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Structural Organization of the Nervous SystemStructural Organization of the Nervous System

The Nervous System has:• Parts, Regions, Systems.• Its Main Parts are:

– Encephalon, i.e. inside cranial cavity. Suspended in semi compartmentalized fluid (CSF) containing spaces.

– Medulla Spinalis, i.e. the part in the vertebral canal. In contrast to the encephalon, its dura is not adherent to the canal

• Connected to the encephalon are 12 pairs of cranial nerves. And 31 pairs of spinal nerves to the medulla spinalis.

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Structural Organization of the Nervous SystemStructural Organization of the Nervous System

The nerves mediateThe nerves mediate::

Motor, Sensory, and Visceral or Splanchnic Motor, Sensory, and Visceral or Splanchnic nerve fibres (Peripheral Autonomic Nervous nerve fibres (Peripheral Autonomic Nervous System).System).

Peripheral Nervous system is mainlyPeripheral Nervous system is mainly Conductor with very minor integration.Conductor with very minor integration.

From the CNS (containing networks of fibres From the CNS (containing networks of fibres neurons and interneurons):neurons and interneurons):– appropriate patterns of responses to stimuli from appropriate patterns of responses to stimuli from

internal and external environment.internal and external environment.

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Structural Organization of the Nervous SystemStructural Organization of the Nervous System

Learning, Memory, Consciousness.Learning, Memory, Consciousness.

The Spinal cord / upper 2/3 rd. of vertebral canal. The Spinal cord / upper 2/3 rd. of vertebral canal. White matter outside.White matter outside.

Encephalon consists of:Encephalon consists of:– Rhombencephalon (hindbrain) including the Rhombencephalon (hindbrain) including the

MyelencephalonMyelencephalon (medulla), (medulla), MetencephalonMetencephalon (pons), (pons), CerebellumCerebellum..

– Mesencephalon (midbrain)Mesencephalon (midbrain)– Prosencephalon: Prosencephalon:

TelencephalonTelencephalon

Diencephalon.Diencephalon.

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Structural Organization of the Nervous SystemStructural Organization of the Nervous System

The nervous system is divided into:The nervous system is divided into:

1) The central nervous system (CNS) - the brain and spinal 1) The central nervous system (CNS) - the brain and spinal cordcord 2) The peripheral nervous system (PNS) - the 12 pairs of 2) The peripheral nervous system (PNS) - the 12 pairs of cranial nerves and 31 pairs of spinal nervescranial nerves and 31 pairs of spinal nerves Two broad categories of cells make up the nervous Two broad categories of cells make up the nervous system:system: 1) Neurons: Approx. 100 billion located in the CNS, they 1) Neurons: Approx. 100 billion located in the CNS, they communicate with other cells by means of a chemical (or communicate with other cells by means of a chemical (or electrical) synapse.electrical) synapse.

2) Neuroglia 2) Neuroglia - - support/maintain neuronssupport/maintain neurons..

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Neuron StructureNeuron Structure 1) Cell body or Perikaryon, forming nuclei inside 1) Cell body or Perikaryon, forming nuclei inside

the nervous system, and ganglia outside the the nervous system, and ganglia outside the nervous system. nervous system.

2) Dendrites,2) Dendrites, 3) Axon, axon hillock, collateral axons, axon 3) Axon, axon hillock, collateral axons, axon terminals.terminals. IV. Classification of Neurons: IV. Classification of Neurons:

1) Sensory, or afferent1) Sensory, or afferent 2) Motor, efferent 2) Motor, efferent A. Somatic motor neuronsA. Somatic motor neurons B. Autonomic motor neuronsB. Autonomic motor neurons

3) Interneurons Located within the CNS and in 3) Interneurons Located within the CNS and in autonomic gangliaautonomic ganglia

1)

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V. NeurogliaV. Neuroglia

Six primary types of nervous cells support the activity of Six primary types of nervous cells support the activity of neurons: neurons:

1) Schwann’s cells - form a myelin sheath around all axons 1) Schwann’s cells - form a myelin sheath around all axons and some dendrites of the PNS.and some dendrites of the PNS.

2) Oligodendrocytes - form a myelin sheath around some 2) Oligodendrocytes - form a myelin sheath around some of the axons of the CNS.of the axons of the CNS.

Myelin = a lipoprotein.Myelin = a lipoprotein.Forms partial insulating cover around some neuron axons Forms partial insulating cover around some neuron axons = myelin sheath.= myelin sheath.Increases speed of conduction of the action potential.Increases speed of conduction of the action potential.Consistent gaps of the myelin sheath are called Nodes of Consistent gaps of the myelin sheath are called Nodes of Ranvier.Ranvier.

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3) Microglia - phagocytic cells that patrol 3) Microglia - phagocytic cells that patrol the CNS for foreign particles.the CNS for foreign particles.

4) Astrocytes - contribute to the 4) Astrocytes - contribute to the formation of the blood-brain barrier.formation of the blood-brain barrier.

5) Ependymal cells5) Ependymal cells 6) Satellite cells6) Satellite cells