Lecture Notes: Brain Parenchyma and Nervous System

Brain Parenchyma

Key Components

• Neurons: Primary functional units.
• Glial Cells: Support neurons functionally and structurally.
• Blood Vessels & CSF: Critical for nutrient delivery and waste removal.

Neuron Environment

• Barrier Cells: Prevent harmful substances in the blood from contacting neurons.
• Astrocytes:
  • Foot Extensions: Integrate with blood vessel walls to facilitate nutrient transfer.
  • Synapse Support: Reinforce synaptic clefts to maintain neurotransmitter diffusion.
• Oligodendrocytes:
  • Myelination: Provide myelin to multiple axons, enhancing signal speed.

Microglia

• Function: Patrol brain for pathogens and debris, indicate brain pathology by shape change.

Choroid Plexus

• Structure: Tuft of capillaries producing cerebrospinal fluid (CSF).
• CSF Composition: 99% water, 1% protein, glucose, ions, oxygen.
• Ependymal Cells: Line ventricles, circulate CSF through cilia action.

Spinal Cord Parenchyma

Cross-Section Overview

• Gray H: Unmyelinated, central canal lined with ependymal cells.
• White Matter: Myelinated, surrounds gray H.

Neuron Types

• Sensory Neurons: Enter through dorsal roots, somas in dorsal root ganglion.
• Motor Neurons: Somas in ventral horns, exit through ventral roots to skeletal muscles.

Glial Cells

• Schwann Cells: Myelinate peripheral nerves.
• Satellite Cells: Surround sensory neuron somas.

Nerve and Tract Comparison

Definitions

• Nerve (PNS): Bundle of axons with connective tissue, blood supply, adipose, fibroblasts.
• Tract (CNS): Similar to nerves but located in the central nervous system.

Composition

• Nerves: Mixed sensory and motor axons.
• Connective Tissue Layers: Epineurium surrounds bundles (fascicles).

Important Distinctions

• Nerves ≠ Neurons: Neurons are individual cells, while nerves are complex structures.

Exam Preparation

• Understand specific losses from glial cell damage, e.g., astrocyte loss leads to nutrient deficiency and synaptic issues.
• Be prepared for application questions using the concepts covered.

• Note: Upcoming sessions will cover the endocrine system and address student queries. Please review quiz grades and content gaps for discussion.