Neurons and glia Flashcards
What is the size of a neuron?
In the range of 0.01 to 0.05 mm in diameter.
The Nissl stain
Who and when? What? Why useful?
Who and when: The German neurologist Franz Nissl in the late nineteenth century.
What: The Nissl stain only colours the nuclei of the cells as well as Nissl bodies (i.e. rough endoplasmic reticulum).
Why useful: 1. Distinguish between neurons and glia. 2. Study cytoarchitecture (arrangement of neurons).
The Golgi Stain
Who and when? Difference from earlier?
Who and when: The Italian histologist and anatomist Camillo Golgi in the nineteenth century.
Difference from earlier: 1. Colours only a small percentage of the nerve cells (less than 1% of the cells are stained). 2. The cells are stained completely to see their structure (i.e. reveals both the cell body, the dendrites and the axon).
Other names for cell body?
Soma (plural: somata)
Perikaryon (plural: perikarya)
What are neurites?
Any projections from the cell body, i.e. dendrites and axons.
Santiago Ramón y Cajal
Who? What technique? Theory? Concepts? Prize?
Who: Spanish histologist and artist.
Technique: Used the Golgi stain technique in newborn animals (advantage: density of cells small).
Conclusion: The neuron doctrine, i.e. the nerve net not continuous but made up of individual units called neurons who transmit signals in the nervous system and are connected together. In opposition to Golgi’s reticular theory.
Concepts: Individual neurons, synapses, neural circuits.
Prize: Won the Nobel Prize in 1906 together with Camillo Golgi.
The reticular theory
What: The nerve network was continuous (like a high way, connected but no stop signs/traffic lights).
Reason: The staining techniques and microscope could not resolve small details.
Who: Camillo Golgi
The neuron doctrine
What? Who?
What: The nerve net not continuous, but made up of individual units called neurons who transmit signals in the nervous system and are connected together.
Who: Ramón y Cajal
When was the electron microscope developed?
What did it show?
In the 1950s
It showed that the neurites of different neurons are not continous with one another.
Development of the microscope
- The light microscope
- The electron microscope
- The laser microscope and computer display
The soma
Function? Size? Cytosol? Organelles? Cytoplasm?
Function: The metabolic centre of the neuron. Contains mechanisms that keep the cell alive.
Size: About 20 micrometer in diameter.
Cytosol:: The fluid inside the cell (salty, potassium-rich solution).
Organelles: Membrane-enclosed structures, e.g. nucleus, the rough endoplasmic reticulum, the smooth endoplasmic reticulum, the Golgi apparatus, the mitochondria.
Cytoplasm: The entire content within the cell membrane (excluding the nucleus).
Cytoskeleton
A skeleton that gives the neuron its characteristic shape. The “bones” of the cytoskeleton are the microtubules, microfilaments and neurofilaments. The skeleton is not static - the elements are dynamically regulated and in continual motion.
How many neurons are there in the human brain?
85 billion
How many glial cells are there in the human brain?
Roughly 85 billion
