CNS Histology

CNS Histology Notes

Exam Overview

  • Prepared by: Maria Cole, Ph.D.

  • Focus: CNS (Central Nervous System) Histology

  • Important structures discussed:

    • Purkinje cell

    • Folia (leaf-like folds of the cerebellum)

    • Deep white matter

    • Fourth ventricle

    • Brainstem

Learning Objectives

  1. Understanding Nervous Tissue

    • Differentiate between nervous tissue and other tissue types.

  2. Components of Neural Tissue

    • Understand neurons and neuroglia and their classifications.

  3. Types of Neuroglia Comparison

    • Describe the four types of neuroglia, including their functions and locations.

  4. Blood-Brain Barrier (BBB)

    • Components and functions of the BBB.

  5. Neuron Structure

    • Examine neuron structure, myelin's role, axonal transport, and neuronal injury response.

  6. Histologic Organization

    • Describe histologic organization and functions of the cerebrum and cerebellum, including their layers and associated cells.

General Features of Nervous Tissue

  • Neurons transmit electrochemical signals

  • Functions of neurons:

    • Receptive

    • Integrative

    • Motor

  • Neuroglia functions:

    • Insulate

    • Nourish

    • Support and protect neurons

Key Structures in Spinal Cord Histology

  • Nissl Stained Preparation:

    • Shows large motoneurons within the ventral horn of the spinal cord.

  • Anatomical landmarks include:

    • Dorsal Median Septum

    • Dorsal Root

    • White Matter (WM)

    • Gray Matter (GM)

  • Cross-Sectional Features:

    • Dorsal Horn

    • Lateral Horn

    • Ventral Horn

    • Meninges

    • White and Gray Commissures

Histogenesis within the CNS

  • Composition difference:

    • Spinal Cord: Gray matter is centrally located.

    • Brain: Has a core of white matter and gray matter on the surface.

Types of Glial Cells

  • Neuron Support:

    • Glial cells primarily function for support and protection of neurons.

    • Brain Tumors: Most originate from glial cells, highlighting their importance.

    • Types of glial cells include:

      • Schwann Cells

      • Oligodendrocytes

      • Microglial Cells

      • Ependymal Cells

Astrocytes

  • Functional Roles:

    • Form structural frameworks for neuron migration during embryogenesis.

    • Circulatory Role: Ensure blood-brain barrier integrity.

  • Key Regulatory Functions:

    • Interstitial fluid composition

    • Neurotransmitter metabolism

    • Potassium ion balance

  • Interactions at the vascular endothelium to maintain BBB.

  • Protein secretion:

    • Astrocytes secrete hevin (proteins that aid in synapse formation).

  • Ethical implications: Discovering therapeutic targets in astrocyte behavior can improve outcomes in neurodegenerative diseases like Alzheimer’s.

Blood-Brain Barrier (BBB)

  • Structure of CNS endothelium:

    • Composed of unfenestrated capillaries joined by tight junctions.

    • Basal Lamina: Provides mechanical support and acts as a barrier to macromolecules.

    • Pericytes: Regulate endothelial morphology and contribute to immune response.

Oligodendrocytes

  • Characteristics:

    • Most numerous glial cells found in both gray and white matter.

    • Function to form myelin sheath around multiple axons in the CNS.

  • Clinical Relevance:

    • Diseases such as Multiple Sclerosis (MS)—where demyelination occurs—emphasize the importance of oligodendrocytes.

Microglia

  • Functions and Roles:

    • Smallest glial cells that conduct phagocytosis.

    • Derived from the mononuclear phagocyte system.

    • Role in synaptic pruning and immune response to CNS damage.

Ependyma

  • Function:

    • Lines the ventricular system and central canal of the spinal cord.

    • Modified cells form the choroid plexus, secreting cerebrospinal fluid (CSF).

  • Histological Characteristics: Cuboidal epithelium structure, important for CSF regulation.

Response to Injury

  • In PNS:

    • Connective tissue and Schwann cells bridge the severed nerve.

  • Regeneration Steps:

    1. Schwann cells multiply to bridge the gap.

    2. Axon sprouts neurites from the proximal stump.

    3. Neurites re-establish contact with the distal stump.

  • In CNS:

    • Oligodendrocytes are less effective than Schwann cells in supporting regeneration.

    • Glial cells proliferate, causing scar tissue formation that obstructs regeneration.

  • Neurodegenerative Diseases:

    • Progressive decline in neuron function can lead to conditions like ALS (Amyotrophic Lateral Sclerosis).

Development of the Cerebellum

  • General Function:

    • Involved in coordination of motor activities, posture, and balance.

  • Cerebellar Structure:

    • Consists of cortex with folia and a medulla of nerve fibers.

  • Cell Layers:

    • Outermost molecular layer, Purkinje cell layer, and granule cell layer.

  • Purkinje Cells:

    • Important for intricate signal processing in the cerebellum, enabling rapid response and coordination of movement.

Cortical Neurons and Layers

  • Neuron Types:

  • Pyramidal Cells: Large, pyramid-shaped, including Betz cells (upper motor neurons).

  • Stellate Cells: Small and star-shaped (granule cells).

  • Layers of the Cortex:

    • I: Plexiform (molecular) layer

    • II: Outer granular layer

    • III: Pyramidal cell layer

    • IV: Internal granular layer

    • V: Internal pyramidal layer (giant pyramidal cells)

    • VI: Multiform layer

  • Additional references provided throughout transcript indicate visual aids and external links for enhanced understanding of specific structures and functions discussed.