THE CENTRAL NERVOUS SYSTEM(CNS)

Dr.Mohammed Sharique Ahmed QuadriAssistant prof. Physiology

Al Maarefa College

بسم الله الرحمن الرحيم

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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 net-

work 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. Astrocytes 2. Oligodendrocytes3. Microglia4. Ependymal Cells

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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.

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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