Central Nervous System (CNS)

Overview of the CNS

The central nervous system (CNS) is the primary control center for the human body, responsible for integrating sensory information and coordinating bodily functions.

• Components: The CNS consists of two main parts:

  1. The brain

  2. The spinal cord

• Function: The CNS acts as the integration center for almost everything we do, think, and feel.

• Examples of CNS roles:

  • Memory and learning

  • Coordinating movement

  • Decision making

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 cognitive functions.

• Diencephalon: Central part of the forebrain. Consists of the hypothalamus and epithalamus.

• Brainstem: Connects the cerebrum to the spinal cord. Includes the midbrain, pons, and medulla oblongata.

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

Example: A glioma in the midbrain affects the brainstem.

CNS Development

Formation of the CNS

The CNS develops from the neural tube in the embryo, which differentiates into distinct brain regions.

• Neural tube: Embryonic structure that becomes the CNS.

• Primary brain vesicles: The anterior end forms three constrictions:

  • Forebrain (prosencephalon)

  • Midbrain (mesencephalon)

  • Hindbrain (rhombencephalon)

• These vesicles further develop into mature brain structures:

  • Forebrain → Cerebrum, Diencephalon

  • Midbrain → Midbrain

  • Hindbrain → Pons, Cerebellum, Medulla oblongata

Additional info: The caudal (posterior) end of the neural tube becomes the spinal cord.

White & Gray Matter

Types of Nervous Tissue

Nervous tissue in the brain and spinal cord is composed of two types of matter, each with distinct roles.

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

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

• Brain: Outer layer of gray matter is called the cortical matter. Subcortical clusters of gray matter are called nuclei.

• Spinal cord: Outer layer is white matter; inner layer is gray matter.

Example: White matter is optimized for transferring signals rapidly throughout the CNS, while gray matter is responsible for decision-making processes.

Cerebral Hemispheres

Structure and Function

The cerebrum consists of two cerebral hemispheres, each specialized for different functions.

• Left hemisphere: Language, intellect, logical thinking.

• Right hemisphere: Visual-spatial skills, emotion, artistic/musical skills.

• Lateralization: Each hemisphere is specialized for 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 typically affects the left hemisphere, which is dominant for language.

Important Features of the Cerebrum

Gyri, Sulci, and Fissures

The surface of the cerebrum is characterized by grooves and ridges, which increase its surface area and cognitive capacity.

• 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.

• Central gyrus: Prominent ridge separating motor and sensory areas.

• Longitudinal fissure: Divides the brain into left and right hemispheres.

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

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

Functional Areas of the Cerebral Cortex

Specialized Regions

The cerebral cortex contains distinct functional areas responsible for sensory perception, motor control, and higher cognitive functions.

• Motor areas: Control voluntary movements.

• Sensory areas: Receive and process sensory information.

• Association areas: Integrate information for complex functions such as reasoning and memory.

Additional info: The precentral gyrus is the primary motor cortex, while the postcentral gyrus is the primary somatosensory cortex.

Table: Comparison of White and Gray Matter

Key Equations and Terms

• Neural tube development:

• Contralateral control: