- sketetal muscle: attached to bones, arranged in antagonistic pair= muscles working in pairs opposite to eachother.
- Flexors: contract, and bend joints. e.g. Bicep (contracts and tricep relaxs)
- Extensors: contarct, extend/ striaghten a joint. e.g. triceps( contract and biceps relax) striaghten the arm.
- composed of myofibrils = actin (thin filaments ) + Myoson ( think filaments)
contraction of the Skeletal muscle. Sliding Filame
when muscles contracts the thin filaments(light bands/ I bands ) move between the thick myosin filaments( dark bands/ A bands). shortening length of sacromere, therefore shortening ther muscle.
- myosin + actin filaments slide over each other = making sacromere contract- myofibrils do not contract themselves.
- the simultaneous contraction of sacromeres myofibrils and therefore muslce fibres contract.
- when muscle relaxes they return to their original length.
Zones of Scaromere : End of Sacromere = Z line, Middle of Sacromere = M-line, around M-line is H zone., which only contains Myosin filaments.
sliding filament theory
- Stages of sliding filament theory
1. Action potential Tiggers influc of calicium ions.
- action potential from motor neurone, stimulates muscle cell.
- this Depolarises the Sarcolemna
- depolarisation runs through T- tubles into the Sarcoplsmic reticulum.
- depolarisation causes Releases of Ca2+ ions into sarcoplasm from the sacroplasmic reticulum
- calcium ion bind to troponin ( on Actin ), the ion causes the troponin to be pull out of the actin -myosin binding site on to the actin filament. Actin- myosin Binding site now Exposed.
- mysin head binds to the exposed binding site forming cross bridges = Actin - myosin Bridge
muscle contraction due to Action potential
Muscles Fibres: Sarcolemna ( cell membrane of muscle fibre calls ) is infolded into the sarcoplasm ( muscle cell cytoplasm ). Theses infolding are tranverse ( T ) tubles.transverse (T) tubles spread electrical impluses throughout the sarcoplasm, which ensures reach of signal through the muscle fibre.
- for contraction, you need ATP ( which is provided by Mitochondria + Calicium ions( releases and stored in the sarcoplasmic reticulum )
Muscle Contration due to action potential
2. ATP Provides Energy for Movement of Myosin Head
Calcuim ions activate ATPase, which breaks down ATP into ADP + Pi +Energy This Energy is used to change the shape os the myosin head and therefore move the myosin head = The power stroke power stroke, results in pulling of the actin filaments.
3 ATP also Breaks the Actin- myosin Bridge.
ATP provides energy to break actin-myosin cross bridge myosin head detaches from actin filament and thenreattaches to a Different binging site which is further alond the actin filament this process is repeated ( ATTACH --> change shape , Detach, reataach to new binding site ) this process will continue as long as Ca2+ ions are attached to the toponin , which changes shape of tropomyosin and exposes binding site
What happens when Excitation stops.
- muscles stop being stimulated by action potential
- calcuim ions leave binding sites on troponin molecules
- calcuim ions are move back to the sarcoplasmic reticulum by active transport ( process Requires ATP
- troponin molecules return to original shape, pulling tropomyosin mocules with them and blocking the Actin- myosin bind sites
- Actin filaments slide back to original postion ( RELLAXED POSITION) the sacromere lengthens.
- muscles= no contraction, because myosin head not attached to acti filaments. = no actin- myosin cross bridges.
Two types of skeletal muscles: Fast Twitch
1. speacialised to porduce rapis, contractions in short burts.
2.Few mitochondria - ATP comes from Anaerobic respiration( glycolysis) this process consumes gyycogen (stored glucose)
- 3: little mitocondria
- Few Caprillaries
- therefore cannot stores as much oxygen
- whitish in colour
4. Fatigues quikly
5. High levels of creatine phospahate
good for sprinting, wieght lifters
The Two types of Skeletal muscles : Slow Twitch
1. specialised for SLower, sustained contraction
- can cope with long period of exercise
2. MANY mitochondira- ATP comes from aerobic respiration ( from the electron transport chain )
3. lots of Myoglobin ( DARK RED PIGMENT) = to store O2
- lots of capillaries = supply O2.
- known as re muscle fibre/ oxidative