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Understanding the Central Nervous System

Apr 23, 2025

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Anatomy of the Central Nervous System (CNS)

Overview

  • Discussion on the anatomy and structure of the CNS.
  • Key topics: Parts of the CNS, neuron and neuroglia structure, white and grey matter distribution, nerve tracts, and CNS development.

Parts of the Central Nervous System

  • Two main parts:
    • Encephalon (Brain):
      • Brainstem: Medulla Oblongata, Pons, and Mesencephalon.
      • Cerebellum: Located behind the brainstem, crucial for muscle memory.
      • Diencephalon: Contains the hypothalamus.
      • Telencephalon: Highest brain order, associated with personality.
    • Spinal Cord

Neurons

  • Basic cell type in the Nervous System.
  • Structure:
    • Dendrites: Receive signals and send to Cell Body.
    • Cell Body: Contains nucleus.
    • Axon: Long fibers transmitting signals over distances.
    • Axon Terminal: End of the axon.
  • Axons may be wrapped in Myelin Sheath (by Schwann cells in PNS or Oligodendrocytes in CNS).
  • Types of Neurons:
    • Multipolar: Multiple dendrites, one axon.
    • Pseudo-Unipolar: Axon and dendrite emerge from the same place.
    • Bipolar: One axon, one dendrite.
  • Functions:
    • Afferent (Sensory) Neurons: Arrive at CNS.
    • Interneurons: Interpret signals.
    • Efferent (Motor) Neurons: Exit CNS.

Neuroglia

  • Supportive cells in CNS providing mechanical support, nutrition, and protection.
  • Types:
    • Astrocytes: Form blood-brain barrier.
    • Oligodendrocytes: Myelinate nerves in CNS.
    • Microglia: Immune cells of CNS.
    • Ependymal Cells: Line CNS cavities.

White and Grey Matter

  • Grey Matter: Rich in cell bodies and dendrites.
  • White Matter: Rich in myelinated axons and glial cells.
  • Distribution:
    • Spinal Cord: Grey matter centrally, white matter outer.
    • Brain: Grey matter on external border (cerebral cortex), white matter internally.

Nerve Tracts

  • Bundles of axons connecting grey matter or nuclei.
  • Classification:
    • Association Fibers: Connect adjacent structures.
    • Commissural Fibers: Connect one brain side to another.
    • Projection Fibers: Lead tracts up/down spinal cord.
  • Types:
    • Ascending Tracts: Sensory fibers.
    • Descending Tracts: Motor fibers.
    • Indirect Tracts: Interconnect brain parts.

Development of the CNS

  • Primitive Brain: Formed by the 4th week post-fertilization.
    • Structures: Spinal cord, Hindbrain (Rhombencephalon), Midbrain (Mesencephalon), Forebrain (Prosencephalon).
  • Development Stages:
    • 5th Week: Rhombencephalon divides into Myelencephalon and Metencephalon.
    • Prosencephalon: Divides into Telencephalon and Diencephalon.
  • Adult Brain:
    • Hindbrain: Pons, Cerebellum, and Medulla Oblongata (basic functions).
    • Forebrain: Thalamus structures (from Diencephalon), brain cortex (from Telencephalon).

Key Concepts

  • Proximity to the spinal cord correlates with basic function.
  • Cerebral cortex involved in higher-order functions and decision-making.

This lecture provides foundational understanding of CNS structure, function, and development, preparing for more detailed anatomical study in future sessions.

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