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Anatomy and Physiology 1 > 3. Skeletal Muscles 2 > Flashcards

3. Skeletal Muscles 2 Flashcards

1
Q

How does muscle action potential differ/similar from nerve action potential

A

Same: same resting membrane potential
Different: longer lasting action potential, slower rate of conductance

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2
Q
A
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3
Q

skeletal muscle contraction

A
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4
Q

What happens when voltage gated calcium channels open and what does this cause?

A
  • Calcium ions enter the nerve
  • attracts the ACH vesicles and they undergo exocytosis
  • ACH bindsto ACH receptors on the muscle fiber membrane
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5
Q

Explain what happens with the ACH-gated ion channels

A
  1. ACH binds and opens the negative charged channel
  2. Sodium passes through the channel (into the cell)
    - causes a local positive potential change inside the muscle (end plate potential)
    - spreads along the muscle membrane causing contraction
  3. ACH is destroyed by acetylcholinesterase
    - turns into choline and acetate ion
    - choline is reabsorbed into the nerve and is used to produce new ACH
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6
Q

What, why and how do structures carry the action potential through the muscle fiber and how?

A

What: Transverse (T) tubules
Why: Muscle fibers are too large for an action potential just along the surface to cause contraction
How: it carries the action potential through the muscle fiber and causes a release of calcium ions (from sarcoplasmic reticulum) near the myofibrils causing contraction (excitation-contraction coupling)

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7
Q

What does the sliding filament theory of contraction describe? How does it work?

A

Sarcomeres shorten as a result of actin filaments sliding over myosin filaments
- The actin filaments are pulled inward toward the M line in a ratchet like fashion by myosin heads (repetitive attachment and release of myosin heads, actin filaments are anchored to Z discs and sarcomere is shortened)
- Myosin filaments stay stationary

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8
Q

What and why are the two points where myosin heads are flexible?

A
  1. Where the arm leaves the myosin filament (allows head to be extended far from the body or close to the body)
  2. where the head attaches to the arm (participates in actual contraction process)
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9
Q

Actin filament (3 protein structure)

A
  1. Actin - double stranded backbone
    - Active sites interact with the cross bridges of myosin filaments during contraction
  2. Tropomyosin molecules (bike chain)
    - Wrapped around F-actin helic
    - Lays on top of the active sites so that attraction cannot occur between actin and myosin
  3. Troponin complex (bike lock)
    - Troponin I - strong affinity for actin
    - Troponin T - strong affinity for tropomyosin
    - Troponin C - strong affinity for calcium ions
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10
Q

What does the troponin-tropomyosin complex do?

A

Inhibits or physically covers the active sites on actin filaments
- Presence of calcium ins removes the inhibition caused by this complex and muscle can contract

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11
Q

What is the walk along theory of contraction (postulated)

A
  • Head of cross bridge binds with active sites on actin
  • Changes in intermolecular forces cause the head to tilt toward the arm – power stroke
  • Head disengages and returns to its extended direction and engages a new active site farther down the actin
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12
Q

What is the function of ATP before contractions

A
  1. Heads of the cross-bridges bind with ATP
  2. ATPase activity of the myosin head immediately cleaves the ATP
  3. Leaves the cleavage products (ADP and phosphate ion) bound to the head
  4. Conformation of the head is now perpendicular toward the actin filament but not attached
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13
Q

What is the function of ATP when myosin heads bind with active sites on actin?

A
  1. Conformational change that occurred in the head when the ATP was cleaved provides the energy for the power stroke
  2. The tilting of the head during the power stroke releases the ADP and phosphate ion and a new ATP binds to the site
  3. The binding of the ATP causes a detachment of the head from the actin
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14
Q

What are the four sources of energy for muscle contraction?

A

ATP, Phosphocreatine, glycolysis and oxidative metabolism

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15
Q

What is the maximum efficiency of muscle contraction?

A

25%

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16
Q

What is the relationship between sarcomere length and tension?

A

Tension increases as myosin and actin begin to overlap

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17
Q

Explain the points on the graph

A

D - no overlap, no tension
D-C - tension increases as myosin and actin begin to overlap - continues to increase until actin filament has overlapped all the cross-bridges of the myosin filament
B - maintains tension until the ends of the actin filaments begin to overlap
A - when the sarcomere is so short that the Z discs area butting the ends of the myosin filaments, the tension rapidly decreases

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18
Q

What happens after contraction with the active calcium pumps?

A

Active calcium pumps in the walls of the sarcoplasmic reticulum remove calcium

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19
Q

What does methacholine, carbachol and nicotine do?

A

Drugs that enhance or block transmission at neuromuscular junction
- Not destroyed by cholinesterase therefore action potential persists for minutes to hours (muscle spasm)

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20
Q

What does diisopropyl flurophosphate do?

A

Drug that enhance or block transmission at neuromuscular junction
Inactivates acetylcholinesterase - nerve gas poison

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21
Q

What does curare do?

A

Drugs that enhance or block transmission at neuromuscular junction
It blocks the gating action of ACH by binding to the ACH receptor sites

22
Q

What does botulinum toxin do?

A

Drugs that enhance or block transmission at neuromuscular junction
Decreases ACH release from nerve terminals

23
Q

Explain this graph

A

Velocity of contraction decreases with weight

24
Q

What is muscle efficiency?

A

How much external work is obtained from the input of chemical energy
- Work/(heat+ work)

25
Q

Fast muscles vs slow twitch muscles in efficiency

A

Fast muscles are less efficient than slow twitch muscles

26
Q

What is an isometric contraction and an example?

A

A contraction in which the muscle does not shorten - stationary
- Holding a dumbell

27
Q

What is an isotonic contraction and an example?

A

A contraction in which the muscle shortens and the limb moves but the tension on the muscle remains constant
- Dependent on the load and inertia of load
- Bicep curls

28
Q

Explain this graph

A

Even with the same force, each muscle has different times of force
Ocular muscle: needs to be extremely rapid to maintain accurate vision
Gastrocnemius: moderately rapid to provide for limb movement
Soleus: continual, long-term support of the body against gravity - ex) calf muscle

29
Q

What are the three types of muscle fibers?

A
  1. Slow-twitch or type I (red)
  2. Fast-twitch or type II (white)
  3. Tonic fibers
30
Q

Slow twitch fibers - anatomy, used for, characteristics (4)

A
  1. Smaller fibers - low amounts of force, contract slowly
  2. Used for continuous steady activity, resistance to fatigue
  3. High capacity for oxidative metabolism - more extensive blood supply and large number of mitochondria (why they’re red)
  4. Large amounts of myoglobin
31
Q

What is myoglobin?

A

An iron- and oxygen-binding protein found in cardiac and skeletal muscle tissue of vertebrates

32
Q

fast-twitch - anatomy, used for, characteristics

A
  1. Larger fibers
  2. Produce high amounts of force
  3. Contract quickly - extensive amounts of sarcoplasmic reticula for rapid calcium release
  4. High capacity for anaerobic glycolysis - less extensive blood supply and fewer mitochondria
33
Q

Which subtype of fast-twitch or type II fiber has a greater oxidative capacity?

A

IIa

34
Q

Which subtype of fast-twitch or type II fiber produces the highest amount of force?

A

IIb
- Easily fatigued
- Sprinter muscles

35
Q

tonic fibers - anatomy, used for, characteristics

A
  1. Postural muscles
  2. Contract at a very low frequency rate
  3. Not easily fatigued
36
Q

Where are tonic fibers found in mammals?

A

Neuromuscular spindles and extraocular muscles

37
Q

Where are tonic fibers found in birds, reptiles and amphibians?

A

postural muscles

38
Q

Lobster vs rats vs chimps fibers

A

Lobster - fast twitch, slow twitch, slow-tonic
Rats - hybrid (fast to slow transforming)
Chimps - 2/3 of their body is fast twitch and outperform humans (humans are better at walking though)

39
Q

What is a motor unit?

A

All the muscle fibers innervated by a single motor NERVE fiber
- can range from a few to several hundred

40
Q

What is the relationship between the number of fibers per motor unit and the speed of reaction?

A

Small muscles that need to react quickly have fewer fibers per motor unit

41
Q

What happens when a weak signal is sent to contract a muscle?

A

The smaller motor units in that muscle are stimulated first because they are innervated by smaller motor nerve fibers (more excitable)

42
Q

What happens as the strength of the signal increases?

A

Larger motor units are stimulated
- can be 50x more force than small motor units

43
Q

What is asynchronous stimulation?

A

Smooth contraction of muscle even at low nerve frequencies

44
Q

What is frequency summation?

A

The addition of one contraction to another before the first has ended

45
Q

What is tetanization and why does it occur?

A

The fusion of contractions due to their rapidity
Strength reaches a max
Enough calcium stays in the sarcoplasm between action potentials to maintain full contraction

46
Q

What is muscle fatigue?

A
  • Depletion of glycogen stores
  • diminish the amount of ACh vesicles so that impulse fails to pass to the muscle fibre.
47
Q

What is muscle hypertrophy?

A

An increase in the number of actin and myosin filaments in each muscle fiber
- increases in enzymes involved with glycolysis

48
Q

What is muscle atrophy?

A

The decay of filaments exceeding replacement because of unused muscle
- use it or lose it

49
Q

What is muscle tone - how is it monitored?

A

The tightening of muscle due to asynchronous firing of muscle fibers but not enough for movement
- Essential for maintaining posture
- Monitored by spindle receptors

50
Q

Rigor Mortis - why, when (start and end) and how does temp affect it?

A

Why: loss of ATP (ATP is required to cause seperatiion of cross-bridges from actin
When: start - several hours after death
end - 15-24 hours later - due to muscle protein deterioration
- It occurs rapidly at high temperatures

Anatomy and Physiology 1 (15 decks)

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