• Many biological structures are?too small to be seen by the naked eye
• Optical microscopes?are an invaluable tool for scientists as they allow for tissues, cells and organelles to be seen and studied
• Electron microscopes?provide a much higher magnification and resolution so sub-cellular details can be studied
• Using microscopes to calculate the size of specimens requires the use of an?eyepiece graticule?which should be calibrated to the microscope
• However, it can be very difficult to make out the features of skeletal muscle fibres using an?optical microscope
• Only the banding is visible, this is why it is referred to as?striated muscle

The dark bands produce a characteristic striped appearance under an optical microscope

• Electron microscopes are often used to see muscle fibres in more detail
• They reveal the structure of?myofibrils

The detailed structures of the muscle fibres are visible due to the much stronger magnification of the electron microscope.

In a relaxed sarcomere:

• There will be?visible dark lines?where the?Z-lines are?at either end of the sarcomere
• There will also be a?darker band in the middle?of the sarcomere where the thicker myosin fibres are positioned and in the very centre of that is the M line
• Around the Z-line,?lighter bands are seen where the thinner actin fibres?are positioned

In a contracted sarcomere:

• The?Z-lines and M-lines are still visible with a?shorter distance?between the two z-lines
• The?lighter bands?around the z-line will be?smaller?or not visible
• The?darker band will be the same size?(although may appear a bit darker).