Muscles Flashcards Preview

Science for Medicine > Muscles > Flashcards

Flashcards in Muscles Deck (33):
1

Describe the structure and ultrastructure of skeletal muscle

- 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

2

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

Ca2+ ions are released from the sarcoplasmic reticulum

3

In excitation-coupling contraction, Ca2+ ions bind to

troponin on the actin filament

4

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

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

5

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

Myosin filaments can bind to the actin and form cross bridges

6

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

The binding of myosin filament to actin to form cross bridges

7

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

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

8

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

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

9

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

more tension

10

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

The filaments will interfere with each other

11

What is an isotonic twitch?

Contraction with shortening length

12

What is an isometric twitch?

Contraction with constant length

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?

more motor units are required to compensate

recruitment

allows more muscle fibres to be involved in a movement

14

What is tetanus?

A state of extended contraction via the summation of APs

15

Is tetanic tension greater or less than twitch tension?
Why is this?

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

16

What is the difference between tetanus and normal contraction?

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

17

What is fatigue?

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

18

How much stimulation is require to trigger fatigue depends entirely on

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

19

What are the two types of skeletal muscle fibres?

- oxidative fibres
- glycolytic fibres

20

Describe oxidative skeletal fibres

- 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

21

Slow oxidative fibres

resist fatigue

22

Fast oxidative fibres

have an intermediate resistance to fatigue

23

Describe glycolytic fibres

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

24

Fast glycolytic fibres

fatigue quickly

25

Where does smooth muscle exist?

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

26

What is the supply of smooth muscle?

Autonomic nervous system

27

Describe smooth muscle cels

- 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

28

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

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

29

As calcium is released from the ___ it binds to ___

sarcoplasmic reticulum

calmodulin

30

What happens once calcium has bound to calmodulin?

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

31

Formation of cross bridges results in

contraction and tension

32

Relaxation is brought about through

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

33

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

the low rate of consumption of ATP

blood vessels, as they must stay open for long periods of time