NORMAL CELLS OF CNS NORMAL CELLS OF CNS OBJECTIVES: OBJECTIVES: At the end of this lecture, you At the end of this lecture, you should describe the microscopic should describe the microscopic structure and the function of: structure and the function of: 1- 1- Neurons Neurons : : - Cell body (perikaryon). - Cell body (perikaryon). - Processes: An axon and - Processes: An axon and dendrites. dendrites. 2- 2- Neuroglia Neuroglia : : - Astrocytes. - Astrocytes. - Oligodendrocytes. - Oligodendrocytes. - Microglia. - Microglia.
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NORMAL CELLS OF CNSNORMAL CELLS OF CNS
OBJECTIVES:OBJECTIVES:
At the end of this lecture, you should describe the At the end of this lecture, you should describe the microscopic structure and the function of:microscopic structure and the function of:
1- 1- NeuronsNeurons:: - Cell body (perikaryon).- Cell body (perikaryon).
- Processes: An axon and dendrites.- Processes: An axon and dendrites.
TYPES OF NEURONSTYPES OF NEURONS Based on number of processes Based on number of processes
Has one process only, that divides into two branches; one acts as a dendrite and the other as an axon.e.g. Mesencephalic nucleus of trigeminal nerve and dorsal root (spinal) ganglion.
TYPES OF NEURONSTYPES OF NEURONS Based on number of processes Based on number of processes
Has two processes (one arising from each pole of the cell body). One of them is the dendrite and the other is the axon, e.g. retina & olfactory epithelium.
2. Bipolar Neuron (spindle-shaped neuron):
Dendrite
TYPES OF NEURONSTYPES OF NEURONS Based on number of processes Based on number of processes
3. Multipolar neuron:Has one axon and multiple dendrites.
Types of multipolar neurons:
A.Stellate neuron:• The commonest type.• Distributed in most areas of CNS, e.g.
anterior horn cells of the spinal cord
TYPES OF NEURONSTYPES OF NEURONS Based on number of processes Based on number of processes
B. Pyramidal neurons:• Distributed in motor area 4 of the
cerebral cortex.C. Pyriform neurons:
• Pear-shaped, e.g. Purkinje cells of cerebellar cortex
CELL BODY (Perikaryon)CELL BODY (Perikaryon)
Structure of cell body:
1. Nucleus:• Single, usually central,
rounded and vesicular with prominent nucleolus.
2. Cytoplasm.
CELL BODY (Perikaryon)CELL BODY (Perikaryon)
Cytoplasm:Cytoplasm:
Its main components Its main components include:include:
1. Nissl bodies:1. Nissl bodies:
Are basophilic patches of rER Are basophilic patches of rER and free ribosomes in the cell and free ribosomes in the cell body and bases of wide body and bases of wide dendrites.dendrites.
CELL BODY (Perikaryon)CELL BODY (Perikaryon)
Cytoplasm:Cytoplasm:
2.2. Neurofilaments:Neurofilaments:Are intermediate filaments which are
bundled together to form neurofibrils. Are found in the cell body, axon and dendrites.3.3. Microtubles:Microtubles:
Are found in the cell body, axon and dendrites.4.4. Golgi apparatus:Golgi apparatus:
Surrounds the nucleus all around.5.5. Mitochondria: Mitochondria:
Are numerous.
CELL BODY (Perikaryon)CELL BODY (Perikaryon)
Cytoplasm:Cytoplasm:
6. Centriole: 6. Centriole: Most adult neurons have Most adult neurons have only one rudimentary centriole, so only one rudimentary centriole, so they cannot divide.they cannot divide.
7. Some fat and glycogen granules.7. Some fat and glycogen granules.
8. Pigments:8. Pigments:
-- Lipofuscin pigments (in old age).Lipofuscin pigments (in old age).
-- Melanin pigments (in neurons of Melanin pigments (in neurons of substantia nigra of the midbrain).substantia nigra of the midbrain).
TYPES OF NERVE FIBERS IN CNSTYPES OF NERVE FIBERS IN CNS
1-1- Unmyelinated without neurilemmal sheath Unmyelinated without neurilemmal sheath (in grey matter).(in grey matter).
2-2- Myelinated without neurilemmal sheathMyelinated without neurilemmal sheath(in white mater).(in white mater).
NEUROGLIANEUROGLIA
Definition:Definition:
Are group of cells that act as the Are group of cells that act as the supportive tissue of CNS.supportive tissue of CNS.
Types:Types:
1-1-Astrocytes.Astrocytes.
2-2-Oligodendrocytes.Oligodendrocytes.
3-3-Microglia.Microglia.
4-4-Ependyma.Ependyma.
1. Astrocytes1. Astrocytes
They are the commonest type They are the commonest type of neuroglia cells.of neuroglia cells.
They are found in both the grey They are found in both the grey and white matter.and white matter.
They are star-shaped cells with They are star-shaped cells with numerous long processes.numerous long processes.
– Are found in the grey matter of Are found in the grey matter of CNS.CNS.
– Their processes branch Their processes branch extensively.extensively.
2.2. Fibrous astrocytes:Fibrous astrocytes:– Are found in white matter of CNS.Are found in white matter of CNS.– Their processes have fewer Their processes have fewer
branches but longer.branches but longer.
Functions of AstrocytesFunctions of Astrocytes
1.1. Repair of injury of Repair of injury of CNS tissue (gliosis).CNS tissue (gliosis).
2.2. Supportive and Supportive and nutritive functions to nutritive functions to the neurons.the neurons.
3.3. Participate in the Participate in the formation of blood-formation of blood-brain barrier.brain barrier.
2. Oligodendrocytes2. Oligodendrocytes
Are branching cells with few, short Are branching cells with few, short processes.processes.
They are distributed in the grey They are distributed in the grey and white matter of CNS.and white matter of CNS.
Functions:Functions:
1.1. Formation of myelin sheath in the Formation of myelin sheath in the CNS.CNS.
2.2. Insulation of nerve fibers.Insulation of nerve fibers.
3. Microglia3. Microglia
Are spindle-shaped cells with Are spindle-shaped cells with branching processes raise from branching processes raise from each pole of the cell.each pole of the cell.
Are distributed in the grey and Are distributed in the grey and white matter of CNS.white matter of CNS.
Are rich in lysosomes.Are rich in lysosomes. Their main function is Their main function is
phagocytosis.phagocytosis.
4. Ependymal cells4. Ependymal cells
Are simple columnar Are simple columnar epithelial cells (partially epithelial cells (partially ciliated) lining the brain ciliated) lining the brain ventricles and the central ventricles and the central canal of spinal cord.canal of spinal cord.
Summary / Key wordsSummary / Key words Neurons:Neurons:
