muscular system physiology

Question 1

why do skeletal muscles cells contract?

Answer 1

the muscle cells contract in responce to a stimulas from a motor neuron

Question 2

where do motor neuron communicate with muscle cells?

Answer 2

neuromuscular junction and then the motor unit contracts

Question 3

what is a motor unit?

Answer 3

motor neuron and the muscle fibres it stimulates

Question 4

what difference can motor unit have?

Answer 4

some have only a few muscle cells which permits precise motor control and other units have many muscle cells which allows for powerful contractions or gross motor movement

Question 5

at the neuromuscular junction a motor neuron releases what neurotransmitter?

Answer 5

acetylcholine

Question 6

what triggers the release of ACh?

Answer 6

Ca+ influx into neuron

Question 7

at the neuromuscular junction ACh molecules bind to what?

Answer 7

bind to ACh receptor’s on muscle cell membrane

Question 8

at the neuromuscular junction binding of ACh to muscle cell membrane triggers what?

Answer 8

triggers an action potencial in the muscle cell

Question 9

what is the muscle cell membrane potencial?

Answer 9

charge difference across cell membrane due to differences in ion distribution which is a form of potencial energy

Question 10

changes in the membrane potencial can cause what?

Answer 10

can generate an action potencial which is a sudden change in membrane potencial of an editable cell due to Na+ influx which leads to depolarization

Question 11

muscle cell action potentials occur when?

Answer 11

muscle cells are stimulated by motor neurons

Question 12

what is excitation?

Answer 12

is an action potencial which through t-tubules triggers Ca+ release which causes crossbridge formation which causes muscle contraction

Question 13

what is the 1st step in muscle cell excitation?

Answer 13

Na influx causes muscle cell depolarization
action potencial= excitation

Question 14

what is the 2 step in muscle cell excitation?

Answer 14

action potentials spreads over sacrolemma to t-tubules

Question 15

what is the 3 step in muscle cell excitation?

Answer 15

a.p triggers Ca+ release from cisternae of sarcoplasmic reticulum

Question 16

what is the 4 step in muscle cell excitation?

Answer 16

Ca+ causes crossbridge formation between actin and myosin filaments

Question 17

what is the 5 step in muscle cell excitation?

Answer 17

filaments slide (sacromenes shorten) which gives muscle contraction

Question 18

how does muscle contraction occur then?

Answer 18

when filaments slide and sacromeres shorten

Question 19

what happens with relaxed muscles within sliding of filaments?

Answer 19

myosin binding sites on actin are blocked by troponin-tropomyosin complex

Question 20

what happens after mysoin binding sites are blocked by troponin?

Answer 20

Ca++ release and binds to troponin and the tropomyosin shifts and myosin binding sites are exposed

Question 21

after myosin binding sites are exposed what is crossbridge formation?

Answer 21

mysoin head latches on and binds to the actin filament

Question 22

after the myosin head latches on what is the powerstroke?

Answer 22

actin filaments slides along myosin filament and is repeated many times

Question 23

how does the breaking of crossbridges occur?

Answer 23

triggered by the binding of ATP to myosin

Question 24

how does the myosin head get recocked?

Answer 24

ATP is used and hydrolized to ADP + P

Question 25

what does the contraction of a whole muscle require?

Answer 25

requires stimultaneous contraction of many motor units

Question 26

what is a muscle twitch?

Answer 26

simultaneous contraction of motor units triggered by a single stimulas

Question 27

what is the latent phase of a muscle contraction?

Answer 27

t-tubules depolarize Ca++ released, muscle cannot respond to another stimulas

Question 28

what is the contraction phase of a muscle contraction?

Answer 28

sacromeres shorten and tension increases

Question 29

what is the relaxation phase of a muscle contraction?

Answer 29

Ca++ trasnported back into cisternae of SR

Question 30

what happens if more motor units are recruited?

Answer 30

more motor units stimulate more muscle fibres which creates a stronger contraction and tension icreases

Question 31

what is tension?

Answer 31

force excerted by a contracting muscle measured in grams

Question 32

what affects the amount of tension?

Answer 32

1. muscle length (amount of stretch)
2. strength of stimulas because of motor unit recruitment
3. frequency of stimulas because of motor unit recruitment

Question 33

steps in muscle cell contraction?

Answer 33

1. muscle cell action potencial
2. causes Ca++ to release from SR
3. causes filaments to slide
4. contraction continues as long as Ca++ levels are high

Question 34

steps in muscle cell relaxation?

Answer 34

1. stimulas stops(no action potencial)
2. active transport of Ca++ back into sacroplasmic reticulum (ATP used)
3. crossbridges can no form (tropomyosin covers binding sites) filaments seperate
4. repolarization of muscle cell (Na/k transporter restores resting membrane potencial) ATP used

Question 35

how does moderate stretch affect tension?

Answer 35

maximum number of crossbridges can form (maximum tension)

Question 36

how does unstretched muscle affect tension?

Answer 36

fewer crossbridges can form (low tension)

Question 37

how does overstretched muscle affect tension?

Answer 37

no overlap between actin/myosin, no crossbridges means no tension

Question 38

how does the strength of the stimulas affect tension?

Answer 38

stronger stimulas= increased motor unit recruitment
smaller motor units recruited first then larger ones

Question 39

what varries for different motor units?

Answer 39

threshold