dr kifayat khan kmu peshawer pakistan

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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

18. •Clinical correlates
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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)