Voluntary And Involuntary Muscles

What are the three types of muscle in the body?

• Skeletal muscle.

• Cardiac muscle.

• Involuntary muscle.

What is skeletal muscle?

They make up the bulk of body muscle tissue. These are cells responsible for movement, for example.

What is cardiac muscle?

These are muscle cells only found in the heart. They are myogenic, contracting without the need for a nervous stimulus, causing the heart to beat in a regular rhythm.

What is involuntary (smooth) muscles?

These are muscle cells found in many parts of the body - for example the walls of hollow organs like the stomach. They are also found in the walls of blood vessels and the digestive tract.

What are skeletal muscles made up of?

Bundles of muscle fibres enclosed within a plasma membrane known as the sarcolemme.

What do muscle fibres contain a number of?

Nuclei and are much longer than normal cells, as they are formed as a result of many individual embryonic muscle cells fusing together. This makes the muscle stronger, as the junction between adjacent cells would act as a point of weakness.

What is the shared cytoplasm within a  muscle fibre known as?

The sarcoplasm.

What do parts of the sarcolemma fold inwards  to help spread?

Electrical impulses throughout the sarcoplasm. This ensures that the whole of the fibre receives the impulse to contract at the same time.

What do muscle fibres have lots of mitochondria to provide?

The ATP needed for muscle contraction. They also have a modified version of the ER, known as the sarcoplasmic reticulum

What is the role of the sarcoplasmic reticulum?

It extends throughout the muscle fibre and contains calcium ions required for muscle contractiom.

What does each muscle fibre contain?

Myofibrils.

What are myofibrils?

Long cylindrical organelles made of protein and specialised for contraction. On their own, they provide almost no force, but collectively they are very powerful. They are lined up in parallel to provide maximum force when they all contract together.

What are myofibrils made up of?

Two types of protein filament:

• Actin.

• Myosin.

What is actin?

The thinner filament, it consists of two strands twisted around each other.

What is myosin?

The thicker filament, it consists of long rod-shaped fibres with bulbous heads that project to one side.

What do myofibrils have?

Alternating light and dark bands resulting in their striped appearance.

What are the light bands?

These appear light as they are the region where the actin and myosin filaments do not overlap (I bands).

What are the dark bands?

These areas appear dark because of the presence of thick myosin filaments. The edges are particularly dark as the myosin is overlapped with actin (A-bands).

What is the Z line?

The line found at the centre of each light band. The distance between adjacent Z lines is called a sarcomere, which shortens when muscle contracts.

What is the H-zone?

This is a lighter coloured region found in the centre of each dark band. Only myosin filaments are present at this point. When the muscle contracts, the H-zone decreases.