Chapter 2 - Neurons and Glia Flashcards
How many neurons and glia are in the adult human brain?
Roughly 85 billion of each type.
What are some of the major functions of the NEURONS?
Sensing changes in the environment, communicate these changes to other neurons, and command the body’s responses to these sensations.
What are some of the major functions of the GLIA?
They contribute to the brain function mainly by insulating, supporting, and nourishing neighboring neurons.
What is the average size of most brain cells?
0.01 - 0.05 mm in diameter.
What is one method to harden, or ‘fix’ tissues? How to slice this?
Immerse them in formaldehyde. With a microtome, you can make very thin silces of it.
What is the field of histology?
The microscopic study of the structure of tissues.
What was the major finding by Franz Nissl regarding neurohistology?
A class of basic dyes would stain the nuclei of all cells as well as clumps of material surrounding the nuclei of neurons. These clumps are Nissl bodies, and the stain is known as the Nissl stain.
Why is the Nissl stain useful?
1) It distinguishes between neurons and glia, and 2) it enables histologists to study the arrangement, or CYTOARCHITECTURE, of neurons in different parts of the brain. Cytoarchitecture led us to realize that the brain consists of regions.
What was the major finding by Camillo Golgi regarding neurohistology?
Soaking brain tissue in a silver chromate solution, now called the GOLGI STAIN, makes a small percentage of neurons become darkly colored in their entirety. Thanks to this, we realize that the region around the nucleus is only a small fraction of the neuron.
What are the names used for the swollen region containing the cell nucleus?
Cell body, soma (pl: somata), perikaryon (pl: perikarya).
What are the thin tubes that radiate from the soma?
They are neurites. Neurites are further divided into dendrites and axons.
What is the size ratio of axons and dendrites?
Dendrites are rarely longer than 2mm. However, axons can extend to more than 1 meter.
Describe the properties of the axon.
There is usually a single axon from the neuron. This has a uniform diameter throughout its length, and any branches generally extend at right angles. They act as “wires” that carry the output of the neurons.
Describe the properties of the dendrite.
They are rarely longer than 2mm, and many of them extend from the cell body. They generally taper to a fine point (become thinner towards the end). Dendrites act as the antennae of the neuron and receive incoming signals.
What is the contribution of Cajal to histology?
He used the Golgi stain to work out the circuitry of many regions of the brain. He argued that neurons communicate by contact, not continuity. This idea that cell theory applies to neurons as well came to be known as the neuron doctrine.
Describe the contents of the soma.
The cell body is about 20 um in diameter. The watery fluid inside the cell, the cytosol, is a salty, potassium-rich solution that is separated from the outside by the neuronal membrane. Within the soma, there are membrane-enclosed organelles, same ones you would find in all animal cells.
What is cytoplasm?
Everything within the membrane except the nucleus.
Describe the nucleus.
It is spherical, centrally located, and about 5-10 um across. It is contained within a double membrane, the nuclear envelope, which is perforated by pores about 0.1 um across. Within the nucleus are chromosomes that contain the DNA. The DNA contains the genes, that are parts of the DNA used to assemble the cell.
Describe genes and gene expression.
Gene expression is the reading of the DNA. The final product of gene expression is the synthesis of proteins. This protein synthesis occurs in the cytoplasm.
What is transcription?
The process of assembling a piece of mRNA that contains the information of a gene. The mRNA consists of four different nucleic acids strung together in various sequences to form a chain.
What are the promoters and terminators in a gene?
The PROMOTER is the region where the RNA-synthesizing enzyme, RNA polymerase, binds to initiate transcription. The TERMINATOR, also called the stop sequence, is a sequence of DNA that the RNA polymerase recognizes as the end point for transcription.
What are EXONS and INTRONS?
EXONS are the parts of a gene that are coded into mRNA. INTRONS are stretches of DNA within the gene that cannot be used to code for protein. During RNA SPLICING the introns are removed from the transcription after the initial transcript.
Why do neurons differ from other cells in the body?
Because of the specific genes they express as proteins.
What are some causes of psychic disorders?
In some diseases, GENE COPY NUMBER VARIATIONS cause loss of long stretches of DNA that contain several genes. In other diseases, MUTATIONS appear in a gene or in the flanking regions of DNA that regulate gene expression.
What are KNOCKOUT MICE, TRANSGENIC MICE and KNOCK-IN MICE?
Knockout mice are mice that have had one gene deleted. They can be used to study the progression of a disease.
Transgenic mice are mice in which genes have been introduced and overexpressed.
Knock-in mice are mice where the native gene is replaced with a modified transgene.