Central Nervous System: Structure and Function

Central Nervous System (CNS)

Overview of the CNS

The Central Nervous System (CNS) is the primary control center of the body, consisting of the brain and spinal cord. It is responsible for integrating sensory information and coordinating bodily functions.

• Components: Brain and spinal cord

• Cephalization: Refers to the evolutionary development of the anterior (head) region, resulting in increased neuron concentration and complexity, especially in humans.

• Function: Processes sensory data, initiates motor commands, and is the seat of higher cognitive functions.

Basic Pattern of the Central Nervous System

Brain Structure

The brain is composed of wrinkled, pinkish-gray tissue and includes several major regions.

• Cerebral hemispheres

• Cerebellum

• Brain stem

• Gray matter: Found in nuclei and cortex

• White matter: Composed of myelinated fiber tracts

Spinal Cord Structure

• Central canal: Surrounded by a core of gray matter

• External region: White matter made of myelinated axons

Lobes and Sulci of the Cerebrum

Major Lobes and Landmarks

The cerebrum is divided into distinct lobes and features grooves (sulci) and ridges (gyri) that increase its surface area and functional capacity.

• Frontal lobe: Involved in voluntary movement, planning, and reasoning

• Parietal lobe: Processes sensory information

• Occipital lobe: Responsible for visual processing

• Temporal lobe: Involved in auditory processing and memory

• Central sulcus: Separates frontal and parietal lobes

• Precentral gyrus: Primary motor cortex

• Postcentral gyrus: Primary somatosensory cortex

• Other sulci: Parieto-occipital, lateral, transverse cerebral fissure

Structural Features

• Gyrus: Elevated ridge

• Sulcus: Shallow groove

• Fissure: Deep groove

• Cortex: Outer layer of gray matter

• White matter: Inner region containing myelinated axons

Gray and White Matter

Distribution and Function

The CNS is organized into regions of gray and white matter, each with distinct roles.

• Gray matter: Contains neuron cell bodies and unmyelinated fibers; responsible for processing and integration

• White matter: Composed of myelinated axons; facilitates communication between regions

• Brain: Gray matter in cortex and nuclei; white matter internally

• Spinal cord: Central gray matter core surrounded by white matter

Cerebral Cortex

Structure and Function

The cerebral cortex is the outermost layer of the cerebrum, consisting of gray matter. It is essential for higher brain functions.

• Accounts for 40% of brain mass

• Functions: Sensation, communication, memory, understanding, voluntary movements

• Contralateral control: Each hemisphere controls the opposite side of the body

• Functional specialization: Hemispheres are not functionally identical

• Integration: No area acts alone; conscious behavior involves the entire cortex

Functional Areas of the Cerebral Cortex

Classification of Areas

The cerebral cortex is divided into three main functional areas, each responsible for specific aspects of brain activity.

• Motor areas: Control voluntary movement

• Sensory areas: Provide conscious awareness of sensation

• Association areas: Integrate diverse information for complex processing

Summary Table: Lobes and Sulci of the Cerebrum

Lobe	Main Function	Key Sulci/Gyri
Frontal	Motor control, planning, reasoning	Precentral gyrus, central sulcus
Parietal	Sensory processing	Postcentral gyrus, parieto-occipital sulcus
Occipital	Visual processing	Occipital cortex
Temporal	Auditory processing, memory	Lateral sulcus

Summary Table: Gray and White Matter

Region	Gray Matter	White Matter
Cerebrum	Cortex, nuclei	Internal tracts
Brain Stem	Nuclei within white matter	Surrounding tracts
Spinal Cord	Central core	External columns

Key Terms and Definitions

• Cerebrum: Largest part of the brain, responsible for higher functions

• Cerebral cortex: Outer layer of gray matter in the cerebrum

• Gray matter: Neuron cell bodies, dendrites, and unmyelinated axons

• White matter: Myelinated axons connecting different brain regions

• Gyrus: Ridge on the cerebral surface

• Sulcus: Groove between gyri

• Fissure: Deep groove separating major brain regions

• Contralateral control: Each hemisphere controls the opposite side of the body

Additional info:

• Further details on the specific motor, sensory, and association areas, as well as their locations and functions, are covered in subsequent sections of the chapter.

• Understanding the organization of gray and white matter is essential for interpreting brain imaging and neurological disorders.