Term
| What are Intercalated disks? |
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Definition
| Join adjacent cardiac muscle cells end to end. |
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Term
| Define A-band, I-band, H-zone, Z-line |
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Definition
A-band = overlapping actin and myosin
I-band = actin without myosin (at ends of sarcomeres)
H-zone = myosin without actin (in middle of sarcomere)
Z-line = actin filaments separating sarcomeres |
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Term
| Roles of ATP in muscle contraction |
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Definition
1) hydrolyzed to provide energy for cross-bridge movement (power-stroke)
2) binding to myosin to break link between actin and myosin, allowing cycle to repeat
- Rigor mortis = no ATP to break actin-myosin binding, stiffness. 40-60 hours after death. |
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Term
| Describe the cross-bridge cycle. |
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Definition
1) ATP binds to myosin and is hydrolyzed, split into ADP and Pi.
2) Ca released from SR and binds to troponin, tropomyosin moves to expose actin binding sites. Actin binds with myosin.
3) ADP and Pi released for power stroke (cross-bridge moves).
4) ATP binds to myosin again to detach cross-bridge |
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Term
| Why is there a latent period between action potential and muscle contraction? |
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Definition
| Electrical activity doesn't directly act upon contractile proteins but instead increases cytosolic Ca concentration first. Ca concentration must accumulate and continues to activate the cross-bridge cycle long after electrical signal has stopped. It takes time for Ca to be reabsorbed into SR. |
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Term
| Function of Neuromuscular Junction |
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Definition
| Ach released into neurosynaptic cleft, binds to post-synaptic receptors, opens ion channels, Na enters motor end plate, adjacent plasma membrane is depolarized, action potential (referred to as End Plate Potential) propagates down muscle fiber. |
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Term
| Describe role of t-tubules in muscle contraction. What do DHP receptors and ryanodine receptors do? |
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Definition
DHP receptor = t-tubule
ryanodine receptor = SR
DHP and ryanodine receptors are linked through foot processes (a structure).
1) Muscle action potential propagates into t-tubule, DHP receptor undergoes conformational change which opens ryanodine receptor channel, releasing Ca from lateral sac of SR. |
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Term
| How does botox work? What is its effect? |
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Definition
| Inhibits neurotransmitter exocytosis by cleaving attachment protein receptors. Effectively paralyzes muscle?? |
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Term
| What is a motor unit? Motor pool? |
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Definition
Motor unit = motor neuron + muscle fibers it innervates (multiple)
Motor pool = all motor neurons that innervate a single muscle (collection of motor units) |
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Term
| Twitch summation vs tetanus |
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Definition
Twitch summation: partial overlapping of multiple twitches
Tetanus: complete overlapping of multiple twitches. |
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Term
| Isometric vs. Isotonic contraction |
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Definition
Isometric = Force generation at constant muscle length. Ascending relationship because filaments interfere with each when length is too short. Has an Optimal Length (100%)
Isotonic = Muscle shortening against constant external load. Slope of isotonic contraction = velocity. Maximum shortening velocity at zero load. Zero shortening velocity = maximum load, same as isometric contraction. |
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Term
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Definition
Fused = action potentials in rapid succession, allow smooth movement.
Unfused = scattered action potentials |
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Term
| How do you calculate muscle power output? |
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Definition
Power = Force x Velocity
Maximum power = intermediate shortening velocity and ~ 30% isometric force |
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Term
| What are the 3 energy sources for muscle contraction? |
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Definition
1) Creatine Phosphate - rapid source of ATP during muscle contraction, used up quickly
2) Glycolysis - generates ATP from glucose very quickly but builds up lactic acid, which interferes with ATP production.
3) Oxidative phosphorylation = generates ATP from fatty acids/proteins (very slow) but doesn't build up lactic acid so hard to fatigue.
4) Free ATP = immediate substrate for myosin ATPase |
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Term
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Definition
Type I - Slow (Oxidative, red, fatigues slowly)
Type IIa - Fast (Oxidative, red, intermediate fatigue)
Type IIb - Fast (Glycolytic, white, fatigues quickly) |
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Term
| Muscle spindles vs. golgi tendon organs? |
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Definition
Muscle spindle: maintain muscle length
Golgi Tendon organs: prevent muscle damage by relaxing muscle when strained. Stretching Golgi tendon organs leads to inhibitory reflex.
Muscle spindles are organized in parallel with muscle fibers, golgi tendon organs are organized in series (at end of muscle fibers). Located in the TENDON that attaches muscle to bone. |
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Term
| What are intrafusal and extrafusal fibers and where are they found? |
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Definition
Intrafusal: specialized fibers innervated by sensory neurons and gamma motor neuron
Extrafusal: "ordinary" muscle fibers innervated by alpha motor neurons
Both are found in muscle spindles. Alpha and gamma motor neurons are co-activated to set intrafusal fiber length in parallel with extrafusal fiber length. |
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Term
| Describe alpha-gamma coactivation. |
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Definition
| When muscles contract (and fibers shorten), gamma motor neurons activate in order to maintain tension and stretch in the central receptor region of the intrafusal fibers (prevents slackening). Activating gamma motor neurons increases the sensitivity of a muscle to stretch. Insures that information about muscle length will be continuously available. |
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Term
| Can you have tetanus in cardiac cells? Why or why not? |
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Definition
| No, because the action potential in cardiac cells undergoes a plateau period that is about as long as the contraction time, meaning that the refractory period is about as long as the contraction time. |
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Term
| Smooth muscle function and structure |
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Definition
Function: regulates dimension of hollow body organs (blood vessels, bladder, intestines, airways) at low energy cost.
Structure: Smooth, no striations. Thin/thick filaments, dense bodies, dense plaques. |
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Term
| Smooth muscle activation-contraction coupling |
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Definition
-Dependent on Ca regulation. (comes in through membrane channels and release from SR)
- Ca regulates myosin light chain phosphorylation (not actin like in striated muscle)
Ca activates calmodulin, which activates Ca-calmodulin myosin light chain kinase which activates cross-bridge towards actin.
NO TROPONIN (still have tropomyosin). Faster cross-bridge cycle in skeletal muscle. |
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Term
| Single-unit vs. multi-unit smooth muscle |
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Definition
single unit = synchronized activation via gap junctions.
multi unit = independent activation |
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Term
| Innervation of a single-unit smooth muscle |
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Definition
| Autonomic nerve fiber with varicosities (containing synaptic vesicles) runs along fiber. Gap junctions connect cells. |
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