Term
| How are twitches like action potentials? |
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Definition
| They are reproducible, all-or-nothing events |
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Term
| Describe an isotonic contraction |
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Definition
| tension is greater than load, muscle shortens, constant tension. |
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Term
| Describe a lengthening contraction |
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Definition
| Muscle lengthens while maintaining contraction, load is greater than the tension on an unsupported muscle. |
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Term
| Define an isomeric contraction |
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Definition
Tension is generated, but the muscle does not shorten because the load is greater than the generated force
Crossbridge cycling still continues, even though muscle doesn't shorten |
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Term
| What factor(s) affect the force generated by individual muscle fibers? |
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Definition
| The number of crossbridges that bind to actin |
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Term
| What factor(s) affect the force generated by whole muscles? |
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Definition
| Force generated in individual fibers, the number of muscle fibers contracting |
|
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Term
| What factors affect the number of muscle fibers contracting? |
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Definition
| Frequency of stimulation, fiber diameter, and changes in fiber length stimulation |
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Term
|
Definition
| When frequency of stimulation causes tension to rise in a stepwise fashion |
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Term
| Why does summation occur? |
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Definition
| Calcium does not have a chance to be retaken by ATPase into the sarcolemma |
|
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Term
| What is the peak of summation called? |
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Definition
|
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Term
| What causes fused tetanus? |
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Definition
| Calcium is completely saturating troponin |
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Term
| What is the term for when a muscle is generating all the force it can? |
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Definition
|
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Term
|
Definition
| An increase in the number of active motor units |
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Term
| Define the size principle |
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Definition
| Both smaller motor units and smaller motor neurons are activated first, before larger ones |
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Term
| What kind of muscle has no striations or transverse tubules? |
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Definition
|
|
Term
| Name three functions of smooth muscle |
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Definition
| Peristalsis, vasoconstriction, and vasodialation |
|
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Term
| Why does smooth muscle lack striations? |
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Definition
| Thick and thin filaments are not arranged in sarcomeres |
|
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Term
| Where does calcium come from for a smooth muscle? |
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Definition
The SR and ECF, but mostly the ECF because the SR is underdeveloped
It gets in by voltage-gated, receptor-mediated, and stretch-activated channels |
|
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Term
| How does calcium get released from the SR in smooth muscle? |
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Definition
| By activating the IP3 second messenger system, activated by influx of extracellular Ca2+ |
|
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Term
| What does released calcium bind to in a smooth muscle? |
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Definition
|
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Term
| What does the calcium-calmodulin complex do in a smooth muscle? |
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Definition
| Bind to and activate myosin light chain kinase (MLCK) |
|
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Term
| What does MLCK do in a smooth muscle cell? |
|
Definition
| Catalyze phosphorlation of myosin crossbridges |
|
|
Term
| What activates Myosin Light Chain Phosphatase in a smooth muscle? |
|
Definition
|
|
Term
| What structure releases neurotransmitters to smooth muscle? |
|
Definition
|
|
Term
| What determines if a smooth muscle is innervated excitatory or inhibitory? |
|
Definition
| Whether the parasympathetic/sympathetic nervous system is dominating |
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Term
| Define pacemaker potentials |
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Definition
| Slow depolarizations caused by increased sodium, increased calcium, or decreased potassium permeability |
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|
Term
| Define slow-wave potentials |
|
Definition
| Cyclical depolarizations and repolarizations caused by fluctations in sodium permeability |
|
|
Term
| How is calcium removed from smooth muscle? |
|
Definition
| 1. Ca-ATPase on SR; 2. Ca-Na countertransport on sarcolemma |
|
|
Term
|
Definition
| Force exerted by muscle on an object |
|
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Term
|
Definition
| Force exerted by object on muscle |
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|
Term
| When is muscle tension measured? When is muscle length measured? |
|
Definition
Tension is measured during isometric contractions
Length is measured during isotonic contractions. |
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|
Term
|
Definition
| Contraction of a muscle fiber in response to a single action potential |
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|
Term
| What is the difference between fast-twitch and slow-twitch muscle fibers? |
|
Definition
| The crossbridge cycling speed, depending on myosin Ca 2+ ATPase activity |
|
|
Term
| What relationship is there between load and distance of shortening? |
|
Definition
An inverse relationship
As load increases, the distance of shortening decreases.
Also, as load increases, velocity of contraction decreases. |
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|
Term
| If there are multiple twitches quickly, what is summated? |
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Definition
| The tension summates, NOT the action potential/end plate potential |
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|
Term
| About how much is maximal tetanic tension compared to the tension of a single twitch? |
|
Definition
|
|
Term
| What happens when maximal tension occurs? |
|
Definition
| Maximal tension occurs when all of the myosin cross bridges can bind to actin at optimal length |
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|
Term
|
Definition
| Initial length that produces maximal active tension. This occurs at the maximal overlap of the thick and thin filaments |
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|
Term
| What is a typical range of muscle length? |
|
Definition
| Muscles normally operate at ± 30% of the maximal muscle length |
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|
Term
| Does smooth muscle have tropomyosin and troponin? |
|
Definition
| Tropomyosin present, but no troponin |
|
|
Term
|
Definition
| Anchor smooth muscle thin filaments, similar to Z-lines in skeletal |
|
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Term
|
Definition
| Attach filaments to membrane in smooth muscle |
|
|
Term
| What links dense bodies and dense bands in smooth muscle? |
|
Definition
|
|
Term
|
Definition
Gaps that allow electrical communication between smooth muscle
cells. |
|
|
Term
| How does the length-tension relationship of smooth muscle compare to that of skeletal? |
|
Definition
| Smooth brother has a broader range that allows for large variations in organ volume |
|
|
Term
| Define phasic contraction |
|
Definition
| Smooth muscle twitches like those in skeletal muscle, but much slower. |
|
|
Term
|
Definition
| Smooth muscle maintenance of tension, but cross bridge cycling at very slow rate |
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|
Term
|
Definition
| In smooth muscle, if myosin is attached to actin when it is dephosphorylated, then the myosin remains attached to actin and a sustained contraction occurs. This allows sustained tension without a large use of ATP. |
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