A Yoel Bakas Web Page


A neuron with it's corresponding axon and dendrites.

(This 3D neuron can be seen by using Chromatek 3D glasses.)


I. Proposal

A neuron, also called a nerve cell, is the basic cell of the nervous system in vertebrates and most invertebrates from the level of cnidarians upward. The neuron transmits nerve impulses. These impulses are carried along a fiber called the dendrite to the cell body. In higher organisms, the axon, a specialized fiber, carries impulses away from the cell body. In the human brain there are over 10,000,000,000 neurons. Neurons are in charge of transporting all the messages to and from the brain and every other part of the body. With few exceptions, most neurons consist of three distinct regions: (1) the cell body, or soma; (2) the nerve fibre, or axon; and (3) the receiving processes, or dendrites. The neuron is bounded by a plasma membrane, a structure so thin that its fine detail can be revealed only by high-resolution electron microscopy. About half of the membrane is the so-called lipid bilayer, two sheets of mainly phospholipids with a space between. One end of a phospholipid molecule is hydrophilic, or water attaching, and the other end is hydrophobic, or water repelling. Embedded within the lipid bilayer are proteins, which also "float" in the liquid environment of the membrane. These include glycoproteins containing polysaccharide chains, which function, along with other carbohydrates, as adhesion sites and recognition sites for attachment and chemical interaction with other neurons. The proteins provide another basic and crucial function: those which penetrate the membrane can exist in more than one conformational state, or molecular shape, forming channels that allow ions to pass between the extracellular fluid and the cytoplasm, or internal contents of the cell. In other conformational states, they can block the passage of ions. This action is the fundamental mechanism that determines the excitability and pattern of electrical activity of the neuron (1). Each neuron contains a nucleus defining the location of the soma. A double membrane, called the nuclear envelope, that fuses at intervals to form pores allowing molecular communication with the cytoplasm surrounds the nucleus. Within the nucleus are the chromosomes, the genetic material of the cell, through which the nucleus controls synthesis of proteins and the growth and differentiation of the cell into its final form. Proteins synthesized in the neuron include enzymes, receptors, hormones, and structural proteins for the cytoskeleton (1).


II. Method and Materials

The human brain sample utilized was obtained through the Alzheimer's Disease Center Brain Bank at Strong Memorial Hospital. The section of brain obtained was a piece of the middle frontal gyrus from a female of unknown age after a post-mortem time of 5 hours and 30 minutes. The brain weight of this patient was 1040 g and she was diagnosed as having a subdural hematoma. The sample was pre-fixed by the Alzheimer's Disease Center Brain Bank in a 4% paraformaldehyde in .1M sodium phosphate buffer (pH 7.2) with .25% glutaraldehyde for 24 hours. The sample was then changes to .15M sodium phosphate buffer and stored at 40C. The sample was then taken through several baths of ethanol. Increasing in concentration through out the process. This was done to replace the water in the cells with ethanol. At 70% ethanol, the sample was frozen using liquid nitrogen which cracked the sample, exposing the neurons to the outside. The sample then was placed in absolute ethanol and then critical point dried. The sample was then coated in gold and then placed in the stage to be seen under the SEM.


III. Data



Neuron in Brain

Neuron with Emerging Axon (visible Schwan cells)




Blood Vessel in Brain

 Red Blood Cells in Brain


The most noticable difference between fixed and non-fixed samples was found in their cellular surface structure. The fixed samples had clearly defined cell walls bordering each cell, while the non-fixed samples had no discernible boundaries at all.


IV. Discussion

When I set out to do my project I was convinced I would not be able to see anything. I was thrilled to find an intact neuron, red blood cells, and blood vessels as parts of my samples. I was even more excited that all my pictures came out well and that I was able to make a pseudo-three dimensional picture using Chromatek® technology. All in all, I had a great time, learned some useful SEM techniques. I had a great time, took incredible pictures, and learned a lot about SEM.


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