Term
Skeletal Muscle
attaches to-
Contraction causes-
Involuntary or Voluntary |
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Definition
Attaches to skeleton
Causes skeleton to move
voluntary |
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Term
Muscle Cells (fibers)
Shape-
Organized in-
Size of Cells- |
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Definition
Elongated cylinder shaped cells
compartimentalized (biceps)
Run the entire length of muscle, Large, 100 micrometers in diameter |
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Term
Muscle cells have a large concentration of cytoskeletal filaments aka-
Two types
1.
2. |
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Definition
Myofilaments
1. Thick Filaments
2. Thin Filaments |
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Term
Thick Filaments are made up of
Thin- |
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Definition
thick-myosin
thin-three components
-actin
-tropomyosin
-troponin |
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Term
Organization of Skeletal Muscle
small->large |
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Definition
thick and thin myofilaments
sacromeres
myofibrils
skeletal muscle cell |
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Term
Thick Filaments Consist of:
Orienatation: |
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Definition
| Many myosin molecules, oriented half in one direction and the other half in the other direction. |
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Term
Myosin consists of:
Each myosin Head contains: |
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Definition
Two Identical subunits wrapped around each other.
One end expanded into head region
Each head contains an actin binding site, ATPase site, and a hinge region that lets the heads rotate |
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Term
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Definition
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Term
| Structure of Thin Filaments: |
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Definition
Actin and Tropomysin arranged in a helix
Troponin is attached to actin/tropomyosin at regular intervals |
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Term
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Definition
One binds to actin
One binds to tropomyosin
One that reversibly binds Ca 2+ |
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Term
| Actin & Tropomyosin interact with Myosin: |
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Definition
Actin has a binding site for myosin
Tropomyosin overlaps myosin binding site on actin |
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Term
Tropin is a --- protein
because: |
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Definition
Regulatory Protein
*Ca 2+ binds to troponin to regulate skeletal muscle contraction |
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Term
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Definition
Thick and thin filaments arranged in a ordered fashion.
* Functional contractile unit of skeletal muscle |
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Term
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Definition
1. Z disk (line) protein
-sacromere extends from Z line to Z line
2. Thick and Thin Filaments |
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Term
| Thick or Thin filaments attach to Z disk? |
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Definition
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Term
| Thick or Thin filaments are in the center of sarcomere |
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Definition
| thick filaments in the center, connected to the Z disk by titin protein (elastic) |
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Term
| Sarcomeres align-- which forms-- |
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Definition
| Sarcomeres align End to end forming myofibrils |
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Term
| Is skeletal Muscle Striated? |
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Definition
| Skeletal Muscle is Striated |
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Term
Current theory of contraction
where which filaments shorten: |
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Definition
Sliding Filament Mechanism
Neither thick or thin filaments shorten, there are ares of overlap between them allowing them to slide past each other |
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Term
| What allows the filaments to slide past each other? |
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Definition
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Term
| Crossbridges form between |
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Definition
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Term
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Definition
| connections between thick and thin filaments where myosin heads can bind to actin on the thin filaments |
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Term
| Define Cross Bridge Cycle |
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Definition
| Cyclical formation of links between actin and myosin resulting in the sliding of thin filaments along the thick |
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Term
| Order of Cross Bridge cycle |
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Definition
1. With appropriate signal, myosin head of thick filaments attach to the thin forming a crossbridge
2.Heads rotate- pulling the thin along the thick towards the sarcomere= Power stroke
3.Heads release and re-cock (can form a 2nd attachment, cycle repeats) |
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Term
| What does the cross bridge cycle result in: |
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Definition
| thin filaments are attached to Z disks, the z disks are pulled together, this Shortens the sarcomere, causing the myofibril to shorten, causing entire muscle cell to shorten= contraction. |
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Term
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Definition
1. Binding of Myosin head to actin releases phospate from ATP= ADP
2. Power stroke, actin gets pulled towards middle of sarcomere
3. ADP is released
4. New ATP binds to myosin head which unbinds myosin from actin
5. The unbinding cocks the myosin head into high energy form.
Cycle repeats |
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Term
| Before cross bridges detach: |
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Definition
| A new ATP must bind to myosin head |
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Term
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Definition
| Muscle stiffness after death bc no new atp can be synthesized after death, cross bridges remain attached and muscles stay contracted. |
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Term
| How much ATP is availabe at onset of muscle activity? |
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Definition
| Small store of ATP, must be replenshised immediately |
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Term
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Definition
1. phosphorylation of ADP by creatine phosphate
2. Oxidative phosphorylation of ADP in mitochondria
3. Anaerobic glycolysis |
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Term
| what enzyme catalyzes the reaction to form ATP from creatine phosphate and ADP? |
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Definition
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Term
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Definition
| the use of atp drives the rxn to the right. |
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Term
| Creatine phospate energy stores |
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Definition
1st source of atp
can provide 4-5x the amount of atp present in cells at rest
the one step process is fast
very limited amount, its used up fast |
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Term
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Definition
| plasma membrane in muscle cells |
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Term
| sarcoplasmic reticulum (SR) |
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Definition
| smooth endoplasmic reiculum in muscles |
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Term
| Excitation-contraction coupling |
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Definition
| sequence of events in which the arrival of an action potentials at the neuromuscular junction leads to contraction of a skeletal muscle cell. |
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Term
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Definition
| can generate action potentials |
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Term
| How are Action Potentials propogated: |
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Definition
| Over surface of cell and into the center by transverse tubules (t tubules) |
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Term
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Definition
| invaginations of sarcolemma that dip into cells interior at regular intervals (at the junction of A and I band) |
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Term
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Definition
specialized for Calcium stroage
wraps around each sarcomere/myofibril |
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Term
| What is the Role of Calcium in a contraction? |
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Definition
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Term
| In skeletal muscle where does most calcium come from? |
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Definition
| SR- sarcoplastic reticulum |
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Term
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Definition
Troponin holds tropomyosin over the myosin binding sites on actin blocking the myosin head to binding with thin filaments
-no cross bridge formed
-muscle is relaxed |
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Term
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Definition
Calcium binds to troponin causing the movement of tropin, causing movement of tropomyosin which exposes the binding site for myosin on actin.
-Binding site is unblocked,
-cross bridges form
-muscle contracts |
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Term
| What stimulates muscle cells to contract? |
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Definition
Motor neurons
are stimulated leading to the release of calcium from the SR |
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Term
| Steps of Excitation-Contraction Coupling |
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Definition
1. AP produced in sarcolemma of muscle cell by acetylcholine released from motor neuron.
2. AP travel down T tubules
3. Voltage sensitive proteins (DHP receptors) of T tubules cause Ca channels (ryanodine recpt) in SR to open releasesing Ca into cytosol
4. Ca increases in cytosol
5. Ca binds to to troponin which shifts tropomyosin
6. Cross bridge cycling occurs |
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Term
| How do AP travel down T tubules release Ca from SR? |
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Definition
The SR Ca channel (ryanodine rcptr) are a type of gated channels
They are closed 'til opened by DHP rcptrs (in T tubes) in response to voltage change in T tube membrane |
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Term
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Definition
Ca leaves troponin allowing tropomyosin to cover myosin binding site on actin
Ca is removed from cytosol by Ca ATPase (pump) in SR which transports Ca back into cytosol of SR |
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Term
| What is the basis of classification of skeletal muscle types |
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Definition
| velocity of contraction and primary energy source |
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Term
| Types of Skeletal muscle cells: |
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Definition
1. Slow oxidative
2. Fast oxidative
3. Fast glycolytic |
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Term
| Slow oxidative cell properties |
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Definition
slow myosin ATPase
high oxidative capacity- aerobic (needs Oxygen)
-mitochondria, rich blood supply, myoglobin (red): o2 binding molecule
Small diameter= little force generated
Fatigue Slowly |
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Term
| ATPase activity determines |
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Definition
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Term
| Fast Oxidative Cell Properties |
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Definition
intermediate
fast myosin ATPase activity
High oxidative capacity -aerobic
myoglobin (red)
slow to fatigue but more rapid than slow oxidative
intermediate diameter |
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Term
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Definition
fast myosin ATPase activity
high glycolytic capacity (anaerobic)
high glycogen stores, many glycoltic enzymes
No myoglobin (white)
Large diameter-greater force generation
Fatigue Rapid |
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Term
| Which muscles have which cell types? |
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Definition
Muscles have a mixture of cell types, the porportions vary depending on function
EX- postural muscles more slow oxidative (fatigue slow)
In single motor unit- all muscle cells are the same type |
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