Examining Skeletal Muscle Under a Microscope
- 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
- For example, the movement of chromosomes during mitosis can be observed using a microscope
How optical microscopes work
- Light is directed through the thin layer of biological material that is supported on a glass slide
- This light is focused through several lenses so that an image is visible through the eyepiece
- The magnifying power of the microscope can be increased by rotating the higher power objective lens into place
Apparatus
- The key components of an optical microscope are:
- The eyepiece lens
- The objective lenses
- The stage
- The light source
- The coarse and fine focus
- Other tools used:
- Forceps
- Scissors
- Scalpel
- Coverslip
- Slides
- Pipette
Image showing all the components of an optical microscope
Method
- Preparing a slide using a liquid specimen:
- Add a few drops of the sample to the slide using a pipette
- Cover the liquid/smear with a coverslip and gently press down to remove air bubbles
- Wear gloves to ensure there is no cross-contamination of foreign cells
- Preparing a slide using a solid specimen:
- Use scissors to cut a small sample of the tissue
- Peel away or cut a very thin layer of cells from the tissue sample to be placed on the slide (using a scalpel or forceps)
- Some tissue samples need be treated with chemicals to kill/make the tissue rigid
- Gently place a coverslip on top and press down to remove any air bubbles
- A stain may be required to make the structures visible depending on the type of tissue being examined
- Take care when using sharp objects and wear gloves to prevent the stain from dying your skin
- When using an optical microscope always start with the low power objective lens:
- It is easier to find what you are looking for in the field of view
- This helps to prevent damage to the lens or coverslip incase the stage has been raised too high
- Preventing the dehydration of tissue:
- The thin layers of material placed on slides can dry up rapidly
- Adding a drop of water to the specimen (beneath the coverslip) can prevent the cells from being damaged by dehydration
- Unclear or blurry images:
- Switch to the lower power objective lens and try using the coarse focus to get a clearer image
- Consider whether the specimen sample is thin enough for light to pass through to see the structures clearly
- There could be cross-contamination with foreign cells or bodies
- Using a graticule to take measurements of cells:
- A graticule is a small disc that has an engraved ruler
- It can be placed into the eyepiece of a microscope to act as a ruler in the field of view
- As a graticule has no fixed units it must be calibrated for the objective lens that is in use. This is done by using a scale engraved on a microscope slide (a stage micrometer)
- By using the two scales together the number of micrometers each graticule unit is worth can be worked out
- After this is known the graticule can be used as a ruler in the field of view
The stage micrometer scale is used to find out how many micrometers each graticule unit represents
Limitations
- The size of cells or structures of tissues may appear inconsistent in different specimen slides
- Cell structures are 3D and the different tissue samples will have been cut at different planes resulting in this inconsistencies when viewed on a 2D slide
- Optical microscopes do not have the same magnification power as other types of microscopes and so there are some structures that can not be seen
- The treatment of specimens when preparing slides could alter the structure of cells
Skeletal muscle under the microscope
- It can be very difficult to make out the features of skeletal muscle fibres using an optical microscope
- Banding is visible, this is why it is referred to as striated muscle
The dark bands produce a characteristic striped appearance
- 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
