Myelencephalon

The myelencephalon or afterbrain is the most posterior region of the embryonic hindbrain, from which the medulla oblongata develops.[1]

Myelencephalon
Afterbrain
Diagram depicting the main subdivisions of the embryonic vertebrate brain. These regions will later differentiate into forebrain, midbrain and hindbrain structures
Details
Identifiers
LatinMyelencephalon
MeSHD054024
NeuroNames698
TA98A14.1.03.003
TA25983
Anatomical terms of neuroanatomy

Development

Neural tube to myelencephalon

During fetal development, divisions of the neural tube that give rise to the hindbrain (rhombencephalon) and the other primary vesicles (forebrain and midbrain) occur at 28 days after conception. With the exception of the midbrain, these primary vesicles undergo further differentiation at 5 weeks after conception to form the myelencephalon and the other secondary vesicles.[2]

Myelencephalon to medulla

Final shape differentiation of the myelencephalon into the medulla oblongata can be observed at 20 weeks gestation.[2]

Neural Tube Primary Vesicles Secondary Vesicles Adult Structures
Brain Forebrain Telencephalon Rhinencephalon, Amygdala, Hippocampus, Cerebrum(Cortex), Basal Ganglia,Lateral ventricles
Diencephalon Epithalamus, Thalamus, Hypothalamus, Subthalamus, Pituitary, Pineal, Third ventricle
Midbrain Mesencephalon Tectum, Cerebral peduncle, Pretectum, Cerebral aqueduct
Hindbrain Metencephalon Pons, Cerebellum
Myelencephalon Medulla Oblongata
Spinal cord

[3]

The embryonic brain develops complexity through enlargements of the neural tube called vesicles; (a) The primary vesicle stage has three regions, and (b) the secondary vesicle stage has five regions.
Primary and secondary vesicle stages of development[4]

Medulla oblongata

The medulla oblongata is part of the brain stem that serves as the connection of the spinal cord to the brain. It is situated between the pons and the spinal cord.

Medulla oblongata- animation

Function

The medulla oblongata is responsible for several functions of the autonomic nervous system. These functions include:[5]

1) Respiration: monitors the acidity of the blood and sends electrical signals to intercostal muscle tissue to increase their contraction rate in order to oxygenate the blood as needed.

2) Cardiac & Vasomotor Center:[6] monitors and regulates cardiovascular activities by:

  • Sympathetic excitation in order to increase cardiac output
  • Parasympathetic inhibition of cardiac output
  • Affecting blood pressure via vasodilation and vasoconstriction

3) Reflexes

  • Coughing
  • Sneezing
  • Swallowing (palatal)
  • Vomiting
  • Gagging (pharyngeal)
  • Jaw jerk (masseter)

Damage/trauma

Because of its location in the brainstem and its many important roles in the autonomic nervous system, damage to the medulla oblongata is usually fatal.

References
  1. "Myelencephalon". Segen's Medical Dictionary. 2011. Retrieved 2015-05-05.
  2. Carlson, Neil R. Foundations of Behavioral Neuroscience.63-65
  3. "Neural - Myelencephalon Development - Embryology". embryology.med.unsw.edu.au. Retrieved 2015-05-05.
  4. "OpenStax CNX". cnx.org. Retrieved 2015-05-05.
  5. Loewy, A. D., & Spyer, K. M. (Eds.). (1990). Central regulation of autonomic functions. Oxford University Press, USA.145-164
  6. "Cardiovascular Regulation" (PDF). www.colorado.edu. Archived from the original (PDF) on 2017-08-30. Retrieved 2015-05-05.
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