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It is important to note that a single neuron does not act alone—neuronal communication depends on the connections that neurons make with one another (as well as with other cells, like muscle cells). Dendrites from a single neuron may receive synaptic contact from many other neurons. For example, dendrites from a Purkinje cell in the cerebellum are thought to receive contact from as many as 200,000 other neurons.

Art connection

Illustration shows a neuron. The main part of the cell body, called the soma, contains the nucleus. Branch-like dendrites project from three sides of the soma. A long, thin axon projects from the fourth side. The axon branches at the end. The tip of the axon is in close proximity to dendrites of an adjacent nerve cell. The narrow space between the axon and dendrites is called the synapse. Cells called oligodendrocytes are located next to the axon. Projections from the oligodendrocytes wrap around the axon, forming a myelin sheath. The myelin sheath is not continuous, and gaps where the axon is exposed are called nodes of Ranvier.
Neurons contain organelles common to many other cells, such as a nucleus and mitochondria. They also have more specialized structures, including dendrites and axons.

Types of neurons

There are different types of neurons, and the functional role of a given neuron is intimately dependent on its structure. There is an amazing diversity of neuron shapes and sizes found in different parts of the nervous system (and across species), as illustrated by the neurons shown in [link] .

Part A shows a pyramidal cell with two long, branched projections on either end of the soma. Dendrites branch from either side. Part B shows a Purkinje cell with highly branched dendrites opposite the axon. Part C shows cells with long, thin axons. The dendrites are less branched than in pyramidal or Purkinje cells.
There is great diversity in the size and shape of neurons throughout the nervous system. Examples include (a) a pyramidal cell from the cerebral cortex, (b) a Purkinje cell from the cerebellar cortex, and (c) olfactory cells from the olfactory epithelium and olfactory bulb.

Multipolar neurons are the most common type of neuron. Each multipolar neuron contains one axon and multiple dendrites. Multipolar neurons can be found in the central nervous system (brain and spinal cord). An example of a multipolar neuron is a Purkinje cell in the cerebellum, which has many branching dendrites but only one axon.

The unipolar cell has a single, long axon extending from the cell body. The bipolar neuron has two axons projecting from opposite sides of the cell body. The multipolar neuron has one long axon and several short, highly branched axons extending in all directions. The pseudounipolar neuron has one axon that forms two branches a short distance from the cell body, each of which extends in a different direction.
Neurons are broadly divided into four main types based on the number and placement of axons: (1) unipolar, (2) bipolar, (3) multipolar, and (4) pseudounipolar.

Everyday connection

Neurogenesis

At one time, scientists believed that people were born with all the neurons they would ever have. Research performed during the last few decades indicates that neurogenesis, the birth of new neurons, continues into adulthood. Neurogenesis was first discovered in songbirds that produce new neurons while learning songs. For mammals, new neurons also play an important role in learning: about 1000 new neurons develop in the hippocampus (a brain structure involved in learning and memory) each day. While most of the new neurons will die, researchers found that an increase in the number of surviving new neurons in the hippocampus correlated with how well rats learned a new task. Interestingly, both exercise and some antidepressant medications also promote neurogenesis in the hippocampus. Stress has the opposite effect. While neurogenesis is quite limited compared to regeneration in other tissues, research in this area may lead to new treatments for disorders such as Alzheimer’s, stroke, and epilepsy.

How do scientists identify new neurons? A researcher can inject a compound called bromodeoxyuridine (BrdU) into the brain of an animal. While all cells will be exposed to BrdU, BrdU will only be incorporated into the DNA of newly generated cells that are in S phase. A technique called immunohistochemistry can be used to attach a fluorescent label to the incorporated BrdU, and a researcher can use fluorescent microscopy to visualize the presence of BrdU, and thus new neurons, in brain tissue. [link] is a micrograph which shows fluorescently labeled neurons in the hippocampus of a rat.

In the micrograph, several cells are fluorescently labeled green only. Three cells are labeled red only, and four cells are labeled green and red. The cells labeled green and red are astrocytes, and the cells labeled red are neurons. The neurons are oval and about ten microns long. Astrocytes are slightly larger and irregularly shaped.
This micrograph shows fluorescently labeled new neurons in a rat hippocampus. Cells that are actively dividing have bromodoxyuridine (BrdU) incorporated into their DNA and are labeled in red. Cells that express glial fibrillary acidic protein (GFAP) are labeled in green. Astrocytes, but not neurons, express GFAP. Thus, cells that are labeled both red and green are actively dividing astrocytes, whereas cells labeled red only are actively dividing neurons. (credit: modification of work by Dr. Maryam Faiz, et. al., University of Barcelona; scale-bar data from Matt Russell)

Glia

While glia are often thought of as the supporting cast of the nervous system, the number of glial cells in the brain actually outnumbers the number of neurons by a factor of ten. Neurons would be unable to function without the vital roles that are fulfilled by these glial cells. Glia guide developing neurons to their destinations, buffer ions and chemicals that would otherwise harm neurons, and provide myelin sheaths around axons. Scientists have recently discovered that they also play a role in responding to nerve activity and modulating communication between nerve cells. When glia do not function properly, the result can be disastrous—most brain tumors are caused by mutations in glia.

Section summary

The nervous system is made up of neurons and glia. Neurons are specialized cells that are capable of sending electrical as well as chemical signals. Most neurons contain dendrites, which receive these signals, and axons that send signals to other neurons or tissues. There are four main types of neurons: unipolar, bipolar, multipolar, and pseudounipolar neurons. Glia are non-neuronal cells in the nervous system that support neuronal development and signaling. There are several types of glia that serve different functions.

Questions & Answers

explain why is it that old peoples as from the age of 60 usually have eye problems?
Kenn Reply
most old people suffere eye problems.because of short sight where individuals with this kind of problems see only near objects clearly but not distance objects, this is cause by elongated eyeball so light from distance is focus infront the retina so the image on the retina is blurred .
Munyah
plasma DNA cytoplasm Ribosome
Pearl Reply
cell, tissue,organ, organ systems,organism
Pearl Reply
cell is the build block of Life
Pearl
also a smallest unit of life
Frankline
sure..
Pearl
consistsof cytoplsm enclosed with in a membrane which contains many biomolecules such as proteins and nucleic acids
Frankline
differences in the effects of infection by HIV and influenza A virus on host genetic variability.
Yo Reply
i dont know
Ubah
hiv is direct contact of blood or body fluid and if not treated can break down the immune system faster and lead to acids with complications of pneumonia skin infections inflammation of the brain etc.while influenza A is a air borne virus which can cause the common cold pain fever and can be cured
Maureen
A.I.D.S
Maureen
suggest bioingormatics research article plz
peermehirali
what makes the heart to pumps blood?
Jamer Reply
sa node
Ubah
i do think its the nerve tranmission to the brain
Frankline
The contracting and relaxing of the atria and vertricles but the electrical system of the heart is what makes this possible.
keynia
yes which is called autorhymicity
Maureen
adrenoline action in brains
Frankline Reply
please describe the human heart brefly
Shah Reply
the size of the heart is like a fist. it has four chambers. the left and right upper atrium which push blood in the lower left and right ventricles which in turns pump blood to the lungs or the rest of the body.
Maureen
how do u prove it
Frankline
Maureen is correct ,
Davis
right
Kenn
right
Ubah
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horyaal
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horyaal
What is housing?
Baldwin Reply
is where located you
Ubah
Hi, my name is Syedul Mostafa from Bangladesh Refugees camp. I would like to study under your.
Mostafa Reply
what is Endocytosis
Alice Reply
Endocytosis is the process where by organism lives inside it host and feed on it
Aboagye
cell
Mostafa
Endocytosis is the process where by substances are taken in to the cell of an organism
Abena
the taking in of matter by a living cell by invagination of its membrane to form a vacuole.
Amber
Exocytosis... is the durable, energy-consuming process by which a cell directs the contents of secretory vesicles out of the cell membrane and into the extracellular space. Endocytosis is an energy-using process by which cells absorb molecules (such as proteins) by engulfing them.
Amber
There are three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis. In phagocytosis or “cellular eating,” the cell's plasma membrane surrounds a macromolecule or even an entire cell from the extracellular environment and buds off to form a food vacuole or phagosome.
Amber
what are hormones
Abena
what the meaning of adenosine triphosphate
Alice Reply
what the full meaning of ADP
Alice
ATP as simply called is substance which provide energy during active transport
Aboagye
what is biology
Alice Reply
biology simply means the study of life
Aboagye
pls HV u get it
Aboagye
what is the cardiovascular disease
Kami Reply
heart disease
Ashley
heart disease
Aboagye
kidney failure
John
heart failure
John
what is the largest cell
Aboagye Reply
tanx wae
Aboagye
what is the name of the largest virus
Aboagye
oohh
Rihan
this is in female body which have ovum which is without fertilization if ovum is fertilize then it is called egg
Abdullahjavaid
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Sanjay
Am new
Sanjay
what is cell division
Kami
in female lagest cell in overy cell
Kami
what is the difference between DNA and RNA?
Jackson Reply

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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