What are the components of the brain?

Cellular Composition of the Brain

The brain is composed of two major cell categories: neurons and glial cells (neuroglia), which together form the functional architecture of the nervous system. 1

Primary Cellular Components

Neurons and Glial Cells

• The nervous tissue consists of neurons and neuroglia working in tightly coordinated manner to define nervous system function 1
• Glial cells outnumber neurons and occupy approximately equal space in nervous tissue 2
• These two cell types form the complete cellular framework of brain tissue 1

Glial Cell Types in the Central Nervous System

Macroglia:

• Astroglia (astrocytes): Include protoplasmic, fibrous, velate, and marginal astrocytes, plus specialized forms like Bergmann glial cells, neural stem cells, and tanycytes 1
• Oligodendroglia: Represented by oligodendrocytes and oligodendrocyte precursor cells (OPCs), primarily responsible for myelination and axonal support 1, 3
• Ependymoglia: Part of the extended astroglial class 1

Microglia:

• Cells of myeloid origin that invade the neural tube during early embryonic development 1
• Function as tissue macrophages adapted to nervous system requirements 1
• Contribute to both CNS physiology and innate immunity 1

The Neurovascular Unit

Beyond neurons and glia, the brain contains critical vascular components that form the neurovascular unit:

• Vascular cells including endothelium, smooth muscle cells/pericytes, and adventitial cells 4
• These components are closely related developmentally, structurally, and functionally with neurons and glia 4
• Astrocyte endfeet maintain close apposition to endothelium across the basal lamina matrix 5

Functional Significance

Glial Cell Functions

• Glial cells represent at least half of all cells in the human brain and perform critical neuron support roles 6
• They maintain appropriate ion concentrations and neurotransmitter levels in the neuronal environment 2
• Glial cells are essential regulators of synapse formation, maintenance, and function 2
• They provide homeostatic and defensive functions for the nervous system 1

White Matter Considerations

• The human brain has a higher proportion of white matter relative to rodent brains 6
• This structural difference emphasizes the importance of oligodendrocytes and myelination in human brain composition 6

Clinical Relevance

The concept of the neurovascular unit emphasizes that all multiple cell types must be considered together:

• Not only neurons but also glial and vascular elements require preservation for brain function 6
• Cell-cell signaling that maintains neurovascular unit integrity is essential 6
• Brain pathology is largely a pathology of glia, which determines the degree of neuronal death and neurological deficit 7