currents
  2. Depolarization of T-tubules -> conformation change in
    dihydropyridine receptors
  3. Opens SR Ca-release channels (ryanodine receptors)
  4. Increase in intracellular [Ca2+]
  5. Ca2+ binds troponin C cooperatively -> conformation
    change in troponin complex
  6. Tropomyosin moves, allows interaction b/w actin and
    myosin.
  7. Cross-bridge cycling and force generation
  8. Ca2+ reaccumulated by SR -> relaxation
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11
Q

describe the steps of cross-bridge cycling and force generation

A
  1. Myosin tightly bound to actin (rigor state) + no ATP bound
  2. ATP binds myosin head -> myosin released from actin
  3. Myosin cleft closes tightly around ATP -> conformation
    change -> displacement of myosin head towards actin (+)
    end
  4. ATP -> ADP + Pi (still bound to myosin)
  5. Myosin binds new site on actin (power stroke)
  6. ADP released -> myosin returns to rigor state w/ no ATP/
    ADP bound
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12
Q

what is the main difference b/w cardiac and skeletal muscle?

A

individual cardiac muscle cells are linked via gap jxns to ensure that all fibers contract together

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13
Q

how is smooth muscle different from skeletal muscle?

A
  • no sarcomeres
  • respond to a variety of neurotransmitters (IP3) and hormones in addition to APs
  • no troponin
  • contractile machinery controlled by MLCK and MLCP (and calmodulin)
  • rise in internal [Ca2+] due to both Ca2+ coming across the plasma membrane and release from SR stores
  • amount of tension produced depends on Ca2+ levels
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14
Q

functions of smooth muscle

A
  • to produce motility

- to maintain tension

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15
Q

describe the steps of excitation-contraction coupling in smooth muscle

A
  1. multiple mechanisms lead to increased [Ca2+] in cell.
  2. Ca2+ binds calmodulin cooperatively
  3. Ca2+-CaM complex binds to, activates MLCK
  4. Phosphorylation of myosin light chains -> conformation
    change
  5. Increase in myosin ATPase activity
  6. Myosin binds actin -> cross bridge cycle + tension
    (amount of tension proportional to intracellular [Ca2+])
  7. Relaxation when intracellular [Ca2+] drops below level
    needed to form Ca2+-CaM complexes or when MLCP is
    activated
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16
Q

what is the length-tension relationship?

A

active tension that develops is proportional to the number of cross-bridges that cycle
-therefore, maximal tension when maximum overlap of thick/thin filaments

17
Q

isometric contraction vs. isotonic contraction

A 
isometric = keep same length 
isotonic = keep same force
18
Q

percentage breakdown of energy usage during maintained contraction

A

50-80% for cross-bridge cycling

20-30% powers pumping of Ca2+ back into SR

19
Q

what are the sources of energy for contraction?

A
  • oxidative phosphorylation

- anaerobic glycolysis

20
Q

oxidative phosphorylation vs. anaerobic glycolysis

A

ox phos:
-when there is high supply of O2
-operates continually if adequate circulation
-slow
-cannot meet maximal ATP consumption rates of rapidly
contracting cells
-36 mol ATP/mol glucose

glycolysis:
- when there is low supply of O2
- very rapid
- can readily meet ATP demands of rapidly contracting cells
- ATP production limited by glycogen stores
- 2-3 mol ATP/mol glucose

21
Q

what is a motor unit?

A

a single motor neuron + all the muscle fibers it innervates

22
Q

what is the innervation ratio?

A

the number of muscle fibers innervated by a single motor neuron

23
Q

what causes tetanus?

A

repeated stimulation -> insufficient time for SR to reaccumulate Ca2+ -> intracellular [Ca2+] remains high -> continued binding of Ca2+ to troponin C -> continued cross-bridge cycling -> continued contraction

24
Q

describe S (slow) fibers

A

-contract slowly
-small peak force
-highly fatigue-resistant during prolonged activation
-small somas, dendrites, axons
-low conduction velocity
-relatively long after-hyperpolarizations (limits range of
repetitive firing)

25
Q

describe FR (fast fatigue-resistant) fibers

A
  • contract rapidly
  • medium peak force
  • some resistance to fatigue
  • large somas, dendrites, axons
26
Q

describe FF (fast fatigable) fibers

A
  • contract rapidly
  • large peak force
  • fatigue quickly
  • large somas, dendrites, axons
  • high conduction velocity
  • relatively short after-hyperpolarizations
27
Q

what determines how a muscle will function?

A

the nature of the muscle’s innervation

28
Q

how does the nervous system increase the force of contraction?

A

-recruiting more motor units (first S, then FR, then FF)
-increasing the rate of firing of individual units -> individual
twitches summate to increase FOC

29
Q

what does the size principle allow?

A

allows the higher motor centers to simply determine the overall level of drive to the motor neuron pool and not have to specify the exact combination of motor units to be recruited
(first S, then FR, then FF)

Physio (12 decks)

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