Chapter 12: The Central Nervous System (12.1–12.3) – Study Notes

Word Roots in Neuroanatomy

Common Roots and Their Meanings

Understanding word roots helps in learning anatomical terminology, especially in neuroanatomy.

• Cephal-: head (diencephalon)

• Gangli-: swelling (ganglion)

• Chiasm-: cross (optic chiasma)

• Mening-: membrane (meninges)

• Cerebr-: brain (cerebrum)

• Plex-: interweaving (choroid plexus)

• Nemi-: long rope or cord (funiculus)

• Soma-: body (somatosensory)

Overview of the Central Nervous System (CNS)

Definition and Major Components

The Central Nervous System (CNS) consists of the brain and spinal cord. It is responsible for integrating sensory information, coordinating movement, maintaining homeostasis, and higher mental functions such as thought and emotion.

• Brain: Processes sensory information, initiates motor commands, and is the center for thoughts and emotions.

• Spinal Cord: Conducts signals to and from the brain, controls reflex activities.

The CNS communicates with the Peripheral Nervous System (PNS), which includes motor and sensory functions.

Functions of the Nervous System

• Motor functions: Stimulation of muscle contraction or gland secretion (primarily PNS).

• Sensory functions: Detection of sensations inside and outside the body (primarily PNS).

• Integrative functions: Decision-making processes, interpretation of sensory information, planning and monitoring movement, maintenance of homeostasis, and higher mental functions (exclusive to CNS).

Brain and Spinal Cord Structure

Major Divisions and Protection

The brain is the largest and most complex part of the nervous system, consisting of:

• Cerebral hemispheres (cerebrum)

• Diencephalon

• Cerebellum

• Brainstem

It contains approximately 100 billion multipolar neurons. The brainstem connects the brain to the spinal cord, allowing two-way communication between the CNS and PNS.

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

• Spinal cord: Lies within the vertebral canal.

• Meninges: Membranes between bone and nervous tissue, providing protection.

White Matter and Gray Matter

Structural Differences and Functions

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

• White matter: Found in both brain and spinal cord; consists of myelinated axons. Bundles are called tracts. Responsible for transmitting signals between different regions.

• Gray matter: Found in both brain and spinal cord; consists of neuronal cell bodies, dendrites, and unmyelinated axons. Responsible for processing information.

In the cerebrum, the outer few millimeters are gray matter (cerebral cortex), while deeper portions are mostly white matter with some gray matter nuclei. In the spinal cord, gray matter is central, surrounded by white matter tracts.

• Nuclei: Clusters of cell bodies in the CNS.

• Ganglia: Clusters of cell bodies in the PNS.

Comparison Table: White Matter vs. Gray Matter

Feature	White Matter	Gray Matter
Main Components	Myelinated axons	Cell bodies, dendrites, unmyelinated axons
Location in Brain	Deep regions	Outer cortex, scattered nuclei
Location in Spinal Cord	Outer tracts	Central region
Function	Signal transmission	Information processing

Example: The corpus callosum is a large tract of white matter connecting the two cerebral hemispheres, allowing communication between them.

Additional info: White matter's myelination increases the speed of electrical signal transmission, while gray matter is the site of synaptic integration and neural processing.