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. It consists of two main components:

• Brain: The organ responsible for higher cognitive functions, sensory interpretation, and voluntary actions.

• Spinal cord: The conduit for signals between the brain and the rest of the body, also involved in reflex actions.

The CNS functions as the control center for almost everything we do, think, and feel.

Key Functions of the CNS

• Memory and learning

• Coordinating movement

• Decision making

• Regulating homeostasis

Example: The CNS is involved in answering questions, coordinating muscle movements, and making decisions about daily activities.

Major Regions of the Brain

Division of the Adult Brain

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

• Cerebrum: The largest, most anterior part of the brain. Responsible for higher cognitive functions, voluntary movement, and sensory perception.

• Diencephalon: Central part of the forebrain. Includes the thalamus, hypothalamus, and epithalamus. Functions in sensory relay, autonomic control, and hormone regulation.

• Brain stem: 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: Located at the back of the brain. Coordinates motor activity and balance.

Example: A glioma in the midbrain is located in the brainstem.

Relative Positioning of Brain Regions

• The diencephalon is superior to the brainstem and anterior to the cerebellum.

CNS Development

Embryonic Development of the CNS

The CNS develops from the neural tube, an embryonic structure. The anterior end expands and forms three primary brain vesicles:

• Prosencephalon (Forebrain)

• Mesencephalon (Midbrain)

• Rhombencephalon (Hindbrain)

The caudal (inferior) end of the neural tube becomes the spinal cord.

Transformation of Brain Vesicles

During development, the primary brain vesicles differentiate into structures of the mature brain:

Example: The prosencephalon gives rise to the cerebrum and diencephalon in the mature brain.

Additional info: The term "encephalo" refers to the brain.

White & Gray Matter

Composition of Nervous Tissue

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

• White matter: Mostly myelinated axons. Responsible for rapid signal transmission throughout the CNS.

• Gray matter: Contains neuron cell bodies, dendrites, and unmyelinated axons. Involved in processing and integration of information.

Organization in the Brain and Spinal Cord

• Brain: Outer layer of gray matter is known as the cortex; inner layer of white matter. Subcortical clusters of gray matter are called basal nuclei.

• Spinal cord: Outer layer of white matter surrounds an inner core of gray matter.

Functions of White and Gray Matter

Example: White matter is responsible for transferring signals, while gray matter is responsible for decision-making processes in the brain.

Distribution of Cortical Areas

• All cortical areas of the brain are found around the outer edge (surface) of the brain, forming the cortex.