There are three types of muscle tissue:

 

• Skeletal Muscle

• Smooth Muscle

• Cardiac Muscle

 

Skeletal (striated) Muscle

 

Skeletal muscle attaches to the bones of the skeleton and its function is concerned with movement. It is the only muscle tissue in the body that is controlled by the voluntary part of the nervous system. It is also the most abundant muscle tissue in the body.

 

Skeletal muscle cells (known as muscle fibres) are very long and cylindrical shaped. When skeletal muscle is viewed under a microscope the fibres appear to have stripes of light and dark bands running across them. These bands are called striations and are a result of the arrangement of protein fibres inside the cells.

 

The skeletal muscle cells are multi-nucleated (contain numerous nuclei) and also have many mitochondria. 

 

Smooth Muscle

 

Smooth muscle is usually located in the walls of internal organs and its function is to cause organs to contract, allowing substances to move through them e.g.

 

1. Alimentary Canal (oesophagus, stomach, intestines, rectum) of the digestive system required for peristalsis; the movement of food through the system

2. Blood vessels allowing vasoconstriction (narrowing) and vasodilation (widening ) controlling the blood flow through the vessels and blood pressure

3. Bronchioles allowing bronchoconstriction (narrowing) and bronchodilation (widening) of the airways controlling the flow of air

4. Urinary bladder to push the urine out

5. Iris of the eye allowing constriction and dilation of the pupil controlling the level of light entering the eye

 

Structure of smooth muscle

• No striations present

• Small simple cells (much smaller than skeletal muscle cells)

• One nucleus

• Packed together, joined by gap junctions (electrically joined)

• Controlled by the autonomic nervous system (Involuntary part of the nervous system

 

Cardiac Muscle

Cardiac muscle is found in the myocardium (the thickest and middle layer) of the heart. It contains striations like skeletal muscle, but not as prominent.

 

The myocardial cells are short, branched, and closely interconnected to form a continuous structure. They only have one nucleus and are joined by intercalated discs. The primary function of these discs is to provide sites of strong adhesion, to hold the adjacent cells together.

 

The gap junctions located in these discs promote diffusion of ions between cells, enabling the cardiac muscle to function and contract as a coordinated unit