Organisms respond to changes in their internal and external environments Flashcards
What are skeletal muscles?
Muscles that are attached to bone.
What are skeletal muscles made up of?
Large bundles of long cells called muscle fibres.
What is the Sarcolemma?
The cell membrane of muscle fibre cells.
What are transverse tubules?
Bits of the sarcolemma that fold inwards across the muscle fibre and stick into the sarcoplasm.
What is the role of transverse tubules?
Help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.
What is the sarcoplasmic reticulum?
A network of internal membranes that run through the sarcoplasm, it stores and releases calcium ions for muscle contraction.
What are myofibrils?
Long cylindrical organelles that are made up of proteins and are highly specialised for contraction.
What do myofibrils contain?
Bundles of thick and thin myofilaments that move past each other to make muscles contract. Thick are made of myosin and thin are made of actin.
What are A bands?
Dark bands that contain thick myosin filaments and some overlapping actin filaments.
What are L bands?
Light bands that contain actin filaments only.
What is a myofibril made of?
Many short units called sarcomeres.
What is the Z line?
Ends of each sarcomere.
What is the M line?
Middle of the myosin filaments.
What is the H zone?
Around the M line and only contains myosin filaments.
What is the string filament?
Myosin and actin filaments slide over one another to make the sarcomeres contract, but the myofilaments themselves don’t contract.
The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract.
