Nervous system - biology

1. Cells of the Nervous
System

2. Cells of the Nervous System
•Neurons,
•Supporting cells,
• The blood-brain barrier

3. Cells of the Nervous System
• The nervous system consists of two kinds of
cells:
Neurons
Glia.

4. Neurons receive information and transmit it to
other cells.
Glia serve many functions that are difficult to
summarize. But Glia do not convey
Information over great distances, but they aid
the functioning of neurons in many ways.

5. According to one estimate, the adult human brain contains
approximately 100 billion neurons (R. W. Williams & Herrup,
1988) Cerebral cortex
and associated
areas:12 to 15
billion neurons
Cerebellum:
70 billion
neurons
Spinal cord:
1 billion neurons
Figure: Estimated numbers of neurons in humans Because of the small size of many
neurons and the variation in cell density from one spot to another, obtaining an accurate count
is diffi cult. (Source: R. W. Williams & Herrup, 1988)

6. In the late 1800s, Santiago Ramón y Cajal used
newlydiscovered staining techniques to establish
that the nervous system is composed of
separate cells, now known as neurons.

7. Basics Structure of Neuron
• Neuron cosists of the following things:
• 1. Cell body or soma
• 2. Detrites
• 3. Axon
• 4. Terminal Button

8. • It contains the nucleus and much of the
machinery that rovides for the life processes
of cell
• Its shape varies considerably different kinds of
Neuron

9. 2. Dentrites
• Greek for tree, the dendrites of the neuron
look very much life trees
• Between neuron conversion so it serves as
important receipients of these messages.
• The message that pass from euron to neuron
are transmtted across the synapse.
• Synapse:
A junction between the terminal button of
an axon and the membrane of another neuron

10. Continued……..
• Synapses-Greek word “ sunaptein”(to join
together

11. NEURON
CLASSES OF NEURON
Neurons are classified into four classes
1. Unipolar neuron
2. Bipolar Neuron
3. Multipolar Neuron
4. Multipolar Interneuron

12. Axon
• It is a long, slender tupe covered by a myelin
sheath
• It carries information form the cell body to the
terminal buttons.
• Action potential
The process of carrying basic messages by
axon is called Action Potential.

13. Types of Neuron
• The neuron is the most common type of found
in the CNS are following:
1. Unipolar Neuron
2. Bipolar Neuron
3. Multipolar

14. 1. Unipolar Neuron: A neuron with one axon
and attached to its soma, the axon divides
with one branch receiving sensory
information and othe other sending the
information to the central nervous system.
2. Bipolar Neuron: A neuron with one axon and
one dentrites attached to its soma

15. 3. Multipolar Neuron: A neuron with one axon
and many detrites attached to its soma.

18. Structure of Neuron
Neurons have four major parts:
Their shapes vary greatly depending on their
functions and their connections with other cells.
•a cell body
•Dendrites
•an axon
•and presynaptic terminals.

19. External Anatomy of Neurons
The major external features of a typical neuron
has following parts:
• Cell Membrane : The semipermeable
membrane that encloses the
neuron
• Dentrites : The short processes emanating
from the cell body which receive
most of the sya

20. External Anatomy of Neurons
Axon Hillock :
The cone-shaped region at the junction between the
axon and the cell body.
Axon
The long , narrow process that projects from the
cell body.
Myellin:
The fatty insulation around many axons.

21. External Anatomy of Neurons
Nodes of Ranvier:
The gaps between sections of myelin.
Buttons:
The buttonlike endings of the axon
branches, which release chemicals into
synapses.
Synapses:
The gaps between adjacent neurons across
which chemical signals are transmitted.

22. Internal Anatomy of Neurons
• The major features of a typical neuron is
following:
• Endoplasmic Reticulum
• Cytoplasm
• Ribosomes
• Golgi Complex
• Nucleus
• Microtubules
• Synaptic vesicles
• Neuron transmitters

23. Internal Anatomy of Neurons
• Endoplasmic reticulum :
– A system of folded membranes in the cell body;
rough portions (those with ribosome) play a role
in the synthesis of proteins; smooth protiens
(those without ribosome) play a role in the
synthesis of fats.

24. Internal Anatomy of Neurons
Cytoplasm:
The clear internal fluid of the cell.
Ribosomes:
Internal cellular structures on which proteins are
synthesized; they are located on the endoplasmic
reticulum.
Golgi Complex:
A system of membranes that packages molecules
in vesicles.

25. Internal Anatomy of Neurons
Nucleus:
The spherical DNA containing structure of the cell
body.
Mitochondria:
Sites of aerobic (oxygen-consuming) energy
release.
Microbules:
Tubules responsible for the rapid transport of
material throughout neurons.

26. Internal Anatomy of Neurons
Synaptic vesicles:
Spherical membrane packages that store
neurotransmitter molecules ready for release
near synapses.
Neruontransmitters:
Molecules that are released from active
neurons and influence the activity of other
cell.

27. Variations Among Neurons
• Neurons vary enormously in size, shape, and
function.
• The shape of a given neuron determines its
connections with other neurons and thereby
determines its contribution to the nervous
system.
• Neurons with wider branching connect with
more neurons.

28. Variations Among Neurons
• The function of a neuron relates to its shape.
For example, the widely branching dendrites
of the Purkinje cell of the cerebellum enable it
to receive input from a huge number of axons.
• By contrast, certain cells in the retina have
only short branches on their dendrites and
therefore pool input from only a few sources.

29. Glia
Glia (or neuroglia) the other major components
of the nervous system, do not transmit
information over long distances as neurons
do, although they do exchange chemicals with
adjacent neuron
In some cases, that exchange causes neurons to
oscillate in their activity

30. Glia
The term glia, derived from a Greek word
meaning “glue,” reflects early investigators’
idea that glia were like glue that held the
neurons together (Somjen, 1988).
• Although that concept is obsolete, the term
remains.
• Glia are smaller but also more numerous than
neurons.
• Overall, they occupy about the same volume

31. Astrocytes
• A glial cells that provides support for neurons
of the central nervous system provides,
nutrients and other substances and regulates
the chemical composition of extracellular fluid
• Some of the astrocyte’s process (the arms of
the star) are wrapped around blood vessels.
• Other process are wraped around parts of
neurons

32. 1. Astrocytes
• These particular astrocytes appear to play a
role in allowing the passage of some
chemicals from the blood into CNS neurons
and in blocking other chemicals (see Paixão &
Klein, 2010), and they have the ability to
contract or relax blood vessels based on the
blood flow demands of particular brain
regions (see Howarth, 2014; Muoio, Persson,
& Sendeski, 2014

33. 2. Oligodendrocytes
• A type of Glial cells in the central nervous
system that forms myelin sheaths
• Support axon
• Some axon not mylinated
• Formation of Myelin: 80% lipids+20%Proteins
that are produced by oligodenocytes to
produce surrounding the axon

34. • Myeling speed up the transmission of
electrical signals in the neuron

35. 3. Microglia
• Microglia make up a third class of glia.
• Microglia are smaller than other glial cells—
thus their name.
• They act as pagocyles and protect the brain
from invading microorganisms.

37. Schwann cells
• A similar function is performed in the
peripheral nervous system by Schwann cells, a
second class of glia.
• Notice that each Schwann cell constitutes one
myelin segment, whereas each
oligodendrocyte provides several myelin
segments, often on more than one axon.

38. • Another important difference between
Schwann cells and oligodendrocytes is that
only Schwann cells can guide axonal
regeneration ( regrowth) after damage. That is
why effective axonal regeneration in the
mammalian nervous system is restricted to
the PNS

39. Blood Brain Barrier
• Blood–brain barrier a semipermeable barrier
formed by cells lining the blood capillaries
that supply the brain and other parts of the
central nervous system.

40. • Entry is also possible for lipid-soluble (Fat
soluble) compounds, such as anesthetics,
which diffuse through plasma membranes.

41. Blood Brain Barrier
• It prevents large molecules, including many
drugs, from passing from the blood to the
fluid surrounding brain cells and to the
cerebrospinal fluid, and thus it protects the
brain from potentially harmful substances.
• Ions and small molecules, such as water,
oxygen, carbon dioxide, and alcohol, can
cross relatively freely.

42. Blood Brain Barrier

43. What is the function of the Blood Brain
Barrier
• Transmission of the message from place to
place in the brain depends on a delicate
balance between substances within neurons
and in the extracellular fluid that surrounds
them.
• If the composition of the extracellular is
changed even slightly the transmision of these
messages will be desrupted, which means that
brain functions will be desrupted

44. • The presence of the blood brain barrier makes
it easier to regulate the composition of this
fluid.
2 Many of the foods contains many chemicals
that would infere with the transmission of
information bettween neurons. The BBB
prevents these chemicals from reachig the
brain.

45. • It is not uniform throughout the NS
• In several places the barrier is relatively permeable.
Allowing substances that are excluded elsewhere to
cross freely.
• Area Postrema:
– Part of the brain that controls vomiting
– A blood brain barrier much weakere there, permitting
neruons in this region to detect the rpesence of toxic
substancees in the blood. A Poison that enters the
circulatory system from the stomach can thus stimulate
this are to initiate vomiting. If the organism is lucky, the
poison can be expelled from the stomach before it causes
too much damage.