The cerebral cortex is the outer layer of the cerebrum, responsible for higher brain functions including thought, action, emotion, and sensory processing. It plays a critical role in neurodegenerative diseases through cortical neuron loss, atrophy, and connectivity disruption. [@mesulam2000]
Anatomy and Organization
The cerebral cortex is organized into six distinct layers (I-VI), each with specific neuronal compositions and connectivity patterns: [@brodmann1909]
Layer I (molecular layer): Sparse neurons, predominantly dendrites and axons
Layer II (external granular layer): Small pyramidal neurons, interneurons
Layer III (external pyramidal layer): Medium pyramidal neurons, cortico-cortical connections
Layer IV (internal granular layer): Star pyramidal neurons, thalamocortical inputs
Layer V (internal pyramidal layer): Large pyramidal neurons, cortico-subcortical outputs
Layer VI (multiform layer): Mixed neurons, corticothalamic projections
Cortical Neuron Types
Pyramidal Neurons
Pyramidal neurons are the primary excitatory neurons in the cortex, comprising ~70-80% of cortical neurons. They are characterized by: [@kandel2013]
Triangular soma (cell body)
Apical dendrite extending toward the cortical surface
Basal dendrites extending laterally
Long axonal projections to other brain regions
...
Overview
The cerebral cortex is the outer layer of the cerebrum, responsible for higher brain functions including thought, action, emotion, and sensory processing. It plays a critical role in neurodegenerative diseases through cortical neuron loss, atrophy, and connectivity disruption. [@mesulam2000]
Anatomy and Organization
The cerebral cortex is organized into six distinct layers (I-VI), each with specific neuronal compositions and connectivity patterns: [@brodmann1909]
Layer I (molecular layer): Sparse neurons, predominantly dendrites and axons
Layer II (external granular layer): Small pyramidal neurons, interneurons
Layer III (external pyramidal layer): Medium pyramidal neurons, cortico-cortical connections
Layer IV (internal granular layer): Star pyramidal neurons, thalamocortical inputs
Layer V (internal pyramidal layer): Large pyramidal neurons, cortico-subcortical outputs
Layer VI (multiform layer): Mixed neurons, corticothalamic projections
Cortical Neuron Types
Pyramidal Neurons
Pyramidal neurons are the primary excitatory neurons in the cortex, comprising ~70-80% of cortical neurons. They are characterized by: [@kandel2013]
Triangular soma (cell body)
Apical dendrite extending toward the cortical surface
Basal dendrites extending laterally
Long axonal projections to other brain regions
In neurodegenerative diseases, pyramidal neurons are particularly vulnerable in specific cortical regions: [@seeley2008]
Alzheimer's disease: Early loss in entorhinal cortex and hippocampus
Frontotemporal dementia: Severe loss in frontal and temporal cortices
Corticobasal syndrome: Asymmetric loss in frontoparietal cortices