Muscoskeletal System 1

Question 1

define excitability?

Answer 1

capacity of muscle to respond to stimulus

Question 2

define contractility?

Answer 2

ability of muscle to shorten + generate pulling force

Question 3

define extensibility?

Answer 3

muscle can be stretched back to original length

Question 4

elasticity?

Answer 4

ability of muscle to recoil to original resting length after stretched

Question 5

what are the different types of muscle?

Answer 5

• skeletal
• smooth
• cardiac

Question 6

skeletal

Answer 6

• makes up 40% body weight
• responsible for locomotion, facial expressions, posture, respiratory movements
• controlled by somatic motor neurones (VOLUNTARY)

Question 7

smooth

Answer 7

• in walls of hollow organs, blood vessels, eyes etc
• functions: properly urine, mix food in digestive tract, dilate/constrict pupils, regulate blood flow
• controlled by endocrine + autonomic nervous systems (INVOLUNTARY)

Question 8

cardiac

Answer 8

controlled involuntarily by endocrine + autonomic nervous systems

Question 9

what is the epimysium?

Answer 9

dense regular connective tissue surrounding entire muscle

• separates muscle from surrounding tissues + organs
• connected to deep fascia

Question 10

what is the perimysium?

Answer 10

collagen + elastic fibres surrounding group muscle fibres = fascicle

contain blood vessel + nerves

Question 11

what is the endomysium?

Answer 11

loose connective tissue that surrounds individual muscle fibres

contains blood vessels, nerves + satellite cells

Question 12

motor neurones

Answer 12

• stimulate muscle fibre to contract
• neurone axons branch so each muscle fibre = innervated
• forms NMJ (myoneural junction)

Question 13

sarcolemma

Answer 13

= cell membrane

surrounds sarcoplasm

• has abundance of myoglobin
• has openings called Transverse T tubules

Question 14

what are T tubules?

Answer 14

narrow tubes that extend into sarcoplasm at right angles to surface

filled with extracellular fluid

Question 15

what are myofibrils?

Answer 15

cylindrical structures in muscle fibre

Question 16

a bundle of protein filaments is known as…

Answer 16

myofilaments

Question 17

what are the 2 myofilaments?

Answer 17

actin (thin)

myosin (thick)

Question 18

what is the sarcomere?

Answer 18

region between two z lines

Question 19

what is the I band?

Answer 19

zone of thin filaments not superimposed by thick filaments

Question 20

what is the A band?

Answer 20

entire length of single thick filament

Question 21

what is the H zone?

Answer 21

zone of thick filaments not superimposed by thin filaments

Question 22

what is the M line?

Answer 22

middle of sarcomere

Question 23

what is the sarcoplasmic reticulum?

Answer 23

smooth ER

forms chambers = terminal cisternae on either side of T tubule

Question 24

a single T tubule + 2 terminal cisternae form …

Answer 24

triad

Question 25

what is tropomyosin?

Answer 25

elongated protein that winds along groove of F actin double helix

Question 26

troponin is composed of 3 subunits, what are they?

Answer 26

- Tn-I site ; binds to actin - Tn-T site ; binds to tropomyosin - Tn-C site ; binds to ca2+ ions

Question 27

the tropomyosin/troponin complex regulates the...

Answer 27

interaction between active sites on G actin + myosin

Question 28

describe the myosin heads?

Answer 28

- form cross bridges with actin - attached to rod portion by hinge region that can bend + straighten during contraction - have ATPase activity —> breaks down ATP

Question 29

what are the components of the synapse (NMJ)?

Answer 29

- synaptic knob (swollen at end of axon terminal) contains ACh - motor end plate (region of sarcolemma that abuts synaptic knob - highly folded) - synaptic cleft

Question 30

what is the function of the motor end plate?

Answer 30

- inc surface area to allow more ACh receptors | - contains AChE that breaks down ACh and causes relaxation

Question 31

what is the synaptic cleft?

Answer 31

tiny gap between synaptic knob + sarcolemma of muscle fibre

Question 32

what are the 4 actions involved in muscle contraction + relaxation?

Answer 32

- excitation - excitation-contraction coupling - contraction - relaxation

Question 33

describe the sliding filament theory?

Answer 33

- calcium binds to troponin - troponin moves, moving tropomyosin, exposing actin active site - myosin head forms crossbridge + bends towards H zone - ATP allows release of cross bridge

Question 34

muscle contraction summary

Answer 34

- nerve impulse reaches NMJ - ACh released from motor neurone - ACh binds with nicotinic receptors in muscle membrane to allow na+ ions to enter - na+ influx generates AP in sarcolemma - AP travels down t tubule - SR releases ca2+ - ca2+ binds to troponin, to move troponin tropomyosin complex - binding site in actin exposed - myosin head attaches to binding sites = power stroke - atp detached myosin head + energises for another contraction - when AP cease, muscle stop contracting

Question 35

functions of ATP in skeletal muscle contraction

Answer 35

- energises cross bridges - providing energy for force generation - dissociates cross bridges bound to actin - energises ca2+ pumps that actively transport ca2+ back into SR - lowers cytosolic ca2+ levels —> relaxation - runs na+-k+ pump in sarcolemma - maintains resting membrane potential of sarcolemma

Question 36

ATP is produced from 3 sources, what are they?

Answer 36

- creatine phosphate - aerobic respiration - anaerobic respiration (glycolysis)

Question 37

what are the 2 types of skeletal muscle fibre?

Answer 37

fast twitch slow twitch

Question 38

slow twitch/ high-oxidative fibres

Answer 38

- contract slowly - moderate power output - consume atp at moderate rate - rich blood supply - more mitochondria - smaller in diameter (minimise diffusion distance) - large amount myoglobin - more fatigue resistant

Question 39

fast twitch/ low oxidative fibres

Answer 39

- rapid movement - anaerobic resp (glycolysis) - less blood supply (pale colour) - fewer mitochondria - fatigue rapidly - lower limbs in sprinter, upper limbs of most people - contain myosin

Question 40

what is a motor unit?

Answer 40

motor neurone and all muscle fibres it supplies

Question 41

muscles that control fine movements have ...

Answer 41

small motor units

Question 42

large weight bearing have...

Answer 42

large motor units

Question 43

back muscle motor unit ratio

Answer 43

1:100

Question 44

finger muscle motor unit ratio

Answer 44

1:10

Question 45

eye muscle motor unit ration

Answer 45

1:1

Question 46

what is the force of contraction affected by?

Answer 46

- relative size of muscle - number of muscle fibres contracting - degree of muscle stretch

Question 47

relative size of muscle

Answer 47

- larger muscles have larger + more muscle fibres - larger fibres generate more force - more muscle fibres generate more force

Question 48

number of muscle fibres contracting

Answer 48

greater no of motor units generate more force than smaller no of motor units

Question 49

degree of muscle stretch

Answer 49

muscles contract strongest when muscle fibres = 80-120% normal resting length

Question 50

smooth muscle features?

Answer 50

- cells not striated - smaller fibres - more actin - no sarcomeres (not arranged symmetrically) - cavoeolae- indents in sarcolemma - dense bodies instead of Z disks

Question 51

what is the longitudinal layer?

Answer 51

muscle fibres run parallel to organs long axis

Question 52

what is the circular layer?

Answer 52

muscle fibres run around circumference of organ

Question 53

role of ca2+ ions?

Answer 53

ca2+ binds to calmodulin + activates it activated calmodulin activates MLCK enzyme activated kinase transfers P from ATP to myosin cross bridge phosphorylated cross bridge interacts with actin —> shorten smooth muscle relaxes when intracellular ca2+ drop