Ibra Cham

USR

Microscopic Anatomy of Cerebral Cortex

Objectives• Type of cortical cells

• Layers of cortex

• Function of the layers

Few Demarcations• the cerebrum is the principal portion of the brain and contains the cell

bodies of nerves that receive and store sensory information, nerves that control voluntary motor activity, and nerves that integrate and coordinate the activity of other nerves, as well as the nerves and neural pathways that constitute memory

• however, functional part is only the outer 2-5 mm thick layer

• it has roughly an area of a square meter

• inhabited by ~100 billion neurons

Types of cells in CC• Glial cells:

support and protect neurons, and participate in neural activity, neural nutrition, and defense of cells in the central nervous system

ten times more numerous than neurons

• Neurons or nerve cells:

form the neuronal functional layers of the cortex: Isocortex (neocortex), Juxtalocortex (mesocortex) and Allocortex (archicortex)

Glial Cells• Oligodendrocyte

• Astrocyte

• Ependymal cell (VCNS)

• Microglia

• Neurolemmocyte (PNS)

Oligodendrocyte• produce the myelin sheath that

provides the electrical insulation for neurons

• mainly white matter

Astrocyte• structural support, repair

processes, blood-brain barrier, metabolic exchanges

• protoplasmic astrocytes (grey matter)

• fibrous astrocytes (white matter)

• most numerous

Ependymal cell• lining cavities of CNS, facilitate

movement and (also likely) absorption of CSF, providing that they are provided with cilia for the former function and long microvilli for the latter function

Microglia• constitute the major mechanism

of immune defense in CNS, turn into phagocytic cells

• evenly distributed throughout gray and white matter

Nerve Cells• Granular (stellate) neurons:

1. dendrites from all sides

2. axons are within the cortex

• Fusiform neurons:

1. deep layers, a large dendrite reaches cortical surface

2. axons send to cortical areas or beyond

• Pyramidal neurons:

1. horizontal dendrites, an apical dendrites reaches CS

2. axons send to cortical areas or beyond

3. more abundant than fusiform neurons

• These cells contribute to those three layers’ composition (Isocortex ~6L, Juxtalocortex ~3-6L, and Allocortex ~3L)

How many layers do you expect the CC has?

The Six Layers of CC• (I) The plexiform layer (molecular layer):

fibers parallel to the surface

• (II) The small pyramidal cell layer (outer granular layer):

small pyramidal cells, and granule cells (stellate cells)

• (III) The medium pyramidal cells layer (outer pyramidal layer)

larger pyramidal cells

The Six Layers of CC –continued• (IV) The granular layer (inner granular layer):

small granule cells

• (V) The large pyramidal cells layer (inner pyramidal layer):

Betz cells (large pyramidal cells)

• (VI) The layer of polymorphic cells (fusiform/multiform layer):

cells have spindles of fusiform shape

• BV, blood vessel

• Cap, capillary

• CC, cerebral cortex

• FC, fusiform cells

• GC, granule cells

• NN, neuroglial nuclei

• PC, pyramidal cells

• PM, pia mater

• V, vein

• WM, white matter

Layer I

Layer II

Layer IV

Layer VI

White matter

To Mention I-VI Function-wise• cortex neurons works in a vertical fashion

• this makes columns of interconnected neurons working as a unit

• this neuronal complex extends 30 to 100 micrometer in diameter

Pathways of The Signals in Neocortex• The layer IV get excited to send signals to the surface area

• The layers I & II receive signals from lower brain

• The layers II & III send axons to corresponding areas of the other hemisphere via (What structure?)

• The layer V send axons to distal areas e.g. spinal cord

• The layer VI send axons to thalamus controlling the level of excitation

Queries• What is the composition of White Matter (the area other than cortex)?

• What is in the interstitium?

References• Guyton, Ed-12, Ch-47, Pg-576-577, Ch-57, Pg-697-698

• Junqueira, Ed-12, Ch-9, Pg-140, 147-153

• Stephen Waxman, Ed-26, Ch-10, Pg-136-138

• Michael Ross, Ed-6, Ch-12, 382, 394-395

• Grey’s, Ch-16, Pg-282-286