Muscles

Question 1

Describe the structure and ultrastructure of skeletal muscle

Answer 1

• skeletal muscle cells are multinucleated striated fibres which are created in utero by myoblasts
• muscles are made of bundles of these fibres wrapped in connective tissue sheaths
• the striations are caused by sarcomeres

Question 2

In excitation-coupling contraction, after the action potential has been fired, what is released?

Answer 2

Ca2+ ions are released from the sarcoplasmic reticulum

Question 3

In excitation-coupling contraction, Ca2+ ions bind to

Answer 3

troponin on the actin filament

Question 4

In excitation-coupling contraction, what happens once Ca2+ ions bind?

Answer 4

Tropomyosin - the blocking protein - is removed, exposing the actin binding sites

Question 5

In excitation-coupling contraction, what happens once the actin binding sites are exposed?

Answer 5

Myosin filaments can bind to the actin and form cross bridges

Question 6

In excitation-coupling contraction, what causes the contraction of the muscles?

Answer 6

The binding of myosin filament to actin to form cross bridges

Question 7

In excitation contraction coupling, what happens once the cross bridges have been formed?

Answer 7

Ca2+ ions return to the sarcoplasmic reticulum through the use of ATP

Question 8

In excitation-coupling contraction, what happens once the calcium ions return to the sarcoplasmic reticulum?

Answer 8

Tropomyosin is free to return to its original positions so the contraction ends and cross bridges are broken

Question 9

In excitation-coupling contraction, as the filaments slide over each other - more overlap means

Answer 9

more tension

Question 10

In excitation-coupling contraction, as the filaments slide over each other - what will happen if there is too much overlap?

Answer 10

The filaments will interfere with each other

Question 11

What is an isotonic twitch?

Answer 11

Contraction with shortening length

Question 12

What is an isometric twitch?

Answer 12

Contraction with constant length

Question 13

In the generation of controlled force through the recruitment of motor units, as the load increases ___

What is this process known as and what does it allow?

Answer 13

more motor units are required to compensate

recruitment

allows more muscle fibres to be involved in a movement

Question 14

What is tetanus?

Answer 14

A state of extended contraction via the summation of APs

Question 15

Is tetanic tension greater or less than twitch tension?

Why is this?

Answer 15

Much greater, as there is no respite in which the calcium can return to the sarcoplasmic reticulum

Question 16

What is the difference between tetanus and normal contraction?

Answer 16

Tropomyosin is always held in the non-blocking state and so the cross bridges cannot be broken

Question 17

What is fatigue?

Answer 17

A state caused by repeated muscle stimulation which prevents using up vast quantities of ATP in breaking and reforming cross bridges to sustain contractions

Question 18

How much stimulation is require to trigger fatigue depends entirely on

Answer 18

• the individuals fitness
• muscle fibre type
• length of contraction

Question 19

What are the two types of skeletal muscle fibres?

Answer 19

• oxidative fibres

- glycolytic fibres

Question 20

Describe oxidative skeletal fibres

Answer 20

• more mitochondria for oxidative phosphorylation
• more vascular to allow for delivery of O2 and nutrients
• contain myoglobin to help oxygen delivery
• fibres are red and tend to be of low diameter

Question 21

Slow oxidative fibres

Answer 21

resist fatigue

Question 22

Fast oxidative fibres

Answer 22

have an intermediate resistance to fatigue

Question 23

Describe glycolytic fibres

Answer 23

• have very few mitochondria
• higher conc of glycolytic enzymes and glycogen
• lower blood supply
• white fibres with large diameter

Question 24

Fast glycolytic fibres

Answer 24

fatigue quickly

Question 25

Where does smooth muscle exist?

Answer 25

In hollow organs e.g. GI tract, bladder, airways

Question 26

What is the supply of smooth muscle?

Answer 26

Autonomic nervous system

Question 27

Describe smooth muscle cels

Answer 27

- mononucleated non-striated spindles - can divide throughout life - actin and myosin filaments arranged diagonally across cells and anchored to membranes and cell structures by dense bodies

Question 28

What is the difference between contraction/relaxation in smooth muscle and cardiac muscle?

Answer 28

Cardiac muscle also forms cross bridges between myosin and actin filaments but the mechanism is different

Question 29

As calcium is released from the ___ it binds to ___

Answer 29

sarcoplasmic reticulum calmodulin

Question 30

What happens once calcium has bound to calmodulin?

Answer 30

Calmodulin binds to myosin light chain kinase which phosphorylates the myosin with ATP and forms cross bridges to actin filaments

Question 31

Formation of cross bridges results in

Answer 31

contraction and tension

Question 32

Relaxation is brought about through

Answer 32

the action of myosin light chain phosphatase which dephosphorylates the cross bridges

Question 33

Contraction can be held for longer in smooth muscle due to ___ which is useful in ___

Answer 33

the low rate of consumption of ATP blood vessels, as they must stay open for long periods of time