Brain: Developmental Divisions

Original Editor - Lucinda hampton

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Introduction[edit | edit source]

4 week embryo brain.jpg

The three main parts of the brain are split amongst three regions developed during the embryonic period: the forebrain, midbrain and hindbrain also known as the prosencephalon (telencephalon and diencepalon), mesencephalon, and rhombencephalon respectively. 

  1. Forebrain: Most anterior division of the developing vertebrate brain, containing the most complex networks in the central nervous system.
  2. Midbrain:  The midbrain makes up part of the brain stem. It is located between the hindbrain and forebrain.
  3. Hindbrain:  The well-protected central core of the brain.[1]

Forebrain[edit | edit source]

Telencephalon.gif

The forebrain is the large and complicated structure that distinguishes the human brain from other vertebrate brains. The forebrain is responsible for a variety of functions including receiving and processing sensory information, thinking, perceiving, producing and understanding language, and controlling motor function It has two major divisions: the diencephalon and the telencephalon.

  1. The diencephalon (below the telencephalon), contains the thalamus and hypothalamus and the limbic system, which are responsible for such functions as motor control, relaying sensory information, and controlling autonomic functions.
  2. The telencephalon (above the diencephalon) and contains the cerebrum (largest part of the brain). It is the home of the highest-level cognitive processing in the brain with most of the actual information processing in the brain takes place in the cerebral cortex.[1][2].

Midbrain[edit | edit source]

Brain Anatomy - Mid-Fore-HindBrain.png

The midbrain or mesencephalon, is the portion of the brainstem that connects the hindbrain and the forebrain. All sensory and motor information that travels between the forebrain and the spinal cord passes through the midbrain, making it a relay station for the central nervous system. 

  • The midbrain is small compared with the hindbrain and particularly the forebrain.[1] This region of the brain is involved in auditory and visual responses as well as motor function[2].

Hindbrain[edit | edit source]

The hindbrain extends from the spinal cord and is composed of the metencephalon and myelencephalon. It includes the cerebellum, reticular formation, and brain stem, which are responsible for some of the most basic autonomic functions of life, such as breathing, heart rate, digestion and movement. The brain stem contains the pons and medulla oblongata.

  • Evolutionarily speaking, the hindbrain contains the oldest parts of the brain, which all vertebrates possess, though they may look different from species to species. These regions assists in maintaining balance and equilibrium, movement coordination, and the conduction of sensory information.[2].

Neural Tube Development[edit | edit source]

Neurulation-02.jpg

The brain is a complex organ composed of gray parts and white matter, which can be hard to distinguish. The embryonic nervous system begins as a very simple structure, essentially just a straight line, which then gets increasingly complex.

To begin life, a sperm cell and an egg cell fuse to become a fertilized egg. The fertilized egg cell (zygote) starts dividing to generate the cells that make up an entire organism. Sixteen days after fertilization, the developing embryo’s cells belong to one of three germ layers that give rise to the different tissues in the body.

  1. The endoderm (inner tissue), is responsible for generating the lining tissues of various spaces within the body, such as the mucosae of the digestive and respiratory systems.
  2. The mesoderm (middle tissue) gives rise to most of the muscle and connective tissues.
  3. The ectoderm (outer tissue) develops into the integumentary system (the skin) and the nervous system.

As the embryo develops, a portion of the ectoderm differentiates into a specialized region of neuroectoderm, which is the precursor for the tissue of the nervous system[3].

Image 4: Early Embryonic Development of Nervous System

  • The neuroectoderm begins to fold inward to form the neural groove.
  • As the two sides of the neural groove converge, they form the neural tube, which lies beneath the ectoderm.
  • The anterior end of the neural tube will develop into the brain, and the posterior portion will become the spinal cord.
  • The neural crest develops into peripheral structures.
  • A neural groove forms, visible as a line along the dorsal surface of the embryo. The ridge-like edge on either side of the neural groove is referred as the neural fold.
  • As the neural folds come together and converge, the underlying structure forms into a tube just beneath the ectoderm called the neural tube[3].

References[edit | edit source]