PH1124 - Neuromuscular junction and muscular contraction

Question 1

What are the 3 types of muscle?

Answer 1

skeletal, cardiac, smooth

Question 2

What is the characteristics of skeletal muscle?

Answer 2

Has striations and multinucleated fibres.

It is of voluntary control.

Question 3

What are the characteristics of cardiac muscle?

Answer 3

Is striated with uninucleated fibres.

It is involuntary.

Question 4

What are the characteristics of smooth muscle?

Answer 4

Non-striated rod shaped cells with uninucleated fibres.

It is involuntary.

Question 5

What is the role of skeletal muscle?

Answer 5

Enables movement of the limbs and other parts of the skeleton and is connected via tendons.

Question 6

What is the role of cardiac muscle?

Answer 6

Pumps blood around the circulation system.

Question 7

What is the role of smooth muscle?

Answer 7

Used in the gut, regulates blood flow in arteries and expels urine from bladder as well as regulating air flow through the lungs.

Question 8

What is the sarcolemma?

Answer 8

plasma membrane of a muscle cell

Question 9

What is the sarcoplasmic reticulum?

Answer 9

the endoplasmic reticulum of a muscle cell

Question 10

What is a sarcosome?

Answer 10

mitochondria of muscle cell

Question 11

What is sacroplasm?

Answer 11

cytoplasm of a muscle cell

Question 12

What are muscle fibres?

Answer 12

Skeletal muscles that consist of bunches of long, rod shaped cells.

Question 13

What is a myofibril?

Answer 13

These are long ribbonlike organelles. They are bundles of myofilaments. They are aligned to give distinct bands.

I-band and A band (These bands give the muscle cell as a whole a striped appearance)

Question 14

What are the function of T tubules?

Answer 14

Makes sure action potential spreads over the muscle fibre as well as passing glucose oxygen and salts to the muscle fibre.

Question 15

Where is calcium stored in a muscle?

Answer 15

sarcoplasmic reticulum

Question 16

What is the H zone?

Answer 16

The zone within the A band which contains just myosin.

Question 17

What is the M line?

Answer 17

The middle of the H zone.

Question 18

What is the A band?

Answer 18

The portion of the myofibril that contains myosin.

Question 19

What is the sarcomere?

Answer 19

smallest contractile unit of a muscle cell.

Question 20

What are the 2 proteins the myofibril is made from?

Answer 20

actin and myosin.

Question 21

What is the I band?

Answer 21

Part of the sarcomere that just contains actin.

Question 22

What is the Z line?

Answer 22

Connection of actin filaments the dividing line between 2 adajacent sacromeres.

Question 23

What is the structure of myosin?

Answer 23

2 heads that can bind to actin filaments and use ATP. The tail is a shaft of the thick filament.

Question 24

What is troponin?

Answer 24

This term refers to a complex protein attached at regular intervals to actin strands and tropomyosin.

Question 25

What is tropomyosin?

Answer 25

It is a long, fibrous protein that winds around the actin polymer, blocking all the myosin-binding sites.

Question 26

How is contraction of a muscle achieved?

Answer 26

Calcium is released by the sarcoplasmic reticulum which binds to troponin causing it to change shape which moves tropomyosin out of position. Myosin can then cross bridge to actin which produces tension and shortening.

Question 27

What is cross-bridge cycling?

Answer 27

Myosin heads hydrolyse ATP to become reoriented and energized.
Myosin heads bind to actin forming cross bridges.
Myosin cross-bridges rotate toward centre of sarcomere (power stroke). As myosin heads bind ATP the cross bridges detach from actin.

Question 28

How is the signal for a muscle to contract initiated?

Answer 28

Depolarization has to occur at the neuromuscular junction. Depolarization moves along the sarcolemma down the T-tubules.
Depolarization causes calcium ion release through voltage gated L-type calcium channels in the cisternae of the sarcoplasmic reticulum- these free calcium ions then bind to troponin changing the structure of tropomyosin in the process.

Question 29

How does the signal to stop contraction finish?

Answer 29

Calcium pumps restore the calcium ions to the sarcoplasmic reticulum.

Question 30

What are the differences between smooth and skeletal muscle?

Answer 30

Smooth muscle contracts and relaxes more slowly as well as having layers of muscle that run in different directions.
There are no sacromeres and less energy is needed to create force. Smooth muscle is controlled by the autonomic nervous system where as skeletal muscle is controlled by the somatic motor division.

Question 31

What are the similarities between smooth and skeletal muscle?

Answer 31

Force is generated from actin-myosin cross bridge/ sliding filaments.
Contraction is initiated by an increase in free cytosolic calcium.

Question 32

How is contraction in smooth muscle achieved?

Answer 32

Action potential cause increase in cytostolic calcium. The calcium binds to calmodulin. Calmodulin changes shpe and forms a complex which binds to MLCK (myosin light chain kinase). This uses ATP to phosphorylate myosin cross bridges.
The cross bridges bind to actin filaments producing tension and shortening.

Question 33

What are non-depolarizing blockers?

Answer 33

Block activity by stopping depolarization.

Question 34

What are depolarizing blockers?

Answer 34

Block activity but allowing one depolarization but not permitting repolarization hence only one signal can be sent.

Question 35

What is the mechanism of non-depolarizing blockers?

Answer 35

To antagonise Nicotinic receptor, more acetylcholine must be released to attain a threshold potential in the motor end plate.

Question 36

What is the mechanism of depolarising blockers?

Answer 36

Prevents repolarisation of motor end-plate preventing subsequent contractions. Phase 1 is a depolarisation block and phase 2 is receptor desensitisation (resembles non-depolarising block.)

Question 37

What are the properties of Non-depolarising blockers?

Answer 37

Competitive.
No channel activation as well as no initial contraction.
Flaccid paralysis.
Reversible by cholinesterase inhibitors.

Question 38

What are the properties of depolarising blockers?

Answer 38

Non-competitive.
Initial channel activation.
Blockade preceded by fasciculations or twitching then relaxation as calcium is restored to sarcoplasmic reticulum.
Followed by paralysis.
Not reversible by anti-cholinesterase inhibitors.

Question 39

What are 2 ways the inhibition of acetylcholine can be achieved?

Answer 39

By irreversible inhibitors of acetylcholinesterase. Or by reversible inhibitors of acetylcholinesterase.

Question 40

How does inhibition of vesicular release work?

Answer 40

Alters proteins required for vesicular fusion with the presynaptic membrane e,g Botulinum toxin.