There are two main cell types in nervous tissue: neurons and neuroglia. Neurons are excitable cells that transmit electrical signals down axons and dendrites. They have a cell body containing organelles and long processes. Neuroglia, also called glial cells, support and protect neurons. The four main types of neuroglia in the central nervous system are astrocytes, microglia, ependymal cells, and oligodendrocytes. Astrocytes connect neurons to blood vessels and regulate the neuronal environment. Microglia monitor neuronal health and act as phagocytes. Ependymal cells line cavities and circulate cerebrospinal fluid. Oligodendrocytes wrap myelin

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2. Cell types
 Despite the complexity of organization, there
are only two functional cell types
 A) neurons - excitable nerve cells that transmit
electrical signals
 B) neuroglia (glial) cells - support cells

3. A) Neurons
 responsible for conduction, propagation, and
reception of nervous impulses. Processes called
axons or dendrites extend from these cells.
 extreme longevity – neurons live and function
normally for a lifetime
 amitotic
 once mature, neurons lose the ability to divide
 damaged nervous tissue cannot regenerate
 high metabolic rate
 need a large, constant supply of oxygen and glucose
 can survive only a few minutes without oxygen

4. Neuron Structure
 Consists of
 a) cell body
 b) dendrites
 c) axon

5. Neuron Structure
a)Cell body
 Contains the usual cellular organelles
 Receptive: membrane receptors initiate and
transmit graded potentials (not action potentials)
in response to incoming stimuli
 nerve cell body contains
1)nucleus
 large, central in most, large amount of euchromatin
(intense synthetic activity), and nucleolus..

6. Neuron cell body
2) Rough endoplasmic reticulum (RER)
 lots of RER for synthesis of structural and transport
proteins, Nissl bodies/substance are condensations
of this RER and free ribosomes
3) Golgi apparatus
 found near nucleus.
 Expected, since intense synthetic activity of
neurotransmitters and/or neuro hormones that must
be packaged in vesicles.
4) Mitochondria
 abundant for high energy requirements

7. a) Cell body
5) Neurofilaments
• intermediate filaments
6) Microtubules
 important in transport
of materials.

8. Neurons cell body

9. b) dendrites
b) Dendrites
• cell process extending away from the perikaryon
 conduct impulses toward the cell body
 forms receptive area for synaptic contacts from
other neurons
 has tiny rough projectons or spines called gemmules
or dendritic spines that are points of synaptic
contact
• Cytoplasm in these processes similar to that of
perikaryon, but no golgi bodies or nucleus.

10. b) dendrites

11. c) Axons
c) Axons
 one long thin cell process extending away from
perikaryon
 conduct impulses away from the cell body
• ends of branches form synapses with other
neurons or muscle cells
• may be unmylenated or may be myelinated by
either oligodendroglia in CNS or Schwann cells in
PNS

12. b)Axon structre
1) axon hillock
• pyramid shaped region associated with
perikaryon) - where axon begins
• cytoplasm in this region lacks ribosomes and
organelles; however, neurofilaments and
microtubles are present.
2) initial segment
 unmyelinated intitial portion of axon) between
axon hillock and beginning of myelination
3)remainder of axon
 (may be myelinated, may be branched

13. 4) axonal terminals
 Axonal terminals contain small sacs with
neurotransmitters (chemicals)
 Axonal terminals are separated from the next
neuron by a gap (they never really touch)
 Synaptic cleft — gap (space) between adjacent
neurons
 Synapse — junction between nerves

14. Structure of neuron

15.  Myelin sheath — whitish, fatty material
covering axons
 protects/insulates the cells and increases the
transmission rate of nerve impulses
 Schwann cells — produce myelin
 Nodes of Ranvier — gaps in myelin sheath
along the axon

16. Neurons classification
 Structural:
 Multipolar - three or more processes
 Bipolar - two processes (axon and dendrite)
 Unipolar - single process diverges into 2 conductive
regions
 Functional:
 Sensory (afferent) — transmit impulses toward the CNS
 Motor (efferent) — carry impulses away from the CNS
 Interneurons (association neurons) — shuttle signals
through CNS pathways

17. Neuron types

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20. B) Neuroglia(supporting cells)
 Support cells in the Central Nervous System
(CNS) are grouped together as neuroglia
 Neuroglia literally means “nerve glue” cells
associated with neurons. No axons or
dendrites.
 The function of neuroglia is to support,
insulate, and protect the delicate neurons of
the brain.

21. B) Supporting cells
Supporting cells re of the following types
 Astrocytes
 Microglial cells
 Ependymal cells
 Oligodentrocytes
 Schwann cells
 Satellite cells

22.  4 types in the C NS
astrocytes
 star shaped with many
processes
 connect to neurons;
help anchor them to
nearby blood capillaries
 control the chemical
environment of the neurons

23. microglia
 oval with thorny projections
 monitor the health of neurons
 if infection occurs, they
change into macrophages
(eating viruses, bacteria and
damaged cells ie act as
phagocytes (WBC)

24. B)Neuroglia
3) ependymal cells
• shape is squamous
to columnar ciliated
 Lines the cavities of
the brain and spinal cord
 Circulate cerebrospinal
fluid by beating their cilia
 Cerebrospinal fluid fills
the space the brain does not
take up and forms a protective
cushion around the brain
and spinal chord

25. oligodendrocytes
• have few processes
• line up along neurons
and wrap themselves
around axons
• form the myelin
sheath – an insulating
Membrane
• Myelin is a fatty,
insulation covering
the nerve cells;
allows for the electrical
signal to transmit
faster (like wire coating)