Wrist Injury - 112 Flashcards
Describe (really simply) the structure of collagens
They are composed of 3 polypeptide chains wound into a triple helix
What is the most abundant class of proteins in the body?
Collagen
Collagen molecules are staggered to form fibrils. What cross links strengthen this assembly?
Lysine and hydroxylysine cross links
What is the role of tendons?
Link muscle to bone - have a high tensile strength to transmit muscle forces with minimal elongation
Describe the composition of tendons
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).
Name some of the functions of tendons
- 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
What is present where the tendon inserts on the bone?
fibrocartilage - enthesis
What is the major proteoglycan of cartilage?
Aggrecan
What happens at myotendinous junctions?
Force is transferred from muscle to tendon
There is increased S/A for anchorage
What do ligaments connect?
Bone to bone
What is more vascular, ligaments or tendons?
Ligaments
Name some roles of ligaments
- stabilise joints and guide joint motion
- supply proprioceptive information
What kind of cells do ligaments contain?
fibroblastic. They are mostly broad and flat and are more cartilage-like at bone insertion
What collagens do ligaments contain?
Type I (90%) and type III (10%)
Which glycosaminoglycan gives synovial fluid its lubricating properties?
Hyaluronan
What is a motor unit?
A single motor neurone and the muscle fibres it innervates
What is a motor neurone pool?
All the motor neurones that supply 1 complete muscle
What is a motor end plate?
The region of a muscle fibre membrane directly under terminal portion of an axon
What is the NMJ?
The junction of the axon terminal with the motor end plate
What is the resting potential and threshold potential for an AP at a motor nerve terminal? What happens when threshold potential is reached?
RP = -70mV
TP = -50mV
When threshold is reached an AP is fired
What happens at the NMJ when an AP arrives?
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
What poison can block the ACh receptor?
Curare
What are thin filaments in muscle fibres and what do they contain?
Actin. Also contain troponin and tropomyosin - which regulate contracion
Describe the structure of a mysoin molecule
Thick filament with myosin heads extending from it. Each globular head has binding sites for actin and ATP
During contraction, what happens to the sarcomere lenght,the H zone and the I band?
Sarcomere shortens, H zone and I band are both reduced
Describe briefly the 4 steps of the cross bridge cycle in muscle contraction
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)
What is the role of calcium in muscle contraction?
Tropomyosin molecules block actin binding site. When Ca binds troponin, tropomyosin molecules are moved away from blocking actin.
What is isometric contraction?
A muscle develops tension but does not shorten or lengthen. It stays constant in length. e.g. lifting an object that is too heavy
What is muscle cramp?
Painful strong muscular contraction in response to ischaemia or metabolic disturbance
What commonly occurs at the myotendinous junction and is associated with explosive activities and eccentric contractions?
Muscle strains/pulls
What can be used to diagnose neuromuscular disorders?
Electromyography
What is poliomyelitis?
A virus that destroys motor neurons -> affects lower motor neurons
Name a disorder of the NMJ
Myasthenia gravis
Name a disorder of the muscle fibres
Muscular dystrophy
