Microstructure and contraction

Question 1

What are the 3 muscle types?

Answer 1

Smooth

Cardiac

skeletal

Question 2

What is the smooth muscle under the control of?

Answer 2

Autonomic nervous system- causes involuntary movement

Question 3

What influences the cardiac muscle?

Answer 3

Autonomic nervous system and circulating chemicals

Question 4

What is the significance of skeletal muscle?

Answer 4

• Under voluntary control
• attached to bones usually and contract to bring about movement

Question 5

Classify the structure of skeletal muscles from macroscopic to microscopic

Answer 5

Muscle - Fascicles– Myofibres– myofibril- Myofilaments

Question 6

Name as much shape of muscles as you can and give examples of where you can find them

Answer 6

• Triangular- Deltoid
• Fusiform- biceps brachii
• bipennate

Question 7

What are the connective tissues of the muscles and what do they cover? Any significance ?

Answer 7

• Epimysium- covers muscle
• perimysium- covers fascicles
• endomysium- covers muscle fibre(myofibres)

they are rigid and doesnt allow expansion

Question 8

Why is a myofibre multinuleated?

Answer 8

Myoblasts fuse together to form more than one nucleus

Question 9

What is contained in the sarcoplasm of a myofibre?

Answer 9

Myoglobin and mitochondria

Question 10

What is a network of fluid filled tubules in myofibres called?

Answer 10

Sarcoplasmic reticulum

Question 11

What is the diameter of a myoFIBRIL? Explain their structure across myofibre

Answer 11

1. 1-2uM
2. it extends along the entire length of myofibres

Question 12

What’s the difference between myofibril and myofilament?

Answer 12

Myofilament DOES NOT extend across the who length of the myofibres unlike myofibrils

Question 13

Draw and label a sarcomere

Answer 13

Question 14

Describe the structure of myosin

Answer 14

2 globular heads

single tail formed by 2 alpha helixes

tails of several hundred molecules form one filament

Question 15

Describe the structure of actin filament

Answer 15

• Actin molecules twisted into helix
• has a myosin binding site
• contains tropomyosin and troponin complex

Question 16

Explain what happens to the bands during contraction according to the sliding filament theory?

Answer 16

• I band becomes shorter
• A band stays the same
• H zone narrows or disappears

Question 17

Describe what happens after AP propagates along surface membrane and into T- tubules

Answer 17

• The change in AP activates DIHYRDOPYRIDINE receptor in T tubule membrane- changes shape of protein linked to ryanodine receptor
• This then opens the RYANODINE receptor Ca²⁺ channels in sarcoplasmic reticulum (as they’re coupled)
• calcium ions relases into space surrounding filaments from sarcoplamsic reticulum

Question 18

What causes CrossBridge to form? How is calcium ions transported back in to SR

Answer 18

Ca²⁺ binds to troponin and tropomysoin movies allowing cross bridges to form

Active transport; during AP , uptake is lower than or equal to release rate

Question 19

Describe what happens during sliding of actin and myosin filaments

Answer 19

Question 20

One average how many muscle fibres is supplied by a motor neurone? What is this called?

What is the significance

Answer 20

600- motor unit (name given to a single motor neurone and the fibres it innervate)

stimulation of one motor unit causes contraction of all muscle fibres in that unit

Question 21

What is the significance of the innnervation ratio ?

Answer 21

The lower innervation ratio the greater dexterity and control of the muscle

Large number of muscle fibres and low axons are for muscles for power

Question 22

what are the 3 different types of mtor units? what are the properties of the msucles in each unit

Answer 22

1. S type- slow
2. FR type IIA; Fastand fatigue resistant
3. FF type IIB- very Fast, Fatugueable

Question 23

what are the neuronal features of the S type motor unit

Answer 23

• smallest diameter of soma
• small dendrtitic trees
• thinnest axons
• slowest conduction velocities

Question 24

what are the neuronal features of the FR and FF fibres

Answer 24

• Larger soma diameter
• Largers dendritic trees
• thicker axons
• faster conduction velocity

N/B FF is faster and thicker than FR

Question 25

how are the muscle fibre types distributed around the muscle?

Answer 25

Randomly Muscles have different proportions of slow and fast fibres

Question 26

What are the fibre characteristics of slow type fibre in terms of myoglobin content, colour, aerobic and anaerobic capcity

Answer 26

* Myoglobin content- High * colour- red due to high myoglobin * Aerobic capacity- high * Anaerobic capacity- Low

Question 27

what are thefibre characteristics of FR fibres?

Answer 27

1. Myoglobin content- High 2. Colour- pink 3. aerobic capacity- moderate 4. anaerobic capacity- high

Question 28

what are the fibre characteristics of FF fibres?

Answer 28

* Myoglobin cointent- Low * Colour- white * aerobic capacity- low * anaerobic capacity- high

Question 29

what are the properties of slow motor unit

Answer 29

* low contraction forcce but stays for a longer period of time * no fatigue ,doesnt generate force quickly

Question 30

what are the properties of type IIA fibres?

Answer 30

* moderate force of contraction for a moderate amount of time * fatigue resistant

Question 31

what are the properties of FF fibres?

Answer 31

* High force of contraction generated very quickly * high fatiguability * doesnt keep this large force for a long amount of time

Question 32

How does the brain regulate muscle force? what are the 2 mechanism?

Answer 32

Recruitment and Rate coding

Question 33

Explain recruitment of muscle fibres

Answer 33

Size principle- smaller slow fibres are recruited first, as more force is needed, more units are recurited- this allows fine control also then larger units recruited (FR to FF) they are then DERECRUTIED FROM LARGE TO SMALL

Question 34

explain rate coding

Answer 34

at first slow units fire at LOWER frequency as more force is required, firing rate increases to increase force produced by the units. this can continue if necessary until summation is reached.

Question 35

describe the effects of neurones of muscle fibre type

Answer 35

if a fats and slow muscle fibre are CROSS INNERVATED, the fast brie becomes slow and the slow becomes fast.

Question 36

what are the 3 types of muscle contraction?

Answer 36

isometric concentric eccentric - causes tear and injury

Question 37

explain how muscle fibres can show plasticity WITHOUT CROSSINNERVATION what are the other condiotn

Answer 37

most common form is conversion from FF to FR- gym Microgravity in space case typeI to change to Type II Ageing- MORE loss in type II than Type I; higher proportion of type I

Question 38

where would you expect to find msucles with highest proportion of slow, FR or FF muscles

Answer 38

1. Slow- back muscles or calf muscles 2. FR-; hamstring 3. FF- Orbicularis oculi, or extrinsic eye muscles

Question 41

what is the effect of neurotrophic factors?

Answer 41

* prevent neuronal death * promote growth of neurons after injury