BL - Muscle

Question 1

What is the prefix used to denote muscle?

Answer 1

“My-“ eg myalgia, myasthenia

Question 2

What is the prefix used to denote a components of a muscle?

Answer 2

“Sarco-“ eg sarcolemma

Question 3

What are the three major categories of muscle?

Answer 3

Skeletal (striated), cardiac (striated), smooth (non-striated).

Question 4

What are the three types of skeletal muscle fibre?

Answer 4

Red, intermediate and white.

Question 5

Which type of skeletal muscle fibre is the largest?

Answer 5

White, then intermediate, then red is the smallest.

Question 6

Give some differences between red and white muscle fibres.

Answer 6

Red have rich vascularisation and myoglobin content, numerous mitochondria, slow/weak contraction and fatigue slowly. White is opposite. Intermediate is intermediate.

Question 7

Which type of skeletal muscle has more neuromuscular junctions?

Answer 7

White

Question 8

What is the difference in enzyme content between red and white muscles?

Answer 8

Red is rich in oxidative enzymes and poor in ATPase, white is poor in oxidative enzymes but rich in ATP-ase.

Question 9

What is myoglobin?

Answer 9

Red protein containing haem which functions as an oxygen storing molecule. Structurally similar to haemoglobin subunit.

Question 10

Which muscle types contain myoglobin?

Answer 10

Skeletal and cardiac - not smooth.

Question 11

What conditions make haemoglobin more likely to give up oxygen to myoglobin?

Answer 11

Low pH - active muscles produce CO2 which dissolves and lowers pH, causing oxygen to be transferred.

Question 12

What is a perimysium?

Answer 12

Connective tissue carrying nerves and blood vessels that surrounds a fascicle.

Question 13

What is the plasmalemma of a muscle cell called?

Answer 13

Plasmalemma

Question 14

What is it known as when muscles are destroyed?

Answer 14

Atrophy

Question 15

What is it known as when muscles are remodelled?

Answer 15

Hypertrophy

Question 16

How and when would disuse atrophy occur?

Answer 16

Loss of protein leads to reduced fibre diameter and loss of power. Occurs due to bed rest, limb immobilisation, sedentary behaviour.

Question 17

Give two reasons other than disuse for atrophy to occur.

Answer 17

Age and denervation.

Question 18

How does hypertrophy lead to increase in muscle size?

Answer 18

More contractile proteins, so increase in fibre diameter.

Question 19

Gove some examples of metabolic changes that occur due to hypertrophy?

Answer 19

Increased enzyme activity for glycolysis, more mitochondria, more stored glycogen, increased blood flow.

Question 20

True or false - muscle length is increased by frequent stretching?

Answer 20

True, due to addition of sarcomeres. The converse is also true.

Question 21

What are the thin muscle filaments called?

Answer 21

Actin

Question 22

What are the thick muscle filaments called?

Answer 22

Myosin

Question 23

What are skeletal muscles composed of?

Answer 23

Fascicles -> muscle fibres (cells) -> myofibrils -> myofilaments (actin and myosin)

Question 24

What can a troponin assay be used for?

Answer 24

Can be measured as a marker for cardiac ischaemia, as is released from ischaemic cardiac muscle within an hour. Must measure within 20 hours.

Question 25

What is creatine kinase?

Answer 25

An enzyme released into the blood by damaged skeletal muscle and brain.

Question 26

What is the role of calcium in muscle contraction?

Answer 26

Increased amounts of ionic calcium bind to troponin causing a conformational change which moves tropomyosin away from actin's binding sites, so binding can begin.

Question 27

Describe the sequence of muscle contraction

Answer 27

- myosin cross bridge attaches to actin myofilament - myosin head pivots and bends as it pulls the actin filament, sliding it towards the M line - new ATP attaches to myosin head, cross bridge detaches - ATP splits to ADP and Pi causing myosin head to cock.

Question 28

Summarise events leading to contraction of skeletal muscle.

Answer 28

- nerve impulse arrives an NM junction and stimulates release of Ach causing depolarisation - Na+ enters cell and T tubules are depolarised, causing conformation change. - Ca2+ enters sarcoplasm from terminal cisternae and binds to TnC subunit of troponin. - Contraction occurs.

Question 29

A picture of muscle in LS shows striations, centrally positioned nuclei, intercalated discs and branching. What type of muscle is it?

Answer 29

Cardiac

Question 30

What is the difference between the tubule placement in skeletal muscle compared with cardiac muscle?

Answer 30

In skeletal muscle they are on the Z bands rather than with the A-I bad junction.

Question 31

What are the two ways that muscles can increase in size?

Answer 31

Hypertrophy (enlargement of individual cells) or hyperplasia (multiplication of cells)

Question 32

What is a heart muscle cell also known as?

Answer 32

A cardiomyocyte

Question 33

What are natriuretic peptides?

Answer 33

Peptide hormones synthesised by the heart, brain and other organs. Their release is often stimulated by heart failure. Their function is to reduce arterial pressure.

Question 34

How do natriuretic peptides reduce arterial pressure?

Answer 34

Decreasing blood volume and systemic vascular resistance.

Question 35

When might a patient have elevated levels of ANP?

Answer 35

Hypervolemic states which occur in congestive heart failure.

Question 36

What can BNP and NT-pro-BNP be used for?

Answer 36

They are sensitive, diagnostic markers for heart failure in patients.

Question 37

What is the function of Purkinje fibres?

Answer 37

They transmit action potentials to the ventricles from the atrioventricular node.

Question 38

Give some features of Purkinje fibres.

Answer 38

Large cells with abundant glycogen, sparse myofilaments and extensive gap junction sites

Question 39

True or false - smooth muscle does not contain T tubules?

Answer 39

True, it also does not contain sarcomeres. It is not striated so no banding is present.

Question 40

What are myoepithelial cells?

Answer 40

Stellate cells forming a network around secretory units of exocrine glands, where they contract to aid secretion.

Question 41

What is the function of myofibroblasts?

Answer 41

Produce collagenous matrix at wound healing sites and contract to draw wound together.

Question 42

Can cardiac muscle be repaired?

Answer 42

No, following damage fibroblasts lay down scar tissue

Question 43

Can skeletal muscle cells repair themselves?

Answer 43

They cannot divide but tissue can regenerate using mitosis in satellite cells, which can also fuse with existing muscle cells to increase mass.

Question 44

Can smooth muscle regenerate?

Answer 44

Yes - smooth muscle cells retain their mitotic activity and can form new smooth muscle cells.

Question 45

Give some examples of diseases caused by smooth muscle dysfunction.

Answer 45

Asthma, irritable bowel syndrome, primary hypertension, detrusor instability

Question 46

What are the three indicators of muscle injury?

Answer 46

Creatine kinase , myoglobinuria, troponin

Question 47

What is the significance of "fixed" mottling?

Answer 47

It does not change when pressed, so the change is irreversible