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Histology of the Cerebral Cortex

The cerebral cortex is the outermost layer of the brain, composed of gray matter, and is essential for higher-order brain functions such as sensory perception, motor control, and cognition. The cortex is organized into layers and contains various types of neurons and glial cells.

Layers of the Cerebral Cortex

The cerebral cortex is traditionally divided into six distinct layers, each with its unique composition and function:

• Layer I - Molecular Layer: The outermost layer, composed primarily of dendrites and axons, with few cell bodies. It functions mainly in the integration of synaptic inputs.
• Layer II - External Granular Layer: Contains small pyramidal and stellate cells. This layer is involved in the processing of information and local connections within the cortex.
• Layer III - External Pyramidal Layer: Composed of medium-sized pyramidal neurons. These neurons have long axons that contribute to corticocortical connections, linking different regions of the cortex.
• Layer IV - Internal Granular Layer: Dominated by densely packed stellate cells. This layer receives the majority of sensory input from the thalamus and is particularly prominent in sensory areas such as the primary visual and somatosensory cortices.
• Layer V - Internal Pyramidal Layer: Contains large pyramidal neurons, including Betz cells in the motor cortex. Axons from these neurons project to subcortical structures, such as the brainstem and spinal cord, playing a crucial role in motor control.
• Layer VI - Multiform Layer: The deepest layer, containing a variety of cell types, including fusiform cells. Neurons in this layer send outputs to the thalamus, regulating thalamic activity and feedback to the cortex.

Neuron Types

The cerebral cortex contains several types of neurons, each with specific roles:

• Pyramidal Cells: The most common type of excitatory neuron in the cortex. They are large, with a triangular-shaped cell body, and are found primarily in layers III and V. Pyramidal cells play a key role in sending signals to other parts of the brain and spinal cord.
• Stellate Cells: These are small, star-shaped interneurons primarily found in layer IV. They are involved in processing sensory information received from the thalamus.
• Fusiform Cells: Found mainly in layer VI, these cells have a spindle-shaped body and project to the thalamus.
• Glial Cells: Include astrocytes, oligodendrocytes, and microglia, which support and protect neurons, maintain homeostasis, and provide myelination.