Central Nervous System (CNS)

Overview of the CNS

The central nervous system (CNS) is the primary control center for the human body, responsible for processing and integrating information, and directing responses. It consists of two main components:

• The brain

• The spinal cord

The CNS is responsible for almost everything we do, think, and feel, including memory, movement, and decision-making.

Example:

• Trying to remember the answer to an anatomy and physiology question

• Coordinating your skeletal muscles to catch and throw a ball

• Deciding what you want to have for dinner

All of the above actions involve the CNS.

Major Regions of the Brain

Brain Divisions

The adult brain is divided into four major regions, each with distinct functions and structures:

• Cerebrum: Largest, most anterior part of the brain. Responsible for higher brain functions such as thought and action.

• Diencephalon: Central part of the forebrain. Consists of the hypothalamus and epithalamus. Involved in sensory and autonomic functions.

• Brainstem: Connects the cerebrum to the spinal cord. Consists of the midbrain, pons, and medulla oblongata. Controls basic life functions such as breathing and heart rate.

• Cerebellum: Structure at the back of the brain. Coordinates motor activity and balance.

Example:

If a patient has a glioma on the midbrain, the affected region is the brainstem.

CNS Development

Neural Tube and Brain Vesicles

The CNS develops from the neural tube in the embryo. The anterior end expands to form three primary brain vesicles:

• Forebrain (prosencephalon)

• Midbrain (mesencephalon)

• Hindbrain (rhombencephalon)

These vesicles further differentiate into mature brain structures:

Example:

Throughout fetal development, the prosencephalon becomes the cerebrum and the diencephalon.

White & Gray Matter

Types of Nervous Tissue

Nervous tissue in the brain and spinal cord is composed of two types of matter:

• White matter: Mostly myelinated axons, optimized for rapid signal transmission.

• Gray matter: Contains neuron cell bodies, dendrites, and unmyelinated axons. Responsible for processing and integration.

In the brain, the outer layer of gray matter is known as the cortical matter, while subcortical clusters are called nuclei. In the spinal cord, the outer layer is white matter, and the inner layer is gray matter.

Example:

• White matter is optimized for transferring signals rapidly throughout the CNS.

• Gray matter is responsible for decision-making and processing information.

Cerebral Hemispheres

Structure and Function

The cerebrum consists of two cerebral hemispheres, making up the superior portion of the brain. Each hemisphere is responsible for complex functions and exhibits specialization:

• Lateralization: Each hemisphere specializes in certain functions.

• Cerebral Dominance: One hemisphere is dominant for particular functions (e.g., language).

• Contralateral Control: Each hemisphere controls the opposite side of the body.

Example:

Aphasia (difficulty speaking) is often due to issues in the left hemisphere, which is dominant for language.

Important Features of the Cerebrum

Gyri, Sulci, and Fissures

The surface of the cerebrum features prominent grooves and ridges:

• Gyrus (plural: gyri): Elevated ridge of tissue on the surface of the brain.

• Sulcus (plural: sulci): Shallow groove that separates gyri.

• Fissure: Deep groove that separates larger regions of the brain.

Examples include the central gyrus, lateral fissure, and longitudinal fissure which divides the two cerebral hemispheres.

Example:

Gray matter is present in gyri and sulci on the surface of the cerebrum.

Summary Table: Major Brain Regions and Functions

Additional info: The notes above expand on brief points with academic context, definitions, and examples to ensure completeness and clarity for exam preparation.