ORTHO 112 Wrist Injury Flashcards
What is the function of a tendon?
Links muscle to bone, transmits force. Allows muscle belly to be some distance from site of action. Enables muscle pull to be accurately focuses. Reinforces joint capsure
What is the area called where tendon inserts on the bone and what is present there to reduce risk of wear and tear?
enthesis and fibrocartilage
What is the function of ligaments?
Link bone to bone, hold joint together, passive mechanical functions, proprioreception, muscle attachments
What is a motor unit?
A single motor neurone and all the muscle fibres innervated by it
What is a motor neurone pool?
All motor neurones that supply one whole muscle
What is the NMJ?
terminus of axon and motor end plate of muscle fibre/cell
What does a muscle fibre contain?
Many nuclei, sarcoplasm, sarcolemma, T-tubules, sarcoplasmic reticulum and motor end plate
What is the sarcoplasm?
The muscular cytoplasm
What is sarcolemma and describe it?
The muscle fibre membrane
Outer coat: thin polysaccharide/collagen layer that attaches to tendons
Inner plasma membrane
What are T-tubules?
Deep invaginations of sarcolemma into centre of fibre to allow the inner speedy depolarisation
What is the sarcoplasmic reticulum?
Enlarged endoplasmic reticulum assoc. with t-tubules and releases calcium on stimulation
What is the motor end plate?
Sarcolemma directly under axon with infoldings to increase the SA
What is a myofibril?
an intracellular fibril of multiple protein layers
Describe the 4 myofibril proteins?
Myosin- thick protein, multiple heads that bind to actin and use ATP to recock heads
Actin - thin filaments
Tropomyosin - lies over actin filaments and blocks myosin binding sites
Troponin bound by calcium, changing its shape so that it pulls tropomyosin out of the way
What are myofilaments?
Single protein chains
Describe the sarcomere and it’s bands
Contractile unit of the muscle extending from one z line to the next
Abands: dark and stay constant on contraction
I bands: light and reduce length on contraction
Influx of what cation causes depolarisation at the NMJ?
Na+
What cation causes release of the NT?
Calcium
What is the neurotransmitter released into the synaptic cleft at the NMJ?
AcH - acetylcholine
What receptors does acetylcholine bind to at the NMJ and what does it subsequently cause?
binds to nicotinic receptors and causes Na+ influx into the muscle sarcoplasm
Once depolarisation of the muscle sarcoplasm has reached threshold post-synaptically what potential is generated?
end-plate potential which spreads over the sarcolemma
What structure does the endplate potential penetrate?
T-tubules
What cation in the sarcoplasm stimulates what cations release in the sarcoplasmic reticulum?
Na+ stimulates calcium release in the sarcoplasmic reticulum
Once calcium has been released from the sarcoplasmic reticulum, where does it diffuse into and to what protein does it bind?
It diffuses into myofibrils and binds to troponin
What does troponin do?
Pulls tropomyosin out of the way clearing the myosin binding site
What does myosin head bind to to form a cross bridge?
Actin
What binds to myosin to allow it to dissociate from actin?
ATP
What splitting allows the myosin head to “recock”
ATP into ADP and Pi
Name the 4 ATP sources in Skeletal muscle
Phosphocreatinine, Anaerobic respiration, aerobic respiration, free fatty acids
What does muscle contraction strength depend on?
The number of motor units recruited and the frequency of impulses
What is an hypotonic muscle contraction?
Shortening - load or weight on the muscle remains the same whilst the muscle shortens
What is an isometric muscle contraction?
Stays the same length - despite contraction of the muscle the load remains in constant position supported by the muscle
What is eccentric muscle contraction?
Lengthening - force against against muscle is greater than that exerted by contraction
What are the 3 main muscle fibre types?
Type 1, Type 2a and Type 2b
Describe Type 1 muscle fibres
Slow twitch, oxidative fibre. Red, high myoglobin, well vascularised and resistant to fatigue
Describe Type 2a muscle fibres
Fast twitch, oxidative fibre, red, high ,myoglobin and well vascularised but glycogen stores for anaerobic respiration also
Describe type 2b muscle fibres
Fast twitch, glycolytic fibre, white, low myoglobin, low vascularity, few mitochondria, large glycogen stores, fatigue rapidly
