13. Muscle

Question 1

Define myasthenia.

Answer 1

Weakness of the muscle.

Question 2

Define myocardium.

Answer 2

Muscular component of the heart.

Question 3

Define myopathy.

Answer 3

Any disease of the muscle.

Question 4

Define myoclonus.

Answer 4

A sudden spasm of the muscle.

Question 5

What is the sarcolemma?

Answer 5

The outer membrane of a muscle cell.

Question 6

What is sarcoplasm?

Answer 6

The cytoplasm of a muscle cell.

Question 7

What is sarcoplasm in reticulum?

Answer 7

The smooth endoplasmic reticulum of a muscle cell.

Question 8

What are the three types of muscle?

Answer 8

Skeletal muscle, cardiac muscle and smooth muscle.

Question 9

What is the widest and longest male type?

Answer 9

Skeletal.

Question 10

What type of muscle has long parallel cylinders, multiple peripheral nuclei and striations?

Answer 10

Skeletal.

Question 11

What type of muscle is under voluntary control?

Answer 11

Skeletal.

Question 12

What type of muscle has short branched cylinders, single central nucleus and striations?

Answer 12

Cardiac.

Question 13

What type of muscle has spindle-shaped, tapering ends, single central nucleus and no striations?

Answer 13

Smooth.

Question 14

How are skeletal muscles developed?

Answer 14

Mesodermally derived. Multi potent myogenic stem cells give rise to my oblasts. There is near-synchronous fusion of myoblasts to form a primary myotube with a chain of multiple central nuclei. The nuclei are gradually displaced to the cell periphery by actin and myosin filaments.

Question 15

What are the three type and colours of skeletal muscle?

Answer 15

Red (smallest and narrowest), white (larger and wider) and intermediate (in colour and size).

Question 16

Compare red and white skeletal muscle fibres in terms of the following: vascularisation, myoglobin, mitochondria, contraction, fatigue, enzyme, inner action and typical location.

Answer 16

Red are richly vascularised, rich in myoglobin, have numerous mitochondria. Their contraction is slow, repetitive and weak but they fatigue slowly. They have lots of oxidative enzymes but have few ATPase. They have few neuromuscular junctions. They’re typically found in the limb muscle of animal, postural muscles of back and the breast muscle of migrating birds.
White are poorly vascularised, poor in myoglobin and have few mitochondria. Their contraction is faster and stronger but they fatigue rapidly. They have few oxidative enzymes but a lot of ATPase. They have more neuromuscular junctions. They are typically found at extracellular muscles, muscles controlling finger and the breast muscle of domestic hen.

Question 17

What are skeletal muscle fibres surrounded by?

Answer 17

Endomysium.

Question 18

What are skeletal muscle fascicles surrounded by?

Answer 18

Perimysium.

Question 19

What is skeletal muscle surrounded by?

Answer 19

Epimysium.

Question 20

Which muscle bands are within each other?

Answer 20

MHAZI - M line is within the H band which is within the A band. The Z line is within the I band.

Question 21

List the following in order of increasing size: myofibrils, fascicles, skeletal muscles, myofilaments and muscle fibres.

Answer 21

Myofilaments, myofibrils, muscle fibres, fascicles, skeletal muscle.

Question 22

Which molecules form the thin filaments of skeletal and cardiac muscle?

Answer 22

Actin, tropomyosin and troponin.

Question 23

How can troponin assays be used as a diagnostic tool?

Answer 23

For cardiac ischaemia. Ischaemic cardiac muscle releases troponin within an hour but only stays around for up to 20 hours. This means small changes in troponin blood levels are indicative of cardiac muscle damage.

Question 24

What is the importance of calcium in muscle contraction?

Answer 24

Calcium binds to TnC if troponin and causes a conformational change that moves tropomyosin away from actin’s binding sites. This allows myosin heads to bind actin which starts contraction.

Question 25

What is the sequence of events in muscle contraction after calcium’s action?

Answer 25

Myosin cross bridges attaches to the actin myofilament.
ADP and PI are released in a working strike, where the myosin head pivots and bends as it pulls on the acting filament and slides it toward the M line.
As new ATP attaches to the myosin head, new cross bridges detach.
ATP splits into ADP and Pi and cocks the myosin head.

Question 26

What is the neuromuscular junction?

Answer 26

Small terminal swellings of the axon containing vesicles of acetylcholine.

Question 27

What is the process of events that lead to contraction of skeletal muscle?

Answer 27

A nerve impulse goes along motor neurone and arrives at the neuromuscular junction.
The impulse prompts release of acetylcholine into there synaptic cleft and causes local depolarisation of sarcolemma.
Voltage gated Na+ channels open and Na+ enters the cell.
General depolarisation spreads over the sarcolemma and into T tubules.
Voltage sensor proteins of T tubule membrane change their conformation.
Gated Ca2+ release channels of adjacent cisternae activated by the step before.

Question 28

What can be seen in a LS of cardiac muscle?

Answer 28

Striations, centrally positioned nuclei, inculcated discs and branching.

Question 29

What can be seen on a TS of cardiac muscle?

Answer 29

Central nuclei, endomysium with a rich supply of capillaries and some lobular profiles showing incipient branching of fibres.

Question 30

What is the function of Punkinje fibres?

Answer 30

To carry the impulses generated by the sinoatrial node to the ventricles.

Question 31

What are three key features of Punkinje fibres?

Answer 31

Abundant glycogen, sparse myofilaments and extensive Gla junction sites.

Question 32

What are some features of smooth muscle presentation?

Answer 32

They are non striated, have no sarcoma res and have no T tubules.

Question 33

What stimuli does smooth muscle contract in response to?

Answer 33

Nerve signals, hormones, drugs, or local concentrations of blood gases.

Question 34

In what disorders can smooth muscle be of clinical significance?

Answer 34

High blood pressure, dysmenorrhea, asthma, atherosclerosis, abnormal gut mobility.

Question 35

Describe the nature of repair possible for the three types of mature muscle.

Answer 35

Skeletal - can’t divide but tissue can regenerate by mitotic activity or satellite cells so hyperplasia follows muscle injury. Satellite cells can also cause skeletal muscle hypertrophy.
Cardiac - incapable of regeneration. Following damage, fibroblasts invade, divide and lay down scar tissue.
Smooth - retain their mitotic activity and form new smooth muscle cells. This is evident in pregnant uterus because the wall has hypertrophy and hyperplasia of individual cells.

Question 36

Define myalgia.

Answer 36

Muscle pain.