Central Nervous System: Structure and Functional Organization

Central Nervous System Overview

Major Components of the CNS

The central nervous system (CNS) consists of the brain and spinal cord. These structures are responsible for integrating sensory information and coordinating bodily functions.

• Brain: The control center for processing information, thought, and emotion.

• Spinal Cord: The main pathway for transmitting signals between the brain and the rest of the body.

Protection of the CNS

The CNS is protected by several structures:

• Meninges: Three connective tissue layers (dura mater, arachnoid mater, pia mater) that surround the brain and spinal cord.

• Ventricles: Internal cavities within the brain filled with cerebrospinal fluid (CSF).

• Cerebrospinal Fluid (CSF): Cushions the CNS and removes waste products.

Directional Terms in CNS Anatomy

Unique Directional Terms

Directional terms are used to describe locations within the CNS:

• Rostral: Toward the nose or higher brain regions (anterior/superior).

• Caudal: Toward the tail or lower brain regions (posterior/inferior).

Major Regions of the Brain

Four Main Regions

The adult brain is divided into four main regions, each with distinct functions:

• Cerebrum: Largest region, responsible for higher cognitive functions.

• Diencephalon: Includes the thalamus and hypothalamus, involved in sensory relay and homeostasis.

• Brainstem: Controls basic life functions; includes the midbrain, pons, and medulla oblongata.

• Cerebellum: Coordinates movement and balance.

The Cerebrum

Basic Organization

The cerebrum is the largest part of the brain, comprising about 83% of its mass. It consists of two hemispheres and is characterized by surface landmarks:

• Fissures: Deep grooves separating major regions.

• Sulci: Shallow grooves on the surface.

• Gyri: Ridges between sulci.

Internal Structure

The cerebrum is organized into three main types of tissue:

• Cerebral Cortex: Outer layer of gray matter responsible for conscious thought.

• Basal Ganglia: Deep gray matter involved in movement regulation.

• White Matter: Myelinated axons connecting different brain regions.

Surface Landmarks of the Cerebrum

Definitions and Examples

Surface landmarks are important for identifying regions and functions:

• Sulci: Grooves on the surface of the cerebrum.

• Fissures: Very deep grooves separating major regions.

• Gyri: Ridges between sulci.

Major Fissures

• Longitudinal Fissure: Separates right and left cerebral hemispheres.

• Transverse Fissure: Separates cerebrum from cerebellum.

Major Sulci and Gyri

• Central Sulcus: Separates frontal and parietal lobes.

• Lateral Sulcus: Separates temporal lobe from frontal and parietal lobes.

• Parieto-Occipital Sulcus: On the medial surface, separates parietal and occipital lobes.

• Precentral Gyrus: Primary motor cortex.

• Postcentral Gyrus: Primary somatosensory cortex.

Cerebral Lobes

Identification and Location

The cerebrum is divided into five lobes, each named for the overlying skull bones:

• Frontal Lobe: Anterior to central sulcus, superior to lateral sulcus.

• Parietal Lobe: Posterior to central sulcus, superior to lateral sulcus, anterior to parieto-occipital sulcus.

• Temporal Lobe: Inferior to lateral sulcus, anterior to occipital lobe.

• Occipital Lobe: Posterior to parieto-occipital sulcus and temporal lobe.

• Insula: Deep within lateral sulcus, covered by parts of temporal, parietal, and frontal lobes.

Medial Surface Landmarks

• Parieto-Occipital Sulcus: Separates occipital lobe from parietal lobe on the medial surface.

Insula

The insula is considered the "fifth lobe" and is located deep within the lateral sulcus.

Summary Table: Surface Landmarks and Lobes

Lobe	Location	Key Landmark
Frontal	Anterior to central sulcus, superior to lateral sulcus	Precentral gyrus
Parietal	Posterior to central sulcus, superior to lateral sulcus, anterior to parieto-occipital sulcus	Postcentral gyrus
Temporal	Inferior to lateral sulcus, anterior to occipital lobe	Lateral sulcus
Occipital	Posterior to parieto-occipital sulcus and temporal lobe	Parieto-occipital sulcus
Insula	Deep within lateral sulcus	Covered by other lobes

Functional Areas of the Cerebral Cortex

Overview of Functional Areas

The cerebral cortex is the site of conscious mind and is divided into three main functional areas:

• Sensory Areas: Process sensory information and provide conscious awareness of sensation.

• Motor Areas: Initiate and control voluntary movements.

• Association Areas: Integrate information to enable complex and purposeful action.

All neurons in the cerebral cortex are interneurons.

Motor Areas

• Primary Motor Cortex

• Premotor Cortex

• Frontal Eye Field

• Broca’s Area

Multimodal Association Areas

• Posterior Association Area

• Wernicke’s Area

• Anterior Association Area (Prefrontal Cortex)

• Limbic Association Area

Sensory Areas

• Somatosensory Areas

• Visual Areas

• Auditory Areas

• Gustatory Cortex

• Olfactory Cortex

• Vestibular Cortex

Additional info:

• The organization and landmarks of the cerebrum are fundamental for understanding brain function and clinical neuroanatomy.

• Functional areas are mapped using techniques such as MRI and histological staining.