8.1 Muscle

Question 1

Describe the structure of skeletal muscle, how its cells are joined, somatic/autonomic and power.

Answer 1

1. Long parallel cylinders, multiple peripheral nuclei, striations
2. Cells joined by fascicles
3. Somatic
4. Rapid, forceful

Question 2

Describe the structure of smooth muscle, how its cells are joined, somatic/autonomic and power.

Answer 2

1. Spindle shaped, single central nucleus no striations
2. Joined by connective tissue, gap and desmosome junctions
3. Autonomic
4. Slow, sustained

Question 3

Describe the structure of cardiac muscle, how its cells are joined, somatic/autonomic and power.

Answer 3

1. Short branched cylinders, single central nucleus, striations
2. Joined by gap junctions cell to cell
3. Autonomic
4. Variable but lifetime rhythm!

Question 4

What is myalgia?

Answer 4

Muscle pain

Question 5

What is myasthenia?

Answer 5

Weakness of the muscles

Question 6

What is myopathy?

Answer 6

Any disease of the muscles

Question 7

What is a myoclonus?

Answer 7

A sudden spasm of the muscles

Question 8

What is the sarcolemma?

Answer 8

The outer membrane of the muscle cell

Question 9

What is the sarcoplasmic reticulum?

Answer 9

The smooth endoplasmic reticulum of a muscle cell

Question 10

What is a myocardium?

Answer 10

Muscular component of the heart and contains cardiomyocytes

Question 11

What is atrophy? Name the 3 types.

Answer 11

Destruction of muscle > replacement of muscle

1. Disuse atrophy - muscle fibres do not fire so loss of protein
2. Age
3. Denervation - nerve cut and muscle receives no firing so loss of protein

Question 12

What is hypertrophy?

Answer 12

Replacement > destruction
Increase in fibre diameter
E.g. Due to exercise

Question 13

What is myoglobin and which type of muscle is it present in?

Answer 13

Oxygen storing molecule in blood to give to muscles
Similar to 1 sub unit of Hb
Contained in skeletal and cardiac but not present in smooth

Question 14

What is fibrillation?

Answer 14

Contraction of individual muscle cells

Question 15

What is fasciculation?

Answer 15

Contraction of whole groups of muscle cells

Question 16

Describe the structure of skeletal muscle.

Answer 16

Myofibrils formed by actin, myosin, troponin and tropomyosin
Myofibrils come together and form muscle fibre (cell)
Muscle fibres held together by endomysium forming fascicles
Fascicles held together by perimysium forming muscle
Muscle wrapped in epimysium
Goes onto form tendon, which attaches to bone

Question 17

Ultra structure of actin myosin filaments

Answer 17

A band darker (actin + myosin)
I band lighter (just actin)

Z band (just actin zig zag) in I band 
M band (half way) in A band

Question 18

Name the two types of muscle fibre

Answer 18

Red and white

Question 19

Where do T tubules lie in skeletal and cardiac muscle respectively?

Answer 19

Skeletal - A-I band

Cardiac - Z band

Question 20

What is cell hypertrophy

Answer 20

Cells become enlarged (abundance does not change)

Question 21

What is cell hyperplasia

Answer 21

Cells multiply and become more abundant (size does not change)

Question 22

What are satellite cells?

Answer 22

Precursor of skeletal muscle

Plays a part in repair

Question 23

Talk briefly about the ability to repair skeletal, cardiac and smooth muscle

Answer 23

Skeletal - cells cannot divide but mitotic activity of satellite cells repairs. Satellite cells then fuse with existing muscle cells (hypertrophy).

Cardiac - incapable of regeneration, fibroblasts just repair damage by laying down scar tissue

Smooth - cells retain mitotic acitivity e.g. Woman’s uterus (hyperplasia)

Question 24

What is a sarcomere?

Answer 24

Z-Z containing actin and myosin

Question 25

What are the markers for muscle damage?

Answer 25

1. Creatine Kinase - present in all muscle
2. Myoglobinuria - skeletal muscle and passed into urine
3. Troponin I - cardiac
4. ANP/BNP - atrial and ventricular stretching. Levels correlate with symptom severity.

Question 26

Outline the muscle contraction process.

Answer 26

1. A nerve impulse arrives via motor neurone axon and reaches the neuromuscular junction
2. ACh released into the synaptic cleft, binds and depolarise the sarcolemma
3. Voltage gated Na+ channels open causing Na+ to enter
4. Depolarisation travels down T tubules
5. Gated Ca2+ released from SR to sarcoplasm
6. Increased amount of calcium, Ca2+ binds to TnC of troponin and causes a conformational change, causing tropomyosin to move away from actins binding sites
7. Myosin head tightly binds to actin molecule (Cross bridge)
8. ATP hydrolysis uncoupled myosin and causes the head to bend and advance a short distance
9. Myosin binds weakly this time causing release of Pi which causes power stroke - the myosin returns to its former position
10. ATP binds causing detachment from actin
11. Cycle repeats

Question 27

What are the two types of modified smooth muscle cells that occur in smooth muscle?

Answer 27

1. Myoepithelial cell - basketwork around secretory units of exocrine glands - contraction of glands!
2. Myofibroblasts - produce collageneous matrix, for wound healing, they have actin and myosin so contract too!

Question 28

Why is muscle striated?

Answer 28

Longitudinal nature of actin and myosin

Question 29

What are the two types of muscle fibres?

Answer 29

Red

• more vascularised, mitochondria, myoglobin
• slow repetitive contractions so not easily fatigued
• lots of oxidative enzymes, not much ATPase
• limb muscle e.g.

White

• less vascularised, mitochondria, myoglobin
• faster, stronger contractions but easily fatigued
• not much oxidative enzyme, but rich in ATPase
• muscles controlling fingers e.g.

Question 30

What is the H zone?

Answer 30

Section of myosin where there is no overlap with actin

Contains the M line

Question 31

What are the Purkinje fibres? (4)

Answer 31

1. Modified muscle cell
2. Sparse myofilaments and extensive gap junction sites
3. Carry action potentials from AV node to ventricle muscle
4. Allow rapid and synchronous contraction

Question 32

Where are T tubules found in smooth muscle?

Answer 32

They are not present.

Question 33

How are thick and thin filaments arranged in smooth muscle cells and how do they contract?

Answer 33

Arranged diagonally spiralling down long axis
Muscle contracts in a twisting way
Less ATP needed than cardiac/skeletal muscle but still relies on actin and myosin

Question 34

What do smooth muscle contractions rely on?

Answer 34

They are innervated by the ANS that release NT from varicosities to wide synaptic cleft.

They respond to stimuli from nerve signals, hormones, drugs and local conc of blood gases

Question 35

Why do muscles stiffen after death and what is it called?

Answer 35

Rigor mortis - no ATP

Question 36

What can happen from the dysfunction of smooth muscle?

Answer 36

Asthma
IBS
Hypertension
Detrusor muscle instability (found in wall of bladder)