Week 6- Muscle Microstructure & Contraction

Question 1

What are the 3 types of muscle?

Answer 1

Smooth muscle
Cardiac muscle
Skeletal muscle

Question 2

What type of control is associated with smooth muscle?

Answer 2

Involuntary control

Question 3

What branch of the nervous system controls smooth muscle?

Answer 3

Autonomic nervous system

Question 4

What type of control is associated with cardiac muscle?

Answer 4

Contracts autonomously

Question 5

What branch of the nervous system controls cardiac muscle?

Answer 5

Influenced by the autonomic nervous system and circulating chemicals

Question 6

What type of control is associated with skeletal muscle?

Answer 6

Voluntary control

Question 7

What is the purpose of skeletal muscles?

Answer 7

To cause movement by contracting (they are attached to bone)

Question 8

Where is smooth muscle found?

Answer 8

In the walls of airways

Question 9

What are some different arrangements of muscle fibers?

Answer 9

Parallel- all fibers in same direction
Fusiform- large bulge of fibers in the middle
Triangular-fibers form a triangle
Multipennate
Bipennate
Unipennate
Pennate- offset at an angle

Question 10

What is the significance of having different arrangements of muscle fibers?

Answer 10

Where the ligament is attached, the direction of the muscle fibers etc has an impact on the movement. The different orientations of fibers effects the tension in the muscle

Question 11

Describe the structure of muscles from macroscopic to microscopic

Answer 11

Muscle, fascicles, myofibre, myofibril, myofilaments (actin and myosin)

Question 12

What are fascicles?

Answer 12

Bundles of muscle fibers

Question 13

What surrounds muscle fiber?

Answer 13

Endomysium

Question 14

What is compartment syndrome? How is this significant in connective tissue?

Answer 14

When blood leaks into a compartment
Connective tissue is very rigid and doesnt allow expansion so if it happens in connective tissue can be very very painful and cause death of the tissue

Question 15

What surrounds fascicles?

Answer 15

Perimysium

Question 16

What cells give rise to myocytes?

Answer 16

Myoblasts

Question 17

What is special about the nucleation of muscle?

Answer 17

It is multinucleated

Question 18

What is the plasma membrane that covers myofibres called?

Answer 18

Sarcolemma

Question 19

What is the network of fluid filled structures called in muscles?

Answer 19

Sarcoplasmic reticulum

Question 20

What is the rough size of a myofibril?

Answer 20

1-2 micrometer

Question 21

What are the 2 main proteins that make up a myofibril?

Answer 21

Actin and myosin

Question 22

Out of actin and myosin which is the thin filament and which is the thick filament?

Answer 22

Actin-thin

Myosin- thick

Question 23

What is the repeating unit of a muscle called?

Answer 23

Sarcomere

Question 24

What muscle types are striated?

Answer 24

Cardiac and skeletal

Question 25

What separates z discs?

Answer 25

Dense protein

Question 26

What letter represents dark bands?

Answer 26

A band

Question 27

What letter represents light bands?

Answer 27

I band (actin thin)

Question 28

Where is the m line in a sarcomere found?

Answer 28

In the middle of 2 z discs

Question 29

What structures mark the boundaries of a sarcomere?

Answer 29

2 adjacent z discs

Question 30

What is actin attached to?

Answer 30

The z disc

Question 31

Describe the structure of myosin

Answer 31

Has 2 globular heads Single tail formed by 2 alpha helices Tails of several hundred molecules form one filament

Question 32

Describe the structure of actin

Answer 32

Actin molecules are twisted into a helix Each molecule has a myosin binding site Contain troponin and tropomyosin

Question 33

On actin what molecule cover myosin binding sites

Answer 33

Troponin

Question 34

What happens to the H, A and I bands during contraction?

Answer 34

``` H= narrowed or disappeared A= stayed the same I= becomes shorter ```

Question 35

What filament is pulled during contraction?

Answer 35

Actin is pulled by myosin, z plates move closer together

Question 36

How is muscle contraction initiated?

Answer 36

Lower motor neurone sends down a signal into the musculoskeletal synapse Action potential opens voltage gated Ca2+ channels Calcium enters presynaptic terminal Vesicles fuse w membrane and Ach is released Ach binds to postsynaptic receptors Local currents are set up Ach is brocken down and contraction stops

Question 37

What breaks down acetylcholine?

Answer 37

Acetylcholinesterase

Question 38

What happens in the muscle fiber once action potential is set up on the sarcolemma to cause release of calcium?

Answer 38

AP goes down t tubules At edge of t tubules are receptors ( DHP receptor and ryanodine receptor which is connected to calcium) Activation of receptors cause calcium to be released from the sarcoplasmic reticulum

Question 39

What are the names of the 2 receptors found at the end of t tubules? What do they do?

Answer 39

DHP receptor Ryanodine receptor They trigger the release of calcium from the sarcoplasmic reticulum

Question 40

How does calcium cause muscle contraction?

Answer 40

Calcium binds to troponin Tropomyosin moves, exposing myosin binding site Crossbridges on the actin filment form due to myosin binding to actin The binding and discharge of ADP causes the myosin head to pivot (power stroke) pulling the actin fiber to the center of the sarcomere ATP binding releases the myosin head from the actin chain

Question 41

What does calcium bind to on an actin fiber?

Answer 41

Troponin

Question 42

What causes the myosin head to pivot (ie cause a power stroke)

Answer 42

The binding and discharge of ADP

Question 43

What molecule is required to release the myosin head from actin after a power stroke?

Answer 43

ATP

Question 44

What recharges the myosin head after a power stroke?

Answer 44

ATP hydrolysis

Question 45

Which protein does the pulling in muscle contraction?

Answer 45

Myosin

Question 46

Where are upper motor neurones located?

Answer 46

In the primary motor cortex of the brain (sits in front of the central sulcus)

Question 47

Where are lower motor neurones located?

Answer 47

Brainstem or spinal chords

Question 48

Define a motor unit

Answer 48

A single motor neuron together with all the muscle fibers it innervates

Question 49

What does the stimulation of one motor unit cause?

Answer 49

The contraction of all muscle fibers in that unit

Question 50

How many neurons can innervate a muscle fiber?

Answer 50

Only one!!!

Question 51

On average, how many muscle fibers are innervated by one motor neuron?

Answer 51

600

Question 52

What causes us to have more dextrous control over a muscle?

Answer 52

Motor neurons innervating fewer muscle fibers

Question 53

What is an innervation ratio?

Answer 53

The number of muscle fibers controlled by a motor neurone

Question 54

What are the 3 types of motor units?

Answer 54

Slow (S- type I) Fast, fatigue resistant (FR- type IIA) Fast, fatiguable (FF-type IIB)

Question 55

Describe the cell body diameter, dendritic trees, axons and conduction velocity of slow motor units

Answer 55

Small cell body diameter Small dendritic trees Thinnest axons Slowest conduction velocity

Question 56

Describe the cell body diameter, dendritic trees, axons and conduction velocity of FR and FF motor units

Answer 56

Larger cell body diameter Larger dendritic trees Thicker axons Faster conduction velocity

Question 57

How does myoglobin content differ in slow, FR, FF motor units

Answer 57

Slow: high FR: high FF: low

Question 58

How does colour differ in S, FR, FF motor units?

Answer 58

S: red FR: pink FF: white

Question 59

How does aerobic capacity differ in S, FR, FF motor units?

Answer 59

S: high FR: moderate FF: low

Question 60

How does anaerobic capacity differ in S, FR and FF motor units?

Answer 60

S: low FR: high FF: high

Question 61

Out of S, FR and FF motor units, which one has the lowest tension generated?

Answer 61

S

Question 62

What are the 2 ways the brain regulates muscle force?

Answer 62

Recruitment and rate coding

Question 63

Describe recruitment as a method of regulating muscle force by the brain

Answer 63

Motor units are not randomly recruited, there is and order Smaller units are recruited first (slow twitch units) As more force is needed, more units are recruited allowing fine control under which low level force is needed

Question 64

Describe rate coding as a method of regulating muscle force by the brain

Answer 64

Motor units can fire at a range of frequencies, slow units fore at lower frequencies As firing rate increases, force produced by the unit increases Summation is when units fire at a frequency that is too high to allow muscles to relax between action potentials

Question 65

What is summation (in reference to motor units)

Answer 65

When during rate coding motor units fire at a frequency thats too high to allow muscles to relax between action potentials

Question 66

What is it called when a muscle wastes away?

Answer 66

Atrophy

Question 67

What are motor unit and fibre characteristics dependant on?

Answer 67

The nerve which innervates them

Question 68

What effects do neurons have on the muscle they innervate?

Answer 68

Its characteristics eg how fast it contracts and with what force

Question 69

What are the 3 types of muscle contraction?

Answer 69

Concentric Eccentric Isometric

Question 70

What is concentric muscle contraction?

Answer 70

When a load is overcome and the muscle is shorten (with the load being pulled towards you)

Question 71

What is isometric muscle contraction?

Answer 71

When a muscle is contracting and attempting to pull a load towards the body but is unable to and the load stays in the same place

Question 72

What is eccentric muscle contraction?

Answer 72

When force is generated but the muscle gets longer eg someone places a heavy book in your hand and you dont let it fall but it stretches your hand

Question 73

Out of eccentric and concentric muscle contraction, which can generate more force?

Answer 73

Eccentric

Question 74

What motor units/muscle fibres can undergo a change in properties?

Answer 74

FF to FR is most common

Question 75

What can rarely cause a change from slow to fast muscle fibres?

Answer 75

Severe deconditioning Spinal chord injury Microgravity during space flight

Question 76

What motor units does ageing cause a loss of?

Answer 76

Slow and fast but preferentially fast