Muscles

Question 1

What are the two types of muscle?

Answer 1

Striated and smooth

Question 2

What makes muscles and when?

Answer 2

By mononucleate myoblasts in utero

Question 3

What are muscles made of?

Answer 3

Bundles of fibers wrapped in connective tissue sheathes

Question 4

What causes striations in muscles?

Answer 4

Sacromeres

Question 5

What repairs muscle cells after injury?

Answer 5

Satellite cells which differentiate to form new muscle fibres

Question 6

What is hypertrophy?

Answer 6

Gain in muscle size/mass

Question 7

What happens once an action potential is fired on a muscle?

Answer 7

1. Ca ions released from sacroplasmic reticulum.
2. Ca ions bind to blocking protein troponin, altering its shape
3. Change of troponin’s shape causes removal of blcoking protein tropomyosin.
4. This exposes actin binding sites, letting myosin filaments bind to actin and form cross bridges.

Question 8

How does Ca ions return to the SR?

Answer 8

Using ATP

Question 9

What is an isometric twitch?

Answer 9

Contraction with a constant length

Question 10

What is an isotonic twitch?

Answer 10

Contraction with a shortening load

Question 11

What does less overlap of filaments mean?

Answer 11

Less tension in muscle

Question 12

What happens with too much overlap of filaments?

Answer 12

They start to interfere with each other

Question 13

What happens when muscles are stretched?

Answer 13

They contract hard to compesate

Question 14

What happens when muscles are stretched too much?

Answer 14

Contraction becomes less efficient

Question 15

What is recruitment?

Answer 15

When load increases, more motor units are required to compensate, allowing more muscle fibres to be involved in a movement.

Question 16

What is the order in which type of fibres are recruited/activated first?

Answer 16

Slow oxidative - Fast oxidative - Glycolytic

Question 17

What is a motor unit?

Answer 17

A motor neuron and a muscle fibre

Question 18

What is denervation atrophy?

Answer 18

Muscle wasting due to destruction of the NMJ/nerve

Question 19

What is disuse atrophy?

Answer 19

When muscle isn’t used, causing atrophy/wasting

Question 20

How does aerobic exercise cause hypertrophy?

Answer 20

Increases number of mitochondria which increases vascularisation and diameter in fibre

Question 21

How does anaerobic exercise cause hypertrophy?

Answer 21

Increase in glycolysis rate in fibre increases diameter

Question 22

What is tetanus and what causes it?

Answer 22

Extended twitches caused by summation of action potentials

Question 23

What is unfused tetanus?

Answer 23

When action potentials fire rapid enough to cause twitching, but also not fast enough to stop cell repolarising

Question 24

What is fused tetanus?

Answer 24

When cells fire action potentials so rapidly it never repolarises

Question 25

Why is tetanic tension/ tension caused by tetanus greater than normal twitch tension?

Answer 25

Because Ca ions never get a chance to be low enough to allow tropomyosin to return to a blocking stage

Question 26

What is fatigue?

Answer 26

A state caused by over muscle stimulation, stops large amounts of ATP breaking and reforming cross bridges to sustain contraction.

Question 27

How is ATP used in contractions?

Answer 27

Hydrolysis of ATP energises X bridges ATP binds to myosin causing disassociation of bridge bound to actin, starting new cycle ATP powers return of Ca ions to SR

Question 28

What are oxidative fibres?

Answer 28

Have more mitochondria for oxidative phosphorylation More vascular for O2 and nutrient delivery Fibres are red and have low diameter

Question 29

Difference between slow and fast oxidative fibres?

Answer 29

Slow - can resist fatigue | Fast - has a intermediate resistance to fatigue

Question 30

What are glycolytic fibres?

Answer 30

Few mitochindria High supply of glycolytic enzymes and glycogen. Lower blood supply, white and large diameter.

Question 31

Where is smooth muscle found and what is it supplied by?

Answer 31

Hollow organs | Autonomic Nervous System

Question 32

What is the action of Ca ions on smooth muscle?

Answer 32

Ca ions released from SR Binds to calmodium which binds to myosin light chain kinase The kinase phosphrylates myosin x bridges with ATP, allowing it to form cross bridges with actin filaments

Question 33

What causes relaxation of the smooth muscle?

Answer 33

Myosin light chain phosphotase dephosphoryates the cross bridges

Question 34

Why can contraction be held for longer in smooth muscle? Example of use?

Answer 34

Low ATP consumption rate Useful in blood vessels which need to stay open for longer periods of time

Question 35

Sources of cytosolic Ca ions?

Answer 35

The SR which is less in smooth than skeletal muscles. SR has no tubules and is randomly arranged. Extracellular Ca ions - through voltage gated Ca channels