Glossary of Skeletal muscle
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- what does skeletal muscle do?
- causes the bones to which muscle is attached to move.
- What does skeletal muscle allow?
-heat generation - regulation of homeostatic systems.
- how is skeletal muscle organised? describe...
- in a hierarchical system.
Muscle > muscle fiber > myofibrils > thick/thin filaments
- what is a muscle cell?
- a myofibril
as long as the muscle.
- what are each made of?
- thick = myosin
thin = actin
- what is the nucleation like in skeletal muscle?
- multinucleated, from fusing of many cells
- what is a
- Z = disc-shaped protein that holds thin filaments aligned.
M = disc-shaped protein that holds thick filaments aligned.
- what are thick filaments made of?
- several hundred myosin proteins
- how is myosin arranged?
- tail = light meromysin
head = heavy meromysin
- What two parts compose Heavy meromysin?
- S1 and S2 chains
S1 = light chains, head portion.
S2 = the hinge.
- What are the S1 regions of heavy meromysin?
- what is the light meromysin composed of?
- 2 myosins coiled together in a tail.
- what are the two binding sites on the crossbridge of myosin?
- -ATP binding site
-Actin binding site
- What binding site does Actin have?
- Myosin binding site.
- What other two molecules are with Actin?
- Troponin and Tropomyosin
- what is the role of
- Troponin: the coordinating molecule - binds everything!
Tropomyosin: covers the myosin bindng site in resting states.
- what is the sliding-filament theory?
- just the statement that during sarcomere shortening, filaments move past ea. other, but don't shorten.
- which bands in the sarcomere get reduced during contraction?
- -I band narrows
-H band disappears
- how is the ATP binding site on myosin an enzyme?
- -it hydrolyzes atp when bound
- what is the crossbridge cycle?
how many steps?
- the events that occur btwn cross-bridge binding to thin filament, its movement, and resetting to repeat.
- What are the four steps in the cross-bridge cycle?
- 1. Attachment - crossbridge to thin filament.
2. Movement - thin fil tenses
- What is the myosin crossbridge like in a resting muscle?
- -cocked and ready to go; ATP is split and ADP and Pi are still bound.
-Cytosplasmic Ca+ is low tho so no binding to actin.
- What molecule initiates crossbrg cycling?
- CALCIUM!!! in the cytosol
- what is a Power Stroke?
- the movement caused when energized myosin crossbrg (with ADP and Pi) binds actin. immediately releases energy and causes movement.
- What breaks the link between myosin and actin? How?
- ATP binding decreases myosin's affinity for actin.
- What happens when ATP binds to myosin?
- Hydrolyzes and re-energizes myosin.
-If Ca still present, another cycle.
- What are ATP's two roles?
- 1. Hydrolysis provides energy for movement
2. Binding allosterically regulates myosin to decr. actin affinity.
- What is rigor mortis?
- stiffening of dead body because ATP is not present to unbind myosin from actin.
- what is tropomyosin, and what does it do?
- rod like protein that binds 7 actin molecules, blocking their myosin binding sites.
- what is troponin, and what does it do?
- small globular protein that binds tropomyosin and actin; when Ca+ binds actin, it drags tropomyosin away and allows actin to bind myosin.
- What is excitation-contraction coupling?
- the link between action potential excitation in a muscle fiber's membrane, and how it causes a crossbridge cycle.
- In general, how does an action potential cause a crossbrg cycle?
- by increasing cytosolic calcium
- what is the cytosolic [Ca] in a resting muscle?
- very low = 10-7
- what is the source of cytoplasmic calcium when excited?
- sarcoplasmic reticulum
- what are lateral sacs?
what are they for?
- -enlarged regions of the SR sheaths around myofibrils;
-store calcium for release during excitation.
- what are T-tubules?
- structures that are between SR sheaths around myofibrils; they circle at the A-I junction.
-continuous with plasma membrane; conducts Action potentials to the cell center.
- what are the functions of the sarcoplasmic reticulum?
- -take up Ca
- how does a T-tubule cause calcium release?
- action potential conducts through the T-tubule, to where it contacts Lateral sacs of SR, which release calcium into the cytosol.
- how is contraction stopped by the SR?
- Calcium ATPase pumps take calcium back up - takes a while though, so contraction lasts a long time.
- How can contraction strength of skeletal muscle be controlled?
- 1. By motor unit recruitment
2. By summation and tetany
3. By changing the initial muscle fiber length.
- what kind of contraction is caused by ONE action potential?
- a twitch - very small contraction.
- how do you get more than a twitch?
- by motor unit recruitment:
-making more motor units fire.
-making more muscle cells contract.
- what prevents fatigue over time in muscle?
- asynchronous firing
- What is asynchronous firing?
- Variation in which muscle cells are firing during a contraction. 10 might be on, 10 off.
- What is summation?
- the concept that repetitive action potentials cause stronger and longer contractions.
- How are contraction strengths varied?
- By varying the number of AP within a given period of time; very fast/repetive firing causes summation so much that the cell doesn't even relax.
- What is tetani?
- fused contraction of muscle due to rapid firing of neuron - continuous action potentials - cytosolic Ca2+ is always high.
- How does changing initial muscle fiber length control muscle strength?
- If muscle is too short to begin with, less force will be generated. If too long, no crossbridges interact.
- what is the optimal crossbrdg overlap for muscle contraction?
- between 1.95 um and 2.25
-flat line because between these points, the H band will change no further.
- what are two types of skeletal muscle contractions?
- what is isometric contraction?
- That when muscle length stays the same.
-Load > force developed
-Force increases but you're not moving anything yet.
- what is isotonic contraction?
- that when muscle length changes because force > load.
-Force stays constant as the muscle contracts/relaxes.
- what are 3 things that affect skeletal muscle energetics?
- -ATP source
-Type of skeletal muscle
- what are 3 sources of ATP?
- -Creatine phosphate
- How does Creatine phosphate generate ATP?
-What is ATP supplied for?
- by phosphorylating ADP to produce Creatine and ATP.
-Supplies for FAST movement.
-1 sec needed for reaction.
- CP + ADP -> ?
- Creatine + ATP
- What generates ATP for endurance movement? Why?
(when O2 is present)
- -Oxidative phosphorylation - aerobic metabolism.
-B/c 36 ATPs are generated from every 1 glucose.
- -What can be used for oxydative phosphorylation to generate ATP?
-What is required for Oxid phos?
- Fatty acids OR Glucose.
-Requires Oxygen and TIME -slow.
- How much ATP is generated when no oxygen is present?
By what process?
Is this for fast or endurance movement?
- -2 ATP + Pyruvate (breaks to lactic acid) from one glucose.
-Glycolysis - anaerobic metabolism.
-fast - no enzymatic steps.
- What is better for ATP generation, Creatine phsosphate or glycolysis? Why?
- Creatine phosphate - much higher yield, more efficient.
-Glycolysis generates 2 ATP but pyruvate has to be broken down to lactic acid.
- what are 3 types of skeletal muscle based on their metabolic processes?
- SOX - slow oxididative
FOX - fast oxidative
FGL - fast glycolytic
- what is
- red = slow oxidative/fast oxid.
white = FGL - fast glycolytic.
- where would fast oxidative muscle (type 2) be found?
- in your arms.
- which type of tissue resists fatigue the best?
whihc has least mitochondria?
- slow oxidative
- what type of meat do sprinters have more of?
- white meat = fast glycolytic
- what type of meat do cross country runners have?
- slow oxidative
- If a sprinter trained to run long distance, what type of meat would develop?
- His type 3 fast glycolytic would become type 2 fast oxidative.
- on the force vs. length curve, what is the Optimal length?
- the length at which max isotonic force is developed - about 2 um.
- what effect does stretching a muscle beyond optimal length have on force developed?
- decreases it. b/c thick and thin filaments are overlapping and so fewer slide during the crossbridge cycle.
- what effect does contracting a muscle shorter than its optimal length have on force development? what two reasons?
- decreases it.
1. the z lines run into the thick filaments.
2. Thin filaments collide and no more contraction can occur - or they overlap and interfere with crossbg forming
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