skeletal muscle II (wk9) Flashcards
what does myosin bind to form a cross bridge
g actin
what are the 3 tropoins and what do they bind to to expose the myosin binding site of g actin
§ When calcium binds to Troponin C, The troponin complex undergoes a conformational change and Troponin T “pulls” tropomyosin and Troponin I off of the myosin-binding site of G-actin subunits
§ Myosin is now able to bind to G-actin and form a cross bridge
4 steps of the cross bridge cycle
- ATP hydrolysis
2.cross bridge formation - power stroke
- detachment of myosin from actin
when myosin is bound to ATP what affinity does it have for actin
low; so no cross bridge form
how does myosin turn ATP into ADP + Pi
intrinsic ATPase ; myosin head hydrolysis
what is a power stroke
The cross bridge generates force as myosin neck rotates toward center or sarcomere
w
* Actin and myosin filaments slide post one another
* Z lines get closer together, shortening the sarcomere & generating force
what gets closer together to shorten the sarcomere and generate force
z line
how does myosin detach from actin
ATP binds myosinw
what happens if no ATP to bind myosin so that it can detach from actin
rigor mortis
why does sarcomere length matter
The amount of actin and myosin filament overlap determines the tension that is developed by a contracting muscle.
need some overlap to have tension and contract
isotonic vs isometric
which is force > load and load > force
isometric: load>force
isotonic: force> load
isotonic vs isometric which one does the muscle length shorten and which one doesnt change length
isometric- no change
isotonic- shortens
how do muscles relax
When the sarcolemma is no longer depolarized, the L-type calcium channels no longer trigger release of calcium from the SR through the ryanodine receptor
§ L-type channels return to their resting membrane potential state
where does calcium get re sequestered into
SR
how does calcium go back into SR in muscle relaxation
SERCA
what binds calcium in the SR to sequester it and keep it there in muscle relaxation
calsequestrin and calreticulin
where does cross bridge and muscle contraction take place
cytosol
where to put calcium for muscle relation
out of cytosol; mainly into SR but some into ECF
what is the fuel storage for type I vs type II muscle fibers
I- fat
II- glycogen
how does exercise effect slow vs fast twitch muscls
hard to change proportions in body but can change size of individual muscle fibers w particular training
lots of it is genetics
what activity is type I used for
low force, endurance ie. marathon
what activity is type II used for
high force, quick fatigue i.e. sprint
contraction time for type I vs II
I- slow
II- quick
size of motor neuron/ nerve fibers for type I vs II
I- small
II- large
oxidative vs oxidative glycolytic vs glycolytic
type I - O
type IIA- OG
type IIB- G
what can be found more in type I slow fibers
capillaries (w oxygen), mitochondria, myoglobin
what can be found more in type II fast fibers
SR (Ca2+), glycolytic enzymesw
what are the 3 metabolic systems responsible for recycling AMP and ADP back into ATP to provide a continuous supply of ATP in muscle fibers
§ 1. Phosphagen system
§ 2. Glycogen Lactic acid system
§ 3. Aerobic system
phosphagen system; which bond has lots of energy
High energy phosphate bond of phosphocreatine has more energy than the bond of ATP
what 2 things make up phosphagen system
phosphocreatine and ATP
what time length is the phosphagen system used for
8 to 10 seconds of maximal power
glycolysis steps
glycose - 2 pyruvate - 2 ATPf
enough vs not enough oxygen
enough; oxidative phosphorylation (aerobic)
not enough is lactic acid
what do type IIB fibers do with minimal mitochondria
lactic acid;; insufficient oxygens
after pyruvate if insufficient oxygen
latin acid (via lactate dehydrogenase) which diffuses out of muscles into, ISF, blood and make NAD+
how long does the glycogen lactic acid system work for
1.3-1.6 minutes
how does aerobic system work
- In presence of oxygen, pyruvate is broken down into carbon dioxide, water and energy via citric acid cycle and ETC
§ As long as nutrients in the body last, the aerobic system can be used for unlimited duration
what is cori cycle purpose and what is gain/loss of ATP
net loss of A4 ATP
propose; get lactate out of muscle and ATP in from liver
how to replenish energy system and ATP
Energy systems must be replenished
§ Phosphocreatine can be used to replenishes levels of
ATP
§ Glycogen-lactic acid system replenishes both phosphocreatine and ATP
§ Oxidative metabolism can replenish all systems: ATP, phosphocreatine and glycogen-lactic acid system
* Additional oxygen is needed – “oxygen debt”
- Glycogen levels must be replenished
oxygen debt
after exercise breath lots
what is muscle strength determined by
size
i.e. put a lot of force on tendon and could rupture or avulse it
how is muscle power measured
Measure of the amount of work that the muscle can perform in a given period of time
muscle endurance
via CARBS
Depends on nutritive support for the muscle
* Amount of glycogen that has been stored in the muscle
prior to the period of exercise
§ High CHO diet stores more glycogen in muscles than mixed diet or high fat diet
* Also greatly depends on the type & size of muscle fibre that is predominant in the muscle under investigation
mechanisms of skeletal muscle remodeling- growth
hypertrophy, hyperplasia, legthening
hypertrophy
increase muscle fibre size by adding more myosin and actin
hyperplasia
increase # of fibers
lengthening
add new sarcomeres to ends of fibers
hypertrophy vs hyperplasia vs lengthiening
Hypertrophy (common, weeks)
-Caused by near maximal force development (eg. weight lifting)
Increase in actin and myosin
Myofibrils split
- Hyperplasia (rare)
– Formation of new muscle fibers
– Can occur with endurance training - Hypertrophy and hyperplasia
– Increased force generation
– No change in shortening capacity or velocity of contraction - Lengthening (normal)
– Occurs with normal growth
– No change in force development
– Increased shortening capacity
– Increased contraction velocity
muscle atrophy
§ Muscle no longer receives contractile signals required to
maintain normal muscle size
§ Causes of muscle atrophy * Denervation/neuropathy * Tenotomy
* Sedentary lifestyle
* Plaster cast
* Space flight (micro-gravity)
acute vs chronic muscle atrophy
§ Acute/subacute
* Degeneration of contractile
proteins
* Decrease max force of contraction
* Decrease velocity of contraction
* If contractile signals return, full return to function can occur in as little as 3 months
§ Eg. Nerve supply grows back,
§ Functional return of the muscle decreases, with no return of function after 1 to 2 year
§ In final stages, muscle fibers are destroyed.
* Number of sarcomeres/fibre will often be lost, resulting in a shortening of the muscle + fibrosis à contracture
* Fiber are replaced by fibrous and fatty tissue with little contractile proteins
