Wrist Injury - 112

Question 0

Describe (really simply) the structure of collagens

Answer 0

They are composed of 3 polypeptide chains wound into a triple helix

Question 1

What is the most abundant class of proteins in the body?

Answer 1

Collagen

Question 2

Collagen molecules are staggered to form fibrils. What cross links strengthen this assembly?

Answer 2

Lysine and hydroxylysine cross links

Question 3

What is the role of tendons?

Answer 3

Link muscle to bone - have a high tensile strength to transmit muscle forces with minimal elongation

Question 4

Describe the composition of tendons

Answer 4

Water = 55% wet weight.
Tendons consist of: collagen (mostly type I, which provides the tensile properties), elastin (provides the elastic properties), and proteoglycans (these bind water and help resist compression and regulate collagen fibril size).

Question 5

Name some of the functions of tendons

Answer 5

• Allow muscle belly to be away from site of action
• Enable muscle pull to be focused
• Eliminate the need for muscle to be an unnecessary length
• Act as springs
  etc

Question 6

What is present where the tendon inserts on the bone?

Answer 6

fibrocartilage - enthesis

Question 7

What is the major proteoglycan of cartilage?

Answer 7

Aggrecan

Question 8

What happens at myotendinous junctions?

Answer 8

Force is transferred from muscle to tendon

There is increased S/A for anchorage

Question 9

What do ligaments connect?

Answer 9

Bone to bone

Question 10

What is more vascular, ligaments or tendons?

Answer 10

Ligaments

Question 11

Name some roles of ligaments

Answer 11

• stabilise joints and guide joint motion

- supply proprioceptive information

Question 12

What kind of cells do ligaments contain?

Answer 12

fibroblastic. They are mostly broad and flat and are more cartilage-like at bone insertion

Question 13

What collagens do ligaments contain?

Answer 13

Type I (90%) and type III (10%)

Question 14

Which glycosaminoglycan gives synovial fluid its lubricating properties?

Answer 14

Hyaluronan

Question 15

What is a motor unit?

Answer 15

A single motor neurone and the muscle fibres it innervates

Question 16

What is a motor neurone pool?

Answer 16

All the motor neurones that supply 1 complete muscle

Question 17

What is a motor end plate?

Answer 17

The region of a muscle fibre membrane directly under terminal portion of an axon

Question 18

What is the NMJ?

Answer 18

The junction of the axon terminal with the motor end plate

Question 19

What is the resting potential and threshold potential for an AP at a motor nerve terminal? What happens when threshold potential is reached?

Answer 19

RP = -70mV
TP = -50mV
When threshold is reached an AP is fired

Question 20

What happens at the NMJ when an AP arrives?

Answer 20

Ca influxes, causing the release of ACh from vesicles.
ACh binds to nicotinic receptors on the motor end plate in the muscle fibre, causing Na influx.
This depolarises the membrane and generates an end plate potential

Question 21

What poison can block the ACh receptor?

Answer 21

Curare

Question 22

What are thin filaments in muscle fibres and what do they contain?

Answer 22

Actin. Also contain troponin and tropomyosin - which regulate contracion

Question 23

Describe the structure of a mysoin molecule

Answer 23

Thick filament with myosin heads extending from it. Each globular head has binding sites for actin and ATP

Question 24

During contraction, what happens to the sarcomere lenght,the H zone and the I band?

Answer 24

Sarcomere shortens, H zone and I band are both reduced

Question 25

Describe briefly the 4 steps of the cross bridge cycle in muscle contraction

Answer 25

1) Attachment of cross bridge to thin filament 2) Movement of cross bridge -> causes tension 3) detachment of cross bridge from thin filament 4) energising of cross bridge so cycle can repeat (ATP split to ADP and Pi)

Question 26

What is the role of calcium in muscle contraction?

Answer 26

Tropomyosin molecules block actin binding site. When Ca binds troponin, tropomyosin molecules are moved away from blocking actin.

Question 27

What is isometric contraction?

Answer 27

A muscle develops tension but does not shorten or lengthen. It stays constant in length. e.g. lifting an object that is too heavy

Question 28

What is muscle cramp?

Answer 28

Painful strong muscular contraction in response to ischaemia or metabolic disturbance

Question 29

What commonly occurs at the myotendinous junction and is associated with explosive activities and eccentric contractions?

Answer 29

Muscle strains/pulls

Question 30

What can be used to diagnose neuromuscular disorders?

Answer 30

Electromyography

Question 31

What is poliomyelitis?

Answer 31

A virus that destroys motor neurons -> affects lower motor neurons

Question 32

Name a disorder of the NMJ

Answer 32

Myasthenia gravis

Question 33

Name a disorder of the muscle fibres

Answer 33

Muscular dystrophy