(13) CNS Part 5 Cerebrum

Cerebrum Overview

• Definition: The cerebrum, meaning "the understanding," is the largest part of the brain, necessary for higher cognitive functions.

• Functions: Responsible for reading, writing, speaking, memory, imagination, and creativity.

• Structure: Consists of an outer cerebral cortex (gray matter) and inner white matter, along with gray matter nuclei embedded within.

Cerebral Cortex

• Composition: 2 to 4 mm thick layer of gray matter containing billions of neurons.

• Development: This area expands significantly during brain development due to neuron growth causing folding (convolutions).

• Components of Folds:

  • Gyri (singular: gyrus): Raised folds of the cortex.

  • Sulci (plural: sulcus): Shallow grooves between gyri.

  • Fissures: Deep grooves separating lobes (e.g., the longitudinal fissure).

Key Features of Cerebral Folds

• Longitudinal Fissure: Separates cerebrum into left and right hemispheres.

• Central Sulcus: Divides frontal lobe from parietal lobe, indicating the position of motor and sensory areas.

  • Precentral Gyrus: Located anterior to the central sulcus, known as the primary motor area.

  • Postcentral Gyrus: Located posterior to the central sulcus, responsible for simple somatosensory functions (e.g., temperature, pain).

• Additional Sulci:

  • Parieto-occipital Sulcus: Separates parietal lobe from occipital lobe.

  • Lateral Cerebral Sulcus: Separates frontal lobe from temporal lobe.

White Matter of Cerebrum

• Definition: Composed of myelinated axons that form tracts within the central nervous system.

• Types of Tracts:

  • Association Tracts: Connect gyri within the same hemisphere.

  • Commissural Tracts: Bridge left and right hemispheres (e.g., corpus callosum, anterior commissure).

  • Projection Tracts: Conduct impulses from the cerebral cortex to lower parts of the brain and spinal cord.

Primary Somatosensory and Motor Areas

• Primary Somatosensory Area: Located in the postcentral gyrus, processes general sensory information (touch, pressure, pain, etc.).

  • Homunculus Representation: More neural resources devoted to areas with greater sensory feedback (e.g., hands, face).

• Primary Motor Area: Located in precentral gyrus, responsible for voluntary motor movements. Also mapped via homunculus which indicates regions controlling various body parts.

• Additional Sensory Areas:

  • Primary Visual Area: Occipital lobe; processes vision.

  • Primary Gustatory Area: Parietal lobe; responsible for taste.

  • Primary Auditory Area: Located along the lateral cerebral sulcus; processes auditory information.

• Speech and Language Areas: Involved in coordination of speech and gestures, as well as interpreting language.

Summary of Motor Functions

• Motor Output Initiation: Predominantly occurs from the primary motor area located in the anterior side of the brain which controls muscle movements.

• Additional Motor Areas:

  • Premotor Area: Prepares and coordinates movements.

  • Speech Area: Coordinates muscle movements for speech.

  • Homunculus for Motor Area: Represents body part movement control with larger areas indicated for finer movements (e.g., face and hands).

Conclusion

• The cerebrum integrates rapid processing of sensory input and initiates motor outputs, contributing to our complex behaviors and cognitive functions.