Myofibrils, Actin and Myosin.

https://www.youtube.com/watch?v=MSdRQim4Y24

Key idea about skeletal muscle fibres.

Consists of hundreds of long thin cells (muscle fibres)

Whats the sarcolemma.

Muscle fibres are surrounded by a plasma membrane, this is called the sarcolemma.

Contains T tubules.

What is the sarcoplasm

Muscle fibres contain cytoplasm , this is also called the sarcoplasm, and within sarcoplasm we find multiple nuclei. Thats because the muscle fibre was formed from multiple cells fusing together

Also find a large number of mitochondria, as this provides ATP for muscle contraction.

Where are myofibrils found

Within the muscle fibre, a large number of myofibrils are found.

This is the part where contraction takes place.

Explain structure of myofibrils.

Shaped like a cylinder, and lined up so they’re parallel with each other, so when they contract or shorten it happens in the same direction.

Contain myosin (thick filament) and actin (thin filament)

What are the 2 proteins that myofibrils consist of

Myosin and actin. They are arranged to form strands called filaments.

What are the light bands (isotropic or I bands)

Where we only have thin actin filaments, so appears light

What are the dark bands (anisotropic or A bands)

Where we have thick myosin filaments, so appears dark

Where myosin and actin overlap.

What is the H zone

In centre of dark band, we have slightly lighter region.

Myosin only.

What is the Z line

The centre of the I band.

A sarcomere is the distance between the two Z bands.

What happens during contraction

The sarcomere shortens (Z lines move closer together)

The h zone becomes narrower as theres more overlap between actin and myosin

The I band becomes narrow as more overlap

The A band remains same width