Understanding the Brain: White Matter, Parts, and Functions

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White Matter:

Formed by neurons' axons, white matter acts as communication cables and the connection between control centers.


Part of the central nervous system found within the cranium, the brain weighs 1.4kg and is the largest organ in our body. It serves as the center of integration and consciousness. The brain is organized with grey matter making up the outer surface and white matter in the interior. Cranial nerves emerge directly from the brain, which is part of the peripheral nervous system.

Parts of the Brain:

  • Cerebellum:

    The largest part of the brain, consisting of hemispheres, the corpus callosum, the hippocampus, the thalamus, and the hypothalamus.
  • Hypothalamus:

    The master gland of the endocrine system, controlling most of its activity.
  • Cortex:

    The surface of the brain.
  • Thalamus:

    Regulates communication between several parts of the brain.
  • Corpus Callosum:

    Made of nerves, it bridges the two hemispheres.
  • Hippocampus:

    Part of the limbic system, responsible for long-term memory.
  • Cerebellum:

    Responsible for motion.
  • Brainstem:

    Subdivided into several regions, the brainstem elongates into the spinal column and contains several centers of involuntary nervous control.

The Spinal Cord:

The arrangement of grey and white matter in the spinal cord is the opposite of that in the brain. White matter is found around the perimeter, and grey matter is in the center. In the very center of the cord, surrounded by grey matter, is an open tube called the central canal, which is filled with cerebrospinal fluid. The fundamental role of the spinal cord is to bring messages back and forth between the brain and body. It is also capable of rapid, automatic responses known as reflex arcs.

Reflex Arcs:

Involuntary movements that involve two steps:

  1. Receiving the sensory input, the nerve impulse moves toward the brain, relaying the message.
  2. A "short-circuit" occurs within the spinal cord, allowing a rapid automatic response.

Dual Network:

The parasympathetic branch is associated with relaxation, while the sympathetic branch is associated with stress.

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