MEC322: Muscle system

Question 1

Name the three muscle types

Answer 1

cardiac, smooth and skeletal

Question 2

Which is the most abundant muscle type?

Answer 2

skeletal
40-45% of total weight
more than 430 pairs of skeletal muscle

Question 3

Where will you find skeletal muscles?

Answer 3

attached to bones or for some facial muscles to skin

Question 4

Where will you find cardiac muscles?

Answer 4

walls of the heart

Question 5

Where will you find smooth muscles?

Answer 5

mostly in walls of hollow visceral organs (other than heart)

Question 6

Describe the shape of skeletal muscle

Answer 6

single, very long, cylindrical, multinucleate cells with very obvious striations

Question 7

Describe the shape of cardiac muscle

Answer 7

branching chains of cells, uninucleate, striations, intercalated discs

Question 8

Describe the shape of visceral muscle

Answer 8

single, fusiform, uninucleate, no striations

Question 9

What are the five key functions of muscles?

Answer 9

producing body movements
stabilizing body positions
regulating organ volume
moving substances within the body
producing heat

Question 10

What is a tendon?

Answer 10

extensions of connective tissue beyond muscle fibers that attach muscle to bone

Question 11

What are skeletal muscles well supplied with?

Answer 11

nerves and blood vessels, which provide nutrients and oxygen for contraction

Question 12

Skeletal muscles are separate organs made up of….

Answer 12

muscles fiber (cell)

Question 13

What does each muscle fiber contain?

Answer 13

myofibrils that contain thin filament and thick filament

Question 14

What are the filaments in the myofibrils arranged in?

Answer 14

sarcomeres

Question 15

What do thick filaments in myofibril composed of?

Answer 15

mysoin

Question 16

What do thin filaments in myofibril composed of?

Answer 16

actin, tropomyosin and troponin

Question 17

How are sarcomeres separated from each other?

Answer 17

zig-zagging zones of dense protein material called z discs

Question 18

What is an A band?

Answer 18

within each sarcomere a darker area called an a band extends the entire length of the thick filament

Question 19

What is at the centre of each a band?

Answer 19

h zone, which contains only the thick filaments

Question 20

Describe the i band

Answer 20

lighter coloured area either side of the a band contains the rest of the thin filament

Question 21

what is the contraction cycle?

Answer 21

Repeating sequence that causes sliding of filaments

Question 22

Describe the contraction cycle

Answer 22

Splitting ATP – myosin ATPase splits ATP and becomes energized
Forming cross-bridges – the myosin head attaches to actin, forming a cross-bridge
Power stroke – the cross-bridge generates force as it swivels or rotates toward the center of the sarcomere
Binding ATP & detaching – myosin detaches from actin. The myosin head again splits ATP, returns to its original position, and binds to a new site on actin as the cycle continues

Question 23

What is the sliding filament mechanism of muscle contraction?

Answer 23

the sliding of filaments and shortening of sarcomeres that cause the shortening of muscle fibers.

Question 24

What is ATP?

Answer 24

ATP (adenosine triphosphate) is the energy-carrying molecule used in cells because it can release energy very quickly.

Question 25

What is needed for muscle contraction?

Answer 25

Ca2+ and energy in the form of ATP

Question 26

What must happen before a skeletal muscle fibre can contract?

Answer 26

It must be stimulated by an electrical signal called a muscle action potential delivered by its neuron called a motor neuron.

Question 27

What is a motor unit?

Answer 27

A single motor neuron along with all the muscle fibres it stimulates

Question 28

What is the neuromuscular junction (NMJ)?

Answer 28

the synapse between a motor neuron and a skeletal muscle fiber.

Question 29

What does the neuromuscular junction (NMJ) include?

Answer 29

the axon terminals, synaptic end bulbs of a motor neuron and the adjacent motor end plate of the muscle fiber sarcolemma.

Question 30

How does a motor neuron excite a skeletal muscle fiber at the NMJ?

Answer 30

- acetylcholine (ACh) release from synaptic vesicles - ACh diffuses across synaptic cleft - binds to ACh receptors - muscle action potential initiated - the flow of Na+ generates .a muscle action potential - breakdown of ACh by enzyme called acetylcholinesterase

Question 31

What is a record of a contraction called?

Answer 31

myogram consists of latent period, contraction period and relaxation period

Question 32

What is wave summation?

Answer 32

the increased strength of a contraction that occurs when a second stimulus arrives before the muscle has completely relaxed

Question 33

What can repeated stimuli produce?

Answer 33

unfused (incomplete) tetanus

Question 34

What can rapid repeated stimuli produce?

Answer 34

fused (complete) tetanus

Question 35

What is motor unit recruitment?

Answer 35

the process of increasing the number of active motor units

Question 36

What increases force potential?

Answer 36

synchronisation large number of fibres in motor units type IIA and IIB

Question 37

Which type of motor unit decrease force potential?

Answer 37

Type I

Question 38

What are the three types of skeletal muscle fibres?

Answer 38

``` slow oxidative (SO) fibers, fast oxidative-glycolytic (FOG) fibers, fast glycolytic (FG) fibers ```

Question 39

Which fibre do most skeletal muscle contain?

Answer 39

most contain a mixture of all three fibres in varying proportions fibre type distribution is genetically determined

Question 40

what is the order the motor units of a muscle are recruited?

Answer 40

first SO fibers, then FOG fibers, and finally FG fibers.

Question 41

What is type I muscles fibre?

Answer 41

slow oxidative (SO) fibers

Question 42

What is type IIA muscles fibre?

Answer 42

fast oxidative-glycolytic (FOG) fibers

Question 43

What is type IIB muscles fibre?

Answer 43

fast glycolytic (FG) fibers

Question 44

When do sarcomeres produce maximal tension?

Answer 44

when thick and thin filaments overlap 100-120%

Question 45

What are muscles designed to do?

Answer 45

Optimise the force produced during contraction through sarcomere contraction

Question 46

What happens when a sarcomere is stretched too far?

Answer 46

Force reduced due to insufficient overlap of myofibrils

Question 47

What happens when the muscle is over contracted?

Answer 47

force reduce as potential for further contraction reduced

Question 48

What must the force of contraction for the whole muscle account for?

Answer 48

active (contractile) and passive (series and parallel elastic elements) components

Question 49

What is isometric contraction?

Answer 49

muscle contracts but does not shorten (held at position) often used for measurements as safer to conduct

Question 50

What is concentric contraction?

Answer 50

shortening

Question 51

What is eccentric contraction?

Answer 51

lengthening

Question 52

Is the force greater during eccentric or concentric contraction?

Answer 52

eccentric

Question 53

Greater concentric velocity.....

Answer 53

smaller the force

Question 54

When can the largest force be applied?

Answer 54

fastest eccentric motion

Question 55

Why are fibres in fusiform muscle parallel to the long axis of the muscle?

Answer 55

advantage for length of contraction

Question 56

What does fusiform mean?

Answer 56

Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends (think long lemon)

Question 57

How are fibres arranged in pennate muscle?

Answer 57

Fibers arranged obliquely to long axis of muscle | uni-, bi-, and multi-

Question 58

How is the arrangement of pennate fibres advantageous?

Answer 58

advantage for force of contraction

Question 59

Which fibre arrangement tends to have a larger physiological cross-sectional area?

Answer 59

pennate

Question 60

What is the force of muscle contraction proportional to?

Answer 60

physiological cross-sectional area

Question 61

What is the velocity and excursion of muscle proportional to?

Answer 61

length of myofibril