Tegmentum

Brain: Tegmentum
Transverse section of mid-brain at level of superior colliculi, with anterior side pointing downward. ("Tegmentum" visible center right.)
Section through superior colliculus showing path of oculomotor nerve. (Tegmentum not labeled, but surrounding structures more clearly defined.)
Latin	Tegmentum
NeuroLex ID	birnlex_1031

The tegmentum (from Latin for "covering"^[1]) is a general area within the brainstem. It is located between the ventricular system and distinctive basal or ventral structures at each level. It forms the floor of the midbrain whereas the tectum forms the ceiling.^[2] It is a multisynaptic network of neurons that is involved in many unconscious homeostatic and reflexive pathways.

The tegmentum is the location of several cranial nerve (CN) nuclei. The nuclei of CN III and IV are located in the tegmentum portion of the midbrain. The nuclei of CN V to VIII are located in the tegmentum at the level of the pons. The nuclei of CN IX, X, and XII are located in that of the medulla.^{[citation needed]}

Development

In embryos, the tegmentum is the anterior half of the neural tube. However, for fetuses to adults, tegmentum refers only to the parts of the brain that remain relatively unchanged after development is complete, i.e. at the brain stem and midbrain. Other parts, on the other hand, develop further, through folding and thickening, and have different names. Still, it is considered a continuous central region through all levels of the brainstem.

Structures that develop to grow ventral or lateral outside this primitive tube as add-ons (e.g., the crus cerebri in the anterior of the midbrain) are not considered part of the tegmentum, as they are not part of the primitive neural tube but grow as projections from the cerebral cortex. However, parts that were inside the primitive neural tube and remained an integral part of it after complete development (e.g., the red nucleus) are considered part of the tegmentum.

Divisions

The tegmentum forms distinguished divisions in the midbrain, pons, and medulla.

Midbrain tegmentum

The midbrain tegmentum is the part of the midbrain extending from the substantia nigra to the cerebral aqueduct in a horizontal section of the midbrain.

Pontine tegmentum

Lateral tegmental field

The lateral tegmental field (LTF) ^[3] is the source of several neurons of the noradrenaline system of the brain

Other

Other pertinent areas of the tegmentum are:

• Ventral tegmental area (VTA)
• Periaqueductal gray matter
• Reticular formation
• Red nucleus
• Substantia nigra

References

1. ↑ "Glossary of Latin Terms T". Bible-history.com. Retrieved 2012-11-07. 
2. ↑ http://old.lf3.cuni.cz/physio/Physiology/education/materialy/cns/neuro2.ppt
3. ↑ Lateral Tegmental Field Neurons of Cat Medulla: A Source of Basal ...