MUSCLES Flashcards
ANTAGONISTIC PAIR
muscles acts in antagonistic pairs against an incompressible skeleton.
sarcolemma
the cell membrane of the muscle fiber cells is called the sarcolemma.
transverse tubules
sarcolemma folding inwards and sticking to the sarcoplasm is called transverse tubules,
- helps to spread electrical impulses throughout the sarcoplasm.
sarcoplasmic reticulum
stores and releases calcium ions needed for muscle contraction.
myofibrils
long, cylindrical organelles in the muscle fibres which are made up of proteins and are highly specialised for muscle contraction.
proteins in myofibrils
actin( thin filaments) and myosin ( thick filaments) that makes up the sacromere.
dark bands
dark bands contain thick myosin filaments overlapped by some actin filaments - these are called the A bands.
i bands
the light bands contain only thin actin filaments which is called the i band.
sacromeres
a myofibril is made up of many short units called sacromere.
z line
ends of sacromere are marked with a z line.
m line
m line is the middle of the myosin filaments.
h zone
h zone only contains myosin filaments.
sliding filament theory
myosin and actin filaments slide over each other to make the sacromere contract - the myofilaments dont contract themselves - the sacromeres get shorter when muslces are contracted.
myosin filaments and globular heads
- myosin filaments have globular heads.
- each myosin head has a binding site for ATP and actin.
- actin filament have binding sites for myosin heads called the actin myosin cross bridge.
- a protein called tropomyosin is found between actin filaments which helps myofilaments move past each other.
tropomyosin
when muscles are relaxing, the actin - myosin binding site is blocked by tropomyosin so thr myofilaments canmnot slide past each other.
muscle contraction and influx of calcium ions
- when an action potential from a motor neuron stimulates a muscle cell, it depolarises the sarcolemma and depolaridation spreads down the t - tubules to the sarcoplasmic reticulum.
- which causes the sarcoplasmic reticulum to release the stored calcium ions into the sarcoplasm.
- calcium ions binds to a protein attatched to tropomyosin causing it to change its shape which pulls tropomyosin out of the actin myosin binding sites.
- now the binding sites are exposed and the myosin head can now bind to actin. the bond formed when a myosin head binds to the actin filament is called the actin myosin cross bridge.
muscle contraction and atp and calcium ions ( more )
- ca+2 ions also activates the enzyme atp hydrolase which hydrolyses the enzyme atp into adp and pi providing the energy needed for muscle contraction.
- the energy relesed causes myosin head to bend which pulls the actin filament in a rowing action.
- another atp molecule provides energy to break the actin myosin cross bridge so the myosin head detatches from the actin filament.
- the myosin head then reatttaches to a different binding site and a new cross bridge is formed and the cycle is repeated .
- sacromeres are shortened causing the muscles to contract. the cycle continues as long as there is the presence of calcium ions.
calcium ions and muscle relaxation
when muscles are not stimulated, calcium ions leave their binding sites and are moved by active transport back to the sarcoplasmic reticulum which also requires atp.
- tropomyoisn molecules moves back blocking the actin myosin binding site.
- no muscle contraction as there is no binding between myosin head and actin filaments.
- actin filaments slides back to its original position and the sacromere lengthens.
what provides the energy for muscle contraction
atp and phosphocreatine
3 ways in which atp is generated
- aerobic respiration, anaerobic respiration and atp phosphocreatine system.
