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RUSVM Physiology I > Muscle - Part 2 > Flashcards

Muscle - Part 2 Flashcards

1
Q

How mechanism does muscle contraction occur by?

A

Sliding filament mechanism

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2
Q

What is the sliding filament mechanism?

A

Forces generated by interaction of cross-bridges from the myosin filaments with the actin filaments.
Activated by Ca+ released from SR by AP

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3
Q

What filaments are thick filaments? Thin?

A

Myosin. Actin, troponin, tropomyosin.

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4
Q

What is the structure of thick filaments?

A

Myosin molecules whose heads protrude at opposite ends of the filament, with actin-binding sites at the ends of the heads, ATP binding sites on the side, and flexible hinge regions

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5
Q

What is the structure of thin filaments?

A

Two strands of actin subunits in a helix plus two types of regulatory proteins (troponin and tropomyosin). Active sites on the actin subunits for myosin attachments are inhibited by troponin/tropomyosin complex.

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6
Q

How does the “walk along theory” function?

A
  • myosin heads bind with ATP
  • ATPase cleaves ATP producing ADP and phosphate. myosin head is energized in cocked position with the energizing myosin head
  • troponin-tropomyosin complex binds to Ca+ ions and uncovers active site on actin strand
  • cocked myosin heads bind to open actin sites forming cross bridge, releasing ADP and phosphate
  • cross bridge bends myosin heads towards center of sarcomere, causing actin to slide toward m-line in a POWER STROKE
  • ATP binds to myosin head causing detachment from actin filament
  • begin again
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7
Q

What are the three types of muscle contraction?

A

Twitch, summation, tetanus

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8
Q

What is the latent period of muscle contraction?

A

Time between stimulus to motor neuron and subsequent contraction of the muscle

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9
Q

What is a single contraction and relaxation cycle?

A

Twitch

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10
Q

What is summation?

A

A action potential that occurs before complete relaxation which will add onto the previous

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11
Q

What are the two methods of summation?

A

Multiple fiber summation and frequency summation

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12
Q

What is multiple fiber summation?

A

Increasing the number of motor units contraction simultaneously.

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13
Q

What is size principle? What is is involved with?

A
  • As more and larger motor units are activated the force of contraction becomes progressively stronger. Larger motor units can have up to 50x the strength. ie: size matters
  • multiple fiber summation
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14
Q

What is frequency summation?

A

Increasing frequency of contraction via arrival of action potentials so that the stimulation overlaps and adds to overall contraction strength.

*AP do not arrive synchronously

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15
Q

What is tetanization?

A

Critical frequency level in which contractions are so rapid in succession that they fuse together at maximal strength, appearing smooth and continuous

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16
Q

What is the length-tension relationship?

A

The relation between the length of the muscle before onset of contraction and the tension that each contracting fiber can develop at that length.

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17
Q

What is the amount of tension in a muscle fiber dependent on?

A

The number of cross bridge interactions that occur in all of the sarcomeres along the myofibrils, which are determined by the degree of overlap between thick and thin filaments.

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18
Q

When sarcomeres are in ________________ , maximal tension can be produced.

A

Optimal resting length

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19
Q

What does deceased length of a sarcomere mean and what does it cause? Increased length?

A

The sarcomere is contracted with a high degree of overlap so that muscle contraction cannot progress or produce any tension.

The sarcomere is pulled away with a small degree of interaction between filaments (or none at all)

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20
Q

What are the sources of energy for muscle contraction? What are they needed for?

A

Phosphocreatine
Glycolysis
Oxidative metabolism

  • walk along mechanism, calcium pump in SR, Na-K pump in sarcolemma
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21
Q

What is phosphocreatine used for? How does it function?

A

Used to reconstitute the ATP molecule

  • Creatine from aa’s in the liver is phosphorylated in the muscle by the enzyme creatine phosphokinase, producing phosphocreatine
  • cleavage of phosphocreatine then releases energy to bind a new phosphate ion to ADP to reconstitute ATP
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22
Q

What is glycolysis?

A

Enzymatic breakdown of carbohydrates as glucose and glycogen with the release of energy and production of pyruvic acid and lactic acid. Energy is used to reconstitute both ATP and phosphocreatine.

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23
Q

What energetic process can occur in the absence of oxygen?

A

Glycolysis

24
Q

Does glycolysis or oxidative metabolism produce ATP faster? How much?

A

Glycolysis, 2.5X as rapid

25
Q

What is oxidative metabolism?

A

The combining of Oxygen with the end products of glycolysis (lactate) and other sources of energy (proteins, lipids - long term activity, carbs - short term activity ) to produce ATP

26
Q

What are the types of smooth muscle?

A

Multi-unit smooth muscle and single-unit smooth muscle

27
Q

What smooth muscle type has discrete, separate muscle fibers that contract independently with independent inervation

A

Multi-unit smooth muscle

28
Q

What smooth muscle fiber is arranged in sheets with adherent cell membranes so that forces can be transmitted along the fibers to the next and contract together?

A

Single-unit (visceral) smooth muscle

29
Q

What are other names for single-unit smooth muscle fibers

A

Visceral, syncytial, unitary

30
Q

How are visceral smooth muscle fibers joined together?

A

Cell membranes are adhered via gap junctions

31
Q

Where is visceral smooth muscle located?

A
  • GI tract
  • bile ducts
  • ureters
  • uterus
  • many blood vessels
32
Q

Where is multi-unit smooth muscle located?

A
  • ciliary muscles of the eye
  • iris muscles of the eye
  • base of hair follicles
  • smaller airways of the lungs
  • walls of large blood vessels
33
Q

What are gap junctions?

A

Cell to cell junction that allows passage of small water-soluble molecules from cell to cell (ex: ions, glucose)

34
Q

What are particularities of smooth muscle?

A
  • does not have the same striated arrangement of actin/myosin
  • myosin filaments have side-polar cross-bridges
  • sarcoplasmic reticulum is slightly developed
35
Q

What is the arrangement of smooth muscle microfilaments?

A
  • large numbers of actin filaments attached to dense bodies (some attached to cell membrane)
  • no troponin/tropomyosin complex
  • myosin filaments intercalculate among actin filaments
36
Q

What allows myosin filaments to contract up to 80% of their length?

A

Side-polar cross bridges arranged so that they bend in opposite directions, pulling actin filaments simultaneously in opposite direction

37
Q

What is the major source of Ca+ for smooth muscle contraction?

A

Extracellular fluid

38
Q

If a smooth muscle fiber has extensive SR it contracts _______

A

Rapidly

39
Q

What factors can initiate contraction in smooth muscle?

A
  • nervous stimulation
  • hormonal stimulation
  • local tissue chemical factors
  • self-excitation
40
Q

Smooth muscle is innervated by ________________

A

Autonomic nervous fibers

41
Q

What is the autonomic nervous system? What are its branches?

A

A division of the peripheral nervous system that influences the function of internal organs (involuntary)

  • sympathetic nervous system - “fight or flight”
  • parasympathetic nervous system - “rest and digest”
42
Q

T/F : nerve fibers make direct contact with smooth muscle fiber cell membranes

A

False; they form diffuse junctions that secrete their neurotransmitter into the matrix coating of the smooth muscle

43
Q

What purpose do varicosities in fine terminal axons serve?

A

Contain vesicles that store neurotransmitters such as acetylcholine and norepinephrine, which can stimulate or inhibit contraction depending on location

44
Q

What causes contraction in multi-unit smooth muscle?

A

The neurotransmitter (ACh or NE) causes depolarization of the membrane and contraction without generating an action potential (junctional potential) due to fibers being to small (stimuli spreads over entire fiber)

45
Q

What are the two types of action potentials in visceral smooth muscle?

A

Spike potential and action potentials w/ plateau

46
Q

What are spike potentials?

A

Action potentials in smooth muscle similar to those in skeletal muscle.

47
Q

T/F : spike potentials can be spontaneous

A

True; some cells are self-excitatory, associated with basic slow wave rhythm of membrane potential (ex: peristalsis)

48
Q

What are action potentials with plateau?

A

Similar onset to spike potentials but undergoes a delayed repolarization phase (instead of rapid depolarization) causing prolonged contraction seen in some muscles (ex: uterus, vascular smooth muscle)

49
Q

T/F : smooth muscle membrane has more voltage-gated sodium channels and fewer voltage-gated calcium channels

A

False; calcium channels are important in generating the APs and to cause contraction. Sodium has little participation

50
Q

What tasks do calcium ions perform in smooth muscle?

A
  • flow of calcium into the interior of the fiber is responsible for action potentials
  • calcium ions act directly on smooth muscle to cause contraction
51
Q

Local tissue chemical factors can cause excitation via

A

Changes in conditions in the surrounding interstitial fluid and changes in blood flow to cause stretch
(lack of nerve supply in small vessels)

52
Q

What mechanisms are involved in excitation by chemical and hormonal factors?

A

Stimulate contraction by opening of Na and Ca ion channels. (Inhibits by closing)

Ex: calcium, cAMP, cGMP

53
Q

What are the 5 steps of smooth muscle contraction?

A

1- Ca concentration in cytosol of the smooth muscle cell increases via influx from ECF through Ca channels
2- Ca ions bind reversibly with calmodulin
3- the Ca-Calmodulin complex joins with and activates myosin light chain complex (phosphorylating enzyme)
4- one of the light chains of each myosin head (regulatory chain) is phosphorylated (responsible for attachment-detachment cycling of myosin)
5- contraction of smooth muscle

54
Q

What activates myosin light chain kinase? What does this do?

A

Ca-Calmodulin complex. Phosphorylates one light chain of each myosin head to allow binding to actin filaments.

55
Q

How does the Ca pump and myosine phosphate act to stop smooth muscle contraction?

A

Ca pump (required for relaxation) moves Ca ions back to the ECF or SR, lowering concentration and activating enzyme Myosin Phosphate (splits phosphate from regulatory light chain) ending the cycle and contraction

56
Q

What are some features of smooth muscle contraction?

A
  • slowing cycling of myosin cross-bridges (compared to skeletal) to increase force of contraction
  • low energy requirements to sustain contraction (to maintain tonic muscle contraction almost indefinitely, think intestines)

RUSVM Physiology I (7 decks)

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