Muscles Flashcards
Myosin
Thick protein filament. Point at which ATP is is transferred into energy. Myosin heads pull the actin to pull the unit inwards
Sarcomere
Smallest part
Arranged in parallel
Each sarcomere contains actin and myosin
Actin
thin protein filement
contains binding sites
on the binding sites are troponin which prevents the myosin from grabbing onto the actin
Troponin
A complex of three proteins
attached to tropomyosin
tropomyosin
an actin binding protein which regulates muscle contraction
holds troponin in place
motor unit
nerve impulse and bunch of muscles fibres
spatial summation
changes in strength of contraction brought about by altering the number and size of motor units involved
sarcoplasmic reticulum
releases calcium
the calcium ions shifts the tropomyosin which also moves the troponin
action potentials
in order for the skeletal muscles to contract, an action protential needs to be sent from the nervous system to the muscle fibres
this triggers the release of calcium
perimysium
skeletal muscles are separated from their surroundings by a membranous layer of connective tssue
tendons
tough relatively inelastic bands of tightly packed collagenous fibres that form connective tissue
motor end plate
the specialised synapses separation the nerve and muscle cell membrances
sarcolemma
each muscle fibre is surrounded by a hormogenous membrane that contains collagen fibres
the contractile mechanism
a nerve impulse arrives at the neuromuscular junction which causes the release of acetylcholine which causes calcium to be released from th sarcoplasmic reticulum
Calcium binds to troponin changing itsshape and so moving tropomyosin from the active site
myosin filaments cannot attach to actin forming a cross bridge
the breakdown of ATP releases energy which enables the myosin to pull the actin filaments inwards and so shortening the muscle
the myosin detaches from the actin and the cross bridge is broken
What are histochemical characteristics
Way of examining muscles
Biopsy
Long hollow needle put into the muscle, pull a vacuum and you get a bulge of muscle tissue
Type 1 slow twitch
Small in size fatigue resistant many mitochondria high capillary density slow contraction time red (myoglobin) less force and takes longer to produce
type 2a fast twitch
fast contraction time
fatigue resistance
used mainly during short high intensity events such as 400m
less red
can produce some amount of force but faster than slow twitch
Type 2b fast twtich
fatiguable low oxidative capacity short sprints high velocity contraction few mitochondria high glycogen stores low myoglobin
Muscle contractile mechanism (detailed)
- Sliding of the filaments begins when the myosin heads form cross bridges
- A nerve impulse from the motor nerve causes an action potential along the sarcolemma
- Action potential arriving at the motor end plate causes release of neurotransmitter acetylcholine which cause opening of sodium channels
- This causes action potential to be conducted along the muscle fibre
- Transmission of the action potential to the sites where the T tubules adjoin the sarcoplasmic reticulum which releases calcium
- This calcium binds to troponin, changing its shape and so moving tropomyosin from the active site of actin
- Myosin can now attach to actin forming a cross bridge
- Sequence of events repeated when another nerve impulse arrives at the motor end plate
Biochemical characteristics
The maximum shortening velocity of a single fibre with its maximum ATP utilisation rate
If can’t use ATP quickly, won’t contract quickly
Mean Vmax of type 2 is 10 times greater than type 1
Myosin head binding sites
One is a binding site for actin, second acts as ATPase
Recruitment of fibre types factors
Genetic component
Ageing influences the mix
Detraining
