Muscles Flashcards
What are the two types of muscle?
Striated and smooth
What makes muscles and when?
By mononucleate myoblasts in utero
What are muscles made of?
Bundles of fibers wrapped in connective tissue sheathes
What causes striations in muscles?
Sacromeres
What repairs muscle cells after injury?
Satellite cells which differentiate to form new muscle fibres
What is hypertrophy?
Gain in muscle size/mass
What happens once an action potential is fired on a muscle?
- Ca ions released from sacroplasmic reticulum.
- Ca ions bind to blocking protein troponin, altering its shape
- Change of troponin’s shape causes removal of blcoking protein tropomyosin.
- This exposes actin binding sites, letting myosin filaments bind to actin and form cross bridges.
How does Ca ions return to the SR?
Using ATP
What is an isometric twitch?
Contraction with a constant length
What is an isotonic twitch?
Contraction with a shortening load
What does less overlap of filaments mean?
Less tension in muscle
What happens with too much overlap of filaments?
They start to interfere with each other
What happens when muscles are stretched?
They contract hard to compesate
What happens when muscles are stretched too much?
Contraction becomes less efficient
What is recruitment?
When load increases, more motor units are required to compensate, allowing more muscle fibres to be involved in a movement.
What is the order in which type of fibres are recruited/activated first?
Slow oxidative - Fast oxidative - Glycolytic
What is a motor unit?
A motor neuron and a muscle fibre
What is denervation atrophy?
Muscle wasting due to destruction of the NMJ/nerve
What is disuse atrophy?
When muscle isn’t used, causing atrophy/wasting
How does aerobic exercise cause hypertrophy?
Increases number of mitochondria which increases vascularisation and diameter in fibre
How does anaerobic exercise cause hypertrophy?
Increase in glycolysis rate in fibre increases diameter
What is tetanus and what causes it?
Extended twitches caused by summation of action potentials
What is unfused tetanus?
When action potentials fire rapid enough to cause twitching, but also not fast enough to stop cell repolarising
What is fused tetanus?
When cells fire action potentials so rapidly it never repolarises
Why is tetanic tension/ tension caused by tetanus greater than normal twitch tension?
Because Ca ions never get a chance to be low enough to allow tropomyosin to return to a blocking stage
What is fatigue?
A state caused by over muscle stimulation, stops large amounts of ATP breaking and reforming cross bridges to sustain contraction.
How is ATP used in contractions?
Hydrolysis of ATP energises X bridges
ATP binds to myosin causing disassociation of bridge bound to actin, starting new cycle
ATP powers return of Ca ions to SR
What are oxidative fibres?
Have more mitochondria for oxidative phosphorylation
More vascular for O2 and nutrient delivery
Fibres are red and have low diameter
Difference between slow and fast oxidative fibres?
Slow - can resist fatigue
Fast - has a intermediate resistance to fatigue
What are glycolytic fibres?
Few mitochindria
High supply of glycolytic enzymes and glycogen.
Lower blood supply, white and large diameter.
Where is smooth muscle found and what is it supplied by?
Hollow organs
Autonomic Nervous System
What is the action of Ca ions on smooth muscle?
Ca ions released from SR
Binds to calmodium which binds to myosin light chain kinase
The kinase phosphrylates myosin x bridges with ATP, allowing it to form cross bridges with actin filaments
What causes relaxation of the smooth muscle?
Myosin light chain phosphotase dephosphoryates the cross bridges
Why can contraction be held for longer in smooth muscle? Example of use?
Low ATP consumption rate
Useful in blood vessels which need to stay open for longer periods of time
Sources of cytosolic Ca ions?
The SR which is less in smooth than skeletal muscles. SR has no tubules and is randomly arranged.
Extracellular Ca ions - through voltage gated Ca channels
