Structure of a Muscle

Types of muscle 

- Skeletal - Attached to skeleton, brings about movement 

- Cardiac - Contracts without the need of external stimulation

- Smooth - Lines gut and blood vessels. Contracts slowly

Skeletal muscle is attached to bone via tendons. Here is a breakdown of what a skeletal muscle is

Muscle --> Bundle of fibres --> fibres --> myofibrils --> filaments --> myofilaments --> Actin and Myosin 

In a myofibril there a few main observable sections 

The A band - The band of myosin. This is where there is a dark band because it is mostly an overlap of myosin and actin. There is a lighter band within the A band called the H zone. This is where there is only myosin and hence appears lighter when where the myosin and actin over lap. 

The I band - The I band is just actin and hence appears lighter than the A band. Within the I band is the Z line. The Z line is where the actin are joined together. 

The sarcomere is the measurement from one Z line to another. When the muscle is in a contracted state the sarcomere is shorter compared to when it's in its relaxed state.

The myofilaments are arranged so that 6 actin surround one actin. 

  

 

Above is a picture which pretty much sums up what I just said, except it's a lot easier to understand and probably doesn't have any spelling mistakes.