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38 Cards in this Set

  • Front
  • Back

1. Skeletal muscle is divided into bundles of muscle fibers by?

2. muscles attached to bones by?

3. tendons formed by?

1. connective tissue covering muscle divides it internally into bundles

2. tendons

3. connective tissue extends beyond ends of muscle to form tendons

What is a twitch>

when a single action potential in muscle fiber produces a brief, weak contraction - too short and too weak to be useful

What are 2 factors that can be adjusted to accomplish muscle contraction?

1. # of muscle fibers contracting within a muscle

2. tension developed by contracting fiber

Characteristics of contraction of whole muscle

1. motor unit

2. motor unit recruitment

Motor unit

1. what is a motor unit

2. to accomplish greater tension

3. the larger the muscle, more the fibers

1. (motor neuron) + (all fibers it innervates)

2. greater number of muscle fibers must contract

3. greater the tension

One motor neuron innervates ______________ but each muscle fibers is supplied by __________________

a number of muscle fibers, but each muscle fiber is supplied by only one motor neurons

1. What is motor unit recruitment?

2. strength of muscle contraction depends on

1. for a stronger contraction, more and more motor units are recruited or stimulated to contract

2. depends on recruitment of each additional motor unit

1. muscles that produce precise, delicate movements contain ________ fibers per motor unit

2. muscles performing powerful, coarsely controlled movements have ___________ number of fibers per motor unit

1. fewer

2. larger

Recruitment of motor units in powerful muscle results in

large increment in whole muscle tension

Factors that affect the extent to which tension develops (4)

1. frequency of stimulation

2. length of fiber at onset of contraction

3. extend of fatigue

4. thickness of fiber

Length-Tension Relationship

1. maximal tetanic contraction can be achieved when

1. a muscle fiber is at its optimal length before the onset of contraction - because this is the point of optimal overlap of thick filament cbs thin filament cb binding sites

The percentage of maximal tetanic contraction decreases when

the muscle fiber is longer or shorter than optimal length before contraction

- longer: fewer thin filament binding sits are accessible for binding with thick fil. cbs

- shorter: fewer thin filament binding sites are exposed to thick filament cbs because thin filaments overlap - further shortening and tension developement impeded because thick fil forced against zlines

in the body, resting muscle length is

at optimal length

because of restrictions imposted by skeletal attachments, muscles cannot

vary beyond 30% of their optimal length in either direction - beyond that can stillachieve about50% of maximal tetanic contraction

contractions with longer duration and greater tension can be achieved by

repetitive stimulation of the fiber

What is twitch summation

- when a muscle fiber is restimulated before it has completely relaxed, second twitch is added onto the first twitch

1. What is tetanus?

2. occuris if

3. how much stronger than a twitch

1. a maximum sustained contraction

2. occurs if a muscle fiber is stimulated so rapidly that it does not have a chance to relax b/w stimuli

3. 3-4x stronger than single twitch

1. what is fatigue

2. fatigue occurs

1. the inability to maintain muscle tension at a given level

2. when exercising muscle no longer responds to same degree of contractile activity

Factors that affect muscle fatigue (3)

1. local increase of inorganic phosphate results from the break down of creatine phosphate

2. accumulation of lactic acid (can inhibit key enzymes involved in excitation-contraction coupling)

3. depletion of energy reserve

Power stroke

1. when is Pi released?

2. when is ADP released

from myosin cross bridge

1. released during power stroke

2. ADP released after power stroke

How is the link b/w actin and myosin broken after power stroke?

by fresh molecule of ATP binding to myosin cb (cb assumes original conformation)

What are the 3 basic methonds of ATP synthesis?

1. creatine phosphate

2. oxidative phosphorylation

3. glycolysis

One step process and is a fast-ATP forming method for contractile activity of a muscle

Creatine phosphate

ATP derived from creatine phosphate supports what activities

1. short burst of high contractile efforts such as high jumps, sprints or weight lifting

2. first minute or less of exercise (warm up)

Oxidative phosphorylation

1. sources of O2 for it

2. is it a slow or fast process

3. it produces how much ATP

4. supports what ativities

1. increased breathing and heart rate, increased myoglobin (store O2 in muscle), blood vessel dilation in exercised muscles, increased hb mols carrying more O2 to musles

2. slow, requires # of steps

3. 36 ATP

4. light exercise to moderate exercies (walk -> jogging/swimming)

During relaxation ATP is needed to

run the Ca pump that transports Ca back into SR lateral sacs

1.Main source of ATP when O2 present

2. Main source of ATP when O2 absent

3. Immediate source of ATP

1. oxidative phosphorylation

2. glycolysis

3. creatine phosphate

During glyolysis glucose mol broken down into

pyruvic acid

Glycolysis and oxidative phosphorylation

1. near max contracting, muscle compress blood vess. severely limiting O2 available for muscle contraction

2. reduced O2 slows down ox phos and therefore ATP needed during intense activity

3. glycolysis yields product for entry into ox phos (pyruvic acid further degraded by ox pho to extract more energy)

4. glycolysis yelds fewer ATP but is faster than ox phos if sufficient glucose mols present

Accumulation of lactic acid during exercise causes (3)

1. soreness of muscle during exercise

2. lactic acid picked up by blood causes acidosis (increased H+)

3. depletion of energy reserve and fall of muscle pH (sole cause of onset of muscle fatigue)

Muscle fatigue is a ________ mechanism

defense mechanism that protects muscle from reach point that it can no longer produce ATP

Types of Fatigue (3)

1. muscle fatigue

2. central fatigue

3. neuromuscular fatigue

1. What is central fatigue?

2. it causes

3. is often _________ based

4. what can cause it?

5. in less strenuous activities, central fatigue may reduce physical performance in association with

1. failure of CNS to activate motor neuron supplying working muscles

2. person to slow down or stop exercising even though muscles still bale to perform

3. psychologically

4. biochemical insufficiency within brain

5. association with boredom or tiredness

1. what causes neuromuscular fatigue?

2. a person with ___________ can experience NM fatigue

1. inability of active motor neurons to synthesize ACh rapidly to sustain chemical transmission of action pot from motor neuron to muscle

2. myasthenia gravis

1. What is oxygen debt?

2. O2 is needed for ______________ of energy systems

3. during recovery period, fresh supplies of ___________ formed by _________________ using newly acquired ___________

1. process of repayment of O2 that is incurred during exercise

2. recovery

3. supplies of ATP formed by ox phos using newly acquired O2

Major types of muscle fibers

1. classified based on

2. 3 major types

1. differences in ATP hydrolysis


slow oxidative (type I)

fast oxidative (type IIa)

fast glycolytic (type IIb or IIx)

Glycolytic white fibers

1. need how much O2

2. contains higher content of

3. contain abundant of stored ___________ to ...

4. why do they appear white/pale?

1. relatively low O2

2. glycolytic enzymes

3. glycogen to provide large amound of glucose for glycolysis

4. very little myglobin

What 3 levels of input control motor neuron output?

1. input from afferent neurons

2. input from primary motor cortex

3. input from brain stem