Muscles

Question 1

What is skeletal muscle responsible for?

Answer 1

Voluntary movement of bones that underpins locomotion
Control of inspiration through contraction and relaxation of diaphragm
Skeletal muscle pump helps venous blood return to the heart

Question 2

What is the neurotransmitter used at neuromuscular junctions?

Answer 2

Acetylcholine

Question 3

What is the sarcoplasmic reticulum? What is a triad?

Answer 3

Specialised endoplasmic reticulum in skeletal muscle cells
T tubule runs through two areas near the SR which forms a triad- this is where the wave of depolarisation caused by an AP travels

Question 4

What does the arrival of an action potential at a neuromuscular junction cause?

Answer 4

Increase in intracellular calcium

Question 5

What are the three classes of skeletal muscle?

Answer 5

Slow oxidative (I)
Fast oxidative (IIa)
Fast glycolytic (IIX/B)

Question 6

What muscle type is fatigueable?

Answer 6

Fast glycolytic

Question 7

What are the differences between the appearance of different muscle types?

Answer 7

Fast glycolytic is white whereas the two oxidative types have a red appearance

Question 8

Types of muscle in order of most mitochondria to least

Answer 8

Fast oxidative, slow oxidative, fast glycolytic

Question 9

Types of muscle in order of highest to lowest glycogen content

Answer 9

Fast glycolytic, fast oxidative, slow oxidative

Question 10

What are the differences between slow and fast muscle fibres?

Answer 10

Slow fibres are half the diameter of fast fibres and take longer to contract after nerve stimulation
Fast fibres take 10msec or less to contract

Question 11

What is aerobic exercise?

Answer 11

Typically sustained, low level exercise stimulating slow fibres
Conversion of IIx to IIa
Increased muscle fatigue resistance but no change in muscle strength

Question 12

What is anaerobic exercise?

Answer 12

Typically brief, intense exercise stimulating fast fibres
No change in the number of muscle fibres but enlargement of myofibril size by addition of new myofilaments- increased diameter of muscle fibres which is called hypertrophy

Question 13

How is energy delivered in the initial stage of exercise?

Answer 13

Body relies on stored energy and anaerobic glycolysis

Question 14

How is energy released in the intermediate stages?

Answer 14

Muscle cells have reserves of ATP and phosphocreatine
Build up of AMP, ADP and phosphate stimulates metabolic pathways involved in energy production
Creatine is recycled into P-creatine in mitochondria at rest

Question 15

What enzyme catalyses the formation of ATP + creatine from ADP + PCr?

Answer 15

Creatine kinase

Question 16

What enzyme catalyses the formation of ATP + ADP from ADP + ADP as it accumulates from the breakdown of ATP?

Answer 16

Adenylate kinase

Question 17

At what two points of the glycolysis pathway does glycogen enter during anaerobic energy release?

Answer 17

Glycogenolysis of glycogen to produce glucose-1-phosphate

Glucose-1-phosphate conversion to glucose-6-phosphate

Question 18

How does glucose enter the glycolysis pathway?

Answer 18

Uptake from blood via GLUT4 transporters

Question 19

What is muscle fatigue and how is it caused?

Answer 19

Inability to maintain a desired power output
Build up of pyruvate from anaerobic energy release which is converted into lactic acid
H+ from lactic acid lowers cell pH and causes fatigue

Question 20

What are the advantages and disadvantages of anaerobic respiration in muscles?

Answer 20

Advantage- produces ATP in the absence of oxygen

Disadvantage- ATP yield is low and toxic products are generated

Question 21

How much ATP does aerobic and anaerobic respiration yield per glucose molecule?

Answer 21

30

2

Question 22

What happens during extended periods of exercise?

Answer 22

Lactate and alanine used by the liver to generate new glucose
Lactate can be released by non-exercising muscles, body acts to replenish glucose stores
Mobilisation of non-muscle lipids by increasing circulating fatty acids which are taken up by muscles
Break down of triacylglycerols stored in muscle

Question 23

What is central fatigue?

Answer 23

Minor factor in trained exercise

Question 24

What is peripheral fatigue?

Answer 24

At the level of the muslce fibre, with multiple factors

Question 25

What is high and low frequency fatigue?

Answer 25

High- alteration in cell Na/K balance, particularly relevant to type II fibres
Low- reduced release of Ca2+ from sarcoplasmic reticulum which is more apparent at low frequency stimulation, involves type I fibres

Question 26

What is ATP depletion?

Answer 26

Intense stimulation can cause large drops in ATP near sites of cross bridge formation and ATPases

Question 27

How is cardiac muscle different to skeletal muscle?

Answer 27

Striated like skeletal muscle but myocytes are shorter and are more branched
Myocytes join together at the intercalated disc through gap junctions which enables electrical coupling

Question 28

What is smooth muscle responsible for?

Answer 28

Mechanical control of organ systems
Control of blood vessel and airway diameter
Can involve circulating hormones, autonomic NS input or inflammatory mediators

Question 29

What are the two types of smooth muscle?

Answer 29

Multi unit- electrical isolation of muscle cells allows finer motor control
Unitary- gap junctions permit coordinated contraction

Question 30

Smooth muscle structure

Answer 30

Non striated, multiple actin fibres join up at spots known as dense bodies and thick filaments are interspersed around thin filaments

Question 31

How is intracellular calcium increase different in cardiac muscle compared to skeletal muscle?

Answer 31

There is no mechanical interaction between voltage gated Ca2+ channels in the T tubule and ryanodine receptors in the SR
Influx of Ca2+ through T tubule channels activates ryanodine receptors- this is called calcium induced calcium release

Question 32

How is Ca2+ removed from the cytoplasm?

Answer 32

Across the cell membrane by means of plasma membrane calcium ATPase or the electrogenic Na/Ca exchanger
Back into the sarcoplasmic reticulum via the sarco/endoplasmic reticulum calcium ATPase

Question 33

How does the structure of smooth muscle cells change how their intracellular calcium is increased?

Answer 33

Smooth muscle lacks lacks T tubules and tryad or dyad structures
Instead have shallow invaginations called caveolae
Peripheral SR encircles the caveolae and central SR runs through the cell

Question 34

How is intracellular calcium increased in smooth muscle?

Answer 34

Change in vm or AP can activate L-type calcium channels
Leads to CICR via activation of ryanodine receptors in the SR membrane
Activation of Gq coupled receptors leads to IP3 production and stimulation of IP3 receptors in the SR membrane

Question 35

What is the role of calcium and troponin in the formation of cross bridges in skeletal and cardiac muscle?

Answer 35

When Ca2+ falls, it dissociates from TnC and the subsequent movements of TnT, tropomyosin and TnI block any further myosin-actin interactions
When Ca2+ rises it binds to TnC, conformational changes causes TnT to pull tropomyosin and TnI out of the way so myosin and actin can interact

Question 36

What molecules tonically inhibit cross bridge formation in smooth muscle?

Answer 36

Calponin and Caldesmon
There is no troponin in smooth muscle cells
Stimulation of contraction involves stimulation of calmodulin by Ca2+

Question 37

What are the downstream effects of activation of calmodulin in smooth muscle?

Answer 37

Activates myosin light chain by phosphorylating it

Removes inhibitory effects of calponin and caldesmon so cross bridge formation is facilitated

Question 38

How is contraction stopped in smooth muscle?

Answer 38

De-phosphorylation of myosin light chain by myosin light chain phosphatase