THE CENTRAL NERVOUS
SYSTEM(CNS)
Dr.Mohammed Sharique Ahmed Quadri
Assistant prof. Physiology
Al Maarefa College
ORGANIZATION OF NERVOUS SYSTEM
• The Nervous system is organized into
1. Central Nervous System (CNS)
 BRAIN
 SPINAL CORD
2. Peripheral Nervous System
 Nerve fibers that carry information between CNS
and other parts of body at periphery.
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Organization of nervous system
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CNS
• Central nervous system regulates body
activities.
• CENTRAL NERVOUS SYSTEM
– BRAIN
– SPINAL CORD
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PERIPHERAL NERVOUS SYSTEM (PNS)
• Peripheral Nervous System is sub divided
into
– Afferent Division (Sensory) – which carry
information to CNS
– Efferent Division (Motor) – which carry
information from CNS to muscle and glands.
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PNS [cont]
• Efferent (Motor) division of PNS is further
divide into
 Somatic Nervous System– it is under our
voluntary control E.g. fibers of motor neuron that
supply skeletal muscle.
 Autonomic Nervous System – it is not under
our control ( involuntary).
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PNS [cont]
Autonomic Nervous System (ANS)
• ANS– supplies cardiac muscle, smooth muscle, glands.
ANS is divided into
 Sympathetic ANS
 Parasympathetic ANS
• Enteric ANS– in the wall of digestive tract
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FUNCTIONAL CLASSES
OF NEURONS
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FUNCTIONAL CLASSES OF NEURONS
• There are THREE functional types of Neurons
I. Afferent Neurons– which carry information
to CNS.
II. Efferent Neurons– which carry information
away from CNS (to the periphery).
III. Interneurons– They form interactive network between neuron.
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FUNCTIONAL CLASSES OF NEURON
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AFFERENT NEURON
• Afferent Neuron has sensory RECEPTOR , that
generates action potential in response to a
particular stimulus.
• Sensory impulse are taken by axon toward the
spinal cord.
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EFFERENT NEURON
• Efferent Neuron lies in the peripheral nervous
system. It has cell body in the CNS .
• Efferent axon leaves the cell body and goes to
innervate muscle.
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INTERNEURONS
• Interneurons lie in the CNS. About 99% of all
neurons are Interneurons.
• Human CNS has more than 100 billion
Interneurons.
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GLIAL CELLS OR NEUROGLIA
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GLIAL CELLS or NEUROGLIA
• Glial cells are connective tissue of CNS.
• Glial cells support the interneurons physically,
metabolically, and functionally.
• They do not conduct nerve impulses.
• Glial cells are of FOUR types.
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GLIAL CELLS or NEUROGLIA (cont)
• There are 4 type of Glial Cells
1.
2.
3.
4.
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Astrocytes
Oligodendrocytes
Microglia
Ependymal Cells
GLIAL CELLS
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Important Functions Of Glial Cells
1. Astrocytes
 Functions
 Formation of blood – brain – barrier
 Formation of neural scar tissue
 Helps maintain optimal ion conditions for neural
excitability
2. Oligodendrocytes
 Functions
 Forms myline sheath around axons in the CNS.
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Important Functions Of Glial Cells
3. Microglia
 Functions
 Phagocytosis [ defense cells of CNS]
 Release nerve growth factor.
4. Ependymal Cells
 Functions
 Formation of Cerebrospinal fluid [CSF].
 Work as Neural Stem Cell – to form new neurons
and glial cells.
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Protection Of The Brain
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Protection Of Brain
 As CNS is very delicate, it is protected by – skull
bone [covers the brain] and Vertebral column
[surrounds the spinal cord].
 Meninges – cover brain and spinal cord.
Meninges lie between bony covering [outside]
and nervous tissue [inside]. Meninges are
Durameter, Arachnoid and Piameter.
 CSF - Cerebro Spinal Fluid is present in
subarachnoid space. CSF works as cushion.
 Blood - brain barrier(BBB) – it selectively allows
the materials to pass to brain.
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MENINGES & CSF
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Cerebro Spinal Fluid [CSF]
• It surrounds brain and spinal cord.
• It is present in subarachnoid space.
• It is formed by choroid plexuses [capillaries in
the piameter] of ventricles in the brain.
• Volume of CSF is about 125 – 150 ml.
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CSF [cont]
 Clinical Note
• Hydrocephalus [water in the brain].
• Occurs if CSF accumulates more, due to the block
in its circulation or reabsorption.
• If hydrocephalus is untreated, increased CSF
pressure can lead to brain damage and mental
retardation.
• Treatment – surgically shunting the excess CSF to
veins elsewhere in the body.
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‘Important Information’
• Brain function depends on
– Oxygen
– Glucose
• Brain needs continuous supply of O2 and
Glucose.
• Brain damage results if
- brain gets no O2 supply for 4 to 5mins
or
- no glucose supply for 10 to 15mins.
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References
• Human physiology by Lauralee Sherwood,
seventh edition
• Text book physiology by Guyton &Hall,11th
edition
• Text book of physiology by Linda .s
contanzo,third edition
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