The nervous system is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS). The nervous system allows for communication between different parts of the body through neurons, which are specialized cells that transmit signals via electrical and chemical processes. Neurons have dendrites that receive signals and axons that transmit them, forming circuits throughout the body. Along with neurons, glial cells provide support and insulation to the nervous system. The complex nervous system regulates bodily functions and allows organisms to interact with their environments.

1. PROJECT
The Nervous System
Group 864
Sarine Yirikian
Teacher: M.Ohanyan

2. Aim
To make people understand the function of the nervous system.

3. Introduction
The nervous system is the part of an human's body that coordinates the actions and transmits
signals between different parts of its body . It consists of two parts, the central nervous system
(CNS) and the peripheral nervous system (PNS). The CNS contains the brain and the spinal cord.
The PNS consists mainly of nerves and connects the CNS to other parts of the body.
In addition to the brain and spinal cord, principal organs of the nervous system include the
following:
 eyes
 ears
 sensory organs of taste
 sensory organs of smell
 sensory receptors located in the skin, joints, muscles, and other parts of the body.
At the cellular level, the nervous system is defined by the presence of a special type of cell,
called the neuron, also known as a "nerve cell". Neurons have special structures that allow
them to send signals rapidly and precisely to other cells. They send these signals in the form of
electrochemical waves traveling along thin fibers called axons, which cause chemicals called
neurotransmitters to be released at junctions called synapses. A cell that receives a synaptic
signal from a neuron may be excited, inhibited, or otherwise modulated. The connections
between neurons form neural circuits that generate an organism's perception of the world and
determine its behavior. Along with neurons, the nervous system contains other specialized cells
called glial cells (or simply glia), which provide structural and metabolic support.

4. Nervous systems are found in most multicellular animals, but vary greatly in complexity. The
only multicellular animals that have no nervous system at all are sponges, placozoans and
mesozoans, which have very simple body plans. In Radiata (radially symmetric animals such as
jellyfish) the nervous system consists of a diffuse nerve net. All other types of animals, with the
exception of a few types of primitive worms, have a nervous system containing a brain, a
central cord (or two cords running in parallel), and nerves radiating from the brain and central
cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to
on the order of 100 billion cells in humans.
Structure
The nervous system derives its name from nerves, which are cylindrical bundles of fibers that
emanate from the brain and central cord, and branch repeatedly to innervate every part of the
body. Nerves are large enough to have been recognized by the ancient Egyptians, Greeks, and
Romans , but their internal structure was not understood until it became possible to examine
them using a microscope. A microscopic examination shows that nerves consist primarily of the
axons of neurons, along with a variety of membranes that wrap around them and segregate
them into fascicles. The neurons that give rise to nerves do not lie entirely within the nerves
themselves—their cell bodies reside within the brain, central cord, or peripheral ganglia.
Structure of a typical neuron
 Dendrite
 Soma
 Axon
 Nucleus
 Node of
Ranvier
 Axon terminal
 Schwann cell

5.  Myelin sheath
The nervous system contains two main categories or types of cells:
 neurons
 glial cells.
Neurons
The nervous system is defined by the presence of a special type of cell—the neuron. Neurons
transmit nerve messages. Neurons can be distinguished from other cells in a number of
ways, but their most fundamental property is that they communicate with other cells via
synapses, which are membrane-to-membrane junctions containing molecular machinery that
allows rapid transmission of signals, either electrical or chemical. Many types of neurons
possess an axon, a protoplasmic protrusion that can extend to distant parts of the body and
make thousands of synaptic contacts. Axons frequently travel through the body in bundles
called nerves.
Even in the nervous system of a single species such as humans, hundreds of different types of
neurons exist, with a wide variety of morphologies and functions. These include sensory
neurons that transmute physical stimuli such as light and sound into neural signals, and motor
neurons that transmute neural signals into activation of muscles or glands; however in

6. manyspecies the great majority of neurons receive all of their input from other neurons and
send their output to other neurons.
What is inside of a neuron? A neuron has many of the same organelles such as mitochondria,
cytoplasm and a nucleus, as other cells in the body.
 Nucleus - contains genetic material (chromosomes) including information for cell development and
synthesis of proteins necessary for cell maintenance and survival. Covered by a membrane.
 Nucleolus - produces ribosomes necessary for translation of genetic information into proteins
 Nissl Bodies - groups of ribosomes used for protein synthesis.
 Endoplasmic reticulum (ER) - system of tubes for transport of materials within cytoplasm. Can have
ribosomes (rough ER) or no ribosomes (smooth ER). With ribosomes, the ER is important for protein
synthesis.
 Golgi Apparatus - membrane-bound structure important in packaging peptides and proteins (including
neurotransmitters) into vesicles.

7.  Microfilaments/Neurotubules - system of transport for materials within a neuron and may be used for
structural support.
 Mitochondria - produce energy to fuel cellular activities.
There are several differences between axons and dendrites:
Axons Dendrites
 Take information away from the cell body
 Smooth Surface
 Generally only 1 axon per cell
 No ribosomes
 Can have myelin
 Branch further from the cell body
 Bring information to the cell body
 Rough Surface (dendritic spines)
 Usually many dendrites per cell
 Have ribosomes
 No myelin insulation
 Branch near the cell body
Types of Neurons

8. Neurons come in many different shapes and sizes. Some of the smallest neurons have cell
bodies that are only 4 microns wide. Some of the biggest neurons have cell bodies that are 100
microns wide. (Remember that 1 micron is equal to one thousandth of a millimeter!).
Neurons are similar to other cells in the body because:
 Neurons are surrounded by a cell membrane.
 Neurons have a nucleus that contains genes.
 Neurons contain cytoplasm, mitochondria and other organelles.
 Neurons carry out basic cellular processes such as protein synthesis and energy
production.
However, neurons differ from other cells in the body because:
 Neurons have specialized extensions called dendrites and axons. Dendrites bring
information to the cell body and axons take information away from the cell body.
 Neurons communicate with each other through an electrochemical process.
 Neurons contain some specialized structures and chemicals

9. One way to classify neurons is by the number of extensions that extend from the neuron's cell
body (soma).
Bipolar neurons have two processes extending from the cell body (examples: retinal cells,
olfactory epithelium cells).
Pseudounipolar cells (example: dorsal root ganglion cells). Actually, these cells have 2 axons
rather than an axon and dendrite. One axon extends centrally toward the spinal cord, the other
axon extends toward the skin or muscle.
Multipolar neurons have many processes that extend from the cell body. However, each neuron
has only one axon (examples: spinal motor neurons, pyramidal neurons, Purkinje cells).

10. Neurons can also be classified by the direction that they send information.
 Sensory (or afferent) neurons: send information from sensory receptors (e.g., in skin,
eyes, nose, tongue, ears) TOWARD the central nervous system.
 Motor (or efferent) neurons: send information AWAY from the central nervous system
to muscles or glands.
 Interneurons: send information between sensory neurons and motor neurons. Most
interneurons are located in the central nervous system.
Neurons are the oldest and longest cells in the body! You have many of the
same neurons for your whole life. Although other cells die and are replaced,
many neurons are never replaced when they die. In fact, you have fewer
neurons when you are old compared to when you are young. On the other
hand, data published in November 1998 show that in one area of the brain
(the hippocampus), new neurons CAN grow in adult humans.
Happy 114th Birthday to the Golgi apparatus! In 1898, the famous
neuroanatomist Camillo Golgi reported his discovery of a ribbon-like
apparatus inside neurons of the cerebellum. This structure now bears his name
as the "Golgi apparatus."
Did You Know???

11. Glial Cells
Glial cells (named from the Greek for "glue") are non-neuronal cells that provide support and
nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the
nervous system. In the human brain, it is estimated that the total number of glia roughly equals
the number of neurons, although the proportions vary in different brain areas. Among the most
important functions of glial cells are to support neurons and hold them in place; to supply
nutrients to neurons; to insulate neurons electrically; to destroy pathogens and remove dead
neurons; and to provide guidance cues directing the axons of neurons to their targets. A very
important type of glial cell generates layers of a fatty substance called myelin that wraps around
axons and provides electrical insulation which allows them to transmit action potentials much
more rapidly and efficiently.
The brain is made up of more than just nerve cells (neurons). Although there are about 100
billion neurons in the brain, there may be about 10 to 50 times that many glial cells in the brain.
But do you hear much about glia? NO! Because neurons get all the attention, you don't hear
too much about glia. Although glia cells DO NOT carry nerve impulses they do have many
important functions. In fact, without glia, the neurons would not work properly!

12. There are a few ways in which glia cells are different from neurons:
1. Glia provide structural support for the neurons in the nervous system
2. Glia have roles during embryonic development... they typically provide paths for
neurons to grow along, enabling neurons to make the appropriate connections.
3. Glia helps to clean up the extracellular fluid of other materials, like excessive
neurotransmitter that might otherwise float around and mistakenly signal neurons
into activity.
Conclusion
The nervous system is a complex, sophisticated system that regulates and coordinates body
activities and provides body’s communication with the environment. We perceive, act and leave
by the function of CNS, so it is important to have healthy CNS, due to this statement, we should
not smoke, we should have healthy life style, we should not eat too much, we should have
physical activities each day…
References:
http://en.wikipedia.org/wiki/Nervous_system
http://faculty.washington.edu/chudler/cells.html
http://faculty.washington.edu/chudler/glia.html
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobooknerv.html
http://kidshealth.org/parent/general/body_basics/brain_nervous_system.html#