VJ

FUNCTIONAL_LOCALIZATION_OF_CEREBRAL_CORTEX

The Cerebrum & Cerebellum

Overview

  • The cerebrum is the largest brain division, making up approximately 83% of the brain's volume.

  • It consists of the cerebral cortex, white matter, basal ganglia, and lateral ventricles.

  • The structure is divided into two hemispheres connected by the corpus callosum.

  • Functions associated with the cerebrum include voluntary movement, sensory perception, and cognitive processes.

Learning Outcomes

  • Understand the general structure of the cerebrum, cerebral cortex, and white matter.

  • Identify key lobes of the brain and significant gyri.

  • Describe primary functions of different lobes and cortical regions.

  • Comprehend gross anatomy and histology of the cerebellum and its functions.

Cerebral Cortex

Structure

  • The cerebral cortex is the outermost gray matter layer, about 2-3mm thick, consisting of six layers.

  • Neurons present:

    • Pyramidal cells: Large neurons primarily responsible for output connections.

    • Stellate cells: Smaller, interconnected with other neurons, serving local processing functions.

Phylogenetic Development

  • The human cortical structure includes more gyri and a thicker neocortex featuring six layers.

  • Variations in layer thickness occur in regions concerning specific functions (e.g., layer IV in the somatosensory area).

  • Some areas, like the insula and some regions of the temporal lobe, have fewer layers recognized as the paleocortex.

Lobes of the Cerebral Hemispheres

Division

  • The cerebrum has four primary lobes:

    • Frontal lobe: Located anterior to the central sulcus, responsible for higher cognitive functions and motor control.

    • Parietal lobe: Positioned posterior to the central sulcus, integrates sensory information.

    • Occipital lobe: Separated from the parietal lobe, primarily associated with visual processing.

    • Temporal lobe: Located inferiorly, involved in auditory processing and memory.

Insula

  • The insula lobe is buried within the lateral sulcus and plays a role in diverse functions including taste and sensory integrative processes.

Functional Areas of the Cortex

Primary Cortex

  • Areas directly receiving sensory input, e.g., motor, somatosensory, visual, auditory.

Association Cortex

  • Adjacent to primary areas; responsible for integrating and processing information from various sensory modalities. Makes up approximately 75% of the cortex.

  • Example: The prefrontal lobe integrates cognitive and emotional functions.

Structural Features

Gyri and Sulci

  • Gyri: Elevated ridges on the brain surface.

  • Sulci: Small grooves separating gyri.

  • Fissures: Deeper grooves dividing major brain regions, e.g., longitudinal fissure separating the two hemispheres.

Cerebellum

Overview

  • The cerebellum is the second-largest brain region, accounting for 10% of total brain bulk yet containing 60% of the brain's neurons.

  • Located in the posterior cranial fossa, it manages balance, coordination, and fine motor skills.

Development and Structure

  • Comprised of two hemispheres and a midline structure (vermis), it is divided into anterior, posterior, and flocculonodular lobes.

  • Main cerebellar functions include the regulation of voluntary movements, posture, and equilibrium.

Functional Connections

  • Afferent connections: Includes input from the cerebral cortex, vestibular system, and proprioceptive signals.

  • Efferent connections: Output to various brain regions for motor coordination and balance.

Histology of the Cerebral Cortex and Cerebellum

Layers

  • The cortex contains:

    • Molecular layer: Contains horizontal fibers and stellate cells.

    • Purkinje cell layer: Contains large neurons crucial for inhibitory signals.

    • Granular layer: Innermost layer, contributes to excitatory signals.

    • White matter: Contains myelinated axons forming the arbor vitae structure.

Cerebellar Nuclei

  • Deep gray matter nuclei regulate various functions, with the dentate nucleus playing a crucial role in motor coordination and fine tuning movements.

Blood Supply

Vascular Supply

  • Supplied primarily by:

    • Posterior inferior cerebellar artery (PICA): Largest, supplying the inferior part of the cerebellum.

    • Anterior inferior cerebellar artery (AICA): Supplies aspects of the anterior regions.

    • Superior cerebellar artery: Supplies parts of the superior cerebellum.

Cerebellar Lesions

  • Symptoms stemming from lesions include ataxia, nystagmus, dysmetria, and loss of balance, affecting activities requiring precise coordinates.