Microscopy Flashcards Preview

Histology > Microscopy > Flashcards

Flashcards in Microscopy Deck (27)
Loading flashcards...
1

What happens at the limit of a microscope's resolution

Separate objects appear to merge

2

What does optical 'resolution' refer to?

The capacity of an optical system to reveal detail in a specimen

3

What is the resolution from a conventional light microscope

0.2 µm

4

What is the resolution available from an electron microscope

1 nm

5

What is the maximum available magnification from a student light microscope

x 1000

6

What is the maximum available magnification from a electron microscope

x 100,000

7

Given the higher resolution and magnification, electron microscopes are said to display what aspect of cells and tissues

Their Ultrastructure

8

What are the two types of electron microscopy

Scanning and transmission EM

9

What are the features of scanning electron microscopy (2)

- 3D images
- Surface of object visible only

10

What are the features of transmission electron microscopy (4)

- 2D images
- Requires electrons to pass through the specimen to produce the image
- Requires ultrathin sections (50-100nm)
- More informative of tissue ultrastructure

11

How thin must sections be for transmission electron microscopy

50-100nm

12

What are the features of light microscopy (as compared to electron microscopy)? (3)

- Able to observe large areas of a specimen, (multiple cm2)
- Wide range of staining methods permitting identification of cell and tissue features (polychromatic)
- Can use slightly thicker sections to identify 3D features in certain specimens

13

What are the features of electron microscopy (as compared to light microscopy)? (4)

- Superior resolution and magnification - allows for identification of tissue ultrastructure
- Much smaller area available (<1mm2)
- Few staining methods, producing only monochromatic images
- Costly and time-consuming

14

What range of magnifications are available for EM

x500 - 190,000

15

How does an electron-dense area of an EM image appear?

Dark

16

How does an electron-lucent area of an EM image appear?

Light

17

EM sections are almost featureless without which process?

Staining with heavy metals - uranium and lead salts

18

How does an area of an EM section come to appear electron-dense?

Heavy binding of the heavy metal staining, leading to impeded transmission of electrons through the specimen at this point (too dense to allow passage of electrons)

19

How does an area of an EM section come to appear electron-lucent?

Poor binding of the heavy metal staining, leading to greater transmission of electrons through the specimen at this point (allows easy passage of electrons)

20

Plasma and organelle membranes have what width?

10nm

21

What are histochemical techniques?

- Staining employing reagents known to react with defined cellular constituents (e.g. lipids, glycogen or DNA), thereby producing selective colourisation recognisable by LM

22

What is enzyme histochemistry?

A subset of histochemistry where staining is of enzyme substrates or end products, allowing demonstration of enzyme activity

23

What is immunohistochemistry?

Antibodies against specific cellular components (the antigen) is conjugated with an appropriate visual marker (for LM or EM) e.g. dyes, enzymes, particles of colloidal gold.

24

What problem with specimens is common to both LM and EM?

The need to prevent autolytic degeneration and preserve cellular ultrastructure

25

What do fixatives do?

Prevent autolytic degeneration by causing cross-linking of macromolecules, reducing and often arresting biological activity. Also renders cells more amenable to staining

26

What are the most common fixatives?

Formaldehyde, Glutaraldehyde

27

What are sections?

Thin slices of tissue allowing for appropriate