Skeletal muscle Flashcards
three types of muscle
striated (skeletal,cardiac) smooth
where is smooth muscle found
blood vessels, vas deferent, airways, uterus, GI itract, bladder etc. places it can constrict and dilate
how are skeletal muscle cells multinucleate
the cells are combined in the womb as we develop as a baby into longer muscle fibre so there are multiple nuclei, all from individual muscle cells. fibre size grows as we grow
how are skeletal muscle cells treated after injury
myoblasts cannot replace muscle cells. satellite cells (stem cells) form new muscle fibres or hypertrophy (other muscles try to get stronger to compensate). lots of scar tissue
what repeating unit allows muscle to contract
sarcomere made up of myosin filament surrounded by actin filament. titan holds myosin in place
how do muscles contract
myosin heads pull towards each other. actin helical structure can interact with myosin easily due to lots of binding sites. lots of Atp binding sites. great capacity for contraction
powerstroke
series of structural changes in the actomyosin cross bridge driven by hydrolysis of ATP
what ion does muscle contraction need
calcium
what partially covers myosin binding site to block it to avoid random unnecessary contractions
tropomyosin cover myosin and troponin holds in position. calcium binds to troponin which causes a change in shape which causes tropomyosin to pull away. if calcium is not there the site is blocked again
what do traverse tubules do
allow signal to reach the part of the cell it needs to by going deeper inside muscle cell as muscle cells are quite thick
sarcoplasmic reticulum
membrane bound structure inside myocyte that contains calcium ions
how is calcium taken back into storage to relax muscle cell after contraction
pumped against concentration gradient into sarcoplasmic reticulum powered by ATP
if one motor neurone is damaged or fails howcome you won’t lose muscle contraction or function in the whole body part eg bicep
one motor neurone is connected to many muscle fibres in the part. so if one neurone dies you have so many left still working
force exerted by muscle is
tension
force exerted on muscle is
load
contraction with constant length is
isometric
contraction with shortening length is
isotonic
contraction with increasing length is
lengthening
contraction time occurs between
start of tension and time when we have peak tension
contraction time depends on
calcium
isometric has ____ latent period but _____ contraction event
shorter, longer
as load increases, contraction velocity and distance shortened ____
decreases
tetanic tension
longer sustained contractions for as long as we want to but then we relax. due to increased frequency of action potentials. calcium doesn’t get low enough to allow troponin yo reblock myosin binding sites due to action potentials
over stretching is bad because
less overlap of filaments means less tension between (actin and myosin filaments)
how are muscles so manoeuvrable
lever system (antagonistic groups of muscles) amplifies muscle shortening velocity
what is fatigue
safety mechanism made up to prevent muscles using vast amounts of ATP which could cause rigor and would mean muscles would not be able to activate new X bridge cycles
high intensity, short duration exercise problems
too much potassium outside cell causes conduction failure, too much lactic acid causes proteins to not work because not at optimum ph, too much ADP and Pi inhibits X bridge cycle, delaying myosin detachment from actin filaments
long term low intensity exercise problems
run out of glycogen, low blood glucose, dehydration
central command fatigue
cerebral cortex cannot excite motor neurons. no will to win
oxidative skeletal muscle fibres
lots of mitochondria which leads to oxidative phosphorylation, more vascularisation to deliver more oxygen and nutrients, contain myoglobin which leads to increase oxygen delivery, red fibres with low diameters
glycolytic skeletal muscle fibres
few mitochondria, more glycolytic enzymes and glycogen, lower blood supply, white fibres with large diameters
3 types of muscle fibres
slow oxidative, fast oxidative, fast glycolytic (fast means has myosin molecules that have high ATPase activity, slow do not)
what order is muscle fibre recruited
slow oxidative, fast oxidative, fast glycolytic
neural control of muscle tension depends on
frequency of action potentials to motor units and recruitment of motor units
what can cause decrease in muscle mass
denervation atrophy or disuse atrophy
what can increase muscle mass
hypertrophy
aerobic exercise causes
increase in mitochondria and increase in vascularisation so exercise type can depends on what muscle fibre types u have
anaerobic exercise causes
increase in fibre diameter and increase in glycolysis so exercise type can depends on what muscle fibre types u have
