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NERVOUS SYSTEM Lecture 1

NERVOUS SYSTEM Lecture 1. OVERVIEW and NEUROHISTOLOGY. ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM. Central Nervous System (CNS). Definition: Unpaired, bilaterally symmetrical structures extending along the longitudinal axis of the midsagittal plane of the body.

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NERVOUS SYSTEM Lecture 1

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  1. NERVOUS SYSTEMLecture 1 OVERVIEW and NEUROHISTOLOGY

  2. ANATOMICAL ORGANIZATION of the NERVOUS SYSTEM

  3. Central Nervous System (CNS) • Definition: Unpaired, bilaterally symmetrical structures extending along the longitudinal axis of the midsagittal plane of the body. Structures arising directly from the neural tube. • Includes: Brain Spinal cord

  4. Peripheral Nervous System (PNS) • Definition: Made up of transmission pathways carrying information between the CNS and external/internal environments. • Afferent (sensory) pathways: Carry information to the CNS. • Efferent (motor) pathways: Carry information from the CNS.

  5. Peripheral Nervous System (PNS) • Includes: Cranial nerves (12 pairs). Spinal nerves (31 pairs).

  6. Autonomic Nervous System (ANS) • May be considered a subdivision of the PNS. • Entirely motor. • Innervates smooth muscle and glands (viscera).

  7. ANS Subdivisions • Sympathetic system (fight or flight): Also called thoracolumbar. • Parasympathetic system (feed or breed): Also called craniosacral.

  8. Parts of a Neuron • Cell body: Trophic unit Perikaryon • Dendrites: Receptive unit • Axon: Conductive unit

  9. Cell Body Definition • That part of a neuron that encloses the nucleus and other organelles necessary to maintain and repair the neuron.

  10. Cell Body Organelles • Nucleus • Golgi apparatus • RER Ribosomes (=Nissl substance)

  11. Dendrites (Characteristics) • Branches off the cell body that carry information to the cell body. • Usually several to many. • Relatively short. • Often branched. • Have receptors for neurotransmitters. • Conduct local potentials.

  12. Axon Characteristics • Carries information to another neuron or muscle cell. • Often relatively long. • Single (one per neuron). • Conducts action potential

  13. Axon Characteristics • Ends in short branched processes called telodendria. • May have collateral branches. • Cell membrane (= axolemma). • Cytoplasm = (axoplasm).

  14. Axon Characteristics • Covered by neurolemma: Made up of Schwann cells. • Often myelinated: Myelin is formed by Schwann cells. • Note: axon is the only part of a neuron that is ever myelinated.

  15. Axon Organelles • Mitochondria • Neurofilaments • Neurotubules

  16. Axonal Transport • Anterograde: Transports vesicles from cell body to end of axon. Kinesin • Retrograde: Transports vesicles from end of axon toward cell body. Cytoplasmic dynein

  17. Axonal Transport • Slow transport: 1-5 mm/day • Fast transport: 200-400 mm/day

  18. General Terminology • Nerve: Bundle of fibers in the PNS. • Tract: Bundle of fibers in the CNS. • Commissure: Tract in the CNS that crosses from one side to the other.

  19. General Terminology • Nucleus: Aggregation of dendrites and nerve cell bodies in the CNS. • Ganglion: Aggregation of dendrites and nerve cell bodies in the PNS.

  20. General Terminology • White matter: Areas of myelinated axons. • Gray matter: Areas of unmyelinated axons, cell bodies, and dendrites.

  21. Synapse • Definition: • Composite structure that allows two neurons or a neuron and a muscle cell to “talk” to each other.

  22. Synapse Components • Presynaptic membrane: With synaptic vesicles filled with neurotransmitters. • Synaptic cleft: • Postsynaptic membrane: With receptors for neurotransmitters. • Monosynaptic pathways. • Polysynaptic pathways.

  23. Reflex Arc • Afferent (sensory) pathways: Somatic. Visceral (splanchnic). • Efferent (motor) pathways: Somatic. Visceral (splanchnic). • Association neurons (interneurons).

  24. Neuroglial Cells • Schwann cells • Astrocytes • Microglial cells • Oligodendrocytes • Ependymal cells

  25. Schwann Cells • Derived from neural crest cells. • Myelinate axons in the PNS.

  26. Astrocytes • Derived from neural crest cells. • Function to physically support neurons. • Channel materials between capillaries and neurons (= Blood-brain barrier). • Support and guide neurons during embryonic building of cerebral cortex. • Act as sinks for ions (i.e., K+). • Remove neuroactive and potentially toxic substances.

  27. Microglial Cells • Derived from embryonic mesenchyme. • May transform into phagocytes within CNS.

  28. Oligodendrocytes • Derived from neural crest cells. • Function to myelinate axons within CNS.

  29. Ependymal cells • Derived from neural crest cells. • Line ventricles of brain.

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